Q&A / Tech

Mailbag: Gear Swaps and Tranny Maintenance

Got questions?

We’ve got the answers—Mondays when the Summit Racing tech department tackles your automotive-related conundrums. This week, we offer advice for choosing the proper gear ratio and performing transmission flushes.

From: Jimmy Stevens, Jr. • Saltillo, MS           
Q: I have a 1981 GMC half-ton pickup with a 350 bored .040 inches over. It has a Lunati Bracket Master cam, Edelbrock Performer RPM intake, and a Carter 600 cfm carb. I’m running a TCI StreetFighter TH-350 transmission with a B&M Holeshot 2,400 rpm stall torque converter and 3.40 gears. The truck is very powerful, but I think my gear set is a weak point. What gears do you think I should be running for the best performance?

A: To find your truck’s ideal gear set, visit SummitRacing.com, click on the Expert Advice tab, and check out the Calculators and Tools section. Our Gear Ratio Calculator will quickly compute your rig’s info to find the proper ring-and-pinion set for max performance. For example, if you run 3.73 gears with your stock 28-inch-tall tires at 60 miles per hour, then your rpm would be 2,686.

 

From: Roger Wilson • Coos Bay, OR
Q: I’m trying to decide whether or not to drain my own automatic transmission fluid. I’ve asked several people about the project and keep getting different answers. Some say not to drain the fluid at all, while others think it should be completely flushed and replaced. I’ve also been told just to drain a little but not the whole thing. What do you think is the proper way? And if it needs drained, then what type of fluid should I use?

A: Transmission projects can be tricky. Your answers are split down the middle because the draining process varies by vehicle. Some new transmissions require a full flush for general maintenance while older transmissions can develop clutch slippage if they’re drained too much. Your safest bet is to call your transmission’s manufacturer to find out the preferred process for draining. Be sure to also ask what type of transmission fluid to use if draining is required.

 

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