SC Transmission question

[cfassett]

While I no longer have a 911 in the stable, a friend of mine does. I'm posting this for him. Hoping for guidance from the group.

He is doing a full restoration on an '80s SC coupe. Going with new 3.1 cylinders and a total engine rebuild along with total suspension rebuild. The car suffered an engine fire about 15-20 years ago, and was then left in a field to die. That's how he acquired it. Outside of engine machine work, he is doing this project himself, with a high attention to detail. But, the car is to be more of an outlaw. AC delete, carbs, etc.

Which bring me to the transmission, which is a 915. No evidence of the tranny failing at any time, but who knows. The tranny is out of the car, and he is pondering sending it off for a rebuild, or trying to swap it for a good G50.

The car would not likely be used for any racing, and wouldn't likely be abused in the least while under his care. Maybe a DE day or two, and some mountain road carving.

So, if this was your project, would you rebuild a 915 or try to swap for a G50? If the latter, what would you expect to pay?

[Marc Bixen]

Stick with the 915!

[Locker537]

I'd stick with the 915. Swapping to a G50 is going to cost more.

[Rodney Nelson]

I have sort of the same question. In that I have a 915 transmission and I don't know anything about the history of it.

And this is where I think your friend is. I would think he would first need to determine the condition of it, and how do you do that?

You would not want to blindly send it out for a rebuild if it does not need it correct?

Is there some procedure that he can follow while it is not mounted to determine the condition?

[yelcab1]

I would strip it down, inspect it, and refresh anything worn out. Don't use it as is.

[john walker's workshop]

Check for a loose pinion roller bearing race in the diff housing while it's down, as well as the 2 races in the center housing. They're getting long in the tooth and have more issues than they did 20 years ago.

[nomore]

I always run something to see if it is broken before I fix it.

[cfassett]

Originally Posted by yelcab1

I would strip it down, inspect it, and refresh anything worn out. Don't use it as is.

Are these things DIY-able? Or best taken to a tranny shop?

[Flat6pac]

It’s way less expensive to install, drive and decide Then the route you’re going to look at.
I remember telling the trans builder “just rebuild it”. His first question would be “what’s wrong with it?” , he needed to know where to start looking...that’s what you need to know.
Bruce

[kevingross]

Originally Posted by cfassett

Are these things DIY-able? Or best taken to a tranny shop?

Read through Pete Zimmerman's tutorial, which will help you decide whether you're up for the challenge.

[john walker's workshop]

A good trans rebuilder doesn't need to know where to start looking. The wear items are obvious to an experienced mechanic.

[Rodney Nelson]

Is there a tutorial on inspection?

[Marc Bixen]

John Walker, always right,"They're getting long in the tooth and have more issues than they did 20 years ago." We had fun working with Pete to make the trans tutorial. It took quite some time, maybe 8 or 9 months. I'm soo happy that so many P-car enthusiasts refer to our tutorial. As for a tutorial about inspections? We never thaught it necessary as each section discusses inspection of individual parts.
Sorry nomore, but when it comes to the unknown, you've got to at least bore scope it and pull and check the diff. A "repair" can become "unrepairable" if there's something loose floating around. BIG risk!

[cfassett]

Thank you for the guidance, gents! Sounds like the consensus is strongly in the "stay with the 915" line. My buddy (who has been following the thread) is wanting to take it to a shop. He has his hands full with the body and engine, and wants an expert to handle the tranny. at a minimum have them check it for him.

Can anyone recommend a trusted transmission shop in NC or SC that has experience with the 915?

[jjeffries]

My 915 was a bit of a pig when I first got my 82 SC, 183K miles. The original owner always had the car pro-maintained, and his shop had replaced 1st and 2nd synchros and dog teeth a few years previously, but it would still frequently refuse to go into 2nd. After doing all the external stuff (coupler, change oil, adjust clutch, etc), I downloaded and read the Zimmerman/Bixen/Red Line tutorial**, gaining much knowledge and understanding, and the feeling I didn't want to tackle it myself. I sent the car to Auto Associates, near me in Conn., a hugely respected shop. Like Pete and JohnW say, they knew what to look for, and (re-) replaced the stuff the other shop had, PLUS the 1-2 slider, very reasonably. The OO had treated and driven the car with respect, so everything else was fine (for now, I realize). The 915 now shifts beautifully and I prefer it's lightness to the G50. Don't buy into the the anti-915 BS; a good one is not difficult to use or require great sacrifices.

** this tutorial was a generous gift to our community from PeteZ, Marc, et al.

Best of luck, John

[FLORIAN1968]

The G50 is bigger in size so you'll have to modify the body of the car. And it is more expensive when it comes to parts and maintenance. At least here in Germany.

[mradovan]

I am just finising up a DIY rebuilt of a 915 from a 1980 car that had 60K miles and was working really well. I openned it to inspect it and to do a WEVO upgrade because my car will be getting a 3.6. I plan to be burried in this car so I want to be sure everything is perfect. Your firend may not be be in this for the long haul so the cost/benefit analysis will yield a different result.

What I found was the following:

1. Normal wear on the syncro rings
2. some strange but minor features on the pinion
3. A bearing just starting to spin.

Jerry Woods told me to do the following:

1. replace synco rings
2. Don't worry about it because it in on the gear tip
3. Pin it and run it or go see Hayden (Wevo) for a better fix.

The bearing in question is the classic problem with all 915s expect for the last version that adopted the smaller input bearing used on the turbo. The WEVO fix is bombproof but will require a complete resetting of differential. This requires specialized tools.

When the case was out for repair the shop also had concerns about the drive shaft output bearing so they fix/ upgraded that too.

Although I have only 1 data point I would recommend having somone inspect it. Tearing it down to check the beaings is a few hours of shop time. If it has issues they cost will go up. Also, i would be wary of anyone advertising a rebult 915 for a few thousand dollars. A full refurb requires a lot of hours if the R&P needs adjusting.

The other option is to get the car back on the road and run it to see how it works. If it is bad pull it and open it. If you have a good setup removing the engine and transmission is a simple task.

Good luck.

[Hcarraro]

As you can see the advice is all over the map both pro and con. I will chime in with my two cents worth. The G50 will not work. The old adage 'if it ain't broke don't fix" it applies as does "if it ain't broke then fix it anyway" also applies. if you are risk averse and money is not a problem rebuild it and don't look back. Add a new clutch and pressure plate to go with the new engine.

Powerhaus II out of Boulder Colorado offers a rebuilt 915 transmission exchange for $2,400.00. Vertex offers a rebuild kit for $1,349.00 and a rebuild service for about $3,600.00 with a core charge.

I have a good used 915 transmission for sale here on Pelican for $1,950.00. It is a good used magnesium transmission with a 8:31 ring and pinion removed last year from a low mileage 911 S. A limited slip 915 was installed in it's place. It has a new clutch cable and has been resealed. Basically a good daily driver.

Tell your friend good luck with his project and please keep us in the loop. Better yet start a build thread here on Pelican.

Henry