We did it: E28 subframe swap...

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billy bee
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Joined: Fri Aug 16, 2019 6:34 pm

We did it: E28 subframe swap...

Post by billy bee » Tue Sep 03, 2019 8:24 am

Greetings all:

I have posed a little bit about the 1981 633CSi we are building for Lemons. We got an E28 subframe donated to the cause and have completed the swap. I searched for information on making this happen and got some good tidbits here. 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.

The first question is this: why even bother? For us the rationale is two-fold: First, the E28 subframe is far more robust. The E12 subframe looks extremely weak 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.

Image

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:

Image

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.

Image

Image

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 to the rear 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. This is too difficult to describe, so here are the pictures:

Image

Image

I spent a lot of time with both the E12 and the E28 bars to see what would work. 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 the bar does not clear the subframe perfectly. There is some contact in the center. It is fine but may make some metal-to-metal noises through the suspension travel. I doubt it will be bad, and we could easily screw a 1/4" Delrin plate to the subframe to mitigate any icky-ness.

I think that's it. Please feel free to post up any questions or comments. 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
Last edited by billy bee on Tue Sep 03, 2019 5:06 pm, edited 2 times in total.

billy bee
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Re: We did it: E28 subframe swap...

Post by billy bee » Tue Sep 03, 2019 8:37 am

I forgot one thing. This post was very helpful. It gave us the guidelines for our swap. Big thanks to onovakind67
onovakind67 wrote:
Sun Feb 24, 2019 9:38 am
I put an E28 rear axle in my E3, and the problems you might incur should be common.
1. As mentioned earlier, you will need the differential cover from an early E28 with the centered mount. It will bolt right on to the stock mounting point. Otherwise you will be fabricating an adapter.
2. You will need to re-route the brake lines to match up.
3. The sway bar mounting points are different. I welded a bracket onto the E28 arms to replicate the original mounting point.
4. The emergency brake cable sheath lengths were different so I made some extenders and couplers to make them match
5. The E28 shocks and springs bolted right up in the stock holes. I originally used the E3 top mounts but found that the E28 top mounts also work and are less complicated. The Bilsteins for the application have the adjustable spring perch, so you will have a few inches of adjustment in the height of the rear of the car. I also found that performance springs for E28's are much easier to find than older versions.

The differential uses a case common to the E23, E24, E28 and E30 so different gear ratios are available and easy to swap. E28's mostly have 3.25:1 ratios, so if you want to swap in a different ratio like the 3.45's from an E23 or 3.73's from an E30 you simply pop out the axle drive flanges from the E28 and install them in the new center section. LSD carriers are fairly easy to come by.
bb

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528i-1981
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Re: We did it: E28 subframe swap...

Post by 528i-1981 » Tue Sep 03, 2019 1:58 pm

Nice work! This is a terrific resource - I think there's a guy in Brazil contemplating something similar (i.e. and E28 rear subframe bolt-up) for his E12.

The pictures don't appear to have make it, unfortunately. You need to host them elsewhere and link to them. I use this:
https://imgbb.com/
It gives you cut-and-paste image/thumbnail links you can drop right into your post. Easy.

Cheers,
Eric
(oo=00=oo) Eric
1981 528i Manual

billy bee
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Re: We did it: E28 subframe swap...

Post by billy bee » Tue Sep 03, 2019 5:08 pm

528i-1981 wrote:
Tue Sep 03, 2019 1:58 pm
The pictures don't appear to have make it, unfortunately.
I was trying to host them on my iCloud account. That's one thing Apple whiffed on. So, I posted them to SmugMug. They should work as long as I keep my SmugMug subscription. Every year I think I'm gonna bail. It just such a good photo hosting site...

Hope this helps.

bb

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Lock
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Re: We did it: E28 subframe swap...

Post by Lock » Tue Sep 03, 2019 11:00 pm

Thanks for this post and the pictures, this is great information. It's all good knowing the theory and the schematics but doing it is another.
1979 528i 5-speed conversion G260/6

onovakind67
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Re: We did it: E28 subframe swap...

Post by onovakind67 » Tue Sep 10, 2019 8:49 pm

billy bee wrote:
Tue Sep 03, 2019 8:24 am
We are in search of an early E28 cover that will bolt up directly.

Bill
PM me with your address and I'll hook you up with one. I have a few in my collection.

I used straight pieces of the steel tubing from the transmission cooling lines from an automatic BMW ( maybe an E34 )for my sheath extenders for the E-brake cables. I think they are 12mm and they worked just fine. I took some 1/2" coupling nuts and drilled them out to 12mm on each end, leaving about 1/8" in the middle undrilled as a purchase for the ends of the joined tubes. They've been working just fine for years. The length of these tubes is 7 or 8" as near as I recall.
'72 3.5L 5-spd Bavarious - E3 with E12 front struts/brakes, E28 3.25 LSD rear axle, E39 wheels, Webers, etc, etc, etc...

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CabbageFumes
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Re: We did it: E28 subframe swap...

Post by CabbageFumes » Wed Sep 11, 2019 11:50 pm

Two quick questions:
What driveshaft did you end up using? From an E28 or E12? Or both?
With the car on the ground, can you tell if the wheel center is pushed off center a bit? When I was considering this, laying everything out, it looked like the rear hubs were slightly off between the E28 setup and the E12 setup. I couldn't remember if it was forward or rearwards, but I seem to remember they differed slightly.
Fiver 12/73
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Sixteen-O-Two-er 11/69
i3 8/14

billy bee
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Re: We did it: E28 subframe swap...

Post by billy bee » Sun Sep 15, 2019 12:24 am

CabbageFumes wrote:
Wed Sep 11, 2019 11:50 pm
Two quick questions:
What driveshaft did you end up using? From an E28 or E12? Or both?
Good question: E12 drive shaft bolted directly to the E28 differential input flange.
With the car on the ground, can you tell if the wheel center is pushed off center a bit? When I was considering this, laying everything out, it looked like the rear hubs were slightly off between the E28 setup and the E12 setup.
Not that I can tell with a visual inspection. I did not measure the wheelbase before and after, which is what I think you are asking about. I will say this: the car felt a little more darty. That could be owing to a number of factors, one of which could be a shorter wheelbase.

Hope this helps,
Bill

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