You’ve got questions, we’ve got answers. We work with the Summit Racing tech department to help you tackle your auto-related conundrums. In this week’s Mailbag, we’re recommending a carburetor and gearing combo to combat an improperly shifting 700R-4 automatic transmission.
Q: I have a 1986 ½-ton Chevrolet pickup with full time four-wheel drive. It has a 350 crate motor and a rebuilt transmission. The truck has 31 x 11.5-15 tires. 3.08 rear axle gears, 700R-4 automatic transmission with overdrive, and a four-barrel carburetor. My problem is that it goes in and out of overdrive all the time.
What would be a good combination of carburetor and gears that would help this problem? Would lockout on the front hubs help?
A: We recommend a 600 cfm carburetor. An Edelbrock Performer would be a good choice because it’s calibrated for maximum mileage. We would also recommend a 4:10 rear gear axle ratio. Doing so will put your engine back into its street-friendly torque band.
And yes, locking hubs would be a good choice also. Your transmission is shifting improperly because of the tire size and gear ratio.
Make sure the TV cable is adjusted properly because 700R-4 transmissions are extremely sensitive to adjustments.