915 trans rebuild

[ourv12]

Since I cant afford a G50 Im going to be looking into rebuilding my 915. Anyone done this job? Is it feasible? Ive done engines but never a tranny. Thanks for any help!

[Peter Zimmermann]

Welcome to Red Line Porsche Wiki - Porsche Wiki

Locate "page tags" and click on "915."

Cheers!

[ourv12]

Thank You so much! I'm almost afraid to read it but on the other hand I cant wait to get started because I don't enjoy driving my Porsche anymore because of the very hard shifting.

[James Brown]

I'm sure after rebuilding the 915, you will be happier than swapping in a G50, lots of work and so-so results. The 915, in good condition, is a great gearbox. Follow Peter's instructions and you can do it yourself. Very rewarding rebuilding these units, but not cheap.

[mack6820]

while your in there, swap your gears to lower ones. Nice improvement!

[ourv12]

Just out of curiosity why do the 915's cause so much trouble? Are people abusing them or neglecting them?(preventive maintenance issue)Is there a design flaw?Wrong fluid?Mine only had 61K on it when it needed to be repaired and now it has 89K and needs to be rebuilt.

[RWebb]

maybe the repair was not complete?

they don't cause a lot of trouble, but a lot of people expect them to be something they aren't & use the wrong fluid

[fanaudical]

I'm somewhat in the same boat and had lots of trepidation at starting this rebuild. I did jump in, am halfway through disassembly - and the internals of that transmission are not nearly as scary as I thought. Other than some special tools, I'm finding this to be very "doable" if you're at all "wrench-savvy".

Thank you, Peter, for the wonderful wiki.

Good luck!

[Peter Zimmermann]

Originally Posted by ourv12

Just out of curiosity why do the 915's cause so much trouble? Are people abusing them or neglecting them?(preventive maintenance issue)Is there a design flaw?Wrong fluid?Mine only had 61K on it when it needed to be repaired and now it has 89K and needs to be rebuilt.

Driver technique and mechanic competency should probably be weighted equally. Did you put the first 61K miles on your car? Do you have a parts list for what was replaced at that point? What is wrong with the trans now?

My '81 SC, for example, was driven by the PO from 85K (when I repaired the 915), to 117K miles. I bought the car then, and my wife and I put 100K miles on the car, then sold it to a friend of the shop. He drove it about 60K miles (always serviced at Red Line), and then sold the car to someone we didn't know. So we were able to track that transmission for almost 200K miles, without problems beyond routine maintenance and a properly working clutch. They are very good transmissions if the right things are done, and the car is driven within its capabilities.

[sc_rufctr]

Originally Posted by James Brown

I'm sure after rebuilding the 915, you will be happier than swapping in a G50, lots of work and so-so results. The 915, in good condition, is a great gearbox. Follow Peter's instructions and you can do it yourself. Very rewarding rebuilding these units, but not cheap.

But much cheaper than rebuilding a G50.

[Christien]

Originally Posted by ourv12

Just out of curiosity why do the 915's cause so much trouble? Are people abusing them or neglecting them?(preventive maintenance issue)Is there a design flaw?Wrong fluid?Mine only had 61K on it when it needed to be repaired and now it has 89K and needs to be rebuilt.

I don't think they cause trouble, so much as they're just so different from a modern standard transmission. They're not crisp and sharp, like you'd expect, and don't just slide into gear with no effort. So it's possible they get abused by people ham-fisting them into gear, expecting them to shift like a modern tranny. Even after rebuilding mine, it still doesn't shift like a boxster, or even our old 5-speed Accord.

The rebuild is definitely DIY-able. It's a lot of work, but very rewarding.

[cdadaa]

I rebuilt my 915 using Peter Z's tutorial. This was my first tranny rebuild and worked out very well. I also was very active on this forum with specific questions during the process. I had to disassemble twice because on my initial assembly, a small detent plunger was placed on the wrong side of the 4/5 shaft. There were a couple of gents on this forum that were a tremendious help and walked me through the troubleshooting.

Pay very close attention to the detail! Take lots of pictures from different angles and carefully organize your components during disassembly.

Good luck...mine was actually fun to complete and works flawlessly.

Dan

[Matt Monson]

Originally Posted by sc_rufctr

But much cheaper than rebuilding a G50.

Not really if it's rebuilt properly. Cheap 915 rebuilds frequently see premature failures because corners were cut the first time around. It's part of why the 915 has a black eye in so many circles. Done properly, using Pete's tutorial as a guide, and a 915 is going to cost near the same as a G50 to thoroughly sort.

[RWebb]

I thought the 915 gears were much cheaper?

[Matt Monson]

Originally Posted by RWebb

I thought the 915 gears were much cheaper?

I wouldn't consider regearing a gearbox part of a proper rebuild. If you're talking new, 915 gears are about 20% cheaper than G50 at $795 versus $995.

[sc_rufctr]

Originally Posted by Matt Monson

Not really if it's rebuilt properly. Cheap 915 rebuilds frequently see premature failures because corners were cut the first time around. It's part of why the 915 has a black eye in so many circles. Done properly, using Pete's tutorial as a guide, and a 915 is going to cost near the same as a G50 to thoroughly sort.

G50 parts are way more expensive than 915 parts. I'm talking about a proper rebuild not a freshen up... = Sliders and synchros only.

Of course the G50 is newer and seems very robust so they don't require the attention a 915 does. (Yet)

[Matt Monson]

Originally Posted by sc_rufctr

G50 parts are way more expensive than 915 parts. I'm talking about a proper rebuild not a freshen up... = Sliders and synchros only.

Of course the G50 is newer and seems very robust so they don't require the attention a 915 does. (Yet)

I think we're actually saying the same basic thing from different ends. There's no denying that G50 parts are more expensive. But with how worn out and beat up 915 gearboxes have become they need more parts to be properly rebuilt. We're starting to see 915's need 3/4 shift forks and a bunch of undergear bearings, and 5th/R sliders, and of course there's the case repairs. What I was getting at with my comment is that while properly rebuilding a G50 gearbox may require 20 new parts, properly rebuilding a 915 is likely to need 30 (arbitrary numbers picked for example purposes only). I really just want the OP and others reading this to be aware that the days of the $2000 915 rebuild are passing. Spending $3000-3500 to make one right is becoming the rule and not the exception, when it used to be the other way around.

Of course, that doesn't negate the cost of entry of going the G50 route. You're gonna pay $3000-4000 for a good used (which is possibly a core needed $3000 worth of work) G50 and then also need all the addition stuff to install it. A G50 conversion is going to cost you as much as rebuilding your 915 and regearing it at the same time. Given those choices, many will choose to stick with the 915 and just rebuild it right which will generally include beefing it up with a sidecover and bearing plate and all the other improvements we've seen over time.

[Peter Zimmermann]

Originally Posted by Matt Monson

I think we're actually saying the same basic thing from different ends. There's no denying that G50 parts are more expensive. But with how worn out and beat up 915 gearboxes have become they need more parts to be properly rebuilt. We're starting to see 915's need 3/4 shift forks and a bunch of undergear bearings, and 5th/R sliders, and of course there's the case repairs. What I was getting at with my comment is that while properly rebuilding a G50 gearbox may require 20 new parts, properly rebuilding a 915 is likely to need 30 (arbitrary numbers picked for example purposes only). I really just want the OP and others reading this to be aware that the days of the $2000 915 rebuild are passing. Spending $3000-3500 to make one right is becoming the rule and not the exception, when it used to be the other way around.

So true, and mechanics are slowly starting to realize that more often than not a 915 "repair" will become a "restoration" before it's back in the car. Wear-through on gear teeth has become common, almost all 5th gears are bad, and the 6 bearings (3+3 on the P/S and M/S) will cost almost $1K. Needle bearings for "loose" gears are almost $100, so there's another quick $300-500. Diff carrier bearings are cheap, but set-up isn't (figure $100+/hour labor). And then there's those pesky synchros and sliders. And the already mentioned case repairs...

[RWebb]

thanks folks - interesting discussion

(of course, my own direct interest is in creating an automotive anachronism by going back in time to the road-racing shift pattern and light feel of a 901/911 - not to get a more modern G50...)

[Matt Monson]

Originally Posted by RWebb

thanks folks - interesting discussion

(of course, my own direct interest is in creating an automotive anachronism by going back in time to the road-racing shift pattern and light feel of a 901/911 - not to get a more modern G50...)

I don't want to get your hopes up, but we may have something soon on our drawing board that would make your dream come true.