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View Full Version : Complex question about e32/e34 rear brake setups...



genphreak
05-29-2006, 07:54 AM
I was just discussing e34 ride-height/alignment in Charles' thread (http://www.bimmer.info/forum/showthread.php?t=22347), and a strange thought came over me.

Some of you may remember I was looking into e34 brake components recently as I posted new info on it and gave it to Bruno to update bmwe34.net's brake upgrade (http://www.bmwe34.net/e34main/upgrade/brakes.htm) pages. Bruno fixed the main issues, but I was surprised he didn't take across any of my research on the 12mm rear brake rotors fitted to all 6 cylinder e32s and 730i V8s. Bruno's position seems to be that these components don't fit e34, period. (He didn't put them in as an option, even an untested one).

Another thing that bmwe34.net makes plain is that rear brake rotors from e32 do not fit normal e34s. The fronts on the other hand are more or less common between the two models.

However the rear brakes on bigger e32s are common to e34 M5, and so are a lot of other suspension components for that matter.

Now Kristian and I recently installed an M-technik suspension package on my e34 535i. It consists of the fat sways M cars have, and (very) lowered springs and the corresponding shocks. We also renewed all the front suspension components at the same time, so after checking all 4 wheels on a decent alignment machine I was wondering why the rear specs were nowhere near the specs listed in the Bently for any of the 3 suspension setups e34s are known to have; Stock, Sport or M-technik.

And my car was well within spec at the stock ride height, so what to do now?

After looking into it I noticed some component differences on M-cars that may account for the rear geometry being different. After reading Charles' thread today I got to thinking about it again.

Looking at rear suspension differences between M5 and normal e34, there are several, namely:
Axle carrier housing (the big rear wishbone that has the diff within it)
Trailing arms
Hubs
Trailing arm bushes
BrakesWhat I was surprised to find was that the bigger e32s share the same overall setup as M5, further suggesting that e32 rear brakes would fit stock e34 (somehow).

So what we need to know (if anyone has had any knowledge on fitting e32 brakes to e34s), is;

If one were to swap the calipers, carriers and rotors straight over from say a 735i to a 525i, why would the rotors not mount up? Do they physically not mount on an e34 hub? One can goto the extra effort of fitting the e32 hub (the trailing arms are common between standard e32 and e34 so we know this (BMW actually call it a side shaft/drive flange assy) would actually fit.

Once mounted, is the rear wheel track altered and by how much? (This could be advantagous or a showstopper of course.)

ie take e32 735 brakes for example;

the difference is that the rear discs are 12mm, not 10mm like on most e34 5er. Slightly different calipers and caliper carriers are thus used.

Now if this swap were indeed possible, it would be great for the community to know as all those 735 brakes rotting in wreckers around the world could be going to new homes on e34s- and would be slightly better than the stock ones to boot.

Of course we already know that e32 740 and 750 rear brakes fit so long as one uses 540 rotors, but if the above is right, perhaps using the e32 hubs as well as e32 rotors one can also net a desirable change in rear wheel track?

Now e34 guru Bruno assures us they do not fit (http://www.bmwe34.net/e34main/upgrade/brakes.htm), but it is plainly obvious that they would if one were to also change the trailing arms, hubs and rear axle carrier (as this makes a standard e34's rear suspension an M5 setup), and we know M5 brakes are the same parts as used on 740 and 750 e32s.

Another question (I'd like to know) is; what happens if one were to change the trailing arms on a stock e34 for M5/big e32 trailing arms, would they fit and what effect would this have? Would one need to also change to an M5 rear axle carrier housing to get the arms to fit or will the trailing arms fit any subframe (ie axle carrier housing)

Does anyone know? Would anyone care to check any of this out? Perhaps we have more brake and rear wheel track options than we know on e34 :)

Simple things we need to know
Measure up a rear trailing arm from an M5, 740 or 750 - and compare to the stock e34 arm.
Measure up the rear axle carrier (I doubt anyone can do this one) -compare any e32 or M5 carrier to stock e34
Measure up a rear drive flange (rear hub assy) from any e32 and compare to a standard e34 unitCheers,
:) Nick

mholbrook
05-29-2006, 08:24 AM
I believe if you look at Bruno's site you will see that the calipers and carriers for the 7xx and 540 are the same. The rotors for the 7xx will not fit but the rotors for the 540 are a match. I have these calipers and carriers on my work bench waiting for the proper brake job time to install. I installed this setup on my last 535 with no problems. The stock rotors are 302x10 and the 540 are 302x20 vented if I remember correctly. I am also going to go with the slight upgrade of 540 rotors on the front of my 535 so I can run 15" winter wheels.

genphreak
05-29-2006, 08:38 AM
I believe if you look at Bruno's site you will see that the calipers and carriers for the 7xx and 540 are the same. The rotors for the 7xx will not fit but the rotors for the 540 are a match. I have these calipers and carriers on my work bench waiting for the proper brake job time to install. I installed this setup on my last 535 with no problems. The stock rotors are 302x10 and the 540 are 302x20 vented if I remember correctly. I am also going to go with the slight upgrade of 540 rotors on the front of my 535 so I can run 15" winter wheels.Thanks Mike! That's absolutely right. The question is; what happens should you try to use e32 rotors, and if they won't fit-why. I mean, what happens if you swap the hubs (or more speciifcally the drive flange and axle shaft assys) to the e32 versions (as then they have to fit)... what kind of result do you end up with? :) Nick

gale
05-29-2006, 09:28 AM
Can't say if the bushings are different, but according to the ETK, the rear trailing arms are common almost accross the board, so that leaves the possibilities wide open to swap just about any brake/hub/bushing combo:

Part Cross-reference
Part 33321133393 (TRAILING ARM, LEFT) was found on the following vehicles:

(the part number I plugged in was for an 02/92 735i)

E24: Details on E24
E24 M6 COUPE


E28: Details on E28
E28 524td SEDAN
E28 528e SEDAN
E28 535i SEDAN
E28 M5 SEDAN


E32: Details on E32
E32 735i SEDAN
E32 735iL SEDAN


E34: Details on E34
E34 530i SEDAN
E34 540i SEDAN
E34 525i TOURING
E34 530i TOURING
E34 535i SEDAN

genphreak
05-29-2006, 07:32 PM
Can't say if the bushings are different, but according to the ETK, the rear trailing arms are common almost accross the board, so that leaves the possibilities wide open to swap just about any brake/hub/bushing combo. Yes it is interesting stuff. BMW kept a tried and tested setup for quite some time. There are lots of common items, so I am glad to get the arrangements BMW used understood more clearly.

I am very interested to know why most e32 740/750 and all e34 M5 use different arms. The possibilities are;
Different diff mounting (or it may be reinforced for the larger diff? or higher loads)
Different rear wheel track as suggested I earlier or
Different (lower) suspension geometry (I hope not)If we could get an answer to the 735 brakes fitting an e34 question we'd know at least know if a small track reduction was possible by using e32 axle-flange/hubs (and this might mandate the use of e32 brake rotors) but then any of us with an e34 could attain the track of an M5, which the more wheel-conscious or performance freaks amongst us would be very interested in.

Perhaps all I have to do is get some new trailing arm bushings toi fix my geometry... but if it is possible to work out how to retrofit the brake calipers from any e32 in the process it would be really handy info.

:) Nick