Our E28 rear subframe swap into E12-based E24...

[billy bee]

Greetings all:

Cross-posting this from BigCoupe in case people have not seen it over there.

We built a 24 Hours of Lemons E24. It is an early car, based on the E12 chassis. Here's a pic of the car during a recent pit stop.

IMG_0046-X2.jpg

We got an E28 subframe donated to the cause and swapped it into the E24. I searched for information on making this happen and got some good tidbits here and there. But I was not able to find a comprehensive write-up. We did a ton of research and spent some time hanging out at the Napa parts counter to finish this up. Thought I'd share our findings. This is not meant to be a definitive how-to guide. YMMV. I hope you can get some ideas for your swap here.

The first question is this: why even bother? For us the rationale is two-fold: First, the E28 subframe is far more robust than the E12 subframe, which looks flimsy by comparison. For endurance racing, heavy duty is more gooder. Second, our options for differentials open up considerably with the E28 subframe. We will have a much easier time finding a limited slip from an E30 or Z3. Both bolt in with the proper diff cover. See more on diff covers below.

The install:
1) Yes, the subframe bolts right up to the car. There are, essentially, three mounting points: driver side, passenger side, and diff. The cross-member bolts directly tp the driver- and passenger-side mounting points. The Bilstein shocks in our E12-based E24 bolted right up, too.

2) The diff will only bolt up if you use a diff or diff cover from early E28s. Our diff came from a 1985 524TD and has an off-set mounting arm on the diff cover. Earlier E28s have the same center mounting location as the E12s. The rear cover from a late ‘82 to late ‘84 E28 will bolt up to the E12 body mount. This picture tells the story a little better. We bolted a plate in place to hold things together. Not ideal as there is some leverage on the plate. We are in search of an early E28 cover that will bolt up directly.

This picture also shows the crappy mount repair that was done to the body. I have seen pictures of the parts that were used. The parts look like a really good fit, but there were welded in very poorly. We will weld this up much better.





3) You will need new rubber brake lines to run from the body to the subframe. One of my team mates spent some time measuring and then went to Napa Auto Parts and found new hoses that bolted in very easily. They are Meyle lines for the front of a 1981 - 1988 VW Vanagon. They were $21. The parts numbering is a little confusing, so, here's a pic of the package:





You can see they were made in Italy. That will make your car faster!

4) The E28 brake cables won't work, either. The sheathing that holds the cable to the body is too short. There are several ways to fix this. The easiest seems to be to extend the sheathing to meet the body of the car. We have not done this yet, but here are two pictures that will give you a good idea of what you are dealing with. I think some copper tubing is a good likely candidate as it needs to be curved.








It may be the case that you have to cut the threaded ends off of the stainless wire that runs inside the sheathing in order to get the sheathing extension on the cable. Those stainless fittings are where the parking brake cable meets the brake lever. Again, we have not done this yet; so, I'm not certain, but you may also need to swage new threaded fittings onto the wire. McMaster has what you'd need: https://www.mcmaster.com/swage-fittings; or: https://www.mcmaster.com/swages.

5) The roll bar doesn't bolt up at all. Nothing doing. This was the most difficult part of the swap to sort out. Our solution is inelegant but pretty effective. With the stock E28 configuration, the bar bolts to the body aft of the subframe. We used the E28 anti-roll bar and flipped it over. Rather than attaching to the body, we welded up some 2" square steel to the subframe to mount the anti-roll bar to the subframe. This is too difficult to describe, so here are the pictures:








I spent a lot of time with both the E12 and the E28 bars to see what would work. The E28 bar is heavier, which may not be a good thing. Yet, this was by far the simplest solution. The downside is that we lose ground clearance and expose the roll bar to damage. I could see hitting some curbing and crushing the bushing clamps. The other downside is that we have a stiffer bar, adding another variable into our suspension/handling puzzle.

I think that's it. Please feel free to post up any questions. We learned a lot about the car in making this swap, but it is not for the shade-tree mechanic. It took the brains of three of us to work through all of the problems. OTOH, you have to consider the brain power of a group of guys who would race Lemons in the first place. You can probably do better.


Bill

[DesktopDave]

Nice job, thanks for posting all that up here.

I believe Winfred also installed a late model rear subframe? Not sure what he ended up doing with the AR bar. Here's a link to your thread, you're being too modest, this is great stuff!

[billy bee]

Here's a link to your thread, you're being too modest, this is great stuff!

I'll get around to posting some Shark Racing updates in here. When we blow up the M30B32, we have an M54B30 ready to go in. Tying to get information out there that will help the community. I find racing updates entertaining but not particularly useful; so, they are an afterthought. But thanks for the mention.

See that you had a 1984 745. To support our racing effort, we recently flipped a 1983 745. Made a little money, saved a cool car, and had fun in the process. That thread is floating around somewhere on BigCoupe, too. Hard to know where to post these things. Too many forums...

--bb