e12 rear suspension e28 upgrade

Discussion pertaining to positive pressure E28s.
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Grapedude
Posts: 6
Joined: Oct 11, 2018 12:29 AM
Location: NZ

e12 rear suspension e28 upgrade

Post by Grapedude »

I'm currently in the middle of building an e12 based 635csi coupe that will have a forced induction motor. As part of this upgrade I have managed to source a couple of large case lsd diffs (3.07 & 3.45) and am now looking into upgrading the rear subframe, driveshafts/hubs and suspension to enable the extra power to be handled and to give me better options for aftermarket shocks/springs/brakes etc. Now the question is: I have been offered a e28 525i rear setup. It is not the same as a 535i/m5 rear which would be ideal but will it be strong enough and enable the changes I want? 535i rear end for e28 are not common in NZ so waiting for one to turn up is fairly pointless. Is there an alternative or a guide to how/what to reinforce/what breaks with added power? thanks!
Boneyard Dynamics
Posts: 73
Joined: Apr 26, 2011 5:46 PM
Location: Bavaria, not far away from the place the e28s where build

Re: e12 rear suspension e28 upgrade

Post by Boneyard Dynamics »

Depending on the production date of the 525i it could have a 528i/535I rear axle or a similiar one with smaller wheelbearings. Or the common 525i and below rear which was used till 4/86. But this only counts for german cars, export e28 have some differences to axles/ interior/ electrics etc. also depending on country of first delivery.

In short look at the axle if the axle has the small "bones" between the outer rubber bearing of the axle and the subframe bushing you have either a axle like the 528i/535i had or a similiar one with smaller wheelbearings. 528i/535i used 80mm bearings, the similiar variant for smaller engines used 74mm bearings. Measure the diameter of the ironcast bearingshousing and you can easily guess if it is for 80mm or 74mm bearings.

Also your typ210 diffs might no fit as there never existed a diff rearcover with a middle mounting positon for the rear diff mounting bearing/bushing (don´t know how you call it). And your diffcase migth eventually colide with steelprofile below your trunkfloor as this could also be a bit different.

Typ188 diffs will fit if you use the correct rearcover with central mounting position.


greetings from Bavaria,
Wolfgang
Grapedude
Posts: 6
Joined: Oct 11, 2018 12:29 AM
Location: NZ

Re: e12 rear suspension e28 upgrade

Post by Grapedude »

Thanks for your reply Wolfgang, I appreciate the depth of answer! I have managed to find a m535i subframe and one trailing arm which has the large knuckle...I believe that for a high power output this is the preferable option. The subframe is set up for large case so no clearance issues there. The key is now to find the other trailing arm from a m535i or an e23 which is the same set up. And then replace bushings and find an anti roll bar and suitable driveshafts. Are standard ones up to the task of high horsepower....I haven't read that they are not...but then it is always better to confirm.

thanks again

Hamish
Boneyard Dynamics
Posts: 73
Joined: Apr 26, 2011 5:46 PM
Location: Bavaria, not far away from the place the e28s where build

Re: e12 rear suspension e28 upgrade

Post by Boneyard Dynamics »

You could also use e34 trailing arms as they are the same depending on the engine, could be a bit like the e28 trailing arms story abbove.

e23 and e32 use also the same trailing arm, but the outer flange for the wheelhub has another position, so you would have to change the outer flange to an e24/e28/e34 flange
Grapedude
Posts: 6
Joined: Oct 11, 2018 12:29 AM
Location: NZ

Re: e12 rear suspension e28 upgrade

Post by Grapedude »

So an e34 trailing arm would solve all issues if i got the correct engine type donor...any clues as to the correct model? The correct one might also allow for larger brakes if required and may have swaybar attachments etc. All uin all the benifits are great as I could get the whole wheel/hub/brake assembly and presumably the only change would be the axel stud pattern for the largecase to hub fitment..e34 mostly mediumcase if i recall other than m5?!!... easier to get e34 parts here so a great result !! Thanks, Hamish.
Boneyard Dynamics
Posts: 73
Joined: Apr 26, 2011 5:46 PM
Location: Bavaria, not far away from the place the e28s where build

Re: e12 rear suspension e28 upgrade

Post by Boneyard Dynamics »

Sway bar and caliper mount are all the same, the only difference with e34 trailling arms is the diameter of the wheel bearing. Tourings should all have the large wheel bearings, and also the more powerful limos.

Just in case, measure the outer diameter of the ironcast part of the trailing arm in which the wheel bearing is mounted. The big wheel bearings have a 80mm outer diameter, if i remember correctly the outer diamter of the cast part should be 93mm or above, post if it´s still important. i would always measure the cast part.

greetings,
Wolfgang
test5
Posts: 46
Joined: May 05, 2011 9:38 AM

Re: e12 rear suspension e28 upgrade

Post by test5 »

Grapedude wrote: Jun 30, 2020 11:32 PM ... The subframe is set up for large case so no clearance issues there. ...
thanks again

Hamish
Have you fitted the large case diff (typ 210) into the car?

If the early e28 is based off the e12 then you might encounter this: viewtopic.php?p=1489973#p1489973b
Grapedude
Posts: 6
Joined: Oct 11, 2018 12:29 AM
Location: NZ

Re: e12 rear suspension e28 upgrade

Post by Grapedude »

Not installed subframe/diff yet but hoping to get hold of e32 rear end and use trailing arms...I had a lead on some in a junk yard but now the guy wants them to stay on the car...so the search continues.... but great link, Thanks! I think a shifted and reinforced mount point would be easiest and most practical. I'll keep you informed!
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