Improved Clutch Over-Center spring - swivel joint upgrade

E28 technical advice asked and given! Troubleshooting, modifications and more.
BenGerman
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Improved Clutch Over-Center spring - swivel joint upgrade

Post by BenGerman »

Another idea that has been floating around in my head, confirmed by a fellow board member, is on the drawing board.
I've read multiple topics about clutch helper or over center springs breaking, bending or the snap ring disengaging.

There is two major issues with the assembly: The soft cast aluminium shaft and the tiny snap ring holding the whole spring assembly together.

Just by the way the forces are being applied into the assembly there is a risk of bending the shaft, especially when running heavier clutches. If you have the original spring in your car, is likely that it is bent.
For better clutch engagement, people would like to tighten the spring more, which increases the risk of destroying the whole assembly.
If it breaks, you have to buy the spare part from BMW which is around $100 now.
For example, the assembly below I pulled apart by hand. You can see how tiny the snapring is that holds the assembly together.

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What if there was a way to redesign the assembly, improving the material and snap ring design, as well as allowing for different spring rates?
I have found a Standard spring that can be used in the assembly and is available in different rates.
Making the shaft assembly won't be easy, but it is doable.

Image

Curious to hear some thoughts.
The first prototype should be ready soon and will hopefully go in a car shortly after.
Last edited by BenGerman on Sep 25, 2018 2:03 PM, edited 2 times in total.
SlickDizzy
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Re: Any interest in an improved Clutch Over-Center spring?

Post by SlickDizzy »

I'm absolutely in as long as the cost is not exorbitant.

I've always suspected there is some flexing going on with the one in my car (not surprising after 300k+ miles). With my upcoming 4500mi roadtrip and the track time the car will experience after, that's an assembly I do not want to let go. I also imagine feel/engagement would be more linear by taking the slop out of the assembly.
BenGerman
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Re: Any interest in an improved Clutch Over-Center spring?

Post by BenGerman »

SlickDizzy wrote:I'm absolutely in as long as the cost is not exorbitant.
That's one of the things I have to keep in mind. I would like to use as many standard parts as possible, trying to keep the costs down.
Ultimately the price will be somewhere in the range of the factory part, maybe slightly higher.
Shawn D.
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Beamter
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Re: Any interest in an improved Clutch Over-Center spring?

Post by Shawn D. »

For a part that's problematic for many folks, it's a good idea.

The part at the bottom can be improved over your depiction, though. There's no need for the intermediate step between the base and "blades," and as long as the assembly can tilt enough one way or another, the "blades" can (and should) be made shorter.
Philo
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Re: Any interest in an improved Clutch Over-Center spring?

Post by Philo »

Great talking with you the other day Ben. As you know I'm 1000% in ! And, I'll do the demo field testing and produce a write up on how to properly adjust the spring. Also, I really think you should consider offering a retrofit kit as well as a new part. If someone recently installed a new original part there is no need to replace the spring and plastic bits. But the adjuster rod and how the snap-ring keeper attaches has to be replaced.

Also, the pedal box reinforcement should be installed as well. I've had zero pedal box side torquing since I installed it.
http://www.mye28.com/viewtopic.php?t=103670

Let me know when you get close to having a demo.

Phil.
RonW
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Re: Any interest in an improved Clutch Over-Center spring?

Post by RonW »

BenGerman wrote:There is two major issues with the assembly: The soft cast aluminium shaft and the tiny snap ring holding the whole spring assembly together.
Actually three issues:
  1. The shaft breaks at the bolt hole. This may be related to pedal bracket failure, common in the E28.
  2. The tiny snap ring (not used once the device is in place) isn't quite up to the task and the assembly can fly apart before you install it.
  3. The pivot blades can fail by bending, wearing down, or getting mashed, especially if they weren't greased during installation.
I've had all three of these problems. The "right" way to fix the shaft design is to allow the circular part to pivot relative to the shaft, maybe by adding a spherical roller bearing, but that's overkill.
Shawn D.
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Re: Any interest in an improved Clutch Over-Center spring?

Post by Shawn D. »

RonW wrote:The "right" way to fix the shaft design is to allow the circular part to pivot relative to the shaft, maybe by adding a spherical roller bearing, but that's overkill.
It's not overkill if it fixes a known problem and is basically only the next step up in the solution chain. Spherical rod ends are fairly inexpensive.
BenGerman
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Re: Any interest in an improved Clutch Over-Center spring?

Post by BenGerman »

RonW wrote:
BenGerman wrote:There is two major issues with the assembly: The soft cast aluminium shaft and the tiny snap ring holding the whole spring assembly together.
Actually three issues:
  1. The shaft breaks at the bolt hole. This may be related to pedal bracket failure, common in the E28.
  2. The tiny snap ring (not used once the device is in place) isn't quite up to the task and the assembly can fly apart before you install it.
  3. The pivot blades can fail by bending, wearing down, or getting mashed, especially if they weren't greased during installation.
I've had all three of these problems. The "right" way to fix the shaft design is to allow the circular part to pivot relative to the shaft, maybe by adding a spherical roller bearing, but that's overkill.
Regarding the Snap ring: you say it’s not used once the assembly is in place? Doesn’t it bottom out every time the clutch pedal is activated and released again? Basically once you take the tension off the spring that’s what the assembly (preload of the spring) rests against, no?
There is a little step in the bottom plastic spring keeper that the snap ring rests against in my assembly. It’s totally worn in.

I can’t quite follow the comment on the circular part pivoting relative to the shaft, would you mind explaining?
I’m open to ideas as long as we can manufacture it with a reasonable effort.
Shawn D. wrote:For a part that's problematic for many folks, it's a good idea.

The part at the bottom can be improved over your depiction, though. There's no need for the intermediate step between the base and "blades," and as long as the assembly can tilt enough one way or another, the "blades" can (and should) be made shorter.
From testing with the assembly that I have (pictures above, rod is bent pretty good) the plastic part would bottom out without the step or shorter blades. While the blades are not worn at all, the plastic retaining them is cracked and would fail at some point.

So far the idea is to make the rod and bottom spring keeper from stainless steel. The blades would be machined into the material in the bottom.
RonW
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Re: Any interest in an improved Clutch Over-Center spring?

Post by RonW »

RonW wrote:The "right" way to fix the shaft design is to allow the circular part to pivot relative to the shaft, maybe by adding a spherical roller bearing, but that's overkill.
Shawn D. wrote:It's not overkill if it fixes a known problem and is basically only the next step up in the solution chain. Spherical rod ends are fairly inexpensive.
I was specifically referring to the spherical roller bearing as overkill.

I like the idea of a spherical rod end, essentially a spherical plain bearing where the existing part just has a plastic insert. You might be able to find a spherical rod end with the right threading and machine it to match the existing part - just remove the thread below a certain point and make a groove for the snap ring.

Possible issues:
  • Side clearance. I'm thinking specifically of the clearance between the updated part and the part it bolts to. It may be that the updated part can simply be shoved a little to the right and the pivot slot in the pedal bracket can accommodate.
  • Bolt design. The bolt may need to be lengthened to have a longer shoulder.
BenGerman
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Re: Any interest in an improved Clutch Over-Center spring?

Post by BenGerman »

But what would the advantage of a spherical plain bearing be, compared to the bushing solution?
I can see the additional axis of freedom to help with any of the existing issue, but I could be missing something.
I’m just trying to justify the added costs. If it solves one of the three issues above, lets do it!
A spherical plain bearing in a size that would be feasible is between $10-15.

There is some room in the bracket to accommodate moving the assembly 2-3mm to each side.

In our current concept, the snap ring will be completely replaced by a different solution.
For this step I was planning on using a glide bushing like the factory does. But again, if there is ideas for improvements, let’s try them!
I’m sure Phil is going to provide us great feedback, even though long term durability is a different discussion.

E: What is the reason the bolt has the eccentric? I know you set the pedal distance with the eccentric on the MC. I couldn't find any installation instructions for the spring assembly regarding the eccentric in the factory manual or Bentley.
The only thing I found is the drawing for the spring height setting, which is supposed to be 34.5mm. If I adjust my assembly anywhere close to this, the snap ring pops out.
cek
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Re: Any interest in an improved Clutch Over-Center spring?

Post by cek »

Of this has ANY chance of fixing my Pedal Buzz I'm in.

Even if it doesn't, I'm in just because this is interesting.
Mike W.
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Re: Any interest in an improved Clutch Over-Center spring?

Post by Mike W. »

BenGerman wrote:me point.

So far the idea is to make the rod and bottom spring keeper from stainless steel. The blades would be machined into the material in the bottom.
You might want to reconsider using stainless. It obviously has great corrosion resistance, but that's not needed in this application. Strength is fair but it's hard to machine and somewhat brittle. I'm way far from a materials expert, but I know a little bit. By all means search on it a bit, don't take my word, as I said I'm no expert.
SlickDizzy
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Re: Any interest in an improved Clutch Over-Center spring?

Post by SlickDizzy »

Mike W. wrote:
BenGerman wrote:me point.

So far the idea is to make the rod and bottom spring keeper from stainless steel. The blades would be machined into the material in the bottom.
You might want to reconsider using stainless. It obviously has great corrosion resistance, but that's not needed in this application. Strength is fair but it's hard to machine and somewhat brittle. I'm way far from a materials expert, but I know a little bit. By all means search on it a bit, don't take my word, as I said I'm no expert.
Agreed, I think hardened steel would be a better choice, especially for the threaded rod and adjusting bolt. If corrosion is a worry the parts could be zinc-plated after fabrication.
BenGerman
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Re: Any interest in an improved Clutch Over-Center spring?

Post by BenGerman »

Mike W. wrote:
BenGerman wrote:me point.

So far the idea is to make the rod and bottom spring keeper from stainless steel. The blades would be machined into the material in the bottom.
You might want to reconsider using stainless. It obviously has great corrosion resistance, but that's not needed in this application. Strength is fair but it's hard to machine and somewhat brittle. I'm way far from a materials expert, but I know a little bit. By all means search on it a bit, don't take my word, as I said I'm no expert.
SlickDizzy wrote:
Agreed, I think hardened steel would be a better choice, especially for the threaded rod and adjusting bolt. If corrosion is a worry the parts could be zinc-plated after fabrication.
All input is valuable.
I've been thinking a little bit about the material choice.
We have machined stuff from 304 Stainless before and it's not horrible with the right tools. The other consideration is 7075 aluminium.
We have also considered using 4140 or 4340, which in my opinion would almost be overkill for the application.
Last edited by BenGerman on Apr 01, 2018 9:56 AM, edited 1 time in total.
RonW
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Re: Any interest in an improved Clutch Over-Center spring?

Post by RonW »

BenGerman wrote:Regarding the Snap ring: you say it’s not used once the assembly is in place? Doesn’t it bottom out every time the clutch pedal is activated and released again? Basically once you take the tension off the spring that’s what the assembly (preload of the spring) rests against, no?
No. The helper spring is the reason the clutch pedal returns all the way. Without the helper spring, the clutch pedal wouldn't return all of the way, and the cruise control clutch switch would not close, so you'd have no cruise control.
BenGerman wrote:I can’t quite follow the comment on the circular part pivoting relative to the shaft, would you mind explaining?
The reason the circular end of the shaft snaps off is that the bolt isn't at the perfect angle. The whole clutch pedal assembly can flex (the common pedal bracket failure we all know and love is evidence of this) and that changes the angle of the bolt. The circular end on the shaft can't accommodate this angular change, so the bolt exerts torque on the shaft, flexing and fatiguing it until it breaks at the usual failure point.

By adding a spherical bearing, you'd be allowing the bolt angle to change without exerting torque on the shaft, so the shaft won't break.
cek
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Re: Any interest in an improved Clutch Over-Center spring?

Post by cek »

BenGerman wrote:
Image
Image
Would someone please post a pic of the the pedal bracket detail where the horizontal flange/rib attaches/sits? I can't see well enough into my cars, assembled, to remember exactly how it works.
RonW
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Re: Any interest in an improved Clutch Over-Center spring?

Post by RonW »

From RealOEM: 5' E28 535i PEDALS/STOP LIGHT SWITCH

The pedal bracket is part #1 on the diagram. On the left of the bracket, toward the middle of the picture, you'll see the extension with the embossment where the tabs sit.
BenGerman
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Re: Any interest in an improved Clutch Over-Center spring?

Post by BenGerman »

I’m still on the road but I have the pedal assembly and spring on my workbench and will some
Pictures later.
I think the bending comes more from the fact that the load on the spring assembly is not fully axial, but you are always pushing in an angle. Instead of only compressing the spring you also bend the shaft.
RonW
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Re: Any interest in an improved Clutch Over-Center spring?

Post by RonW »

BenGerman wrote:I’m still on the road but I have the pedal assembly and spring on my workbench and will some
Pictures later.
I think the bending comes more from the fact that the load on the spring assembly is not fully axial, but you are always pushing in an angle. Instead of only compressing the spring you also bend the shaft.
Theoretically you should put some kind of pivot in the plastic part, down near the blades. This pivot would allow the whole assembly to tilt to the left or right without unevenly loading the blades due to some sideways displacement. If you redesigned the plastic part to be made of metal, you could machine a "living hinge" (probably the wrong term) perpendicular to the blade edge that would allow this pivoting. This hinge would have to tolerate the axial load from the shaft, of course, but it wouldn't have to flex much - no more than +/- 5 degrees, I'd think, so it could be just a thin part of the metal.
BenGerman
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Re: Any interest in an improved Clutch Over-Center spring?

Post by BenGerman »

So here is whats happening under pressure. Was a bit scary compressing it, since the snap ring was not in...
As the spring gets compressed the lever from the clutch pedal also does a rotational motion.
So, the Pedal moves along the red line, while the assembly has it's fixed position (besides the rocking thats allowed) in the yellow position.
Therefore, the force the assembly sees goes somewhere along the blue arrow. I believe that is the main reason for those rods bending.

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cek
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Re: Any interest in an improved Clutch Over-Center spring?

Post by cek »

^ 1 x 10,000 words, right there!
demetk
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Re: Any interest in an improved Clutch Over-Center spring?

Post by demetk »

Wow. Looks like that pot metal rod is definitely not up to the task. My m8 8.8 bolt is working a lot better and shows no signs of fatigue.
BenGerman
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Re: Any interest in an improved Clutch Over-Center spring?

Post by BenGerman »

Tried reversing the assembly to get a different perspective.
This happened:

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BDKawey
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Re: Any interest in an improved Clutch Over-Center spring?

Post by BDKawey »

very cool to see the motion in steps like that, I initially took my center spring out of my car because I have a wildwood clutch master cylinder with an internal spring. but after understanding how these work more and that they reduce effort at the bottom of the pedal and help return it at the top, I plan on reinstalling it because holding my stock clutch in is like a leg day workout.
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Re: Any interest in an improved Clutch Over-Center spring?

Post by davintosh »

I've never had a problem with that spring (knocks on wood) so haven't delved into this issue much, so my question may not be valid, but couldn't you somewhat solve the problem by snugging that nut on the outside to the point where it allows the bushing that's connected to the clutch pedal to rotate? Considering the presence of the brass bushing in the eye and the self-locking nut on the outside, it looks to me like that's the way it was designed.

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:dunno:
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