Rear Gear Ratios
Thread Starter
Racer
Joined: Sep 2003
Posts: 261
Likes: 0
From: Hershey Pa
Rear Gear Ratios
I'm trying to figure out what my rear gear ratio is. I have a 76 auto L48. I spun the tire and counted the driveshaft rotations. For every 1 turn of the tire the diveshaft turns 3 times.
Can you guys tell me what ratio I have? As far as I know it is stock.
Thanks in advance.
Can you guys tell me what ratio I have? As far as I know it is stock.
Thanks in advance.
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
More than likely 3.08's. Doing just one spin is not enough to be certain. I would spin the tire 10 times and count the driveshaft revolutions. It only takes a minute or two. The toughest thing is keeping track of the numbers as your spinning.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
there's an 'ole "rule-of-thumb" to determine rear axle ratio; that has worked every time I have tried it (but I haven;'t tried this on all vehicles... obviously) ...
Shift into the tranny gear that is a 1:1 ratio; drive 75mph and note the RPM on the tachometer. Divide the RPM by 1000 and that gives you the rear axle ratio.
3300 RPM would equate to a 3.30 rear axle ratio.
For automatic trans with non-locking converters, you need to subtract the tc slippage RPM from the overall RPM reading before dividing by 1000. generally 300 to 400 RPM.
For this to work, you must have maintained the factory rear tire heigth.
Shift into the tranny gear that is a 1:1 ratio; drive 75mph and note the RPM on the tachometer. Divide the RPM by 1000 and that gives you the rear axle ratio.
3300 RPM would equate to a 3.30 rear axle ratio.
For automatic trans with non-locking converters, you need to subtract the tc slippage RPM from the overall RPM reading before dividing by 1000. generally 300 to 400 RPM.
For this to work, you must have maintained the factory rear tire heigth.
Last edited by Mike Mercury; Aug 22, 2004 at 11:56 AM.
