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safe
Joined: 18 Mar 2017
Posts: 708
Location: Sweden
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 Posted: Tue Apr 28, 2026 4:51 pm Post subject: |
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| Beartooth wrote: | Very interesting to see the guts of the G31! I'll be there with you sooner or later... I still can't believe how well mine has held up, and how well I've adapted to driving it, despite seemingly no 1st gear syncro left (and probably dog teeth as bad as yours), and 2nd not much better, and shifter bushings that may no longer even exist. When the car does come apart, the transmission will probably be the first thing I'll go into, because finding some of those parts could be a long-term process. One or two pieces (1st/rev slider, I think, is one) may have to be sent to a specialist who welds and re-machines the teeth - and I'm not sure I want to know what that will cost! Someone worth reaching out to if you haven't already is CMS (cms@californiamotorsports.net).
I've got a quote saved, and it includes the 1sst gear dog ring, so they may have them. 2nd and 3rd as well - $250 each a couple years ago... The other things on the quote were 2nd/3rd slider ($470), 1st syncro ($160), 2nd and 3rd syncro ($210 each), and another $100 for a lock nut and seals. Total was about $1900, and that doesn't include the 1st/rev slider that I'll almost certainly need too... I wish it were like the transmission for my Explorer that I just went through, on which I replaced a cluster gear, input shaft, bearings, syncros, 5th/rev slider, 5th gear, reverse gear, and some shims and seals and such, for a grand total around $500. If wishes were horses, beggars would ride though, as I remember hearing back when. Just one of the joys of working on something built by the thousands versus millions.
Looks like I need to start saving up - or sell a car - before I start on that one! Anyway, hopefully you can find some good enough pieces to make it work ok without spending a pile on it! I'm also interested in what you're doing with the LSD, although I'm lucky and my car came with one. I might want to play with making it more aggressive though. I've never even worked on a differential, so tinkering with an LSD would be all new to me. |
Rare and expensive parts!
I don't remember if I checked with CMS, I think they were out of stock.
I thought my 1st slider was very worn, but I got a second opinion that said it wasn't too bad.
He gave me a test to do.
"The groove is for the synchro to lock into. As long as the hump as you enter it isn't too worn, it will still lock into the gear. Once you replace the teeth and synchro on the loose gear, you can check it by hand. You should be able to slip the gear into it, and have enough tension on it to pick up the shift sleeve without the gear falling out."
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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Cedric
Joined: 27 Aug 2004
Posts: 2809
Location: Sweden
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| Posted: Tue Apr 28, 2026 6:52 pm Post subject: |
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| Beartooth wrote: | Very interesting to see the guts of the G31! I'll be there with you sooner or later... I still can't believe how well mine has held up, and how well I've adapted to driving it, despite seemingly no 1st gear syncro left (and probably dog teeth as bad as yours), and 2nd not much better, and shifter bushings that may no longer even exist. When the car does come apart, the transmission will probably be the first thing I'll go into, because finding some of those parts could be a long-term process. One or two pieces (1st/rev slider, I think, is one) may have to be sent to a specialist who welds and re-machines the teeth - and I'm not sure I want to know what that will cost! Someone worth reaching out to if you haven't already is CMS (cms@californiamotorsports.net).
I've got a quote saved, and it includes the 1sst gear dog ring, so they may have them. 2nd and 3rd as well - $250 each a couple years ago... The other things on the quote were 2nd/3rd slider ($470), 1st syncro ($160), 2nd and 3rd syncro ($210 each), and another $100 for a lock nut and seals. Total was about $1900, and that doesn't include the 1st/rev slider that I'll almost certainly need too... I wish it were like the transmission for my Explorer that I just went through, on which I replaced a cluster gear, input shaft, bearings, syncros, 5th/rev slider, 5th gear, reverse gear, and some shims and seals and such, for a grand total around $500. If wishes were horses, beggars would ride though, as I remember hearing back when. Just one of the joys of working on something built by the thousands versus millions.
Looks like I need to start saving up - or sell a car - before I start on that one! Anyway, hopefully you can find some good enough pieces to make it work ok without spending a pile on it! I'm also interested in what you're doing with the LSD, although I'm lucky and my car came with one. I might want to play with making it more aggressive though. I've never even worked on a differential, so tinkering with an LSD would be all new to me. |
It surely hasnt got cheaper, i just checked my invoce from back in the Ideola days and it was quite abit lower than those prices. And i guess its more expensive if you ask today.
On the upside its a very simple box to work on when you actually have taken it out 
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1980 924 Turbo
www.instagram.com/garagecedric/ |
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safe
Joined: 18 Mar 2017
Posts: 708
Location: Sweden
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| Posted: Tue Apr 28, 2026 7:06 pm Post subject: |
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| Cedric wrote: |
It surely hasnt got cheaper, i just checked my invoce from back in the Ideola days and it was quite abit lower than those prices. And i guess its more expensive if you ask today.
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I rebuilt my more modern G50 a couple of years ago, that wasn't cheap either....
A friend rebuilt a 915 just a few days ago, that was in the neighborhood of 40.000 sek ($4000 ish). He still has to pay me another 20+k for the core of the gearbox!  We haven't decided on a price for it yet... at the moment he has just rebuilt my spare gearbox!
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/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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924RACR
Joined: 29 Jul 2001
Posts: 9076
Location: Royal Oak, MI, USA
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| Posted: Tue Apr 28, 2026 9:15 pm Post subject: |
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No, I was thinking more of the springs in the diff, your preload etc... though it's probably a bellville washer stack in this design rather than coil springs (as used in others)...
If you lost grip with more spring... sounds like some attention to your damper setup, work on the valving, is due...
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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safe
Joined: 18 Mar 2017
Posts: 708
Location: Sweden
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| Posted: Tue Apr 28, 2026 9:44 pm Post subject: |
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| 924RACR wrote: | No, I was thinking more of the springs in the diff, your preload etc... though it's probably a bellville washer stack in this design rather than coil springs (as used in others)...
If you lost grip with more spring... sounds like some attention to your damper setup, work on the valving, is due... |
No, I didn't.
It wasn't mentioned in the documentation with the diff. Only on how to adjust Locking up percentage with the friction surfaces.
I'm not sure but I think this a more modern setup to adjusting LSDs than just shimming the preload like on old ZFs.
Maybe, the stock t-bars and sport Bilstein just hocked the road! The GAZ squats a lot less and doesn't grip as good (in a straight line).
_________________
/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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Beartooth
Joined: 05 Apr 2022
Posts: 316
Location: Roberts, MT
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| Posted: Wed Apr 29, 2026 7:57 am Post subject: |
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| safe wrote: |
Rare and expensive parts!
I don't remember if I checked with CMS, I think they were out of stock.
I thought my 1st slider was very worn, but I got a second opinion that said it wasn't too bad.
He gave me a test to do.
"The groove is for the synchro to lock into. As long as the hump as you enter it isn't too worn, it will still lock into the gear. Once you replace the teeth and synchro on the loose gear, you can check it by hand. You should be able to slip the gear into it, and have enough tension on it to pick up the shift sleeve without the gear falling out." |
I'll have to remember this, or look it up, when the time comes. I suspect mine would fail: in addition to being very easy to crunch 1st gear (you have to be at a stop or barely rolling, and at least tap another gear first), it also pops out of 1st pretty easily. It never does it under load, thank God, but if I get rolling down a slight hill where the engine is neither pulling nor holding it back, it'll jump out almost every time. It's also impossible to do 1st-2nd aggressively without crunching 2nd, so 1st really only gets used to get it rolling fast enough that it won't bog in 2nd. One of the joys of driving the "real Porsche" gearbox, I guess!
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1980 931 diamond in the rough |
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Cedric
Joined: 27 Aug 2004
Posts: 2809
Location: Sweden
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| Posted: Wed Apr 29, 2026 4:04 pm Post subject: |
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| Beartooth wrote: | | safe wrote: |
Rare and expensive parts!
I don't remember if I checked with CMS, I think they were out of stock.
I thought my 1st slider was very worn, but I got a second opinion that said it wasn't too bad.
He gave me a test to do.
"The groove is for the synchro to lock into. As long as the hump as you enter it isn't too worn, it will still lock into the gear. Once you replace the teeth and synchro on the loose gear, you can check it by hand. You should be able to slip the gear into it, and have enough tension on it to pick up the shift sleeve without the gear falling out." |
I'll have to remember this, or look it up, when the time comes. I suspect mine would fail: in addition to being very easy to crunch 1st gear (you have to be at a stop or barely rolling, and at least tap another gear first), it also pops out of 1st pretty easily. It never does it under load, thank God, but if I get rolling down a slight hill where the engine is neither pulling nor holding it back, it'll jump out almost every time. It's also impossible to do 1st-2nd aggressively without crunching 2nd, so 1st really only gets used to get it rolling fast enough that it won't bog in 2nd. One of the joys of driving the "real Porsche" gearbox, I guess! |
Even with everything fresh, the 1st should always be used pretty much from standstill or not far from it. But it shouldnt pop out of course if the gear is in decent condition
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1980 924 Turbo
www.instagram.com/garagecedric/ |
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safe
Joined: 18 Mar 2017
Posts: 708
Location: Sweden
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| Posted: Thu Apr 30, 2026 12:49 am Post subject: |
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You should be able to engage 1st from 2nd, the dog teeth are angled (not symmetrical as on 2-5) to help with that. My current NA snail shell wont even think of engaging 1st unless it is standing completely still. Its not grinding, just impossible to move the shifter.
I can do it in my 911 with a 915 box, pretty aggressively.
As a side note, there are threads on forums where our host Dan is debating the right dog ring for a G31. After getting a "new" ring from Cedric I can only come to the conclusion that Dan was wrong, it looks identical to the 915 1st dog ring (whether the teeth are angled right or left).
_________________
/Magnus, Stockholm Sweden
=======================
Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe |
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