Budget 915 Trans re-fresh

[Solamar]

I think we've all heard the joke -

"My 911 will go zero to 60 in under six seconds, of course two of those seconds are spent finding second gear..."

My second gear was cranky, never would grind but sometimes the "first, neutral, second" shift would balk at entry into second requiring a ballet of re-clutching and rev matching.

First gear wasn't bad, but occasionally at a stop in neutral the light would change and first gear would be "out to lunch". Typically a fake into second and then slip up to first would get things going.

I had two Friends (that happen to be Porsche factory trained air cooled mechanics) drive it and both said it really wasn't all that bad and that they wouldn't recommend a tear down unless I was in there for another reason.

As luck would have it the drive train came out for other reasons and while the tranny was out I decided to try a trick I've heard about, flipping the synchros... I know the tranny experts don't recommend it, but what do I have to lose? Few bucks in oil and gaskets, figured it was worth a try.

I guess I got lucky. Second gear is worlds better. Still a slow first, neutral, second shift but never refuses to enter second gear smoothly. Very happy with my second gear now! First gear is noticeably better, but still a second gear 'fake' ensures a smooth first gear entry.

Lots of good resources on 915 tranny tear down, heres just the quick down and dirty of how I did mine -

Remove front cover exposing reverse and fifth, remove all, then remove inner housing -



Then pull the input shaft bearing to allow room to pull the pinion shaft bearing and first gear

(sorry, the tranny is flipped upside down in this picture)


Now first and second along with their synchros will slide right off -



Next remove the snap ring (easier said than done, get a good tool!) and the synchro is released allowing you to flip and reinstall.



Re-assemble and take it for a spin

Disclaimer - I'm just a shade tree hack, proceed at you own peril...

[Trackrash]

Yeah. The book actually says you can do this. As long as the back side of the synchro ring is OK, AND it is still in spec when installed this way, it will work.

Another trick is to swap out 5th synchro for third.

[dennisO]

I can't really tell from your photo, but are the 2nd dog teeth rounded?

[Solamar]

Originally Posted by Trackrash

Yeah. The book actually says you can do this. As long as the back side of the synchro ring is OK, AND it is still in spec when installed this way, it will work.

Another trick is to swap out 5th synchro for third.

What book are you referring to? The factory service manual?


Great tip about 3rd and 5th, makes sense that 3rd would wear faster.

[Solamar]

Originally Posted by dennisO

I can't really tell from your photo, but are the 2nd dog teeth rounded?

Just starting to get a burr on the outer tip (can feel it with your fingernail). They don't look too bad though -

[30westrob]

Thanks for the great tutorial. Did you need any pullers, ect. to remove bearings or gears. Rob

[Jonny042]

I got these snap ring pliers: worth the cost x 10!!!

[Solamar]

Originally Posted by 30westrob

Thanks for the great tutorial. Did you need any pullers, ect. to remove bearings or gears. Rob

I don't want to lead you wrong, so hopefully someone with solid experience will reply, but here's how I did it.

The bearing on the input shaft has to come off first, problem is the gear behind it is the fixed first gear which is part of the shaft. So, little to zero room to get a puller on to that bearing (of course you never want to pull on the outer cage).

I set a small punch in the first gear groves and tried to tap the bearing out. To my surprise It tapped out with little effort. This is probably not the correct procedure...

The pinion shaft bearing was easy. Two jaw puller on the free first gear, came off with little effort.

To reinstall the bearings I used a correct diameter deep socket and tapped then on.

[Solamar]

Originally Posted by Jonny042

I got these snap ring pliers: worth the cost x 10!!!

Nice! I used a quality, but smaller pair that just wasn't quite up to the task. Some old school piston ring expander pliers saved the day.

[2jmotorsports]

My 915 is in the same condition as yours. Thanks for the insight.

[MichaelSJackson]

Solamar,

Nice informative thread.

Instead of getting caught at the light needing to do a "fake into second"; develop the habit of coming to a complete stop, before taking it out of second. Then first is always there.