A little while ago I started to hear an increase in the noise from the (915) gearbox in my 1973 911E. The car has done about 230,000 miles and had the gearbox refreshed about 90,000 miles ago. It has E cams but apart from that is basically 2.7RS spec with 2.7 P&C's, S induction, RS space cam in MFI pump etc so has a bit more Torque than a RS but probably nowhere near some track cars or big engine transplants.
The noise was noticeable in 4th and 5th gear under very low load on the engine. any more acceleration it could not be heard and it was absent under no load or with clutch in. I felt it was a "final drive" issue just by the sound of it and how it presented although it was suggested it could be gearbox bearing noise.
Anyway, bearing noise or not, I decided that safe was better than sorry and I should get the gearbox pulled down and fixed sooner rather than later. I was very surprised however when this was found:
So on last Saturday morning I was told that the pinion in the 7:31 final drive was in the process of self destructing
That was the bad news (along with the cost and availability of a good 7:31 crown wheel and pinion to be available to get the car fixed any time before Christmas - or ever!)
I did a quick call around a couple of contacts as did Mike who looks after the car for me (and delivered the bad news). Not very hopeful. I was told that one person here on the board (who shall remain nameless unless he outs himself) may have even laughed at the prospects of me getting something suitable.
Anyway it seems like the Porsche gods were on my side for a change: not only had I caught it before it stopped working altogether and left me stranded (and no doubt done more damage) but someone well connected in the community rang me that morning about the same time as he had just been talking to a mutual Porsche acquaintance I had helped out with something in Europe earlier in the week. He said that he knew someone who may have a good 7:31 but also mentioned that people were remaking them but he could not remember who at the time.
From that conversation I remembered that Albins gears here in Victoria made a whole range of Porsche related gears including crown wheel and pinions. However as far as I knew they only distributed their products offshore except for the things they make for the V8 supercars and similar.
Then came the surprise silver lining. I looked at their web site and saw they made a 8:35 R&P set for 915's as well as 7:31 and others. I had not heard of an 8:35 until then and did some quick research as it is only about 1% different to the 7:31 in ratio and was about to file it away for future reference as I was still focused on a straight replacement of the 7:31.
There was not much information around on the 8:35 but i thought I should have a look to see what i could find "just in case". I soon found that it had been homologated early on by Porsche and used in racing and especially rallying applications where there was high torque. I also found that it was much stronger than the 7:31 not only because of the extra tooth in the pinion but also because how the gears were cut (and a bunch of other technical stuff that I understood about 10% of). I also found that getting them from the US or Europe would be expensive (and time consuming at this time of year).
Even better the person my contact said may have a second hand 7:31 not only had one but also had a direct link to the Albins factory and thought he may be able to get a new 7:31 and have it delivered direct to me. Albins were out of stock here on 7:31's and I was just about to buy the second hand (March 1973) 7:31 when I asked about a 8:35 instead. To my surprise he said that was able to be done with immediate delivery direct to me (and not too much more that the second hand 7:31.)
So I have ordered that one and expect it to arrive in a day or so, and given the cost spent last night searching through all articles, posts etc I could find on the 8:35.
I have only seen great things about it, but also there is relatively little information about it out there. I consider myself reasonably educated on these things and am surprised i have not run across this before.
7:31's are known to have the weakness that has resulted in my failure, and I suspect that they now have seen 40 or more years service they are more likely to start to fail (even if people are not using a big torque engine).
I have yet to get it installed, let alone use it, But i thought it was worth sharing this in the hope that it will help by providing an alternative to consider if people are unlucky enough to find themselves in the situation I was last weekend.
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