Trying to decide my best transmission option
 

I have a 71 911T that has a 3.2L Carrera engine mated to its original 911/01 gearbox. Replaced the ring and pinion with a good used set and it's working well, going to need syncros and sliders sooner rather than later though. So I got to thinking if long term it would be better in terms of durability to find a 915 before sinking more money in this box.

My primary concern in the ring and pinion. My previous pinion was all chewed up, likely a result of my father running sub par oil in it for too long. New options are ~$2k and used options can be hard to find and also quite expensive ($500-$1000).

I will own and pretty much daily drive this car for a long time (30+ years) so I am trying to plan out my best course of action. The way I see my options are:

1a. Keep the current transmission and rebuild as necessary, scooping up good used R&P sets when available for a good price. Maybe add billet intermediate plate and/or side cover.

1b. Same as above but use new ring and pinion set. "Albins" offer both 7:31 (stock) and 9:31. Have not researched the quality on these yet. New Porsche look to be about $4k, not realistic.

2. Find a 915 and rebuild in prep for when I need it. I realize I will probably spend just as much rebuilding this one but if I get more longevity it will be worth it. Also would be nice to have it ready to go.

3. Find a G50. Probably not realistic as it is expensive and requires many more subsequent modifications. Don't really have time for this right now.

For street use w/ a fairly torquey 3.2 I'd find a 915. Assuming you don't want to change to an electric speedo You are limited to a '73 thru 75 version which all have mechanical speedos. Best of the bunch for street use is a '75 915/40
w/ a 24.4" tire and 6800 redline speed in gear are
40, 69, 101, 127, 155,
compared to the current 901/01 w/ the same parameters 36, 63, 92, 120, 147

You will have a much stronger trans w/ a stock steel girdle and a stronger side plate for insurance and hopefully an lsd. The much more relaxed cruise rpm will be welcome

Trying to decide my best transmission option
 

I agree with Bill. 915 is the way to go [emoji1303]


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Those Albins cwp sets won’t last anywhere near 30 years. Daily driving you would be lucky to get 3.

The Porsche Classic ones made by Hoer are top notch.

Though a 915 is still best. However don’t expect a couple thousand dollar “ good used ( we call them cores) 915 to last long without $2-3k in work.

Thanks for the input.

I'm not overly concerned with keeping the mechanical speedo. In fact that reminds me I need to get to replacing the speedo cable!

In regards to the stock steel girdle are you referring to the steel inlay for the bearings on the magnesium 915s or maybe the bearing retainer plate? Anything really in choosing between a magnesium vs aluminium?

Thanks, I have learned a ton about these transmissions from reading your posts.

If I get a 915 I do plan on rebuilding it in preparation for when I can't deal with the current one anymore.

If the e-speedo isn't an impediment then any of the later 915s would do.

There were incremental improvements right up through the last 915/72 or 73 but from '85(915/72 on) on they all have the larger cv joint flanges which means additional work to adapt to an earlier car and they went to an lsd design that while better for most street use is not as good for a performance application.

so I'd be looking at 915/67 w/ cooler from a RoW car or 915/68 or 70 from a US car

Here's a survey of most 915s, a comparison of speed in gears needs some extra thought because of the different tire oDS involved
http://forums.pelicanparts.com/uploa...1555679667.gif

Yikes, I thought Albins manufactured better quality gear sets. I guess I’ll be in my recently rebuilt 915 sooner than I thought...

Better than what? Definitely not better than OEM.

My comments above were specifically about their ring and pinion sets. That's something all together different than their gearsets. However, I would add that their newer line of "quiet" reground gears they've been marketing to the street crowd seem to wear faster than their older race design gears. I sold their race gears for a number of years under the Powerhaus II brand and people have always been happy with them. In recent years since they released these reground gears I have been hearing complaints about them wearing quickly. YMMV.

+3
This is your long term answer. If you do most of the work figure $5-6k. You can sell your old trans, and have a fresh 915 that will last longer than I will.

Decide on the best transmission for your application, then decide how to make the speedo work. The electronic speedometer is a 2 wire affair, all the other wires are similar to your existing set up. You are buying a lifetime replacement, get the best one you can find, a late model 915 will have most of the good stuff, add a couple of cool bits like an one piece bearing retainer, maybe a Wevo gate shift, and you are there. Limited slip if you want. The late model 915 was designed to work with the 3.2 so you will be in the right application range. My 915 in the Carrera is a 2-3 speed machine in the mountains of Santa Cruz, a 2 speed if I am just cruising.

Do some research. The axles (CV bolt pattern) change around '76 which is something to consider. As does the gearing, depending on if you want low gearing, as the older transmissions had or higher like the newer cars had.

In my case I have a 3,0 with a '72 trans. Works perfect for autocrosses and DEs. Sometimes I wish I had a 6th gear on the freeway though.

The older transmissions can be modified to work with the 3,2s pickups.

The M491 transmissions always had the bigger 930 cv joints, for a regular 911 the change was for the 1985 models
http://forums.pelicanparts.com/uploa...1555775077.gif

I chose a '74 915 for my '69 w/a '77 2.7L. At the time I understood the fifth gear of that year transaxle was slightly higher giving me a little lower cruising rpm's. Now I can't remember if that's actually true or not. Before install I sent the trans to J.W. to do a refresh on it at the time. I like the transmission.