HOT ‘87 tranny goes to surgery
 

doesnt greg brown have a couple of new in crate transmissions..??

The ones I had/have are '85/'86 models. The big difference is that the 928/13 had steel moly lined syncros for increased longevity in 1st -3rd gears, instead of brass moly lined syncros.

Of course, these days, I would be using carbon fiber lined steel syncros, instead of moly lined steel syncros. Insane durability from the carbon fiber, along with increased "bite".

I know of no new '87 and later units, BTW.

Truthfully, I'm not sure what I have left...but I think I have two. One with and one without limited slip. (Limited slips are pretty straight forward to rebuild and install.and unlike gears, bearings, and all the other internal pieces, they don't break from age.)

I can’t find individual part numbers for these:
 

Damn Tuomo, you are young smart man, why should you not understand how manual transmissions work? You have not showed us which part(s) broke.
Åke

Stock engines can break teeth off of individual gears. Higher torque makes this happen more often.

As these transmissions age, the steel gears suffer from wear at the base of the teeth.....easily visible
in almost all used transmissions. Add in some hydrogen embrittlement and the problem gets worse. The lower shaft (layshaft) is supported by a needle bearing on each end, so it can (and does) flex under load, increasing the backlash on already worn gears.

Unless one buys all new gears for a rebuild (huge $$$ and dependent on Porsche inventory) there is no way to "repair" the internal gear wear.

Finding a new transmission for high output engines is a definite advantage....they are just tough/sometimes impossible to find.
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Porshce 928 5 speeds cannot handle the torque of your engine......correct ?

what about just doing the 928motorsports change over to a strongly rebuilt 6 speed gm transmission........c5 or c6 I think I mean all the time and money on the twin turbo set up , just step up to something that can handle the torque.

I am going to come out clean and confess that I really don't know much at all about transmissions. Because of this, I don't have many strong opinions about whether the 928 transmission can handle the torque that John's system produces or not. This particular G28.13 lasted in my car normally aspirated for maybe 22 years and then another 8 years with twin turbos. It also took almost exactly 500 dyno runs, ranging from 10 seconds to over a minute, some sweeping rpms and some holding rpm and sweeping loads. I have only one data point, and I can't quite make up my mind whether it's negative or postive!? I do know that I have a personal preference to keep the car as stock as possible, other than making a lot more power, so if the stock transmission can be made to last, I'd very much like that. Not predicting that it can be, just expressing a preference.

What about this one, from a 1988?
https://rennlist.com/forums/928-foru...on-roller.html

To make stock transmission last you basically need to give up one gear pair in the middle and replace it with third bearing support to keep two shafts together. If you're not willing to live with 4sp gearbox better option is to convert to Corvette 6sp now instead of after next explosion. Just about every modern high TQ manual gearbox has three bearing pairs to support two shafts where gears are located. If you happen to be around in Helsinki we have half dozen late 928 manual boxes in garage in varying dismantle level in case you need to understand how they work.

Way below it as I have dismantled them, managed to put them back together and they have worked for years after it.

You basically take out 3rd gear pair and replace it with two bearings and support around them to keep them together no matter what. Then you have a choice on what gear pair to put in place of current 4th gear. Very likely it can be any 3rd or 4th gear pair from late type 928 gearbox meaning you have few choices on how large gaps between old 2nd to new 3rd/4th and new 3rd/4th to old 5th is. If you spend enough $$$$ on different gear pairs from G28.10, 11, 12, 13, 55 and 57 you might be able to put together fairly even split setup which do not have too large holes between new 2nd, 3rd and direct drive 4th.

Just get 6sp and be done with it. If it has to be 928 get GTS box or at least include oil pump setup to older box.

Did they take the top off to see which gear failed?

Tuomo, this is the way to go with your TT.

Best bet would be the C7 Z06 7-speed which is mated to a 650hp FI engine, so at least twice the strength of a 928 box.