First to Second Grind / Clunk
 

Hey folks!
Settling into life with a running 924S and working out a few bugs. One anoyance is that when shifting from first to second I have a hard time shifting into second unless I do it really slow. A quick shift into second gives a grind or a clunk. I was hoping that with the clutch job or driving a bit, the problem would go away. It has not.

The gates work smoothly when the engine is off and the linkage seems ok.

My initial impression is that it is a 2nd gear synchro.

In searching the posts, It seems as if it is a common problem. Would I be better off just getting a new transaxle, or are these things easy to work on? special tools? can anyone suggest a good rebuilder? I replaced the fluid with some redline synthetic a year ago and that helped a little..

Yes, common problem. It's probably cheapest to get a good used tranny than to have yours rebuilt. Changing the transmission isn't too hard.

MT90 fluid change, first.

Good idea. Lucas makes some interesting additives, too.

A transmission with less worn syncros will improve the problem, but the real problem lies in the fact that the transmission is driven through a 4 or 5 ft long steel drive shaft riding on 3 large bearings that the syncros must accelerate/decelerate to be able to speed match the engagement mechanisms in the transmission. A lot of quick shifting, especially from 1st to 2nd, will only rapidly (at least compared to a standard driveline setup) wear out the syncros again due to this design. I just wait for the driveshaft to slow down on it's own between shifts unless I'm really in a hurry to merge into traffic, or something, in order to preserve the syncros.

This brings up another interesting point about lubricant. I've read that API spec GL-4 lube has less extreme pressure anti wear additives in it than GL-5. The additives in GL-5 are somewhat corrosive to brass syncros, and will decrease the life of them by about 50% over using GL-4. Because of this, GL-4 usually is recommended for transmissions. The problem comes with the fact that that our transmissions are actually transaxles, which also contain a hypoid final drive and a differential. The extra additives in GL-5 are specifically made to offer extra protection for final drives, differentials, and other gearsets that are subjected to very high pressure and shock loads. So the dillema is, sacrifice syncro life or final drive life?

Seeing as I just blew out my final drive, and I always shift easily, I've continued to use Mobil1 75W-90 which is GL-5.
Someone mentioned Lucas additives. Does anyone know much or can speak for how well they work? I got some of their well known oil stabilizer and added it to the transmission oil when I installed the transmission. It's the really thick goo that's supposed to decrease wear, oil breakdown, slow leaks,ect... I figured it was worth a try, my old transmsion felt kind of worn when it came out, and the final drive gears looked kind of worn as well, which could have been part of why they broke. The new box shifts like a dream and doesn't complain if I shift quickly, but it was also fairly low milage. Don't know how much the Lucas stuff helped the shifting, but it might help it last longer, including syncros.

This stuff. They make a synthetic version, too -> http://www.lucasoil.com/products/display_products.sd?iid=25&catid=7&loc=show&headTi tle=%20-%20Lucas%20Heavy%20Duty%20Oil%20Stabilizer