e28 subframe upgrade
Posted: Fri Mar 01, 2024 11:34 pm
I've successfully upgraded my e12 with an e28 subframe, and wanted to share my experiences in case it inspired or helped someone else. As we know, it's a direct swap but the e-brake and swaybar both need to be solved.
Initial pickup
First problem - one of the mounts is badly damaged. I pondered what to do, eventually repaired it by welding in a Garagistic rear subframe camber/caster kit over it and all of the mounts for added reinforcement.
Cleaned and mocked up with the separately purchased e34 trailing arms and cv axles, and e30 diff. I was trying to figure out swaybar solutions.
Painted and installing new rubbers
Out with the old
Pretty clean up there, but the old diff seals were leaking and sprayed
e28 lines up perfectly, as expected
Now time for the e30 diff with early e28 diff cover (center mount). I rebuilt it with an e34 LSD with 3 clutch discs. It's a 3.9:1 which runs out 1st too quickly. A 3.64:1 ratio with the 3.5 would be better.
Subframe and diff installed with new mount. I thought about alternative mount upgrades but I plan to reinforce the stock mount with a plate in the trunk, as others here have done.
It's a close fit, the brake line T piece hits, I had to put in a lower profile bolt. You can see the Garagistic reinforcement plates. I didn't bore out the holes, stock is fine. I'm also not a professional welder.
So the e12 springs did not sit on the new e28 Bilstein shocks. My solution - I cut off the e12 perches and tack welded them in place on the e28 perches and painted them
Springs installed, works great
All assembled. Separately I rebuilt/regreased the e34 cv axles, and also rebuilt and cleaned the e34 brakes
Initial pickup
First problem - one of the mounts is badly damaged. I pondered what to do, eventually repaired it by welding in a Garagistic rear subframe camber/caster kit over it and all of the mounts for added reinforcement.
Cleaned and mocked up with the separately purchased e34 trailing arms and cv axles, and e30 diff. I was trying to figure out swaybar solutions.
Painted and installing new rubbers
Out with the old
Pretty clean up there, but the old diff seals were leaking and sprayed
e28 lines up perfectly, as expected
Now time for the e30 diff with early e28 diff cover (center mount). I rebuilt it with an e34 LSD with 3 clutch discs. It's a 3.9:1 which runs out 1st too quickly. A 3.64:1 ratio with the 3.5 would be better.
Subframe and diff installed with new mount. I thought about alternative mount upgrades but I plan to reinforce the stock mount with a plate in the trunk, as others here have done.
It's a close fit, the brake line T piece hits, I had to put in a lower profile bolt. You can see the Garagistic reinforcement plates. I didn't bore out the holes, stock is fine. I'm also not a professional welder.
So the e12 springs did not sit on the new e28 Bilstein shocks. My solution - I cut off the e12 perches and tack welded them in place on the e28 perches and painted them
Springs installed, works great
All assembled. Separately I rebuilt/regreased the e34 cv axles, and also rebuilt and cleaned the e34 brakes