Opinions on 7:31 R&P for a 3.2...

[NoLift911]

84 3.2 Carrera - lightened/stripped Street/track (mostly street)

I have 39k on the clock and a leaking 915 at the case halves (one closest to passenger compartment) so I need to remove and fix that seal (not sure if they call that the nose cone?) I honestly don't think the tranny is even really broken in yet, shifts great doesn't seem to need anything other than reaseal.

So since I am "in there" was thinking about an LSD and maybe a 7:31

I have read rave reviews about how this wakes up a 3.2. I have driven one in an older car (but with a small motor 2.4) makes for alot of rowing under rapid acceralation it seemed like to me.

I always thought the Carreras were geared tall for the 3.2...you drop to 3rd doing 65-70 and it really hits it's stride (but then you are in jail bate speeds).

I think I will do a Guard LSD regardless. I was going to do this myself but maybe the ticket is just to send it to them and let them do it all once I get it out. We'll see what the winter project list holds.

Or I might just seal up the 915 and call it a day I think I could handle that on my own...I have gotten bit by the while you are in there disease and my car has been on jack stands for 5 years (just now getting done)

Thoughts? Thanks for any advice in advance.

[j911brick]

I think its a bad idea. Gears 1-3 will be way too low. The R/P is also not as strong. If yo want to do it right then re-gear it. replacing the R/P is not something you can do yourself unless you have the experience and tools.

[MBruns]

Strength, cost to replace next time, newest ones were circa 1974, just regear it you will be glad
Mike Bruns

[Patrice911]

On my 73 when I install the 3.2 it was with the original 73, 915 with the 7:31. with 225/50/15 or 225/45/15 it make it short gear.
It give nice acceleration but limited top speed (rev limiter). On track like VIR and Road Atlanta I was hitting the rev limiter in 5th. At the autocross I had to shift in 3rd quite often. Few years ago I change the transmission for a newer 915 from a Carrera with the 8:31. Now I'm not rev limited at the track anymore and I can stay in 2nd more often at the AX.
Since you say you do some track check the top speed that you reach on track and calculate what the 7:31 will give you for top speed.
Hitting the rev limiter in 5th and still having some track left before braking is frustrating.
I will say stay with your current 915 and put an LSD. That something I need to put in mine too an LSD.

[porschenut]

Been discussed many times before. Use the search button and you'll find all the information you need.

[KTL]

It's very easy to reseal the end case. It's simply a matter of removing the M8 nuts and pulling the end case off. Make sure to catch the reverse switch pin and check the o-ring on the countershaft.

A stock '84 trans could use some gear ratio change, but it's really not that bad. In order to get the gears sorted right, you really can't just change one. Usually two or three. 2nd and 5th are common to change, and then you fit 3rd and 4th in between them. But I think the factory ratios are not that bad for track use except for overdrive 5th. You'd be better off doing the LSD instead.

Where are you located? There might be a good shop nearby you, instead of having to ship it to Matt & Co. at Guard in Colorado?

[Matt Monson]

Originally Posted by KTL

Where are you located? There might be a good shop nearby you, instead of having to ship it to Matt & Co. at Guard in Colorado?

See bold. We don't build gearboxes. We manufacture parts for gearboxes and if you need work done recommend you contact one of the dealers listed on our website:
Guard Transmission

I really call that my preferred installers list (and there's a couple missing that got overlooked be accident when we put up the list). If there's noone on the list that's close to you, call me and I can probably make a local referral for a builder. Some of the smaller shops we do business with who have good mechanics aren't on that list.

Regards,

Matt Monson
Guard Transmission llc

[Matt Monson]

Oh, and I almost forgot to mention, our 8:35 short ratio ring and pinion will be back in stock in about 2 weeks. All the acceleration of the 7:31 with none of the strength issues.

[winders]

I had a 7:31 in my 915 with a 3.2 in my '78 911SC autocross/street car. I loved it. If I were doing this today, I would get a GT LSD along with their 8:35 ring and pinion.

Scott