Transmissions and DrivetrainNeed help with your trans? Problems with your axle?
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What speedo gear do I need in my tranny for 3.73's?
I'm swapping 3.42's for 3.73's, and I want to correct the speedometer. What is the tooth count on the gear that goes in the transmission for the 3.73's? My tranny is the 700R4
Thanks,
Eric
__________________ 1985 Trans Am. Dark blue with silver gfx.
Engine: 400 sbc, Forged TRW rods and pistons, Professional Products dampener, Comp Cams 286HR10 (0.560"/0.560" lift, 230/230 duration) with retro roller lifters, Comp Cams 1.52 roller rockers, Sportsman II heads (ported), Professional Products Crosswind intake, Mallory 85 series HEI, Holley 3310, Stewart high-flow water pump, Flowtech coated headers, SLP Loudmouth 3" cat-back.
Suspension: 1LE sway bars with Guldstrand Motorsports poly bushings, Guldstrand adjustable panhard rod, GM wonderbar, Alston SFC's, J&M Products LCA's, Spohn Torque Arm, 9-bolt rear with 3.70:1 gears, 16x8 Formula wheels with Yokohama Avid V4's.
The closest I have found is 15 tooth drive gear and 44 tooth driven gear. Specifically, the optimum ratio for a 15 tooth drive gear with 3.73 rear gears would be 43.8673. But, i think 44 is a closer match than 43.
GM specs on 3.73 gears with 26" tall (215/65/15) tires are 15 teeth drive 45 teeth driven. 245/50/16's are 25.7" tall which would actually require more teeth to slow the spedometer cable down. I.E. 46 Tooth gear. I just run the 45 tooth driven gear and my speedo is very very close!
