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My 915 she go POP!

I posted this on Rlist so repeating here.

After three complete rebuilds in less than two years, my 915 broke at the first auto-x post rebuild. It has a new 1st, 1st gear shift rod and shift fork. New GT gears 2nd and 3rd gears. Every possible WEVO billet upgrade, a Quaife diff, and 7/31 RP. Oh yeah, attached to a 993 varioram 3.6.

So I rolled away in 1st, for slow sighting lap, shifted to 2nd, dropped the clutch and PO, no drive! The shift lever is stuck in 2nd position and will not come out. But ZERO drive. None. I coasted off the course. No sounds, no drag, no nothing. Clutch in or out makes no difference. No drive whatsoever.

Later, with the shifter lever flopping around and in "neutral", and no gears available, now it won't roll the unless clutch is depressed.

No noises, no clunks, no leaks, no drive. I have not tried to restart and move as it now in garage and fear it jump into backwall if started.

Any clues on what might have happened? It's coming out AGAIN and will be taken apart. Maybe even drop in an 8:35 R&P. The world's most expensive 915!!
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Old 06-13-2018, 05:02 PM
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Sorry to hear that! I've beat on my 915 for 4 years with 355 rwhp and still works great. Your tranny sounds cursed. I'll offer $500 to take it off your hands! 😜 I'd like to start to prepare a new tranny for when mine finally goes pop!
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Old 06-13-2018, 05:10 PM
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It sounds like a shift fork came loose - - maybe take off the bottom cover and take a look inside ? With all the work you have done on it must be something simple.

We broke a tooth of R/P and it slide forward into the 5th/reverse area and locked up the shifter . . . some weird stuff sometimes . . .


Regards,
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Old 06-13-2018, 06:50 PM
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It sounds like a shift fork may be mis-aligned for whatever reason, but the 7:31 coupled to a V-Ram 3.6 is rolling the dice. I run a rebuilt 915 with an 8:31 coupled to a turbo 3.2. I never do launches in 1st and even kinda baby 2nd. 3rd gear is the sweet spot. So far so good and its been close to 7 years. The torque from your 3.6 can pretty much break the 915 at will. I cant imagine the torque with that motor and a 7:31.
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Old 06-13-2018, 08:51 PM
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Quote:
Originally Posted by Rodsrsr View Post
The torque from your 3.6 can pretty much break the 915 at will. I cant imagine the torque with that motor and a 7:31.

3.6 at one end and grippy tires at the other... Yep. somethings got to give.
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Old 06-13-2018, 09:04 PM
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Yikes--that truly sucks.

Let's hope it's something simple.

Not to derail, but is a 7:13 the same as a 4.43 ratio? And would an 8:31 be a 3.88?
Old 06-13-2018, 09:30 PM
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Quote:
Originally Posted by madcorgi View Post
Yikes--that truly sucks.

Let's hope it's something simple.

Not to derail, but is a 7:13 the same as a 4.43 ratio? And would an 8:31 be a 3.88?
Correct. Some good info here if you are curious:

915 TRANSAXLE SPECIFICATIONS-GBOX Transmission

Sorry about the misfortune OP, hopefully it's something simple and inexpensive to fix!
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Old 06-14-2018, 08:02 AM
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915 trans. trouble

the 7:31 r&p will become a problem with a 3.6 My friend blew up 2 7:31 r&p's with a 3.2 it's just not strong enough! go with 8:31 maybe a GT racing 7:31 might hold up better but that's $$$$
Old 06-14-2018, 09:44 AM
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If the 7:31 R&P broke badly it'd make some noise on the roll. Speaking of the final drive, why is the 7:31 needed when you have the extra torque of the 3.6?

I would agree that it's a shift fork issue (or something broke and then disrupted the main shift rod action) and you should take off the bottom cover to start. That bottom cover is what transfers the movement of the main shift rod and then relays the movement to the individual shift rod "paddles" Gordo2 here on Pelican made a nice video showing how that bottom cover gate/fork interacts with the main shift rod

https://www.youtube.com/watch?v=LLEWjNRjJTI

I wouldn't be surprised to see the gate knocked free from the bottom cover. Not uncommon for those studs to pull out of the cover
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Old 06-14-2018, 11:02 AM
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Quote:
Originally Posted by '76 911S 3.0 View Post
Correct. Some good info here if you are curious:

915 TRANSAXLE SPECIFICATIONS-GBOX Transmission

Sorry about the misfortune OP, hopefully it's something simple and inexpensive to fix!
Thank you!

BTW, I meant 7:31 not 7:13 in my question.
Old 06-14-2018, 12:35 PM
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Old 06-14-2018, 01:58 PM
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Quote:
Originally Posted by '76 911S 3.0 View Post
Correct. Some good info here if you are curious:

915 TRANSAXLE SPECIFICATIONS-GBOX Transmission

Sorry about the misfortune OP, hopefully it's something simple and inexpensive to fix!
Just don't send them your gear box. They are the MM of trannies.
Old 06-14-2018, 02:26 PM
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Wow. watching to see what happened.
If I were to guess, you have a broken 2nd gear and it's lodged a shiftfork somehow. I only say that because one time when my 2nd gear broke that's how it behaved as well..
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Old 06-14-2018, 03:26 PM
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Just don't send them your gear box. They are the MM of trannies.
Do they paint the axle flanges red? 😂
Old 06-14-2018, 03:29 PM
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i don't see the 7:31 w/ 3.6 vram either

even the SC/RS used an 8:31 on their boxes, top speed on the optional gear stack was only ~130mph, spread was ~40 to 130 w/ 5 pretty close steps, the short steps are what makes these attractive
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Old 06-14-2018, 05:13 PM
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The 7:31 was already in the car with the 2.7 and we discussed switching to 8:31 extensively. But since itís no longer a track car, itís a huge hoot on the street. But we knew the 7:31 was the weak link.

Maybe drop a 8:35 in (not a 8:31) to get the strength but keep the low speed snap.

It goes fast enough to not top out at CODA. (Yes, I did take it back to the track ONCE. Come on Itís a F1 track!) Managed a 2:32 in street car with stock seats and no harness! Embarassed a few 997s, and 991s.
Old 06-15-2018, 02:57 PM
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I put 45,000 miles on an early mag-case 915 with a mildly tuned 964 (chip, light flywheel, Supersport cams, 993 headers) and never babied the car....

A properly built 915 is able to handle the 3.6 power just fine. Itís not a drag-race or speedshift setup but once in gear itíll handle power

I put the later diff cover, a single bearing retainer and the later input shaft in. Other than that itís stock. The input shaft is a known weak link and my original one eventually lost part of its teeth. But nothing catastrophic. I replaced it before the box grenaded.

I agree that something came undone in yours. Maybe a gear broke, or the shift fork gave or something of that nature. Take the shift fork cover off and see what is going on.

Ingo
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Old 06-17-2018, 09:46 AM
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^^^ What tires do you have on the 915/3.6 targa ?
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Old 06-17-2018, 10:03 AM
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225/50/16 on 8 inch - wonít spin unless itís wet....
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How about a NoBadDays DualChip for 964 or '95 993
Old 06-17-2018, 10:08 AM
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Sounds to me like the 1-2 slider exploded.
Is it the late style hub and slider with asymmetrical teeth on 1st?
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Old 06-17-2018, 06:02 PM
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