E28: Eggenberger Group A E28 Tribute Build Thread

stonea · 03-12-2017, 08:51 PM

Damn, this thing is so cool!

SpasticDwarf · 03-12-2017, 06:34 PM

The wheels are probably my favorite part of the build, and might be the most important part. In wanting to build a spiritual “sister car” to the E24s, it was important to use the correct wheel. I found these Ronal splits, off of a Group A car, a few years back, I believe in 2012, and have been sitting on them ever since. They’re a spot-on match for the E24s, and as run on some of the E28s as well.

Using a few reference materials, primarily homologation papers for one of the Gr. A E28s, and an old rear hub I happened to have here at the shop, I joined forces with one of my closest friends, Nic Foster, to build a set of centerlock hubs for the E28. Pictured below is the original hub I had, which I sent to Nic up in Seattle, so that we could replicate it.

The factory E28 race cars are setup slightly different to our road cars, as their strut-to-spindle attachment is a a bit different from the road cars as it’s a BMW Motorsport coilover. However, it does utilize the factory geometry and the stock steering arm, so it’s practical difference is, well, none. You will note, however, that the hub assembly is almost identical. We used my spare factory centerlock hub for measurements and dimensions for both the hub and the drive pins. Pictured below are two photos from the E28 FIA homologation papers - the motorsport strut assembly, and the centerlock unit.

For our hub, we did add some lightening holes (as also used on the original hub I own, but not as seen on the Gr. A E28s in the pic above), however, they do use the drive pins to affix to the car - they’re not a dual-bolt style “adapter”. It’s as close to the factory centerlock hubs as we could venture.

We produced the parts with a 7000-series alloy and FEA testing shows the load capabilites well past 4x the German TUV minimum safety rating, so this is a true race-capable part. A crows foot and torque wrench is used to install them to the car via the drive pins.

Ronals were built, back in the day, to BBS dimensions and to utilize BBS hardware. BBS supplied me with NOS centerlock nuts, as well as the original ’83 CAD drawings so we could perfect our hub and mate them perfectly.

For the wheel build, I simply rebuilt them to factory spec with new BBS inners, outers, bolts, nuts, and sealing rings. I left the wheel centers as-is, opting to not refinish them in favor of retaining the patina and as-raced marring and imperfections.

All of the components fit together perfectly, and I was eager to see them on a car. At the time, the white car had no subframes, so mockup there wasn't an option. Here’s a few photos of initial test-fit on my M5 of all of the components. Sorry for the rusty surfaces - it’s been sitting since ’94, and is on my list of builds to do. Seeing them on an E28 had me excited and eager to finish up the suspension build on the race car.

And the original, for comparison:

Wheels on!

Mounting them on the race car was pretty straight forward, as per above. Torquing the wheels down required me having to have a custom 90mm socket made. While you can buy one ($1200 from SnapOn for the one socket, $400 for the cheapest out there), it was cheaper to have one made. The nuts are torqued to 400lb-ft.

SpasticDwarf · 03-12-2017, 06:33 PM

As said, I don't really have a great chronological collection of photos, so I'm more aiming to showcase the components of the car, or at least parts of it.

The suspension and underside of the car were the most important to me. I worked closely with H&R to build a special setup for it, and BimmerWorld helped to supply to parts necessary to overhaul literally everything.

Most here in the US are unaware that H&R builds complete coilover kits for the E28. While they're expensive, they're also a bolt-on affair engineered specifically for our chassis. For anyone interested in a set, feel free to reach out to me and I can help to get you set up.

We also built a one-off set of sway bars as an exercise in curiosity and experimenting. Aftermarket swaybar options are limited for E28s - M5s are equipped with 25/18mm bars front and rear, and can do so because of special sway bar mounts. Non-M cars have more fragile mounts, and require reinforcement to the chassis in order to upgrade to larger bars. There are a few companies that make larger bars for our cars, with the largest being an M5-spec 25mm front and a slightly upgraded 19mm rear bar, as far as my research has shown. We opted to size up substantially, with 30mm front bars and 25mm rears. At the moment, there's no plan to put these into production, but if others are interested, a group-buy might be something I can help put together.

To mount the sway bars, reinforcement was needed. I opted for Aaron's (limitedslip engineering) front mounts, since he clearly did a nice job with his kit. I ordered a second pair of D-mounts and bushings from him for use in the rear of my car. For the front, I bored out his largest D-bushings to accomodate my bars.

For the rear, he offered an upgrade for the swaybar mounts on late-model E28s, but for the early car, the mounts are different, and much more fragile. Tearing them from the body is a common occurrence with upgraded sway bars, so I designed my own reinforcement setup, and welded it into the car. I fabricated a differential mount reinforcement setup while I was under the car as well, and can find a photo if people are interested.

For the build, I stripped every component from under the car, except for the factory fuel and brake hardlines. I modified the rear subframe with an Ireland Engineering posi-lock style toe/camber adjustment kit, and then had both subframes, and the trailing arms powdercoated in a factory satin black.

With everything apart, I wanted to replace every component underneath the car, so I had BimmerWorld source everything needed. All four wheel bearing assemblies, the hubs, the axles, all of the bushings, control arms, steering components, dog bones, shock mounts, and even brake shields, nuts and bolts were all replaced; some pictured, some not. Every part used was OEM, including the Lemfoerder arms, which I pressed the bushings out of to replace with Powerflex components. I used black Powerflex bushings on every component they offer, except for the sway bars, and the LCAs.

Seen before the bushing swap:

The rear end, mocked up:

Today, the only thing I have planned for the underside of the car is a cryoblast session to restore it to its former shine. I considered stripping and repainting the whole car, but it didn't make sense on a car I actually want to drive and race. A perfect show-car undercarriage would be pretty to look at, but flinging rocks and debris at it with R Comp tires seems like wasted effort.

My original plan was to use the M5's large-case 3.91 diff, but it wasn't until trying to physically install it into the car that I realized that it would take more than just a rear mount modification to pull off. The floor pan is different in early versus late E28s, with the early model floor pan providing inadequate clearance for the larger differential case. I opted for an E30 M3 4.10 LSD, as it was a direct bolt-in solution. I'm currently in the middle of rebuilding it with a Thayer 3-clutch kit, new bearings, seals, and hardware. The 4.10 was a great choice in this car when paired with the G280's long gears. I really enjoy the way it drives.

I wish I had more photos of the suspension to show off the thoroughness of the build, but that'll have to do. No expense was spared in the running gear of this build. I wanted it to be thorough, and true to form in wanting an E28 that drives better than new. The only factors that I am unhappy with would be the lack of true Group A trailing arms. The front components will be swapped out for Group A bits in the coming months, as those are much more simple.

E28: Eggenberger Group A E28 Tribute Build Thread

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