Transmission, Manual

Rebuild Rookie Report

I now have my 5 speed transmission disassembled after a lot of much appreciated moral support from the bologna eating, beer swilling, Pennsylvania Dutchman turned Florida hick machinist [Dave S.] and about 15 minutes of hands-on help from a local Porsche mechanic friend.

This is truly a fine piece of machinery. I was able to do the entire disassembly without having to use a single special tool [master machinist was waiting in the wings to make them, if necessary]. Each shaft and piece came out smoothly and with little resistance. This BTW is the first time I have ever worked on a transmission. I have inspected all of the parts and found a chipped tooth on the lower 5th gear and a slightly bent tooth on the upper 5th gear. There is one dog tooth missing from, I think, 2nd gear.

Okay, so here's what must have happened inside the tranny: a dog tooth at 2nd gear somehow broke off [no wear to speak of at all on any of the remaining teeth on that ring], then the broken off tooth wedged between the two fifth gears, snapped off a small piece of one of the teeth in the lower gear and bent part of the corresponding tooth on the upper gear with a resulting hair line crack. The bent tooth slightly caught on each revolution, accounting for the clang on each revolution. All the bearings and synchos look fine. There is virtually no other visible wear anywhere in the tranny.

My mechanic who has seen the gears thinks that a little grinding to reshape the two damaged teeth will work without causing future damage. There won't be any damaged teeth coming into contact with any good teeth. I never had any noise or gear grinding in 2nd gear or any gear for that matter, so the synchos are probably just fine. I did have a problem with the car sticking in gear when at a stop, because my clutch was not sufficiently disengaging (the nylon bushing at the end of the clutch lever was worn out, and I have already replaced that). That probably was the cause of the tooth coming off. There is simply no wear to see at all on the remaining dog teeth or anywhere for that matter.

The proposed grinding will result in about a 25% surface loss on one tooth and about 50 % surface loss on the other tooth. Being that it is 5th gear I am thinking that there is little danger of any balance or vibration problems. My gut feeling is that if carefully machined down, it will work just fine. Furthermore my mechanic thinks that the grinding would not raise the metal to a sufficient temp to soften it.

I, at this point, intend to replace all the gaskets and seals, but leave the bearings and synchos alone. The main input shaft bearing has marble sized ball bearings, and it looks like it was built for a Sherman tank. There are several sets of needle cage bearings that look brand new on a couple of the shafts. This tranny was already rebuilt once before in 1993 when the 5th gear had a prior failure.

If I had the money I would not hesitate to replace the 5th gear set, all the synchros, all the dog teeth, and all the bearings, but, unless someone on the list knows that I will suffer certain disaster with my preliminary plan, I'm probably going to proceed with my simple repair.

But if anyone out there has a reasonably [cheap] priced 5th gear set, please let me know!

Daniel Shapiro
'82 928 5 speed 226k