Subframe and Steering Reinforcement

E28 technical advice asked and given! Troubleshooting, modifications and more.
George
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Subframe and Steering Reinforcement

Post by George »

I originally wrote this for bigcoupe. Thought it might be useful here too.

This write up is intended to educate those with e28 5 series. Most of you know that the steering box bracket is prone to failure. There are plenty of threads floating around discussing how/why it fails and what can be done to fix it. Pictures are worth a thousand words, so I’d like there to be a central place to discuss this problem.

There are generally three states of the steering box bracket: intact, cracked, and completely snapped off. This procedure will allow you to reinforce the bracket regardless of the condition of your existing bracket.

There are also multiple ways of reinforcing the bracket.

The first and cheapest way is to use the “bolt and spacer” method. This involves using a long bolt that extends all the way through the subframe. A spacer then sits between the top of subframe and bottom of the bracket. As the bolt is tightened down the head of the bolt is put into compression with the bracket and spacer. The compression force increases the lateral friction between these pieces. The frictional force is what prevents the bracket (and thus the gear box) from moving.

I’m not a huge fan of this set-up because frictional force isn’t the greatest way to prevent movement of the box. It's an adequate solution if your bracket is completely intact. If your bracket is cracked or snapped off, DO NOT use this solution. This solution will prevent the gearbox from falling way out of alignment but it will still move during hard turning.

The second solution involves using the Mwrench steel dowel from Ed Raether. The dowel fits through the subframe and features one end that is tapped for a grade 8 bolt. The dowel fits snugly into the subframe. This fix can be done two ways, by removing the subframe and welding it into place or by simply leaving the subframe intact. The later method can be done in less than 30 minutes. I will be covering both of these methods in this write up. Here are the parts involved:

Image

The third solution is to remove the subframe and “box” the existing bracket. You can cut triangular pieces of steel and weld reinforcements. This requires the existing bracket to be completely intact as well as removing the subframe. Personally, I don’t see the point in doing this. Why remove the subframe if your bracket is still intact? Still, I’m just offering up another solution.

Now, on to the write up. The first method of using the Mwrench dowel is to completely remove the subframe. I happen to have a spare M6 subframe and gearbox so I performed the fix on this subframe and I plan to swap it in at a later date. The bracket on this subframe was completely snapped off. A tiny portion of the side wall remained so I used an angle grinder to smooth it out. The advantage to removing the subframe with the Mwrench dowel is that you can weld both ends of the subframe to secure the dowel.

Completely separate subframe:

Image

The first step is to clean both sides of the subframe. You need a clean surface onto which you can weld. A wire brush or electric sander work great. Then sand some of the paint off of the dowel. It should look this when done:

Image

Place the dowel through the hole in the subframe. It is meant to be very snug so, if need be, you can tap it through with a mallet. The inserted dowel will look like this:

Image

Now, I have a couple of spare gear boxes lying around so I used one of them to mock up how it was supposed to fit. Go to the hardware store (Ace is the place) and get a 6” long 15/32” bolt and nut (7/16” will work as well). Most places wont carry the correct metric size bolt of that length.


Image


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With the gear box lined up, you can see how the dowel fits.

With everything lined up, you can insert the bolt into the dowel and secure the box into the correct position. I would place a tack on both sides of the dowel to prevent it from moving. With the dowel tacked into place you can remove the bolt and gear box and then weld the entire dowel on both sides of the subframe. It should look like this when done:

Image

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Your subframe is now ready to be reinstalled in the car.


The second method involves installing the Mwrench dowel without removing the subframe. This procedure can be accomplished in under 30 minutes if you know how to turn a wrench.

Image

The first step is to remove the existing bolt from the bracket. You need a 17mm wrench on the top and a 19mm socket on the bottom. You can use an extension and fit the socket through the subframe. An impact wrench works great to remove the bolt and nut.

Image

With the bolt and nut removed, you then need to clean the bottom of the subframe (as shown before) to assist in a good clean weld. Should look like this:

Image

Place the dowel through the subframe and then screw the bolt into place. In my case, the dowel was snug enough to not move as I screwed the bolt into it. With everything locked down, you can now weld the bottom of the dowel. It should look like this when done:

Image

Image

Retorque the bolt and then clean off the surface again and spray the bottom of the subframe with some rust inhibitor paint to prevent corrosion.

Image

The first method of installing the dowel with the subframe removed was installed on my '89 635csi. The second method was performed on my ’87 635csi. The car was driveable again in under 30 minutes.

I realize that most people either don’t know how to weld or don’t have their own welding equipment. If welding is not something you can do on your own, I suggest that you install the dowel and torque it into place and then drive to an exhaust shop. Most exhaust shops will have welding equipment on hand and will do it for a small fee.

Of note: There are two different subframes used on the e28 based 6 series. The 633 and 635 up to 88 share a subframe and the M6/88-89 635 share a subframe. I honestly don’t know the difference between the two, other than the cars use different gear boxes. The M6/highline 635 use a short ratio gear box (and sometimes servotronic) while the earlier cars use the standard gear box. I sourced the later subframe for my turbo as I wasn’t sure what (if any) modifications would need to be done to install a regular subframe in the car. I also plan on adding additional support and reinforcement to the subframe.

That’s it! You’re done. Now go enjoy your car.
Last edited by George on Aug 12, 2017 5:39 PM, edited 4 times in total.
Nebraska_e28
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Post by Nebraska_e28 »

Excellent write-up! :clap:
Msystem
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Post by Msystem »

good job.
thanks!
Shawn D.
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Post by Shawn D. »

Sweet writeup -- I'm doing the same soon!

BTW, the word is "reinforcement." "Re-enforcement" would be something like two cops giving you tickets for the same incident instead of one. ;)
Nebraska_e28
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Post by Nebraska_e28 »

Shawn D. wrote: "Re-enforcement" would be something like two cops giving you tickets for the same incident instead of one. ;)
Definition: When your 3rd grade teacher smacks you on the hand for shooting pencils at the ceiling with ruler & rubber band setup.
misha
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Post by misha »

that is a great write up. Just makes this forum that much better.

:banana:
ealinn
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Post by ealinn »

bump for a sticky!

Eric
euro635gas
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Post by euro635gas »

You can also just break the bracket off. Grind the old welds away. Weld a beefy washer over the hole and use the aluminum spacer that is stock on any E32 or E34. Fixed for good. Did this to my 533i over 5 years ago and has never had a problem since.

Nice write up.

The nice thing about BMW is that they fix problems. They fixed it on the E32 and E34s.
locusteater
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Post by locusteater »

Any more bulletproof, and some folks' E28's will come under federal scrutiny. :) (Now to find a spare subframe to minimize downtime . . . . . .)
johnnye23
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Post by johnnye23 »

Great writeup !! :laugh:
euro635gas
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Post by euro635gas »

locusteater wrote:Any more bulletproof, and some folks' E28's will come under federal scrutiny. :) (Now to find a spare subframe to minimize downtime . . . . . .)
I have one that the bracket broke off. I recently replaced one on a customers E24 and have his old one. $50 plus shipping
Lee in MD
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Post by Lee in MD »

All this talk about broken brackets made me paranoid, so I just went out and checked mine and found that the PO already did a bolt and spacer job on the intact bracket. That makes him an alright guy in my book. Too bad some street racing punk in a WRX sent him to the hereafter before his time. Might have been a good guy to know.
George
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Post by George »

still no stickeee :|
Lee in MD
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Post by Lee in MD »

Rather than be a sticky in Tech Talk, shouldn't this thread be promoted to the Tech FAQ? Busted steering box mounts seem to be common enough to warrant a FAQ topic.
George
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Post by George »

Thats what I meant, should have clarified better.
Philo
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Post by Philo »

Lee.., what happened to the PO ??

Also, I posted this as a separate thread but feel it's relative to the steering bracket conversation...

http://www.mye28.com/viewtopic.php?p=681612#681612
Lee in MD
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Post by Lee in MD »

Philo wrote:Lee.., what happened to the PO ??

Also, I posted this as a separate thread but feel it's relative to the steering bracket conversation...

http://www.mye28.com/viewtopic.php?p=681612#681612
Apparently, the guy was a bit of a car enthusiast with several other old rides in addition to the E28. According to his college age son who showed me car, he was out driving around D.C. in his RX-7 one day when he got t-boned by a kid in a WRX. Sure enough, some time after I purchased his E28 I found his registration papers buried in the glove box, Google News'd him, and found a small article in the Washington Post about the accident. Apparently he was on some surface street in the D.C. area that I can't recall and trying to make a left turn onto a side street when this asshole kid in a WRX coming the other way and estimated by police to be going over 100 mph, t-boned him and made him into an instant DOA. IIRC the article said the RX-7 went up in flames and the WRX kid was life-flighted to a local hospital with "life threatening injuries". I never could find any follow up articles to find out if the boy racer dickwad survived or not. Call me a big jerk if you like, but I honestly hope he survived with severe debilitating injuries for what he did to that kid and his mother. The college kid showed me the car but the title was in his mother's name. You should have seen the look on that poor woman's face when she signed the title over to me at my kitchen table. I wanted to give her and her son a big hug but that would have been too weird for all of us. I told the kid that I planned to fix the car up and probably even repaint it and he said his dad would have like that. How's that for pressure :laugh:
turbodan
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Post by turbodan »

Never had a problem with my steering box mount.

M30 cars FTL
lmc337
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Post by lmc337 »

Read this previously when the subject came up -
This morning, my bracket snapped...
had to search to find it again - would have though it would be a sticky in Tech FAQ by now -

Please, oh! Please Beamters, give George the fine credit for the fine write up and enshrine this article to the Tech FAQ section!!


Any edits or editing I can assist with (don't seem to see any myself, pretty straight forward in clear plain English with nice photos to boot!). Only one I can suggest is the link to http://www.mwrench.com/
edlocke
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Steering box

Post by edlocke »

turbodan wrote:Never had a problem with my steering box mount.

M30 cars FTL
You won't if you drive it like a girlie girl......... :D
ASLAN
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Post by ASLAN »

so i know my bracket is toast but i wont have time to fix it for awhile. is it dangerous to continue driving the car without fixing it?
edlocke
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Mwrench

Post by edlocke »

ASLAN wrote:so i know my bracket is toast but i wont have time to fix it for awhile. is it dangerous to continue driving the car without fixing it?
Find 20 minutes and install the "mwrench" fix-it dowel and bolt.....it's that easy.
ASLAN
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Post by ASLAN »

reading this write up made me feel that i should pull out the sub frame. i guess ill use bolt/dowel method until i have the time to do it right.
lmc337
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Post by lmc337 »

ASLAN wrote:reading this write up made me feel that i should pull out the sub frame. i guess ill use bolt/dowel method until i have the time to do it right.
No need. Use the bolt, sleeve and big washer method temporarily. No subframe removal necessary unless you like extra work for either repair.

Do not drive with the broken mount!! Steering is essential...
C.R. Krieger
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Post by C.R. Krieger »

ASLAN wrote:so i know my bracket is toast but i wont have time to fix it for awhile. is it dangerous to continue driving the car without fixing it?
YES!

Bump for inclusion in the Tech FAQ.
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