Gear Change now speedometer off

[SLICK79WGN]

hey guys I just swapped in a new rear with 3:73's and now my speedometer is way off since oem it had a 2:41 I am running a thm350/ 3:73 gear/ 27" inch tall tire in the rear. Does anyone know which gear I need to change out in the trans for the speedometer drive to make it read right because as it is now it buries the speedometer before it even hits high gear and I'm not going anywhere near that fast, it seams like the faster you go the more it is off :?

 

[Oldsmoletick]

Most likely both, but beware there is different size gears as well, (ran into this issue), some transmission's have a slightly larger output shaft where the drive gear sits, and also the driven gear varies in stem size, which would require a different adapter. What year th350 is it, or is it the original one? If not what did it come out of? What color and tooth count gears do you have now? There "should" be a part number on the adapter itself and that would help too.

 

[SLICK79WGN]

it is the original transmission and I haven't pulled the gear now to see whats in there

 

[Oldsmoletick]

Ok so, the original transmission, thats good. you will have to change both gears, however you should be able to retain you original adapter. What you probably have is the purple drive gear, and either a blue or natural driven (depends on what size tire your car came with). Issue here is that GM didn't offer 3.73 in the A body, but did in an F body with a 4-speed. But looking at the numbers, it looks like it would work no problem. So take these numbers to your local dealer (12338033 drive gear, 03987922 driven gear) thats for a 78 camaro m21 trans gr70-15 tire and 3.73. (00361002 drive, 3987920 driven) would also get you close to what you are looking for. May not 100%, because of tire size but you'll be close with either of these.

 

[SLICK79WGN]

thanks for the help but I have found this
http://www.maliburacing.com/speedo_correction.html

now I just need to find the parts
14 tooth transmission gear- cant find
39 tooth speedo gear- found on summit

 

[SLICK79WGN]

nevermind I found it I need a 8/22 gear set and summit has them thanks

 

[Oldsmoletick]

Or 7/20 just for you comparison GM wants about $7 each for them (for the 8/22 gears).

 

[SLICK79WGN]

is that the part numbers you gave me? if so that is cheaper and I could pick them up local

 

[Oldsmoletick]

Yes, the 8/22 part numbers are 12338033, and 03987922 they should run $6.83 each.
Oh, and both of those numbers say that they'll work on a th350, so you shouldn't have to worry about getting a different adapter.

 

[SLICK79WGN]

sweet thanks