87+ manual transmission destruction, rebuilding, discussion etc....
#1
Nordschleife Master
Thread Starter
HOT ‘87 tranny goes to surgery
I’m traveling in Europe now, but if someone has G28.13 five speed S4 transmission with LSD and can ship it to an address in the US, I’m interested in buying one (or two). New preferred over reputably rebuilt over used working. Thank you!
Last edited by ptuomov; 07-01-2019 at 06:56 PM.
#4
Former Vendor
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.)
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.)
#5
Nordschleife Master
Thread Starter
I can’t find individual part numbers for these:
I can’t find individual part numbers for these, can anyone help?
I’m too young to have learned how manual transmissions work back in the day and too old to learn how they work today...
I’m too young to have learned how manual transmissions work back in the day and too old to learn how they work today...
#7
Former Vendor
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 $$$ and dependent on Porsche inventory) there is no way to "repair" the internal gear wear.
Finding a new transmission for high output engines is a definite advantage....they are just tough/sometimes impossible to find.
As these transmissions age, the steel gears suffer from wear at the base of the teeth.....easily visible
in almost all used transmissions. Add in some hydrogen embrittlement and the problem gets worse. The lower shaft (layshaft) is supported by a needle bearing on each end, so it can (and does) flex under load, increasing the backlash on already worn gears.
Unless one buys all new gears for a rebuild (huge $$$ 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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#8
Drifting
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.
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.
#9
Nordschleife Master
Thread Starter
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.
#11
Addict
Rennlist Member
Rennlist Member
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.
#12
Nordschleife Master
Thread Starter
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.
#13
Addict
Rennlist Member
Rennlist Member
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.
But four speed manual would totally work for me if I spin the engine a little higher. There’s enough “torque flat” there in the engine.
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.
#14
Former Vendor
Did they take the top off to see which gear failed?
#15
Rennlist Member