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In Reply to: Getrag 280 is extremely strong..... posted by JamesM on December 17, 2001 at 12:29:14:
Here is what I understand:
1. The 44mm center-section is a bulkhead added to prevent the gearshafts from pushing away from each other too much and causing gear teeth to eat into gear flanks from misalignment. Using the non-bulkheaded trannies for the E34 (at least) is likely not wise.
2. The synchro change from Jim Blanton is to give better synchro feel. The Moly stuff wears better, but shifts worse. Something like that.
3. The anti-backlash gears in the E34 box (not on E28 box) often chip and generate gear eating chips in the tranny.
What you say about synchros and forks not gears wearing out is probably right (I have no gear wear information), but just widening the gear tooth does not make a tranny stronger, you have to make sure the whole thing is rigid enough to mesh right. That is where I understand the problem to be.
At any rate, it is a problem tranny in this application.
Neil Deshpande
http://www.neilwerke.com
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That's not exactly true, Neil. From discussions with Jim Blanton and Metric Mechanic (no longer affiliated), the Getrag 280 is a seriously strong transmission. The problem comes from the use of aluminum shift forks and poorly designed synchros. Jim Blanton is the authority on Getrags. He replaces the synchros and forks with Silicon Bronze units, which are much more wear resistant. Once rebuilt, he recommends Red Line MTL or MT-90 tranny oil.
The 260/5 was the weak link in the US 533i. BMW used the Getrag 265/6 in the 1985 535i (with an extra 35lb-ft over the 84 533i) until Getrag redesigned the 260/5 to the 260/6. The only transmissions that will handle the torque of the M5 are the 265, 280, and the ZF 6-speed from the 3.8L Euro E34 M5. The 265 can't handle much more than a modified E28 M5 engine, though. Your best bet is to go with the 280 or ZF 6-speed ($$$).
JamesM
Floyd:
The simple and unfortunate fact is that trannies on this car are marginal and already overloaded. Even with the bulkhead in the center the tranny is simply not strong enough.
I baby the II shift 100% EACH time to avoid the rebuild.
Neil Deshpande
http://www.neilwerke.com
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