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Join Date: Feb 2002
Location: San Francisco, CA
Posts: 604
Grady, thanks for the detailed reply. I'll take the pictures you requested when I visit my shop next. You asked for a few measurements. Other than the thickness of the flywheel, are there any other measurements that you want?

Regarding that odd hole at the pivot seat, I found the same hole in another '70 911 case that I inspected. So it seems that it is not a defect, but rather a feature of all cases. It seems an odd place for such a hole. I am not certain that the oil was coming from the hole. But it didn't seem to be coming from the guide tube, and it certainly looked like the oil was centered around the pivot. I am tempted to seal it up, but I'm thinking it may have some obscure purpose, perhaps similar to that guide tube drain path that you recommend. So I'm worried that sealing it up will cause a problem. Perhaps oil coming out of it is an indication of a problem elsewhere?

One other thing I noticed. Some oil was leaking out of the overflow vent at the top. After some study, I realized that the vent hole was not oriented exactly right. It is supposed to be at a 45 degree angle. However it was actually at a 60 degree angle relative to the centerline of the car. I wonder if that 15 degree difference in the vent orientation would make a difference, and that perhaps the gearbox was not venting correctly? One caveat: this gearbox is in a racecar, so it's definitely experiencing more G force than a street application. On the other hand, the gearbox was presumably designed for racing.

Regarding interference issues with the arm, I am realizing that is a complicated subject for the 911 gearbox. I did notice that the arm on the fork showed signs of contact, as did the the pressure plate. I can't tell for sure, but the contact did not look recent. After comparing my fork to another that was donated to my cause by a friend, I found that the fingers on my fork had been altered, and that the washer under the pivot was cut down about 1mm. Further my pressure plate turns out to be a light weight aluminum one, which is apparently a common performance modification. I gather the washer and fork modifications were needed to add clearance to the pressure plate. I think the washer was cut to move the arm further from the pressure plate, and I'm guessing that the fork was cut so the ends of the tabs on the side of the TOB did not hit the fingers of the fork, which would be at a greater angle. Do you know anything about this type of modification? Perhaps this modification was not done correctly for my gearbox, and perhaps the cause of my problems.

So now, I'm not sure if it's all going to work when I put the new fork in my car. If I use the factory washer, I bet I will find an interference problem with the pressure plate. If I use the cut down washer, I bet I'll have a problem with the fingers contacting the tabs on the TOB. I won't know for sure until I test drive it. It's always something!

-Juan
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SM #34, '04 GT3, '73 911s, '70 911 2.7L PRC Toyo Spec #11
Old 10-11-2005, 06:45 PM
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