I thought this only plagues Mcoupe/roadsters....

[Stu]

I had the E30 in the air this morning to chase down an exhaust problem, and before putting the car back on the ground, I noticed a strange break in the undercoating near the diff mounting point.

Upon closer inspection, it appears that a combination of a high-mileage, relatively whipped chassis and the 3.0L M50 tore the unibody at the differential pickup.

The horizontal unibody rail that the diff ear mounts to is split (looks much like a sawzall zipped through it) and the trunk floor has separated from that unibody rail (the 4-5" separation you see).

Now, I'm not terribly surprised to see this because the chassis has just shy of 350,000 miles and the car has been driven pretty hard in the 7 years I've owned it. I don't drop the clutch, shock the driveline, etc....but it gets doesn't exactly get driven lightly.

Considering that I'll only be using this car for another 1-1.5yrs, the plan as of now is to wirewheel the undercoating to the bare metal and weld in some sort of reinforcement.

I know that a similar problem occurs with the S52/S54 Mcoupe/roadsters due to the single-ear diff mount, and plan to research that this weekend.

I've never seen this happen on an E30--has anyone else?

[e30serg]

Holy crap! I've seen this happen on Mcoupes too, but this is the first time seeing it on an e30. Something to look at for sure. I might want to reinforce the area now, the s52 might be too torquey for a 20-year old unibody with 230k miles. Thanks for the heads up! Keep us updated on the fix!

Did you mean 4-5mm instead of inches?

[SpecM]

....but it gets doesn't exactly get driven lightly.

-thats for darn sure

-Sucks for ya, Stu! I think your reinforcement idea will work, and no, I've never seen that happen before. But then again you have one of the most powererful N/A street e30s around.

[Van Westervelt]

Dang, what is your whp?

[Aptyp]

Hey Stu,

got a question, is that a replaced diff bushing? Because i am looking at mine and it's more solid than yours. perhaps because it was replaced before, the diff moves more than it should under loads.

Something to check out.

[SpecM]

Dang, what is your whp?

-I think he's putting down 230 whp, but Stu should second that. Correct me if I'm wrong here bub, but I thing he has an s50 rotating assm. in a nonvanos block, ported vanos head, s52 cams, and a darn good tune.

[Van Westervelt]

Hey Stu,

got a question, is that a replaced diff bushing? Because i am looking at mine and it's more solid than yours. perhaps because it was replaced before, the diff moves more than it should under loads.

Something to check out.

Someone needs to work on sentence structure. Or am I that tired?

-I think he's putting down 230 whp, but Stu should second that. Correct me if I'm wrong here bub, but I thing he has an s50 rotating assm. in a nonvanos block, ported vanos head, s52 cams, and a darn good tune.

Dang, I am well over that, maybe I need to double check and inspect the arse. I have a little rattle... uh oh...

[Erick]

I'm surprised Stu.... my car has been fine so far.

[318isbmw]

Wow, never heard of that on e30's

[PiercedE30]

If you want some reassurance, go ahead and throw an E36 diff cover on and put in new mounting tabs. Easy and doesn't allow the diff to rotate to one side easily.

[JPStrniste]

I'd hate to see what the rear subframe looks like

[Stu]

OK I've talked to a few people about the issue and it looks like the most practical solution is to clean and weld the cracked areas and then weld in a plate to triangulate the unibody rail to the trunk floor. If I were keeping this car long-term I would probably do the E36 dual-ear diff cover, but it doesn't make much sense on this car.

@E30serg--the 4-5" crack I was referring to is the split between the unibody rail and the trunk floor, where the rail has dropped slightly (from the split to the right of the diff ear) and separated from the trunk floor.

@Micah--It definately sucks but I guess I'm not really surprised that it happened.

@E30Groupie/PiercedE30--It's certainly not the fastest S50/E30 by any means, it's a basicly a standard 3.0 with stock cams; rear wheel torque is only about 215. If I had a car as clean as both of yours I'd probably do the E36 diff mount--but my car will probably get stripped next summer and the body sent to the junkyard.

@atpyp--the diff bushing is an Mcoupe/roadster unit. I wanted a stiffer than stock one but didn't want to do urethane/delrin. Those ribs are reinforcements; it's quite a bit stiffer than the solid E30 rubber one. Whether or not that contributed to the problem I'm not sure.

@JPStrniste--I havn't looked at the subframe closely but I will when I have it on a lift on Monday. The subframe only has about 75,000 miles on it--same for the bushings (stock).

I'll let you guys know how it works out and will be sure to take pics of the repair.

[Stu]

Update:

I had to forgo the SpecE30 race this weekend in order to fix my E30. I put it in the air at a friends garage, stripped the undercoating with a drill/wirewheel bit, and had a friend weld the unibody rail, trunk floor, and stress cracks. He also welded in 16g steel plates at the topside of the trunk floor to reinforce the area.

I've got it all covered with gray primer right now and plan to check it frequently for stress cracks around the welds. If it seems to be holding up well, I may spray it with undercoating eventually. Though I'm hesitant to undercoat it because it will probably cover up newly formed cracks if/when they arise.

I'll try to get pics soon.

[SpecM]

Update:

I had to forgo the SpecE30 race this weekend in order to fix my E30. I put it in the air at a friends garage, stripped the undercoating with a drill/wirewheel bit, and had a friend weld the unibody rail, trunk floor, and stress cracks. He also welded in 16g steel plates at the topside of the trunk floor to reinforce the area.

I've got it all covered with gray primer right now and plan to check it frequently for stress cracks around the welds. If it seems to be holding up well, I may spray it with undercoating eventually. Though I'm hesitant to undercoat it because it will probably cover up newly formed cracks if/when they arise.

I'll try to get pics soon.

-Good to hear that work out for you. Sounds like reinforced it pretty well, tho, good luck with that Stu

[golde30]

damn, im going to have to check out my rear end as well...i drive my s50e30 pretty hard and the chassis has close to 200K miles now...