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rodpaine
Joined: 12 Feb 2006
Location: 50 miles west of D.C. in northern VA
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 Posted: Jun 08, 2006 1:39 PM Post subject: Front End Vibration - Fix (Tec FAQ?) |
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Finally found the problem with the front end vibration at 65 MPH, coming and going most notably in long sweeping curves, where the inner tire changes speed.
Turns out my Style 29 wheels on the E32 rotors (Yoko AVS Sport) don't like to be tightened over the mid-point torque spec of 74 ft-lbs ± 9 ft-lbs. Absolutely no vibration at any speed when torqued to 65-70 ft-lbs. (clean threads, lightly oiled) At 80-83 ft-lbs the vibration appears.
I had the wheels off just prior to the May 7, 2006 BMWCCA Concours, to wash the wheel wells and I put the wheels back on at the upper torque limit. We first noticed the vibration on the way to the Concours and again over the past several weeks, before I finally got a chance to locate the problem starting yesterday morning.
Took a day and a half of testing, but this is the problem. Time was also expended on testing with both the black plastic (1010tire) and aluminum (TireRack) hub centering rings. No difference, other than the plastic rings require more care in handling and wheel install/removal work, to prevent damage to the plastic rings.
HTH,
-Rod |
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BMWCCA2
Joined: 12 Feb 2006
Location: Central Virginia
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| Posted: Jun 08, 2006 9:34 PM Post subject: |
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I find it hard to believe . . . but I believe you! So what do you think? Bending a wheel that doesn't really fit properly? Bending the hub from another fitment issue? You'd think if the mating surfaces were perfect there'd be no way this could have any effect. But I'll remember it next time I torque my wheels, you can be sure of that!
Thanks for sharing. |
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rodpaine
Joined: 12 Feb 2006
Location: 50 miles west of D.C. in northern VA
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| Posted: Jun 09, 2006 4:52 AM Post subject: |
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| BMWCCA2 wrote: | I find it hard to believe . . . but I believe you! So what do you think? Bending a wheel that doesn't really fit properly? Bending the hub from another fitment issue? You'd think if the mating surfaces were perfect there'd be no way this could have any effect. But I'll remember it next time I torque my wheels, you can be sure of that!
Thanks for sharing. |
I really expected to find a small rock coated with tar stuck inside one of the wheels (previous experience), a tossed weight or perhaps a split hub centering ring, but these weren't the problem. I don't know what the problem really is, perhaps my mix of frontend components. The vibration coming and going on curving roads brought to mind a comment from years ago about the two front wheels coming in sync and combining their small imbalance to create a bigger one.
Only thing I do know is that backing off the wheel bolt torque corrects the problem, for now. I'll see what happens as the Yokos wear.
Thanks,
-Rod |
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Steve Haygood
Joined: 12 Feb 2006
Location: Thomaston Ga
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| Posted: Jun 09, 2006 6:47 AM Post subject: |
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| Good tip Rod, I would have never thought that so little difference would have mattered that much |
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E12driver
Joined: 12 Feb 2006
Location: Texas
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| Posted: Jun 09, 2006 9:48 AM Post subject: |
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| Steve Haygood wrote: | | Good tip Rod, I would have never thought that so little difference would have mattered that much |
Yes, good tip, but if you know Rod you know he's picky as hell. We went to dinner several weeks ago and he said "you feel that?" Maybe, but I've got more slop in my E12 steering than what he says he's feeling as a vibration, I told him. It was there, but I'd have never probably noticed it. Gotta watch out for him, he's picky to a fault, but great to have along when looking at a used car. 
Carl |
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C.R. Krieger
Joined: 12 Feb 2006
Location: Halfway up the left side of Lake Michigan
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| Posted: Jun 09, 2006 2:29 PM Post subject: |
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| rodpaine wrote: | | BMWCCA2 wrote: | I find it hard to believe . . . but I believe you! But I'll remember it next time I torque my wheels, you can be sure of that!
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Only thing I do know is that backing off the wheel bolt torque corrects the problem, for now. I'll see what happens as the Yokos wear. |
I, too, would not doubt your findings. If you're going to write it as a Tech FAQ, you might add my own anomalous (voodoo?) experience:
Rotating a front wheel on the bolt circle can make a difference. This may have a more logical cause along the lines of an imbalanced brake rotor combined with an equally imbalanced wheel. Jenny Morgan's immediate response was, "That shouldn't make any difference." and I fullheartedly agree ... but sometimes, it does. Go figure.  |
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Shawn D.
Beamter
Joined: 12 Feb 2006
Location: Alpharetta, GA
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| Posted: Jun 09, 2006 8:00 PM Post subject: |
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Rod,
You might want to reconsider the "lightly oiled" part of your regimen. I believe it might be throwing you off, as the torque spec is for clean and dry threads. You're getting longer bolt stretch (what torque is really measuring) when you use lubricated threads.
-Shawn |
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rodpaine
Joined: 12 Feb 2006
Location: 50 miles west of D.C. in northern VA
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| Posted: Jun 10, 2006 6:29 AM Post subject: |
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| C.R. Krieger wrote: | | Rotating a front wheel on the bolt circle can make a difference. |
Yes sir, us old timers have certainly seen this and I can't rule it out. Good point.
| Shawn D. wrote: | | You might want to reconsider the "lightly oiled" part of your regimen. I believe it might be throwing you off, as the torque spec is for clean and dry threads. |
I am using a lightly coated shop rag and a quick blast of compressed air, more to make sure dirt and grit is removed. Is that enough to be a real factor? I don't know. Good point, Shawn.
| E12Driver wrote: | | Gotta watch out for him, he's picky to a fault... |
Ah, okay, Carl, but only because you bought dinner. 
-Rod |
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M635CSi
Joined: 09 Apr 2006
Location: .From Sea to Shining Sea
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| Posted: Jun 10, 2006 9:55 AM Post subject: Re: Front End Vibration - Fix (Tec FAQ?) |
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| rodpaine wrote: | Finally found the problem with the front end vibration at 65 MPH, coming and going most notably in long sweeping curves, where the inner tire changes speed.
Turns out my Style 29 wheels on the E32 rotors (Yoko AVS Sport) don't like to be tightened over the mid-point torque spec of 74 ft-lbs ± 9 ft-lbs. Absolutely no vibration at any speed when torqued to 65-70 ft-lbs. (clean threads, lightly oiled) At 80-83 ft-lbs the vibration appears. |
Rod, you’re car is a stunning example of a beautiful E28.
I've heard tell of this vibration happening. Even people replacing brake rotors in an attempt to correct vibration(s) because they "thought" the rotors were warped. I've never seen warped rotors on a BMW, but I have seen vibrations and shortened service life caused by incorrect assembly.
Shawn is quite correct when he refers to dry versus lubricated threads. Keep in mind, the difference between a dry torque vs. lubed is ≈20%, so what should be ±74 lbs, you've set to ≈89 lbs.
| rodpaine wrote: | | I had the wheels off just prior to the May 7, 2006 BMWCCA Concours, to wash the wheel wells and I put the wheels back on at the upper torque limit. |
Now you've bumped it from 74 lbs to 83 lbs (74+9=83) which is equivalent (lubed) to ≈100 lbs vs. dry spec of 74 lbs.
| rodpaine wrote: | We first noticed the vibration on the way to the Concours and again over the past several weeks, before I finally got a chance to locate the problem starting yesterday morning.
Took a day and a half of testing, but this is the problem. Time was also expended on testing with both the black plastic (1010tire) and aluminum (TireRack) hub centering rings. No difference, other than the plastic rings require more care in handling and wheel install/removal work, to prevent damage to the plastic rings.
HTH,
-Rod |
I'm not a fan of "hub centering rings" even though they do somewhat solve the fitment problem.
It's a good idea to tighten lug bolts going diagonally as you torque the wheel bolts (not in a circular manor). Be careful to back off each bolt before re-torque to avoid a bad reading caused by stiction. Remember, torque readings should be taken while the bolt/nut is turning.
One of the advantages of centerlock wheels is the issue of wheel/hub/rotor distortion is reduced.
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BMWCCA2
Joined: 12 Feb 2006
Location: Central Virginia
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| Posted: Jun 10, 2006 7:14 PM Post subject: Re: Front End Vibration - Fix (Tec FAQ?) |
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| M635CSi wrote: | | I've never seen warped rotors on a BMW |
You must not be looking very hard.
| M635CSi wrote: | One of the advantages of centerlock wheels is the issue of wheel/hub/rotor distortion is reduced.
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That's if you don't consider the adapter you have to bolt to the hub in the first place to accept the center-lock wheels.   |
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M635CSi
Joined: 09 Apr 2006
Location: .From Sea to Shining Sea
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| Posted: Jun 10, 2006 8:54 PM Post subject: Re: Front End Vibration - Fix (Tec FAQ?) |
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| BMWCCA2 wrote: | | M635CSi wrote: | | I've never seen warped rotors on a BMW |
You must not be looking very hard. |
Phil, I will again say I have "never seen warped rotors on a BMW", and further, that brake rotors do not warp. This is not just on BMWs, this is on any car.
Here's what is incorrectly diagnosed as "warped rotors":
1) Excessive lateral runout caused by improper component installation/assembly, improper lug bolt tightening or worn/improper wheel bearing torque. Excessive lateral runout is felt in the brake pedal as "pulsing".
2) Rotor disc thickness variation precipitated by the above problems. The rotor wears unevenly as each rotation causes the brake pad to wear against the high spot on the rotor resulting in a rotor thickness variation. Rotor disc thickness variation is felt in the brake pedal as "pulsing".
| M635CSi wrote: | One of the advantages of centerlock wheels is the issue of wheel/hub/rotor distortion is reduced.
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| BMWCCA2 wrote: | | That's if you don't consider the adapter you have to bolt to the hub in the first place to accept the center-lock wheels. |
I was thinking of hubs designed for centerlock wheels. On these, the hub is mounted to the spindle or flange the same as any hub, but the hub center has machined threads to receive the centerlock nut directly; there is no adapter.
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rodpaine
Joined: 12 Feb 2006
Location: 50 miles west of D.C. in northern VA
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| Posted: Jun 11, 2006 1:46 PM Post subject: |
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UPDATE -
Okay, with four people in the car last night, the well known steering wheel shake with light application of the brakes showed up at 52 mph. So, it now looks like my problem is probably control arm bushings. Oddly enough, the car returns to its "good behavior" when I am the only one in the car, but added passenger weight brought on new behavior characteristics typically associated with control arm bushings. Live and learn.
Steve Haygood now has my shopping list and we'll go from there.
Thanks to all who jumped in with opinions and ideas about what was happening. A good exchange and we all learned something from each other. Thanks!
-Rod |
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C.R. Krieger
Joined: 12 Feb 2006
Location: Halfway up the left side of Lake Michigan
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| Posted: Jun 12, 2006 4:08 PM Post subject: Re: Front End Vibration - Fix (Tec FAQ?) |
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| M635CSi wrote: |
Here's what is incorrectly diagnosed as "warped rotors":
2) Rotor disc thickness variation precipitated by the above problems. The rotor wears unevenly as each rotation causes the brake pad to wear against the high spot on the rotor resulting in a rotor thickness variation. Rotor disc thickness variation is felt in the brake pedal as "pulsing". |
I think this is what we refer to as 'warped', regardless of its cause. While the term 'warp' may be physically inaccurate, it serves its purpose in describing an annoying phenomenon we all agree exists on E28s. |
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Mike W.
Joined: 12 Feb 2006
Location: Sonoma County, Ca.
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| Posted: Jun 12, 2006 4:46 PM Post subject: |
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I've long believed E28's front ends were so sensitive that the phase of the moon might have some effect, so the torque factor is believeable to me.
| Quote: | | Rotating a front wheel on the bolt circle can make a difference. |
That is more than believeable, I've seen it myself. The only way that could be is if the hub/bolt circle is out of round. Which seems unlikely. But I've seen it go from from "some" to "very little", or from a PITA to drive to a minor irritation by rotating the wheel on the bolt circle.
| Quote: | | I've never seen warped rotors on a BMW |
I've seen the writeups to the contrary, and some of it may be true, and warping may be overstated, but I disagree. First off, theoretically, why should a brake rotor be immune to warping? Granted cast iron isn't as suceptable to warping as say aluminum, but it will surely warp. I've seen warped rotors, warped heads, even a rare warped block. Get it hot, and cool it unevenly, and it will probably warp. Next, even on BMW's, if not on E28's I've had surfacing rotors completely eliminate shimmy and brake pedal pulsation. If it wasn't warped, how come turning them cured the problem. Next, try turning rotor over by hand, without the wheel attached. Often I've seen a spot where it is harder to turn. That is caused by things being distorted. Call it warping, or runout or whatever, it means things aren't parallel.
Now I will allow that E28's are so sensitive that surfacing rotors doesn't seem to do any good, but that doesn't eliminate a cause, just a cure. |
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M635CSi
Joined: 09 Apr 2006
Location: .From Sea to Shining Sea
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| Posted: Jun 12, 2006 10:16 PM Post subject: Re: Front End Vibration - Fix (Tec FAQ?) |
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| C.R. Krieger wrote: | | M635CSi wrote: |
Here's what is incorrectly diagnosed as "warped rotors":
2) Rotor disc thickness variation precipitated by the above problems. The rotor wears unevenly as each rotation causes the brake pad to wear against the high spot on the rotor resulting in a rotor thickness variation. Rotor disc thickness variation is felt in the brake pedal as "pulsing". |
I think this is what we refer to as 'warped', regardless of its cause. While the term 'warp' may be physically inaccurate, it serves its purpose in describing an annoying phenomenon we all agree exists on E28s. |
“If you don't know where you are going, any road will get you there.”
Lewis Carroll |
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M635CSi
Joined: 09 Apr 2006
Location: .From Sea to Shining Sea
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| Posted: Jun 12, 2006 11:47 PM Post subject: |
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| Mike W. wrote: | | I've long believed E28's front ends were so sensitive that the phase of the moon might have some effect, so the torque factor is believeable to me. |
When properly maintained, the E28 front end is just fine.
| Quote: | | Rotating a front wheel on the bolt circle can make a difference. |
| Mike W. wrote: | | That is more than believeable, I've seen it myself. The only way that could be is if the hub/bolt circle is out of round. Which seems unlikely. But I've seen it go from from "some" to "very little", or from a PITA to drive to a minor irritation by rotating the wheel on the bolt circle. |
Upon what do you base your statement "The only way that could be is if the hub/bolt circle is out of round"? I ask because your statement is incorrect.
| Quote: | | I've never seen warped rotors on a BMW |
| Mike W. wrote: | | I've seen the writeups to the contrary, and some of it may be true, and warping may be overstated, but I disagree. |
With whom do you disagree, and about what?
| Mike W. wrote: | | First off, theoretically, why should a brake rotor be immune to warping? |
Because theoretically and in practice, cast iron brake rotors are brittle.
| Mike W. wrote: | | Granted cast iron isn't as suceptable to warping as say aluminum, but it will surely warp. |
Brake rotors don't warp...
| Mike W. wrote: | | I've seen warped rotors, |
How did you determine they were "warped"?
| Mike W. wrote: | warped heads, even a rare warped block. Get it hot, and cool it unevenly, and it will probably warp. Next, even on BMW's, if not on E28's I've had surfacing rotors completely eliminate shimmy and brake pedal pulsation.
If it wasn't warped, how come turning them cured the problem. |
It didn't cure the "problem"; it "cured" the symptom. The symptom being uneven brake rotor thickness.
Unfortunately, the customer was probably clueless that he left the shop with his car having problem that caused the uneven brake rotor thickness in the first place.
| Mike W. wrote: | | Next, try turning rotor over by hand, without the wheel attached. Often I've seen a spot where it is harder to turn. That is caused by things being distorted. |
It's harder to turn because of uneven brake rotor thickness. “distorted” could mean anything when said about "things"…
| Mike W. wrote: | | Call it warping, or runout or whatever, it means things aren't parallel. |
I choose to use a discriptive term that accurately discribes the condition;uneven brake rotor thickness. People who call it "warping" are mistaken, lazy or ignorant. As anyone interested in knowledge will learn upon investigation, brake rotors do not warp.
| Mike W. wrote: | | Now I will allow that E28's are so sensitive that surfacing rotors doesn't seem to do any good, but that doesn't eliminate a cause, just a cure. |
The E28 front end has numerous serviceable parts that need replacing periodically. The E28 front end is not particularly "sensitive". It is, however, difficult for people who don't understand how it works to maintain it properly. They do what so many people do when working on cars; throw parts at it until the symptoms go away.
The problem with "mechanics", is that generally the more you have, the more you need... |
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Mike W.
Joined: 12 Feb 2006
Location: Sonoma County, Ca.
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| Posted: Jun 14, 2006 8:46 PM Post subject: |
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Being the type who will beat a dead horse, I will contine to do so.
| Quote: | I've long believed E28's front ends were so sensitive that the phase of the moon might have some effect, so the torque factor is believeable to me.
When properly maintained, the E28 front end is just fine. |
I've put over half a million miles on BMW's, and closer to a million total on cars between my wife and I, and E28's are the only one I've had trouble eliminating a shimmy or with a regularly recurring shimmy problem . Regular maintaince to me is keeping things in good conditon with little or no play. I've been around a few cars and have certainly found wear in front end parts, so I believe I know what to look for. Additionally, most front end parts on most cars last well over 100K. On my E12, at 300K it was still in good shape.
| Quote: | That is more than believeable, I've seen it myself. The only way that could be is if the hub/bolt circle is out of round. Which seems unlikely. But I've seen it go from from "some" to "very little", or from a PITA to drive to a minor irritation by rotating the wheel on the bolt circle.
Upon what do you base your statement "The only way that could be is if the hub/bolt circle is out of round"? I ask because your statement is incorrect. |
And I feel your statement is rather bold, with hubcentric rings, and no perceptable play, how could I have different radial runout only by moving the wheel to a different lug position without the hub being out of round. And mind you, this is a repeatable condition.
| Quote: | I've seen the writeups to the contrary, and some of it may be true, and warping may be overstated, but I disagree.
With whom do you disagree, and about what? |
OK, poorly phrased, I agree.
| Quote: | warped heads, even a rare warped block. Get it hot, and cool it unevenly, and it will probably warp. Next, even on BMW's, if not on E28's I've had surfacing rotors completely eliminate shimmy and brake pedal pulsation.
If it wasn't warped, how come turning them cured the problem.
It didn't cure the "problem"; it "cured" the symptom. The symptom being uneven brake rotor thickness.
Unfortunately, the customer was probably clueless that he left the shop with his car having problem that caused the uneven brake rotor thickness in the first place. |
Do you disagree that heads and occasionally blocks can warp? If you allow they can, why are rotors immune to that condition? Does a cylinder head become thinner in the middle than on the ends? Even if warping isn't the problem, if E28 front ends aren't sensitive, how come a common and effective procedure on other cars (turning rotors) doesn't work on E28's?
| Quote: | Now I will allow that E28's are so sensitive that surfacing rotors doesn't seem to do any good, but that doesn't eliminate a cause, just a cure.
The E28 front end has numerous serviceable parts that need replacing periodically. The E28 front end is not particularly "sensitive". It is, however, difficult for people who don't understand how it works to maintain it properly. They do what so many people do when working on cars; throw parts at it until the symptoms go away. |
Again, if E28 front ends aren't sensitive, how come a tire/wheel assembly that is completely without shimmy on other BMW's, such as early E24 or E23, will shimmy when put on the front of an E28? And why is it that shaving a tire/wheel "rounder" than BMW spec's will minimize or eliminate shimmy? |
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M635CSi
Joined: 09 Apr 2006
Location: .From Sea to Shining Sea
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| Posted: Jun 15, 2006 1:32 AM Post subject: |
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| Mike W. wrote: | | ...E28's are the only one I've had trouble eliminating a shimmy or with a regularly recurring shimmy problem. |
Mike, if you have "trouble eliminating a shimmy" in your E28 or "a regularly recurring shimmy problem" and even one other person doesn't experience that problem, wouldn't that indicate the "problem" lay elsewhere rather than the design of the E28 suspension?
| Mike W. wrote: | | Regular maintaince to me is keeping things in good conditon with little or no play. I've been around a few cars and have certainly found wear in front end parts, so I believe I know what to look for. |
Mike, you seem like a good guy so I'm asking you to look at these two statements and tell me what is wrong with this picture: 1) "E28's are the only one I've had trouble eliminating a shimmy" and 2) "I believe I know what to look for." One of those statements is suspect, and I'm betting it's the "I believe I know what to look for" one.
Think about it, how can it at once be true that both you "had trouble eliminating the shimmy? Yet "know what to look for"?
| Mike W. wrote: | | Additionally, most front end parts on most cars last well over 100K. On my E12, at 300K it was still in good shape. |
I guess it depends on what you call "last" I like putting new parts on my cars so parts don’t “last" that long without replacement.
| M635CSi wrote: | | Upon what do you base your statement "The only way that could be is if the hub/bolt circle is out of round"? I ask because your statement is incorrect. |
| Mike W. wrote: | | And I feel your statement is rather bold, with hubcentric rings, and no perceptable play, how could I have different radial runout only by moving the wheel to a different lug position without the hub being out of round. And mind you, this is a repeatable condition. |
You've added two qualifiers that weren't in your first post: 1) "with hubcentric rings", and 2) "no perceptable play". Hub centric rings are a source of trouble and would be the first thing I'd remove. Mount a known good wheel/tire assembly and measure radial runout. If the runout is now within spec, the source of the problem is most likely the wheel/tire/hub ring which is/are out of round or does not fit correctly.
| Mike W. wrote: | | Even if warping isn't the problem, if E28 front ends aren't sensitive, how come a common and effective procedure on other cars (turning rotors) doesn't work on E28's? |
Perhaps there was nothing wrong with the rotors to begin with?
If there is excess lateral runout, worn control arm bushings, weak shock absorbers or an out of balance wheel/tire, turning the rotors is unlikely to cure the problem.
FWIW, I do not recommend turning rotors – avoid doing so.
| Mike W. wrote: | | Again, if E28 front ends aren't sensitive, how come a tire/wheel assembly that is completely without shimmy on other BMW's, such as early E24 or E23, will shimmy when put on the front of an E28? |
Because the front end of the E28 needed repair. Once it has been repaired, a wheel/tire within spec will not cause shimmy.
| Mike W. wrote: | | And why is it that shaving a tire/wheel "rounder" than BMW spec's will minimize or eliminate shimmy? |
It will induce less stress into the suspension components, but at the same time, the harder surface will transmit more road noise and give a harder ride. |
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rodpaine
Joined: 12 Feb 2006
Location: 50 miles west of D.C. in northern VA
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| Posted: Jun 15, 2006 5:33 AM Post subject: |
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On a more general point, what is considered the "typical" mileage when the front control arms will probably require replacement on our E28? On my '83 528e the mileage has been:
44,251 BMW warranty replacement with "updated" control arms.
91,829 Control arms replaced, same P/N as above.
127,021 Current replacement project with 750i upper/stock lower.
Average is 42,340 miles. I don't AutoX with the car, but do push it pretty hard on twisties and only usually have a single passenger in the car. This looks about typical in terms of Control Arms life span, true?
-Rod |
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BMWCCA2
Joined: 12 Feb 2006
Location: Central Virginia
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| Posted: Jun 15, 2006 9:36 AM Post subject: |
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Well I'm convinced. I'm going to change out both front hubs/bearings, upper and lower control arms, all three tie-rods, steering idler arm, and install new tires and new wheels and new shocks. I will be leaving the same old Brembo rotors on that Steve sold me over a year ago because, well, they can't possibly be warped. Really, I have all those parts ready to go on.
Saying that the E28 is "more sensitive" than any other BMW model discounts the crap that is the E21 front suspension. Saying it isn't disregards the fact that BMW has been struggling with E28 front-end shimmy, pulsation, brake shake, etc, since the car was first introduced in the U.S.
I worked at a BMW dealership from 1976 to 1995. Believe me, BMW replaced tires, wheels, shocks, brakes—nearly everything they could think of. They had us balancing the tires on the car under load and even truing tires with some machines that looked like a combination of a belt-sander and a treadmill. The best we achieved was a bit of time to get the owners out of warranty . . . or out of the E28. The fact that an E28 can even shake on decelleration without brake application doesn't exonerate the rotors, either. It's obviously a delicate balance of every component involved, but out of round rotors—for whatever reason—are usually the prime suspect, whether that's from sitting with the pads in contact for a long time, or whatever. If you want to fix blame for rotor pulsation on something other than the rotor, what's left? The hub! |
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C.R. Krieger
Joined: 12 Feb 2006
Location: Halfway up the left side of Lake Michigan
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| Posted: Jun 15, 2006 9:56 AM Post subject: |
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| M635CSi wrote: | | Upon what do you base your statement "The only way that could be is if the hub/bolt circle is out of round"? I ask because your statement is incorrect. |
| Mike W. wrote: | | And I feel your statement is rather bold, with hubcentric rings, and no perceptable play, how could I have different radial runout only by moving the wheel to a different lug position without the hub being out of round. And mind you, this is a repeatable condition. |
You've added two qualifiers that weren't in your first post: 1) "with hubcentric rings", and 2) "no perceptable play". Hub centric rings are a source of trouble and would be the first thing I'd remove. Mount a known good wheel/tire assembly and measure radial runout. If the runout is now within spec, the source of the problem is most likely the wheel/tire/hub ring which is/are out of round or does not fit correctly.[/quote]
I am the one who first mentioned this phenomenon and I first encountered it with OEM BMW wheels and no hubcentric rings. If what you say is true, then this must mean:
1) That the E28 has the worst hub tolerances in the industry or 2) That the rather unique design of its front suspension makes it more sensitive to typical manufacturing variances or
3) It's just my sloppy maintenance practices.
Which is it? |
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M635CSi
Joined: 09 Apr 2006
Location: .From Sea to Shining Sea
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| Posted: Jun 15, 2006 11:46 AM Post subject: |
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| BMWCCA2 wrote: | | Well I'm convinced. I'm going to change out both front hubs/bearings, upper and lower control arms, all three tie-rods, steering idler arm, and install new tires and new wheels and new shocks. I will be leaving the same old Brembo rotors on that Steve sold me over a year ago because, well, they can't possibly be warped. Really, I have all those parts ready to go on. |
The value of doing that, assuming you buy quality parts, is you have then eliminated the potential problems.
| BMWCCA2 wrote: | | Saying that the E28 is "more sensitive" than any other BMW model discounts the crap that is the E21 front suspension. Saying it isn't disregards the fact that BMW has been struggling with E28 front-end shimmy, pulsation, brake shake, etc, since the car was first introduced in the U.S. |
The base model E28 was never an expensive car from a design standpoint. It was designed as a reasonably priced four door family sedan so it's not surprising the suspension is one of the cheaper approaches used.
| BMWCCA2 wrote: | | I worked at a BMW dealership from 1976 to 1995. Believe me, BMW replaced tires, wheels, shocks, brakes—nearly everything they could think of. They had us balancing the tires on the car under load and even truing tires with some machines that looked like a combination of a belt-sander and a treadmill. The best we achieved was a bit of time to get the owners out of warranty . . . or out of the E28. The fact that an E28 can even shake on decelleration without brake application doesn't exonerate the rotors, either. It's obviously a delicate balance of every component involved, but out of round rotors—for whatever reason—are usually the prime suspect, whether that's from sitting with the pads in contact for a long time, or whatever. If you want to fix blame for rotor pulsation on something other than the rotor, what's left? The hub! |
What remains, is all the other parts in the BMW E28's inexpensive four door family sedan front end working against the rotors. Worn control arm bushings (example) will continue the vulcanization process after manufacture, causing the bushings to harden over time, become brittle, and fail. This process accelerates when heat and motion are directed toward the bushings. Worn control arm bushings allow the tires to be pushed back putting the front end alignment out of spec. They also allow normal suspension harmonics to go unchecked, and thus, allow vibration that can be felt in the cabin. |
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Shawn D.
Beamter
Joined: 12 Feb 2006
Location: Alpharetta, GA
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| Posted: Jun 15, 2006 12:23 PM Post subject: |
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| Mike W. wrote: | | First off, theoretically, why should a brake rotor be immune to warping? |
| M635CSi wrote: | | Because theoretically and in practice, cast iron brake rotors are brittle. |
That's a bullshit explanation. "Brittle" means that a material cannot withstand a high "delta" (change in length divided by total length) without fracturing. "Brittle" has nothing to do with warping.
| Mike W. wrote: | | I've seen warped rotors, |
| M635CSi wrote: | | How did you determine they were "warped"? |
Well, I don't know how Mike did it, but I've checked rotor runout with a dial indicator, measuring from both sides; I determined that rotors can indeed warp, as an "outboard" or "inboard" deflection of a section was corroborated from both sides. It was also evident visually, as I set the brake lathe on "extra fine" radial feed, used new bits, and shaved a teensy bit off on each pass -- the high spots that got touched on one side corresponded to low spots on the other side that didn't get touched.
| Mike W. wrote: | warped heads, even a rare warped block. Get it hot, and cool it unevenly, and it will probably warp. Next, even on BMW's, if not on E28's I've had surfacing rotors completely eliminate shimmy and brake pedal pulsation.
If it wasn't warped, how come turning them cured the problem. |
| M635CSi wrote: | It didn't cure the "problem"; it "cured" the symptom. The symptom being uneven brake rotor thickness.
Unfortunately, the customer was probably clueless that he left the shop with his car having problem that caused the uneven brake rotor thickness in the first place. |
Well, call it what you want, it has worked perfectly well for me on other cars (albeit only temporarily on my E28).
| Mike W. wrote: | | Call it warping, or runout or whatever, it means things aren't parallel. |
| M635CSi wrote: | | I choose to use a discriptive term that accurately discribes the condition;uneven brake rotor thickness. People who call it "warping" are mistaken, lazy or ignorant. As anyone interested in knowledge will learn upon investigation, brake rotors do not warp. |
I, sir, am not mistaken, lazy, or ignorant. I am indeed interested in knowledge, and as I said before, I did indeed investigate. I found that rotors can warp. Excuse me if I missed it amongst your voluminous responses above, but exactly how have you done any investigation to prove your assertions? |
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M635CSi
Joined: 09 Apr 2006
Location: .From Sea to Shining Sea
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| Posted: Jun 15, 2006 1:11 PM Post subject: |
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| C.R. Krieger wrote: | | M635CSi wrote: | | Upon what do you base your statement "The only way that could be is if the hub/bolt circle is out of round"? I ask because your statement is incorrect. |
| Mike W. wrote: | | And I feel your statement is rather bold, with hubcentric rings, and no perceptable play, how could I have different radial runout only by moving the wheel to a different lug position without the hub being out of round. And mind you, this is a repeatable condition. |
You've added two qualifiers that weren't in your first post: 1) "with hubcentric rings", and 2) "no perceptable play". Hub centric rings are a source of trouble and would be the first thing I'd remove. Mount a known good wheel/tire assembly and measure radial runout. If the runout is now within spec, the source of the problem is most likely the wheel/tire/hub ring which is/are out of round or does not fit correctly. |
| C.R. Krieger wrote: | I am the one who first mentioned this phenomenon and I first encountered it with OEM BMW wheels and no hubcentric rings. If what you say is true, then this must mean:
1) That the E28 has the worst hub tolerances in the industry or 2) That the rather unique design of its front suspension makes it more sensitive to typical manufacturing variances or
3) It's just my sloppy maintenance practices. |
While your logic is flawed, your statements do provide useful information. Here are my thoughts;
1) We have no reason to believe BMW hub tolerances are looser than the competition.
2) I think there may be some truth to this statement in that the E28 front suspension, depending on loading, requires different component tolerances in order for people to find the performance acceptable,
3) Your "sloppy maintenance practices" are in part, a matter of record to which you have previously confessed with your statement against BMW interest "I throw away the rotor mounting screw".
| C.R. Krieger wrote: | | Which is it? |
It’s just your sloppy maintenance practices. |
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M635CSi
Joined: 09 Apr 2006
Location: .From Sea to Shining Sea
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| Posted: Jun 15, 2006 3:01 PM Post subject: |
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| Shawn D. wrote: | | Mike W. wrote: | | First off, theoretically, why should a brake rotor be immune to warping? |
| M635CSi wrote: | | Because theoretically and in practice, cast iron brake rotors are brittle. |
That's a bullshit explanation. "Brittle" means that a material cannot withstand a high "delta" (change in length divided by total length) without fracturing. "Brittle" has nothing to do with warping. |
Oh stop. You've confirmed with your own definition that it does indeed have to do with warping. In point of fact, soft things "warp", hard things crack. That's why you can take a mild steel coat hanger and bend it back and forth until it work hardens and subsequently, cracks.
| Mike W. wrote: | | I've seen warped rotors, |
| M635CSi wrote: | | How did you determine they were "warped"? |
| Shawn D. wrote: | | Well, I don't know how Mike did it, but I've checked rotor runout with a dial indicator, measuring from both sides; I determined that rotors can indeed warp, as an "outboard" or "inboard" deflection of a section was corroborated from both sides. It was also evident visually, as I set the brake lathe on "extra fine" radial feed, used new bits, and shaved a teensy bit off on each pass -- the high spots that got touched on one side corresponded to low spots on the other side that didn't get touched. |
That seems like a very good check of axial runout and uneven thickness. To the extent it seeks to prove "brake rotors warp", the technique fails.
| Mike W. wrote: | warped heads, even a rare warped block. Get it hot, and cool it unevenly, and it will probably warp. Next, even on BMW's, if not on E28's I've had surfacing rotors completely eliminate shimmy and brake pedal pulsation.
If it wasn't warped, how come turning them cured the problem. |
| M635CSi wrote: | It didn't cure the "problem"; it "cured" the symptom. The symptom being uneven brake rotor thickness.
Unfortunately, the customer was probably clueless that he left the shop with his car having problem that caused the uneven brake rotor thickness in the first place. |
| Mike W. wrote: | | Well, call it what you want, it has worked perfectly well for me on other cars (albeit only temporarily on my E28). |
| Mike W. wrote: | | Call it warping, or runout or whatever, it means things aren't parallel. |
| M635CSi wrote: | | I choose to use a descriptive term that accurately describes the condition; uneven brake rotor thickness. People who call it "warping" are mistaken, lazy or ignorant. As anyone interested in knowledge will learn upon investigation, brake rotors do not warp. |
| Shawn D. wrote: | | I, sir, am not mistaken, lazy, or ignorant. I am indeed interested in knowledge, and as I said before, I did indeed investigate. I found that rotors can warp. |
That is interesting. You have found that brake "rotors can warp" and I have found and understand why brake rotors don't "warp"
| Shawn D. wrote: | | Excuse me if I missed it amongst your voluminous responses above, but exactly how have you done any investigation to prove your assertions? |
Why investigate something that doesn't happen? I have studied and understand the design and engineering of modern automotive brake systems and grasp the reasons why brake rotors don't warp. My suggestion for people, who think "brake rotors warp", is to dig into the engineering and design parameters behind brake systems to see and understand why they don't.
I have, in the past, professionally repaired and maintained vehicles. Qualified an automotive authority by General Motors. And considered an automotive expert by numerous automotive professionals. No brag, just fact.
"Education without experience is fantasy, experience without education is chaos." |
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