Re: Transmissions (was upgrade paths)

["Dave Swingle" <swingle@xxxx>]

I've opened up and repaired several DMC manual transmissions now, and 
an convinced that the horsepower "weakness" is somewhat overstated. 
This is a pretty stout transmission, with a couple of weak points 
that don't seem to be related to horsepower. 

- Clutch hydraulics - Failure to replace the plastic line with a 
braided one, and the resultant inability to completely disengage the 
clutch, eats the syncro/sliding gear. For some reason on the trans I 
had, it only "hurt" third gear. This is also what seems to break 
shift fork rollpin. A very common failure, a literally 30-cent part 
that is in the middle of the transmission. Change that clutch line!

- The big nut on the mainshaft unscrews - This is a somewhat random 
occurrence. This is interesting to see, if you didn't know any better 
you'd swear that someone attacked the transmission with a 3/4 drill 
bit. I've seen a couple of these, the fix is to replace the nut, use 
locktite, and weld the hole in the case back up. It does not seem to 
actually damage anything (assuming you don't drive it around once it 
fails). This appears to be a factory defect - like they don't quite 
torque that nut (120 ft-lbs) all the way. I've never heard of this 
happening the second time.

- The most interesting thing I've seen was the transmission out of 
Rich's Turbo GN-Buick-powered car. This one **seemed** to be 
destroyed - it suffered from the nut failure mentioned, AND had been 
installed in the car without the use of a pilot bearing (ouch). That 
destroyed the input shaft. When we drained the oil it looked 
horrible - full of metal shavings. But - once cleaned out, everything 
inside was fine, NO evidence of wear, NO other damage. The metal 
shavings were from the nut drilling its way out the back of the 
trans. Cleaned it up, replaced the input shaft and the nut, put it 
all back together. Repair cost was under $100 (not counting my free 
labor!). This is a 250+ HP car, and based on the clutch wear it had 
not had an easy life. Still an insanely fast car, by the way.

- The wierdest failure is the one I'm working on right now. This 
otherwise stock car has eaten three input shafts (at the collar) in 
25K miles. No other issues. There had to be something wrong other 
than the input shaft, so we kept looking. The issue was that the 
factory (or a prior mechanic, no way to tell) had not installed the 
two alignment roll-pins in the bellhousing that mate it to the 
engine. The mis-alignment caused the input shaft coupling to wear 
tremendously. Based on the bolt fit to the bellhousing, the mis-
alignment could be as much as 1/16" inch. 

The only person I've heard of truly snapping input shafts is the guy 
who was at Memphis with the 350 Chevy engine in the car - and based 
on his driving style it was not completely surprising. I have to 
admit that it is impressive to see a DMC smoke the tires on dry 
pavement, however. That fact that he could do this more than once 
without breaking things was impressive too. 

Dave S


--- In dmcnews@xxxxxxxxxxxxxxx, Andrew <aos+yahoo@xxxx> wrote:

> Any plans to beef up the transmission to match the increased power 
of 
> these upgrade paths? I know I'd be a bit worried about the torque 
a 
> nitrous system would be pushing through.
> 
> It's my understanding that the only real problem with the 
transmission and
> higher powered engines is the input shafts. 

> -andrew
> #4115
> Houston TX