e9stibi

Yesterday, during a track event, the gear box of my car failed. Here are some more details:

Car:
1997 C4S, 69k Miles

Gear Box:
G50, custom re-build in 2002 by Rothsport in Oregon (shorter gear ratios with some RS gears)

What happened:
I down shifted from 4 to 3. The shifter moved into the 3rd gear position but the gears did not engage at all. There was no strange noise when I shifted and I drove at usual speed (~70 mph). It took a while until I figured out what happened because all other gears worked as usual. When I left the track to go to the hotel, I lost the 4th gear with the same symptoms. All other gears including reverse work without issues.

There is some technical track support and they said that there might be a pin broken in the gear box because for my car there is one solid connection from the shifter to the box ans when the other gears are working, it must be in the box.

I would appreciate some input from the experts. However, it looks like box needs to get out. If it needs to get out what would be things to look at while in in addition to the obvious things like general condition of syncros and gears.

Pete Debusmann

It could be a broken 3/4 shift fork. Happened to me. I replaced it with a motorsports part which is all steel as opposed to the standard one which is aluminum with a steel insert. The steel insert breaks loose and causes the problem.

Pete

e9stibi

Pete - as I understand you need to open the gear box to replace this part. Which motorsports part did you put in? How much did you overall pay?

Thanks

Pete Debusmann

Yes the gear box needs to come apart. It is the 3/4 shift fork. 3 years ago it cost me $380. The standard one was the same price. I did the work myself so that plus gaskets was the total cost. I'll dig up the part numbers from PET later.

Pete

tonypai

Shift fork

e9stibi

Thanks for the picture. When I looked at my shop manual, this is what I started to think. It explains why all the other gears are still working. When the problem started occurring, the 4th gear still engaged. Is there something that can get loose or is breaking more probable? Do you suggest to go to the billet steel version, too?

An even more important question, do you think it is safe to drive the car to the shop?

tonypai

I am by no means an expert.....

I don't know enough about the billeted steel version but unless you track it a lot it's probably not necessary.

It might be ok to drive it especially if nothing has broken off. But if something is floating around and it gets caught in the gears it would be catastrophic. Safer to have it flatbedded.

Good luck and report back on your findings. Take pictures if possible.

e9stibi

As most of you guessed correctly, it was a broken shift fork. Here are two pictures of the piece that broke away (and luckily fell straight down without creating further damage) and the damaged shift fork.




The good news is that there is no further damage and all the $$$ custom gears look great. The synchros look good too but I will go steel on 3rd and 4th gear and replace the shift forks 1st/2nd and 3rd/4th with "Albine" products from down under. Combined with the new OS Giken LSD from Japan, I will have a franken gear box with parts from GER, USA, AUS and JAP.

Now it will be only expensive, not f....ng expensive.