As far as i know its a common issue for M6 C5s that after a few years the syncro rings go bad and a problem occurs shifting from 4th to 5th gear.
After a few miles driving the car (till oil was wramed up) it was not possible to shift from 4th to 5th gear without having that terrible "crtsch"... It happened at least twice a day while on my way to work and back home...

Same with my transmission. My 97 showed this signs of wear since a while, and i talked to a tranny shop to have the rings replaced. A guy at work told me, before i have them take the tranny appart, to try a special additive for the transmission.
Additionally some folks of the german corvetteforum recommended to replace the ATFIII Fluid recommended by GM with an oil that is made for manual transimssions.
Mix it with that mentioned additive and see what happens...

The oil they recommend is from CASTROL. Its the TAF-X transmission oil for manual transmissions. The additive is from a german Company called "Mathy". Wensite (only in german: www.mathy.de )

I changed this summer to a mix of 1 qt Mathy additive and topped the transmission with the TAF-X oil (approx. 3 qts).

Since i changed to this combo the problem did not show up again. I drove about 7000 mils since then and no noise so far from the gearbox. After a few hundred miles shifting got definitally more smooth.

The german TUV ist testing their products since a while and found a lot of benefits...

Thats just my experience and would like to share.



Jochen

 

Thanks for the tip Jochen

 

Hi Jochen -

Thanks for the info -

I have right at 47k miles on my tremec with no signs of problems.....

But this is good information to have - thanks again!

best regards -

mqqn

 

i wrote this up because it was the last "desperate" action i did before i planed to let the transmission shop guys put their hands on my car.
I really didnt think that this would help, and during the first few days i always shifted from 4th to 5th with that "scratch" noise waiting for... i couldnt believe it never came back...

Jochen

 

Jochen -- thank you.

Mine was doing this from 6th to 5th. I changed the transmission oil at 75k (prior to that at 36k), and it also seeems to have solved the problem.