I have 70 chevelle,3:31 gears,P225/70R15 tires,and 700R4 transmisson.I have a 72SS dash with tach and gauges. If any one has any idea what speedometer gear set up I need in the transmission I would appreciate the help.

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I am running the same gear/tires on my 66 GTO (powered by 427BBC, 4-speed, and 12-bolt). The M-20 trans has the "purple" driven gear. The speedo is within a 5% of correct. Have the part number of the driven gear. If you want it, e-mail and I'll find it.

You need to calibrate your speedo for 1000 rpm @ 60 mph. For a 700R4 with 225/70R15 tires and 3.31 gears you need a 15 tooth (grey) drive gear and a 37 tooth (red) driven gear. Make sure you also get the correct sleeve for the tooth count of the driven gear, otherwise you'll get a leak. The sleeves usually cover 3-4 tooth counts like 35,36,37 teeth. You can get all of this at the Chevy dealer. The drive and driven gears are about $6 ea and the sleeve is $20. Or you can try to find the parts at a wrecking yard or a good tranny shop. A sleeve that covers 37 teeth should't be too hard to find. I got mine off of an 85 Caprice. The earlier year Caprices had 700R4's with mechanical speedo drives so you can use them as a reference for the parts guy at the Chevy dealer to look up what you need. Also, if you have an electric speedo drive, the mechanical parts bolt right in. No need to change the tailshaft housing. I've used 700R4's out of 90-93 Caprices, 2wd trucks and blazers and have not had to change housings.

Also don't forget to get the clip that holds the drive gear onto the tailshaft if you're replacing an electrical pickup.

For a different approach, see:
www.GeoCities.com/MotorCity/Lane/3969 (http://www.GeoCities.com/MotorCity/Lane/3969)

The best solution is to take your car to a speedo shop that can do an in car speedometer check. They can tell you exactly what gear you need. I went to one here in Albuquerque and only cost $15. They can also either get the gear or tell you where to find it.

Thanks for the advice Wheels68.I have the new gears that I got from my local chevy dealer.I am in the process of restoring my chevelle from the frame up.I just put the body back on the frame and am working on getting it running again.I will let you know how this works out.Thanks to everyone for your help.