Speedo drive and driven gear question...


Jan 8, 2009
Recently got some new wheels and tires for the ride and noticed the speedo is waaay off. Speedo shows about 20 mph slower than actual speed. So I've been looking for replacement gears for both the drive and driven gears. Going to replace the drive gear since I'm planning on flushing the tranny fluid so thought it would be a good time to go ahead and get at the drive gear while its all drained.

Anyways I've been trying to find an 11 tooth drive gear and a 27 tooth driven speedo gear for my combo (3.42 stock gear and 28" tire) but unable to locate any as they are no longer available (the 11 tooth drive gear). So question is what is another available drive and driven gear can I get that will be close or equivelant to the 11/27?

Here is where I was looking for the gears GM Speedometer Gears for Automatic and Standard Transmission

Let me know if you know of other places.

Thanks for the reply but I couldn't find that combo on TCI's site. Also the link above is to PATC site and it show the 27 tooth along with the 11 drive gear is no longer available. Maybe I should just call them and see. I didn't know if anyone else out there was running the same gear and tire combo that used a different speedo gears than what was mentioned.
For what it's worth, I gave PATC a call and alot of the gears are out of stock or no longer available. They ended up recommending a 12/29 combo.
your claim is that now you are 20mph error , if thats at 50mph thats a 40% speedo error
40% is a lot of error not caused by tall tires
assuming you had the correct gears in the trans and that you went from stock (26.1) to a 28" tire
26.1 tire has 82" rollout , 28" has 88 rollout
thats only about 7% increase in actual mph,
you should have only experienced a speedo error of approx 3.5mph slower reading at 50 .
you say that you have 3.42s , unless you recently replaced the trans with one from another vehicle like a monte ss CZ which has speedo gears for 3.73 the problem isnt the gears but the speedo head