There used to be a rumor that
the differential cover from the new M Roadster/Coupe would bolt on to an
E30 M3 differential housing. Jimmy Pettinato was the first enthusiast to
actually go out and tackle the install. I have since followed suit, as have
some other list members. This write-up is a combination
of the experiences gained by Jimmy and I during our install procedures.
You may be wondering; "Why the heck would I want all those fins hanging
down under my rear end?" Well if you track your M3 then that limited-slip
clutch pack will generate some serious heat. And the ultimate enemy of any
clutch is heat.
The fins on the M Roadster diff'
cover reach down into the air flow underneath the car and should therefore
help bring about lower operational diff' temperatures. Furthermore, since the
diff cover only costs less than $200 and can be ordered right from the dealer,
I cannot see any reason not to do it - this mod should be on every E30 M3 owner's
Here Jimmy reports how his original installation went:
To finalize any doubts... the M Coupe diff' cover is an absolute,
slam dunk, just shy of an hour, bolt in. No mod's of any kind are
required, nor is pulling the diff'. Just remove the "ear" mounting
bolt, lower the diff' down with a jack, take out all the cover bolts, remove
the stock cover plate and replace it with the new one. Raise it back
up with the jack and re-stall the mounting ear bolt. Took me under
an hour myself.
M Coupe Diff' Cover Bolts:
The bolts needed for the new cover are different lengths.
Jimmy went out and sourced his own bolts as follows:
All bolts 10 mm diameter @ 10.6 hardness (grade)
2 @ 25 mm
2 @ 75 mm
2 @ 90 mm
No special thread is needed
All bolts are coarse thread (1.5 mm thread pitch)
A good place to get these bolts might be from Steve D' at the Ultimate Garage,
as they may be difficult to find locally.
Alternatively, you can order the factory
bolts at the same time that you order the M Coupe diff' cover. This is what I did.
The factory bolts are all grade 8.8 and the 90mm bolts that Jimmy used are 85mm long
from the factory (both lengths should be fine). The BMW part #'s for the factory
diff' cover bolts are as follows:
07 11 9 914 114 (x2), 10mm x 25mm, $0.20 ea.
07 11 9 921 541 (x2), 10mm x 75mm, $0.84 ea.
07 11 9 921 522 (x4), 10mm x 85mm, $1.08 ea.
Note that these new M Coupe diff cover bolts require
a 16 mm wrench/socket (as opposed to a 17 mm size for the existing E30 M3 bolts).
Make sure you have the right tools before you start the job.
M Coupe Diff' Part Numbers:
|33 11 2 228 335 || M Coupe diff'cover || less than $200 || (required)
|33 11 1 210 405 || gasket || $1.65 (net) || (required)
|33 11 1 206 166 || speedo o-ring || $0.44 (net) || (optional)
|33 11 1 212 682 (x2)|| drain and fill plugs || $0.44 (net) || (optional)
|07 11 9 963 355 (x2)|| crush washers || $0.44 (net) || (required)