in my 87 GTA with the digital dash the speed is pegged at 154 before i even go 20mph, know i now that i have the wrong tranny, it came out of a 89 IROC, but i don't have the original equipment that came for the speedo, like speed sensor and either reluctor gear or speedo gear. I never had the original tranny so i don't know what gear and sensor to use, and finding original parts is almost nonexsistent...even from the GM dealer. Can someone help me out on what i need to buy to make it work right. part numbers would be nice. I need the correct speed sensor and either reluctor gear or plastic speedo gear.

 

Here's a speedo gear calculator.

http://www.700r4.com/speedoCalc/speedocalc.html

And here is some info from this sites FAQ section.

Here is a list of GM part numbers for drive and driven speedometer gears, as well as some combinations that are known to work:



Part No. Teeth Color Sleeve*
25513042 35 Orange 25007338
25513043 36 White 25007338
25513044 37 Red 25007338
25513045 38 Blue 25007338
25513046 39 Brown 25007338
25513047 40 Black 25007339
25513048 41 Yello 25007339
25513049 42 Green 25007339
25513050 43 Purple 25007339
25513051 44 Dk Gray 25007339
25513052 45 Lt Blue 25007339

*Some applications may use Sleeve No. 25007224 or 10456092 in place of 25007338, or 25007308 or 1045089 in place of 25007339.
Red Drive Gear Combinations

With drive gear number 8640517, (red, 17 teeth) the following combinations apply:

Axle Tire Dia. Driven Gear
Ratio (Nominal) (Tooth Count)
2.59 26.0 35
25.7 36
2.73 26.0 37
25.7 38
2.87 26.0 39
3.07 26.0 42
3.31 26.0 45

Gray Drive Gear Combinations
With drive gear number 8642620, (gray, 15 teeth) the following combinations apply:

Axle Tire Dia. Driven Gear
Ratio (Nominal) (Tooth Count)
3.33 25.7 40
3.45 25.7 41
3.54 26.0 42
25.7 43

Lower ratio (higher numerically) rear or smaller diameter tire requires higher driven gear tooth count. Increasing or decreasing driven gear tooth count by one will usually accommodate a 1/4" to 1/2" change in tire diameter.

 

Well if your tranny is a 700r4, and your rear end is a 9 bolt with 3.27 ratio, and you are using the stock GTA size tires I have all the gearing and setups you would need very cheap...

I cant remember the colors off of the top of my head BUT I have the gears, retainers, vss housing, etc...

but the only issue is what rear end ratio you have.... I only have gear sets for the 3.27 or 3.90... those were the 2 ratios I used before Dumping the 700r4 for the turbo 400..