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Old 01-25-2011, 05:45 PM
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corvette 700r4 tramsmission swap

I have a 1985 corvette with a 1988 700r4 transmission that has a fresh build with shift kit and high performance parts. Note: this car was recently in a garage fire and the body plastic and glass destroyed. The engine and transmission were unharmed. I bought a 1991 corvette and the transmission has now failed. I swapped the transmission from the 85 with the 91, being it only has 500 miles on it.
My problem is that I didn't change tail housings and it appears that the 1985 uses a large 45 tooth speedometer gear and the 1991 used a small 36 tooth small gear. I have tried installing both generators on the 85 transmission, but I don't have a small enough (40) tooth gear for the speedometer, as the 45 and even a 42 tooth doesn't read correctly, and it affects the way the car runs, including a service engine soon light, and the dash shift light comes on.
Is it mandatory to switch tail housings or can I get the correct speedometer reading with the large gear by dropping to a 40 or 41 tooth. Both tail shaft gears(drive) are red 17 tooth, but I am assuming that locations where the generator enters the tail housing on each are different making the gear sizes different. (34-39t) (driven1991) small gear (40-45t) (driven1985)large gear. Am I correct, and can I make the speedometer work without changing tail housings. I will need to order the 40 or 41t driven gears, but I will change housings if this is not going to correct this problem. Thanks in advance Russeller

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Old 01-25-2011, 06:13 PM
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