915 gearbox woes

[sting]

hi, been under the 911 this morning and noticed that on the righthand side of the gearbox (from the rear of the car looking forward) there is what looks like a plug/bolt head thats finger tight and will not tighten. the haynes manual states that its a self locking plug but nothing else.I'm reluctant to remove it because i don't know whats on the other end! Can anybody tell me what it is and can I remove it safely. The gearbox was rebuilt 18 months ago and is a pleasure to use and don't want to get into removing it if i can avoid it. thanks:

[Peter Zimmermann]

Sounds like a detent plug with stripped threads. Read the tutorial to be sure...

Porsche Wiki (beta): Forum Categories

Click on "915" under "Page tags."

[Gunter]

The year would help.

Can't think of a self-locking plug on a 915; a picture would help.

Detent-plug? There are 2 on my SC-915 and they're notorious for stripping the threads because the housing is ALU, the plugs are steel and the thread in the housing is very short.

Behind the plugs/bolts is a spring etc. locking the various shift-positions.
If it is stripped, the transmission has to come out and the threads fixed with Helicoil or Case Saver inserts. Repair both holes while you're at it.

Negotiate with the rebuilder cost etc. to do this.

If you keep driving, the spring could pop out the bolt resulting in a lost spring/bolt plus some oil leaking out.


Picture?

[sting]

just looked on the tutorial and it looks like the 3rd / 4th detent plug. think i'll have another xmas drink and start dropping it out! thanks for your help and a happy new year.

[Gunter]

Picture of the 911 and what type/year is required for Newbies.

I fixed the stripped threads by going to the next size SAE NF bolt, then carefully drilled and tapped for the new bolt. To achive the same spring-tension, I selected a slightly longer bolt and then drilled out the end of the bolt on a Drill Press to the diameter of the spring to hold it and at the same time retain the right length to give the same tension as before.

Helicoil or Case-Savers would have required a larger hole to be drilled/tapped and I didn't want that. Plus, by doing the above mods, I got more threads to hold the new SAE NF bolt.

I think the stock bolt is a very short M10? Forgot what the next size SAE NF is but a Vernier Caliper will tell you. Chips from drilling/tapping are a problem. I stuffed a small piece from a rag full of grease in the hole to catch the chips.

[sting]

its an 84 3.2 carrera cab. I,ve just taken the bolt out and it is the detent plug. I think i'll have a go at retapping in situ and replace with a modified bolt as you suggest. seems a shame to strip the box as its fine and lots of people seem to have problems with them. bit worried about metal swarf getting into the box though. a job for the weekend and i'll let you know how i get on. thanks

[mpetry]

Take the same precautions you would when putting a helicoil into a blown spark plug hole. I've done this many time on bus motors.

Make sure you've got some grease on your drill and tap. Then when you're done, get a piece of hose from your brake bleeder and build it with duct tape so you can stick it in your vacuum cleaner. Then use that little "snorkel" to vacuum out any chips that are in the tranny case. Do this after drilling, and again after tapping.

If you are really cautious, you might flush a quart of trans lube thru there - just pour it in the fill hole and let it drain out. Hopefully that won't be necessary.

Nice winter project.

[Gunter]

Hard to do in situ because there is no room for the drill motor.
May be tough to tap without drilling the right size hole.
Tap-sets come in 3: Starter #1, #2 and the #3 bottom tap.
The starter-tap that has a good taper.

Is the stock bolt M10?
The next size would be M12 if you go Metric.
(M11 would have been my choice but is virtually non-existant)
So, I went with SAE-NF but cannot remember what size. Whatever size it was, it worked well and I consider the option of a new modified bolt/plug superior in giving you extra threads without making the hole bigger than necessary.

Helicoils or Case-savers are great and I have used them for spark plug holes.
But they need a large hole to fit the insert and I didn't want to make it larger than necessary on the 915.

You'll see what I mean when you take a closer look and take measurements.
I don't believe you can do it in situ but.........................
Let us know what sizes you'll use, please.