What Happened to these syncros ? Anyone seen this before ?

[David Goodman]

1979 930 gearbox. 6000 miles on a fresh rebuild where everything suspect (including these very syncros) were replaced by a well known east coast transmission building malcontent.

Notice the chunks missing from the syncros. Wrench says he's never seen this before. 2nd, 3rd and 4th were affected. I know that some of you are thinking "that far left pedal is the clutch, Dave", but I assure you this thing was not abused. Wrench thinks maybe it's a material defect. What do you guys think ? Anyone seen this before ?
Thanks,
Dave

BTW this was using Valvoline semi-synthetic 80/90 gear oil.

[john walker's workshop]

i see that a lot on 901,915, 930 rebuilds. kind of normal, but not what you would expect with such low mileage. maybe it was reused.

[wevoid]

David,

Were the drive teeth on the gear replaced at the same time as the synchro ring?

Regards

Hayden

[porschetech]

This is very normal on a transmission with mileage. I would syspect the syncros have nore than 6k on them. We have seen this also when the incorrect fluid is used.

Good luck.

[Jim Sims]

I will speculate that that the synthetic gear oil didn't have the correct friction/viscosity characteristics. Components failed to match speed in expected time and the driver following previous shift patterns ended up forcing parts together too soon. This resulted in higher peak loadings on the synchro ring surfaces which caused the overheating/spalling? I wonder what the dogteeth and operating sleeves look like? Synthetic oils likely are helpful in reducing wear and power losses in the transmission bearings and gear mesh points but can cause grief for friction surfaces like synchros. Best to probably stay with the gear oil types in use when the transmission was designed. Cheers, Jim

[David Goodman]

Guys,
Thanks for the input.

Hayden,
I'm not sure but everything suspect was supposed to have been replaced, and the guy rebuilding it now said everything looks fine except for what he needed to replace (more on that shortly). I am really beginning to wonder now if I got a solid rebuild. I'll explain in a moment.

Jim,
The dogteeth looked fine but the new rebuilder did replace one borderline operating sleeve and one guide sleeve. 2nd, 3rd and 4th were affected, I'd really like to think I'm a better driver than that.

So here is the rest of the story. This is the second time this gearbox has been apart in 11,000 miles. 5000 miles after the first rebuild it stopped going into 4th gear. The cause was that item 2 in the picture, the lockwasher somehow got bent forcing the syncro apart and preventing the slider from getting past it. When I asked him how that could happen, he said it's a design flaw and it happens occasionally. It sounded like BS at the time but I was in such a hurry to get the motor back together for the One Lap last year I didn't have time to press the issue. Now in the cold light of day what do you guys think of that explanation ?

Thanks again for the help,
Dave

[Sonic dB]

Box it up and ship it to JW

[john walker's workshop]

you have to be careful to seat that snap ring all the way around.

[David Goodman]

That's what I thought John. Thanks for your additional input.

Sonic,
I hope I have the opportunity sometime to send him some business. I'm out of time on this project though, the One Lap starts on the 30th.