Trying to find a speedometer gear chart is next to impossible, here is the deal. I'm putting a 700R4 trans in my Formal Chevelle that has a 3.73:1 axle ratio, 235x70x15 tires, and what drive and driven gears should I start out at? The trans is from a 91 Chevy pickup, no idea what axle it had.

Tom,
This should be a real easy one. All Chevrolet dealer parts books have a speedometer gear listing. A 91 truck was certainly available with a 3.73 gear so the only thing else to do is figure out what tire size was available on the truck that is close to what you have. I dont know if that small a tire was available on the full size trucks but I bet there was something close. If not, you may want to check in the S-10 listings or maybe the Camaro's. All of this info should be at your local Chevy store.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Tom
- Get your tire rev/mile from tire manufacturers date. Radial TA in P235/70R15 is 743 rev./mile
- Count teeth on the drive gear that came in your 700R4
- Compute correct driven gear as follows:

N(driven) = N(drive) x 3.73 x 743/1001

If this comes out as something other than a whole number (as it usually will), then go on the small side to keep speedo reading slightly higher than actual.

Principal here is that a correctly calibrated GM mechanical speedo turns 1001 rpm at 60 mph. We can discuss Sunday.

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Fred Aldrich
Web Site: www.GeoCities.com/~69_chevelle (http://www.GeoCities.com/~69_chevelle)

You're going to need a Grey Drive Gear (15 tooth) with the 3.73 ratio. Given the 743 rev per mile of the 235/70R15 your best bet is a 42 tooth speedo gear (Green). This gives a speedo output speed of 990 rpm @ 60.

Thanks for the help guys! The trans had a 18 tooth drive and a 42 tooth driven..donor vehicle may of had a 3.42:1 axle. As soon as I can decide on a converter, we'll slap it in and see what happens.