915 Transmission bolts?

jcgraybeal · 03-26-2021, 05:30 AM

Hello

Can any tell me about these bolts #20 in the photo? Both are stripped on my transmission housing. I can't find anything out about what they are?

Any way to fix them without pulling the transmission? Helicoil? I am concerned it I drill them out? I worried the shavings may go into the transmission?

Jonny042 · Jonny042's Garage

They are commonly stripped - they are the retaining caps for the detent springs. They have a large head so people reef on them even though I thing the torque spec is something like 12 ft/lbs

The only way to properly repair is remove the trans, disassemble, threaded inserts, and put back together. I don't believe #12 was originally installed and must be a repair part.

I'm sure various short cuts exist....

My 85 has one that "feels" a little stripped, the last time I put it in - I left it alone and it does not leak. Trans is coming out for an LSD this spring so I'll fix it then.

Matt Monson · 03-26-2021, 05:48 AM

You've stripped the detent cap bolts? How the hell do you do that?!?!?

Jonny042 · Jonny042's Garage

The detent caps have a 19mm head (IIRC) but a relatively small 10mm thread with a very short thread engagement into soft aluminum. The torque spec is 12 ft/lb DRY. Couple that with spring force that may surprise an unwitting explorer, or complicate the assembly process, and they are a recipe for the sort of disaster the OP is describing.

There's a reason why threaded inserts are shown on the PET. They weren't there from factory, so they must be service parts.

proporsche · proporsche's Garage

Quote:

Originally Posted by Matt Monson

You've stripped the detent cap bolts? How the hell do you do that?!?!?

yup ......this............
Ivan

jcgraybeal · 03-27-2021, 04:07 AM

Anyone know a way to fix the issue of the stripped female threaded part of the transmission case?
There are still threads there and my thread chaser/refinisher catches just fine. But the bold threads will not. I am trying to figure out a way that I can fix this issue without drilling out the hole and using a Helicoil or similar.
If I could find a 10mm 1.5 bolt that had more aggressive threads like the thread chaser I would be set? If there is such a thing.

Thank you
John

Jonny042 · Jonny042's Garage

Is the trans in the car?

john walker's workshop · 03-27-2021, 07:50 AM

Short timesert.

Jonny042 · Jonny042's Garage

Come to think of it if you had the detent suppository in place when you drilled and tapped for the timesert shavings couldn't get into the transmission. Especially if were careful and maybe packed the hole with grease to stop shavings from migrating inward while you worked.

In the worst case scenario a little bit of aluminum probably isn't going to be too damaging to the transmission compared to the stuff that often happens.

jcgraybeal · 03-27-2021, 09:14 AM

Great idea with the grease!
And yes transmission is in car. I just had it rebuilt last year. My 16 year got it stuck in reverse and 1st. So we drained the transmission pulled the inspection plate to popped it out of gear. I was just looking around and removed both cap bolts. And put them back and when I did I stripped one. I am so mad at myself for even messing with them!! The car was ready to roll after we filled it back up.

kevingross · 03-27-2021, 09:58 AM

The case comes with Helicoils installed in each of these bores. Repair would depend on exactly what has been damaged. If you can replace the Helicoil and the bolt then holds torque, that's a good scenario. Otherwise it will require machine shop attention.

I would not try to install a Timesert. They are great in many applications, but this is not one of them.

Jonny042 · Jonny042's Garage

Quote:

Originally Posted by kevingross

The case comes with Helicoils installed in each of these bores. Repair would depend on exactly what has been damaged. If you can replace the Helicoil and the bolt then holds torque, that's a good scenario. Otherwise it will require machine shop attention.

I would not try to install a Timesert. They are great in many applications, but this is not one of them.

Maybe the mag cases did? The two later 915's I've been into did not have them installed.

john walker's workshop · 01:37 PM

Mag case has heli-coils, aluminum ones did not.
Those holes doesn't exit into the trans, there's a cross-shaft in the way, so if the spring and detent are removed, any chips can be blown out.

jcgraybeal · 03-30-2021, 01:48 AM

Got it fixed with a Helicoil. Pretty easy. Had a little trouble getting the spring through the Helicoil “spring”.

Anyone know what the spring does? Number 19 in the photo?

Thanks again everyone.

John

Jonny042 · Jonny042's Garage

Glad you got it fixed.

The spring applies pressure on 22 which is the capsule shaped piece - essentially it holds the shift rail in neutral position. When you select a gear the spring compresses.