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Thread: airport circuit gears

  1. #1

    airport circuit gears

    i have a 69S coupe with transmission type 901/77 and transmission number 7392003. the porsche technical specifications book indicates that this is an optional transmission, and only 9 were produced with those airport circuit ratios. my question is, what do these ratios do for acceleration and top speed, and does that fact that only 9 were produced this way add any value to the car?

  2. #2

    Airport Gears

    This has been discussed on the Pelican board. You might want to post the question there.

  3. #3


    I wonder if your car is a early production 69, your gearbox is a die cast housing of aluminum as compared to the more common 901/82 pressure cast magnesium housing that appeared in the 69 model year. I would imagine that any special ratio gearbox came with a limited slip there for a die cast aluminum gearbox would have used the early style drive axels the with u-joints. The pressure cast mag housings used the later style drive axels all of the same length for the 69 model year regardless of whether it had a limited slip or not, this changed for the 70 model year with the change in the spider gear differential arrangement an then two versions of the drive axels were used, one for open diffs and the longer version for limited slip. I am curious what your car has for drive axels, it seems unusual that they would use the old style unless the car is early production. By the way your gearbox is built around a stock second gear. Tall first, stock second, short third fourth and fifth.

  4. #4


    I may not have mentioned that the 901/82 is the mag version of the airport gear ratio gearbox, which was also produced as early as 69. I have never seen a limited slip 69 car that had a aluminum case and therefore would have to have the early style u-joint drive axels, it must be early production. In any case any special ratio gearbox that is factory in a car is unique and add some value, especially a box that has great ratios like yours.

  5. #5

    airport gears

    schmidt, thanks for the reply. the car was delivered 12/18/68 to its original owner in california. i assume the production was sometime in october , but i am waiting for the certificate of authenticity from porsche so i can know the exact build date. the case is stamped 901/77 and stamped with the transmission number that indicates the airport gears. what is the best way to tell if the case is aluminum vs. magnesium. also, (excuse the naive question), what is the best way to determine if the car has a limited slip differential?

  6. #6


    If the box is stamped 901/77 then it is aluminum. The aluminum is shiny and it is a sand casting which has a rougher surface than pressure cast magnesium. The later magnesium limited slip cars were stamped with a /11 on the gearbox after the type number. This happened for sure by 1972 and maybe even a little earlier on the mag cases but not much not likely in 69 and not at all likely on a alloy case. The aluminum cases were not stamped designating limited slip because they all had the early style limited slips with the nedella drive axels. I have however seen in a box with a lobro cv style axel unit for early style limited slips used in aluminum cases, but this may have been a application for a 910 or possibly an application for the very latest aluminum limited slip gearboxes like you have. Your gear box may or may not have a limited slip, the way to tell is if it has nedella u-joints instead of cv joints its got a LSD. If it uses a unique seldom seen version of the limited slip that has a ungulated disk for preload in a alloy case like you would see in all mag cases in 69 cars with limited slip then you can spin one tire and the other tire should move in the same direction. The early limited slips have no preload which are found in aluminum cases and will act like a open differential when spun, one wheel will move in the opposite direction.

  7. #7


    Hey Schimdty. Whats up dude. The /11 stamp was not used in the 70 model line up either. My 911T with factory installed slip (80% lock) is just 911/01 #7100983. No difference for my 70S either with factory slip. My guess is that the /11 stamp started with the 915 tranny in 72'.

    Quick and easy way to find out if there's a slip in your tranny. Find and open parking lot, stop the car and try a quick donut. It's near impossible without one.


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