Why E34 rearends are loose

[Robert K]

Just finished up reassembling the entire rear end of my 1991 535i. Thought I'd share some hard learned lessons about E34 rear suspensions. The whole purpose of all of the work I just did was to stiffen up the rear end of my car. It had always been a bit mushy feeling, like the rear end was about a half step behind the front. I decided to replace the trailing arm bushings (2 per arm), differential mounts (3), and rear subframe mount. Ordered all the bushings from BMA. So I put it up on jackstands and started tearing it apart. I took the trailing arms out and took them to various machine shops to try to find someone to press the old bushings out and the new ones in. I finally found one that said they'd give it a try. They couldn't budge them and since I told them I wasn't wanting to spend hundreds of dollars to get the job done, I took them back from them. Then I took them to an ag dealer. They had a small, heavy-duty C-clamp looking device that they'd used for similar jobs. However, they'd need a pusher block. So back to the machine shop to get that made. While I was waiting for it to get done, I decided to put a bolt into the old bushing, then put a pipe over it to use as a lever to see how much give they actually had in them. Once I had a feel for that, I put the new bushing in a vise and did the same test. Guess what? There was hardly any difference in deflection versus the old bushing. Since I figured it was still going to be a fight to get the new bushings, and the test seemed to indicate that I'd pick up very little stiffness, I decided to leave the old ones in and put the trailing arms back on.

Then I decided to look at the differential bushings. I used a lever between the diff housing and subframe to see how much deflection there was in the old bushings. I could hardly even move the thing. So I decided once again to leave the old ones in. Finally I moved to the subframe rear mount. I loosened all of the subframe mounting bolts/nuts and used a jack to lower the rear of the subframe so I could access the rear mount. When I got it out, I mounted it in a vise and did a similar test to what I did to the trailing arm bushings. I then repeated the test using the new mount. Guess what??? The old original was stiffer than the new one. So again, I put the old one back in. So after about 10 hours work, my car is back together with all of the original parts that were in it before I started this project and all the new bushings are laying on my bench.

While I still had the car on jackstands, I decided to put a lever between the subframe and the unibody near the large front subframe bushings. That's when I discovered where all of the movement in the rear end is. It's the stupid subframe bushings. I had just replaced mine a little over six months ago with new Mahles. But using a 18" lever, I could move the subframe at least a 1/2 inch. So, the lesson I learned is that although the subframe mounts probably contribute to a cushy ride, the absolutely suck in the handling department. I'm going to send the bushings I didn't use back to BMA and order some of Bruno's subframe inserts. I figure they can only help. I may even try to engineer something up myself to really stiffen them up. I've read about people pouring urethane in the voids in the OE subframe bushings and would probably recommend that to anyone intent on changing them out. I may try to figure out how to pour that stuff in mine while the bushings are in the car. After this whole ordeal, I suppose I'd recommend upgrading your subframe bushings if you're trying to stiffen up your E34 rearend. The OE trailing arm bushings, diff mounting bushings and subframe rear mount all appear to be well engineered and long lasting. In my opinion, the subframe bushings are just poorly designed and contribute the majority of the looseness of the E34 rearend.

One last thing. Even though I experienced quite a bit of frustration in this wrench session, I hope you'll notice that I did not find it necessary to use profanity in my post to explain what I'd learned. I have noticed more and more people on this board who can't seem to say anything unless they pepper their message with profanity. Guess what? It's not necessary and in the past, was rarely found on this forum. I suppose if someone just doesn't have the verbal capacity to say anything without profanity, they could always hop on over to Roadfly. I'm sure they wouldn't mind.

Grace and peace,

Robert K
1991 535i

[myles]

Interesting info Rebert. Thanks for sharing. I've often wondered about how all of those bushings are lasting in my car but have never had the time to look further into it.

[repenttokyo]

could it be that you just got a bad set of subframe bushings when you replaced them 6 months ago?

[Tiger]

Geez and no profanity at all? Not a peep? So you are saying that the front subframe bushing are bad... even though you put in new one... So that bruno's inserts are probably the easiest way to solve the problem?

[Robin-535im]

Well Robert... you are perhaps a wiser man than I...

I did the same as you, but in fact did replace all the bushings. It was a bit stiffer after all 10 (big diff support too) bushings were renewed, but only a bit. I had the benefit of help from Don here on the board, which outweighs a whole city of machine shops as we were able to finally get the trailing arms replaced. My only regret is that I used stock e34 and not m5 bushings as replacements - different part number and presumably stiffer.

In retrospect it was marginally worth the effort, mainly because I had Don's help. Without that it would have been d**n (darn) hard. :)

I do sleep better at night though, knowing I have another 100k miles before I have to worry about the rear end!

- Robin

[Boone.Msi]

What?! A forum full of Aussies and Yanks with no profanity? ...Blasphemy:p

[ThoreauHD]

So, M5 bushings good. Subframe bushings need urethane filler or Bruno's inserts. Works for me. I wonder if the M5 has the same subframe bushing looseness?

[pundit]

What?! A forum full of Aussies and Yanks with no profanity? ...Blasphemy:p
Working on cars without profanity is simply not normal! :p

[BigKriss]

Winfred and Bill R have both told me the trailing arm bushes almost never wear out. I have yet to fit my subframe bushes with liquid urethane. I don't know what rear swaybar your running Robert, maybe you can fit a larger one to get the rear of the car firmer. As for profane language, I'm young and dumb. I don't mind it.

[Robert K]

I don't think I got a bad set of subframe bushings, I just think they are that flexible by design. As I remember, the subframe moved around with the old bushings in too and they weren't degraded that badly. I think BMW just carried away with trying to provide a smooth ride. Also, on the E39, they used four bushings to mount the subframe instead of two and the center rear mount. I think they learned their lesson at our expense. I have a feeling that the E39 does not have the slop in its rearend setup.

Grace and peace,

Robert K
1991 535i

[Robert K]

But after I got under the car and started realizing that I wasn't going to pick up much stiffness, it just didn't seem worth going through all the hassle I was going to have to go through to replace them. It was very apparent to me that if I wanted to tighten things up, I was going to have to do something about the subframe bushings. That's what I'm going to work on now. Congratulations on getting all of your bushings replaced. That had to have been some tough work.

Grace and peace,

Robert K
1991 535i

[Robert K]

I actually bought the Racing Dynamics sway bars shortly after purchasing the car. I've always been a fan of fitting the biggest sway bars possible to my cars. I'll give up a bit of ride to increase the responsiveness of the quicker turnin any day. I've also got the M Technic spring package on mine with stock Boge gas struts. On top of that, I've got 17" Style 5 wheels with Bridgestone Turanza LSZ's. The ride is firm, but certainly not punishing.

Grace and peace,

Robert K
1991 535i

[Ross]

Robert,
Glad you figured this out, sorry you are facing the dreaded subframe bush job.
Also. I find curse words useful. For example, the simple phrase "**** you" succinctly conveys malevolence in two syllables. Should I utter "**** you, you ****in' ****", then of course then your supposition of ignorance would apply. I haven't seen posts here of the latter nature.
Sorry if you are offended, that is not my intent when using them.
You are by now familiar with those of us here who curse and under no obligation to read our posts.
Don't condescend or preach to me.

[repenttokyo]

I actually bought the Racing Dynamics sway bars shortly after purchasing the car. I've always been a fan of fitting the biggest sway bars possible to my cars. I'll give up a bit of ride to increase the responsiveness of the quicker turnin any day. I've also got the M Technic spring package on mine with stock Boge gas struts. On top of that, I've got 17" Style 5 wheels with Bridgestone Turanza LSZ's. The ride is firm, but certainly not punishing.

Grace and peace,

Robert K
1991 535i


If you put a smaller sway bar on the front of the car, and a stiffer one on the rear, you will tighten up your rear end feel in turns.


Also, check out this tutorial about adding a plate underneath the bushing to stiffen things up:

http://bmwe34.net/e34main/upgrade/subframe_plates.htm

[kick7ca]

Thanks RobertK.
This is interesting because I had planned to get under my 535 and basically rebuild the rear end. I've already replaced my rear subframe bushings, shocks/mounts and the rear end is still loose.
Think about it, the front end has how many major bushings?......2 per side right, in the control arms, and how often do those go bad? Often enough that we've all done it at least once (or will). So why would you expect the rear end bushings to last forever? They must wear out and collectively affect the handling and cause drivetrain slop.
Robert you say the new ones didn't feel any stiffer on your bench, but can you accurately bench test the old vs. new bushings? There may be other important qualities to these bushings other than deflection stiffness of a bolt slid through it. I don't know the answer, but it just seems logical that the bushings would wear out.
Awesome thread. It would be great to hear from more guys that have already rebuilt the rear end and what their results were.

And Kudos to RobertK for calling out how nice it is to read clean language. The more you curse the less effective it becomes and you can end up sounding a grade school drop out.

[Fred/Houston]

No prafanity? No wonder it's not fixed! lol
I agree with you, that was a great writeup & I'm saving it because my rear is loose as well. You probably saved me a hell, I mean, a heck of a lot of work trying to find the problem.
Thank you
Fred/Houston

[Morgenster]

Hold on a sec, how do worn bushings contribute to drivetrain slop? By drivetrain slop I hope you mean the jumpyness in 1st or second gear when you let the cluch go or go from accelarating to decelarating (or vice versa) in low gears. I was thinking drivetrain slop is more of a problem with diffs and "guibo's". I have yet to find out what a guibo is actually.
As for lateral movement: I only get some extra sway when doing a long hard turn at high speed. Does this mean that this is actually normal?

[kick7ca]

The rear diff is held in place by bushings (3 I think), if they're worn the diff could squirm around under load / no load changes. I don't think they're the only contributors to drivetrain slop, but certainly play a part. If any of the rear end is loose/worn including the trailing arm bushings, then I think it follows that the entire rear end will squirm around more with the drivetrain torque, this is what I say contributes to that sloppy feel.

[Ross]

Also this contributes to that feeling of the car squirming around under you on the highway.

[RallyD]

thanks RK, I'm just going to fill the original bushings, pop in the "Brunos", change the dogbones and let it sit for a couple of days. I'm also going to fill the front thrust arms prior to install and replace those. While i'm at it should just go ahead and put new springs and shocks in. Why not, its only got 200K

[steve0suprem0]

Also, check out this tutorial about adding a plate underneath the bushing to stiffen things up:

http://bmwe34.net/e34main/upgrade/subframe_plates.htm

correct me if i'm wrong, but this is what we're (or, everyone else, rather. while i eavesdrop) talking about right?

also, great thread, lotsa info. and another thing, you're absolutely right about the profanity. unfortunately, i'm one of those guilty, and there's no excuse for it. other than i'm usually pretty upset when i do it. which is probably worse.

[Barney Paull-Edwards]

Did the same thing myself! The one thing that made more difference than anything else was bruno`s delrin inserts.By the way, the best handling cars on the planet do not have sway bars at all as they are a compromise to support a bendy shell, which the E34 does not have. Try upping the spring rate by 30% and dropping the sway bars altogether,just dissconnect at one end to try.

[repenttokyo]

correct me if i'm wrong, but this is what we're (or, everyone else, rather. while i eavesdrop) talking about right?



\
not quite following you...

[steve0suprem0]

@repenttokyo:


Bruno's subframe inserts. I figure they can only help. I may even try to engineer something up myself to really stiffen them up. I've read about people pouring urethane in the voids in the OE subframe bushings and would probably recommend that to anyone intent on changing them out. I may try to figure out how to pour that stuff in mine while the bushings are in the car. After this whole ordeal, I suppose I'd recommend upgrading your subframe bushings if you're trying to stiffen up your E34 rearend. The OE trailing arm bushings, diff mounting bushings and subframe rear mount all appear to be well engineered and long lasting. In my opinion, the subframe bushings are just poorly designed and contribute the majority of the looseness of the E34 rearend.


these are the same things as the bmwe34.net link you posted, right? or is that something else entirely? not trying to be rude or anything, just double checking my own understanding.

[ILoveMPower]

Not sure how much this helps, mostly due to the fact I don't have experience myself, but I've heard from several people that bruno's inserts make a world of difference and is one of the first mods you should do as far as price is concerned.

Cheers,
- Jeremy

[steve0suprem0]

yeah, mine go in tomorrow. along with the supercharger (!!!) and reiger lip... hmm, i think that's all i have left.

[Blitzkrieg Bob]

It's an F'n passenger car!

[Robin-535im]

yeah, mine go in tomorrow. along with the supercharger (!!!) and reiger lip... hmm, i think that's all i have left.
VF Engineering - I assume that's what VFE is... do they make a kit for the e34 or are you customizing from one for an e36?

[Evan]

get laid, robert

[Tiger]

Gee... everyone is getting mean here.

[attack eagle]

Taking the RTABs out is easy... takes all of 5 minutes.

Use a propane torch to heat the centersleeve until they catch on fire, let em burn a few minutes, then a screwdriver to push the pieces out as the rubber burns away.
Then you can cut the outer sleeve along its length with a jigsaw or hacksaw blade, grab it and bend it inwards and it will drop right out.

Then all you need is someone to press the new ones in.

[Kibokojoe]

My mother always told me that people who use profanity are just covering up the fact that they don't have the verbal capacity to explain themselves without it. You know she was right.

[attack eagle]

Why you are *&^%$ and your mother was *&^%$ too
















*&^%$ = right

[Evan]

where would we be without our mothers!

[Robert K]

To test the control arm bushings, I inserted a bolt about halfway into the bushing, then put a hollow tube over the bolt. With the additional leverage, it wasn't difficult to deflect the bushing. I then mounted a new bushing in a vise, inserted the bolt, put the tube over it, and tried to deflect the bushing. Sure it's not the same as the actual parts in operation on the car. But I expected that the new bushing would be quite a bit harder to deflect than the old one. That was just not the case.

In the case of the large center mount found on the rear of the subframe, my old mount actually was stiffer than the brand new one I intended to put in. After testing both in a vise using the method above, it took about five seconds to decide the new, looser mount was not going in the car. As far as testing the differential mounting bushings, I put a solid bar between the diff housing and the subframe and tried to deflect it. I couldn't hardly get the thing to budge.

However, when I put the same bar between the subframe and the unibody at a point right next to the subframe bushings, I could move the subframe around A LOT! At that point, I knew my best chance of improving the stiffness of the rearend revolved around the subframe bushings. To that end, I now have a set of Bruno's subframe inserts on their way to me. I may also try to fill the ones in the car with urethane if I can figure out how to do it with them still in the car.

Hope this info clarifies how I arrived at my findings.

Grace and peace,

Robert K
19991 535i

[Robert K]

I sort of agree with some of what you said. I believe formula one cars don't have sway bars and they handle great. However, their center of gravity is unusually low and they have high spring rates compared to normal street car. I think you are right in saying that a car with very high spring rates might not need sway bars. However, just how streetable would they really be?

To allow our cars to have a civilized ride, the springs are softer. However, the downside to softer springs is that the body of the car tends to want to lean outward when the car goes around a corner. The unfortunate side effect is that weight is transferred to the outside of the car, which hurts cornering performance. To counter the weight transfer, sway bars are used, which essentially connect the chassis (car body) to the control arms. Now when the car goes around a corner and the body tries to lean towards the outside of the corner, the sway bars act as a lever to resist the lean, helping keep the car body flatter and more centered over the suspension. I think disconnecting the sway bars on an E34, even one with high spring rates, would turn the car into an incredible leaning machine, especially considering the high center of gravity and weight of the car. The ideal system would be the one currently used by some high end manufacturer (Mercedes, BMW,???). They've found a way to turn their sway bars on and off as conditions warrant. However, I can't afford the cars with this technology, so I suppose I'll have to stick with my 155,000 mile E34.

Grace and peace,

Robert K
1991 535i

[ryan roopnarine]

i'm sorry, i'm going to regard your findings with a little bit of skepticism. I don't understand how (lets say your car was a 1991 made in 7/90) 17 year old rubber is going to possess the same characteristics as new stuff, even if the new stuff was produced with "crap" modern methods, or is somehow lacking to the factor/90s era stuff. i don't know if i'd be brave enough to tear the rear end of my car apart and adjudge the suspension components equivalent by the deflection of a bolt.

[paul p (chi-town)]

get laid, robertErr, that’s a little below ze belt.

The use of negative or pejorative language when dealing with an inanimate object OR even a business that sells junk..........especially when days of billable or personal time is wasted, judgment call.
The frustration of two grown men aired out here........as if we are a fly on the wall of the shop. That hot, humid, swamp like shop. Southern poetry to my ears actually (ya gotsta imagine the accent).
Not to mention it’s not like it’s a daily occurrence.

Trying to start a flame war is being an ass hat.
Robert was just reminding us that children could be listening, a dirty look maybe, but no flames. Nothing wrong with that (and i’m not surprised, he has a little more startch in his shorts than most of us). Nothing wrong with him trying to share is experimental findings either, it's what we're all about.
Even if i agree that in certain situations somewhat spicier language is understandable.

Let’s keep the gloves on kids.


”Hang up & Drive!”
94 BMW 530iT&A 135K, ‘Helga’ ( for sale....WHOOPS, haulin again *confused* )
92 BMW 325i 135K, ‘Rolf’ ( perfect ‘cept for raw bumpers *sigh* )
91 Volvo 740 Turbonium Vagon 195K ‘Thor’ ( where’s my check! *rolleyes* )
93 Datsun NX2000 175K ‘Carla’ ( beater rocket is back *whoohoo* )
85 Toyo MR2 125K ‘Jerry’ ( dare i drive it *duh* )
“Do you want the signature On or Off...............too bad." – Captain Murphy

[DanDombrowski]

I had about 165k on my RTABs when I changed them out. It seems to have corrected my camber/toe problem, so while they may not have lost any rigidity, I believe they may have been permanently deformed from where they should be.

I never did an alignment before or after, so I can't say for certain if it helped. I never looked at the subframe bushings when I was in there, but I will next time. Thanks for the info!