Need advice: 915 Transmission rebuild

korbensinclair · 09-23-2011, 07:24 PM

I have not posted much here as I am relatively ignorant with respect to car repairs of any type. I had my starter go out (confirmed it was bad once the engine was dropped and I got it off). While the engine and transmission was out, I figured I would handle something that had really bothered me all summer (I've only driven this 1977 911T for maybe 1k miles). I could never get back into first gear with any sort of ease. After doing hours and hours and hours of research on why this was (thanks to these boards) I decided it was likely the syncros and dogs teeth on first and a partial transmission rebuild would fix all my problems.

I tore into it and have it nearly completely appart and it is bad, even to my untrained eye. According to the previous owner the transmission was a new rebuild with only 5k miles on it. Well I am calling BS on that. I expect his old tranny went out and he just paid someone to throw a random junker in for a sap like me to purchase.

In any case, Zimmerman's wiki (which is one of the many pages I am consulting) specifically stated that:

"Clean the entire pinion shaft and examine the teeth of the pinion head; all of them, on both sides. No pock-marks in the smooth finish of the teeth are permissible for re-use. In other words, any wear that is through the hardened surface means that you are holding a thousand dollar piece of junk; or a paper weight that will be sure to be an unusual conversation starter at the office. "

I can post a photo tomorrow, but my pinion head is so deeply pocked and pitted it puts his example photo of a "bad" pinion to shame.

I am assuming that pinion shafts really are $1000 (I noticed the 7:31s go for $2000), so at this point I am starting to feel I might just be better off with an entire new transmission and hope it does not have the same issues my current one does.

I guess I just need someone else to tell me to suck it up and scrap my rebuild. I'd been hoping to spend no more than $1500 (this was back when I was under the illusion that first/second gears were the only ones that needed rebuilding).

fanaudical · fanaudical's Garage

I recommend posting pics. Peter Z and others with more experience usually pay attention to these threads and may offer some advice.

I was in your position a few months ago. I ended up investing in another rebuilt trans.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by fanaudical

I recommend posting pics. Peter Z and others with more experience usually pay attention to these threads and may offer some advice.

+1

If you need to buy a rebuilt trans don't skimp. Upgrade to pressure cast vs mag if advised and use this forum for vetting your options and thoughts.

Look at it this way, if you become a hardcore 911 nut, a correctly repaired (or properly rebuilt) trans may last 30 years if you don't track it. Take your time. It will pay big dividends.

korbensinclair · 09-24-2011, 08:55 AM

Pinion

First gear (haven't broken it all appart and I'm only guessing it is first as it is the largest and some websites pointed to it as first).

And the best (worst) part was this HUGE piece of metal I found floating around in the center section of the tranny case.

Suggestions? Input? Pinion shaft head good enough to reuse? Should I do a minimalist rebuild and just drive the tranny into the ground and then buy a well rebuild low milage tranny?

korbensinclair · 09-24-2011, 09:05 AM

Quote:

Originally Posted by Bob Kontak

+1

If you need to buy a rebuilt trans don't skimp. Upgrade to pressure cast vs mag if advised and use this forum for vetting your options and thoughts.

Look at it this way, if you become a hardcore 911 nut, a correctly repaired (or properly rebuilt) trans may last 30 years if you don't track it. Take your time. It will pay big dividends.

I agree, I was only hoping to sink a little money into my current transmission and drive my car while I saved up, but if I have to get an entire new one, I am thinking I'll hold off on the tranny for now and focus on my car body instead. Then when that project is done I'll spend GOOD money on a new engine and tranny all at once. This year the wife dominated my "play" money, but next year all my side project income is going to the Porsche fund. I've gone a year without driving my car, I can go a few more. The 1000 miles I did drive it was amazing.

Bob Kontak · Bob Kontak's Garage

Looking forward to comments from those in the know.

I have a few e-mails from Mayo Performance with pics of my 915 parts when it was rebuilt. I would be glad to send you those if you PM me your e-mail. He (Tom P) highlights some of the screw-ups that were made on a previous repair.

Peter Zimmermann · 09-24-2011, 12:14 PM

Quote:

Originally Posted by korbensinclair

I have not posted much here as I am relatively ignorant with respect to car repairs of any type. I had my starter go out (confirmed it was bad once the engine was dropped and I got it off). While the engine and transmission was out, I figured I would handle something that had really bothered me all summer (I've only driven this 1977 911T for maybe 1k miles). I could never get back into first gear with any sort of ease. After doing hours and hours and hours of research on why this was (thanks to these boards) I decided it was likely the syncros and dogs teeth on first and a partial transmission rebuild would fix all my problems.

I tore into it and have it nearly completely appart and it is bad, even to my untrained eye. According to the previous owner the transmission was a new rebuild with only 5k miles on it. Well I am calling BS on that. I expect his old tranny went out and he just paid someone to throw a random junker in for a sap like me to purchase.

In any case, Zimmerman's wiki (which is one of the many pages I am consulting) specifically stated that:

"Clean the entire pinion shaft and examine the teeth of the pinion head; all of them, on both sides. No pock-marks in the smooth finish of the teeth are permissible for re-use. In other words, any wear that is through the hardened surface means that you are holding a thousand dollar piece of junk; or a paper weight that will be sure to be an unusual conversation starter at the office. "

I can post a photo tomorrow, but my pinion head is so deeply pocked and pitted it puts his example photo of a "bad" pinion to shame.

I am assuming that pinion shafts really are $1000 (I noticed the 7:31s go for $2000), so at this point I am starting to feel I might just be better off with an entire new transmission and hope it does not have the same issues my current one does.

I guess I just need someone else to tell me to suck it up and scrap my rebuild. I'd been hoping to spend no more than $1500 (this was back when I was under the illusion that first/second gears were the only ones that needed rebuilding).

You certainly made the right call. I hate seeing this kind of thing happen, and you certainly got the short end of the stick regarding the transmission. I do have a suggestion on how to handle the problem, and will send you a pm.