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Author Topic: 2001 Trans Am 4L60E Transmission Questions and Speed/Shift Control Problem??  (Read 6383 times)

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  • Message Board Member not current NFTAC Club Member
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I have a 2001 Trans Am and my speedometer is reading about 5mph less for every 20mph I drive. I assume it is new gears. I just had my tran overhauled and found out I also have a stall converter. I know I have an aluminum driveshaft and saw the gear case has an aftermarket TA performance cover on it. All this was in when I got it. I don't know the gear size and the dealership won't give me the previous owners info??? The trans people said it could be gears or converter. But it is the gears right? I got a superchips programmer to fix it but it won't because my pcm is custom. Could I clear that? Should I get the JET SCU2000 Trans Control Unit? Is that my quickest or best option? Also, they took out my shift kit and wouldn't another in. Could I put a basic one in even with an overhauled trans?


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Check your Service Parts ID (on the back of the driver's door) and you can look up what gear ratio you're SUPPOSED to have.  Then mark the driveshaft and tire, and count how many rotations of the drive shaft you get for one tire revolution.  That will tell you the ratio you actually have in the car.  For example...if your driveshaft rotates about 3.5 times for one tire revolution, you most likely have 3.42s.  If it rotates three and three-quarters, you have 3.73s, and so on and so forth. Just put the rear end up on jackstands, block the wheels, have the car in neutral and see what you get.  Another common performance gearset is 4.10s, which many people put in for drag racing.

If your PCM is custom, you'll have to have a speed shop reprogram it, most likely.  It's also VERY possible that if the rims are aftermarket, that they're the wrong size tires.  If your car came with 16s, but there are now 17s on it, that will make a 5 mph difference at 60 mph. The bigger you go, the more difference there will be. 

Also, newer 4L60 Transmissions don't need shift kits.  They're programmed to increase pressure with heavier throttle, so that kit is unnecessary.  A stall converter shouldn't make any difference in your speedometer readings, I wouldn't trust them on that.

Start with the BASICS.  That will reveal a lot.
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Thank you very much for the great information. You are very knowledgable. I have tried every gear ratio possible stock/aftermarket.  My door jamb says I had 2.73 gear ratio and my tires and wheels are stock? For a trans am that seems really low! I dont know what else to do. Could it be the computer? Should I swich to a stock computer and see what it does and then use my programmer? Thats all I know to do.

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