E28 rear subframe swap?

[kingoftarmac]

Ive been reading something that you can bolt in a e28 rear subframe? If this is true then can ANY year e28 subframe work (or is it a specific year?) if so then can you also use a e28 diff If you just change the rear cover for mounting? and I assume if that works then you can use e28 axles/rotors/calipers. So all in all you would juse have a stock rear e28 subframe on a e12? Please let me know what works and what does not, I have very interested in this idea. Thanks for your time guys!!! -Paul

[Mike W.]

I've never done it, but I've heard from more than one source it will work. A couple of caveats though. 82, the first year for US E28s, didn't use dogbones, AKA pittman links in the rear suspension, which supposedly do make a significant contribution to eliminating lift throttle oversteer. So you would want a year other than 82. You not only could, but would have to use E28 axles, brakes etc. And you would need a rear cover for the diff that was pre 85, they used an E12 style diff mount. A 3.46 diff would give an accurate speedo readout for all but the very early E12s. The good and bad is there are a wide range of diff ratios available for them, from 2.79 to 4.10 or beyond, with many steps and LSDs in between. But for all but the right one, usually 3.45/3.46 the speedo will be off.

[kingoftarmac]

Im going motronic 1.3 So if I used a Diff with the electronic speedo sensor in it with a electronic speedometer it should all work and be accurate right? this will then give me the option of not needing a 5 speed (doing auto to manual swap soon) that has the cable driven speedo right? Thanks guys for the info.

SO any year e28 subframe. And then a pre 85 diff and diff mount? And im set?

[Blaise]

Im going motronic 1.3 So if I used a Diff with the electronic speedo sensor in it with a electronic speedometer it should all work and be accurate right? this will then give me the option of not needing a 5 speed (doing auto to manual swap soon) that has the cable driven speedo right? Thanks guys for the info.

No, I don't think so.

Motronic 1.3 has nothing to do with your speedometer. It has a wire that can run your tachometer, but that is not the issue here. Your E12 gauge cluster includes a cable driven speedometer. That cable is hooked up to the transmission. The stock E12 mechanical ratio built into the speedometer assumes the stock differential ratio. If you change any of the parts that effect this ratio, it will effect your speedometer accuracy. I would think it would be easier to calibrate your speedometer after you make the changes (they were not accurate in the first place). Jeff Caplan is the expert.

If you go with the E28 rear end, make sure you get the type with the dogbone link and a limited slip unit. That would make it worth the while, in my opinion.

[Mike W.]

Im going motronic 1.3 So if I used a Diff with the electronic speedo sensor in it with a electronic speedometer it should all work and be accurate right? this will then give me the option of not needing a 5 speed (doing auto to manual swap soon) that has the cable driven speedo right? Thanks guys for the info.

SO any year e28 subframe. And then a pre 85 diff and diff mount? And im set?

Yes and no. I'm not sure where and what all electronics are required to run an electronic speedo. But use them along with the speed sensor in the diff, and the later speedo, and yes, it would work and you would not be limited to G265/6 transmissions for a 5 speed. A caveat however, G260/5 trannys are not considered to be the best, if you're going to use something completely different I would use either a 265/6 or a 260/6 such as came in post 85 cars. I think the corresponding driveshaft for a given transmission in an E28 will work but I'm not positive.

And if you're going there, that would give you the option of adding cruise control without too much more work since it runs off the electronic speedo, among other things.