I need some help with a speedometer!!

[black_81_vette]

Hello gang!! I just finished putting a 3.54 gear set in my 81 wich had a 2.72 set. Im also running a 4 speed trans,after reading all the posts I could find here im still a bit confused on how still to fix the problem of my speedometer reading about 20 miles an hour too fast.I am aware that the gear on the output shaft is19t and the one on the cable is a 38t. what I need to know is there is a few of you guys that have 81s that have done this swap what combo of gears in the trans did you use? Did you get a bigger gear for the cable end gear or did you have to swap out the whole deal? help!!!!!!:confused

 

[Ludigdrums]

Hey there. Here's a link that will tell you what you need to know. No one can really tell you based on their car unless they have the exact setup as you do, since gearing and transmission, as well as speedo calibration come in to play.

http://www.tciauto.com/tech_info/speedo_gears.htm

This is also a good general link: http://www.hotrodders.com/t60786.html

I, unfortunately, am having bad luck with my speedo as well. I have the gearing right, but the speedo still reads 10 MPH too slow! However, the miles read almost correctly, as I tested that on the highway with the mile indicators.

So, make sure that both the odometer and speedometer read correctly!

Good luck!

- Jeremy

 

[81 Corvette]

i'll take the info on an 81 swap as well. auto went from 2.87 to 3.54

i emailed some company but never got a reply. the gears are in, so the calulator does me no good as i don't know the number of teeth on either gear

 

[black_81_vette]

Well I dont know what trans you have but I have the stock T-10. the drive gear is 19 teeth and the driven gear should be 38 teeth. Im running a 255 60 15 wich is 27.04 tall.Now the kicker is trying to find a suitable combo of gears to correct the speedo.According to one web site if I keep the stock drive gear I will need a 50 tooth driven gear to make it right, wich as far as know isnt even made.Or find a 15 tooth drive gear to work the original driven gear.The trouble is changing the drive gear on the T-10 is not a easy 20 minute job as the shifter and reverse lever and rod has to come off to remove the tail shaft housing.Im going to call a speedometer shop and get a ideal what can be done ,or if using a reducer adapter is feasable.I will keep you posted on what I find.