915, Chapter Two

[Jack Olsen]

Well, it lasted about a year. My magnesium-cased 7:31 transaxle has a toasted ring and pinion and a handful of bad bearings. It seems C2-era torque and a steady diet of track days has taken its toll on my Nixon-era 915.

I've done a search on what to do next, and here are my options:

1) Rebuild it -- and continued to do so periodically. This is not so expensive in the short run, but seems to not have good long term prospects, especially if I jump to a Euro 3.8 setup (or some similar mod) in the future.

2) Get a good, strong 930 transaxle, but suffer the indignity of only having four gears. This doesn't seem to make too many early Turbo owners thrilled.

3) Go to a stronger, almuminum-cased 915, and shorten second through fourth. Randy Jones seems to have a good recipe for this, with:

1st gear/ 11:35 stock
2nd gear/ 17:34 (down three ratios)
3rd gear/ 21:29 (down two ratios)
4th gear/ 25:26 (down one ratio)
5th gear/ 38:30 stock

Any suggestions, advice?

[scca_ita]

Go to later 915 with alternate gears. Thats what I have for my 993 3.6L. I will also add a LSD sometime, once the motor is broken in after about 2-4K. My project is now approaching engine cost plus $2K so I need to just get it in and running.

You could also change the R&P on the later 915s but it is big $$$.

[tobluforu]

Stuff a G50 in there.

[82SC]

i ve heard around the board that the 7:31 are weaker cuz they are smaller???

Wound sticking to the beefier 8:31 and changing the gear to get back some of that grunt be a sturdier option??

interested to hear how this turns out...maybe the guy at instant-g has some idea...looks like he runs alot of these transplanted 915 3.6 combos....

[Bill Verburg]

I would look for an one of the following

• '84 915/67 or 915/69
• '85 915/72
• '86 915/72

gearing will be as follows

1. 3.1818
2. 1.8333
3. 1.2608
4. 0.9655
5. 0.7631

[PanAmeriCan]

Forgive my ignorance, but what do the numbers after the slashes refer to:

'84 915/67 or 915/69
'85 915/72
'86 915/72

Thanks,

[PanAmeriCan]

[Natchamp]

Jack, your situation sounds kinda familiar. You forgot the other option which is a G50. They are much stronger, remain a 5 speed and have the later Borg Warner syncros. That is the route I am taking. If not, I will prabably be selling my 915 very shortly. It's a later aluminum one with the stronger 8/31.

[CamB]

Jack

I have been umming and aahing over whether to go for an aluminium cased 915 (with an 8:31) or a mag case (7:31) to match to a 230+HP 3.0 "S".

I will probably go with the 8:31 'cause:

- stronger
- cheaper (in this instance - includes axles etc)
- rebuilt rather than refreshed (in this instance)

The major negative is:

- gearing (which you are aware of, given you were one of the major contributors trying to convince me to go for the shorter R&P, and the revised ratios you set out above)
- electronic speedo drive
- it will have a season in a race car by the time it reaches me

Anyone know how I can keep my existing speedo? I figure I find an early SC gauge and have the dial and needle swapped from the '69 gauge?

So Jack, just another thing to deal with

[Bill Verburg]

Forgive my ignorance, but what do the numbers after the slashes refer to

They are the type #s for the transmission. The ones listed are the latest and strongest 915s made. They were OEM on ROW 3.2 Carrera, '84-86. they also incorporate internal gear spray and external cooler via mechanical pump. Next best would be any of the 8:31 al. case 915s(I would at least add an external cooler and ideally the internal spray bars as well). I really like the 3.2 Carrera gearing for large bore engines in lighter cars.

The G50 conversion is ridiculously expensive. You might just as well go all the way with a G50 6spd.

[pwd72s]

Jack...seems to me I've read of transmission coolers, plus "squirter" lube features for the 915? Might be worth looking into with your new gearbox?

[MMARSH]

Paul

Jack has those in his present tranny. The reality is the 7:31 is great for a street car. But they are just not up to the rigors of a high powered car that is used on the track often. My Mechanic has been telling me this since I started my project but the tranny was just rebuilt prior to me buying the car. The 8:31 with changed gearsets is really the best and easiest way to go. Jack is the third person I know that has had a 7:31 fail. I need to sell mine before it's to late.

Jack is about to come out of this in very good shape Hopefully before laguna.


Michael

[Jack Olsen]

Update: I found a freshly-rebuilt 8:31 915 with a new mainshaft, new*wevo shift*kit, new lower*2/3/4/5 gear package (GT), new GT ltd slip, all new bearings, all new syncros, sliders, needle bearings, etc. The owner decided he wanted a 993 Turbo motor in his car instead, and is switching to a Turbo G50 without having installed this one.

The cost? I'm trying not to think about that, right now. But it looks like it might be possible to get it installed by the end of the week, so that I can make it up to Laguna-Seca for the weekend. I'll keep my fingers crossed.

[Matt Smith]

Are you going to cool and squirt this one too jack or has it been set up for it already?