Hey guys, I just swapped from my stock 2.73's to a 3.42 posi set up, but didn't get to swap the speedo gear in my tranny. I was wondering if anyone could tell me exactly how far off my speedo is or if theres a formula i can use to figure it out. Thanks

 

Here is the easy way:

Divide 3.42 by 2.73 = 1.25

Multiply 1.25 times the speed that you want to go to find out what your speedo will say.

Example:

If you want to know what your speedo will say at 50 mph, multiply 1.25 x 50 = 62.5 mph. Drive on the highway a lot? 75 mph = 93.75 on your speedo. Pretty easy, huh?

I did this for my 2.73-3.73 swap and still have not gotten a ticket. Get the speedo gears changed soon, cuz you are just adding miles to your speedo.

If you have any other questions, feel free to respond or email me. Laters, TL

 

where can i pick up the gear that i need to change to correct my speedo? Thanks for the input, it helped a lot

 

No problem. You can get the correct speedo gears at your local Chevy dealer. One of them is like 6.00 and the other is the one that hurts, 25.00 around here. You need them both. Remember to get an extra clip that holds the driven gear. You will probably break the one you have. Do a search on this site for other threads that will talk you thru the whole process. Laters, TL

Check out this thread:
https://www.thirdgen.org/techbb2/sho...t=speedo+gears

 

I just did the swap yesterday using the exact same gears.

I have a 700R4 so here is what works.

The 700R4 has a 17 tooth drive gear if it came from the factory with 2.73 gears. The closest you can get to the correct speed without resorting to changing that drive gear is a 45 tooth driven gear. Mine was a greenish colour. Count the teeth if you are worried. (GM doesn't make any 46 or 47 tooth driven gears, so you are out of luck in that regard.) It will cost about $10 US.

Here is the part that frosted me. I had to get a different sleeve, as the 2.73 sleeve and red gear were totally incompatible with the new green one. Grrrrrrrrr ... It cost me $94.80 Canadian for that blasted little chunk of aluminum

It is AC part number 25512339. And they wonder why people hate GM's parts prices--bunch of corporate thieves!!!!!!!!!!!!!!

Anyway, the greenish 45 tooth driven gear and that part number sleeve is what you need. The speedometer will show you going maybe a couple of mph faster than what you are really going, but that will save you a good number of tickets in the long run

PS You will probably have to reuse the rubber o-ring gasket on the original sleeve because for such a princely sum AC still doesn't include a new o-ring

 

if it helps you feel less robbed about that sleeve, they wanted to charge me $6.80 each for pressure plate bolts (you need 6 of them), and i still had to provide washers.

i went to o'riellys instead, $6 for the whole set.

unfortunately gm is about the only place to get speedo gears

 

Alrighty then guys, sounds like a plan. Thanks a lot for all your help. I have the day off Tuesday, so it'll have to wait til then. Take care.

Rhoadster

 

I STILL feel robbed

 

Those prices really suck! I live down the street from TRANSTAR headquarters (The guys that make rebuild kits). I recently changed my 2.73 to 3.73 and was able to get both the drive and driven gear for $10 through them, over the counter and in the same day. I did not need a new sleeve surprisingly! it is off cetered and gave me enough movement for the new larger gears.