cramus

Trying to find out what my rear end ratio is in my 64. Jacked up one side of car up (it isn't a posi I don't think, tires turn opposite way if both are jacked off the ground and you turn one). One turn of rear wheel = 1 1/2 turn of drive shaft. Didn't seem right to me. So I drove it in 4th gear @ 3000 RPM = 70MPH with 26.5 diameter tires. If I figured right that come out to 1.48 revolution on drive shaft to one revolution of tire. Assuming 4th gear is 1:1. What am I not doing right. Tranny #s 3925660 B8E24.
3000RPM
1st gear = 29mph
2nd gear = 39 mph
3rd gear = 49 mph
4th gear = 70 mph
Thanks Craig

Kensmith

Jack it back up, block one tire, turn the other and count the driveline revolutions. You can use a piece of tape to mark the positions on the tire and drivelive so you can see. 1 full turn of the tire and I would guess about 3 1/2 on the driveline would equal 3.55 gears. Just over 4 turns would be 4.11. 3 3/4 turns 3.70.

cramus

I already marked both the tire and drive shaft 1 to 1.5. Is this possible?

MikeM

If you don't have posi-traction, block one tire and let the driveshaft turn in neutral. Rotate the one wheel until the driveshaft revolves once. Multiply wheel rotation by two and that's your ratio.

In your case, one turn of the driveshaft equals 1 1/2 turn of the wheel times two equals approximately 3.08-1.

If you raise your car, turn one wheel with the car in gear, the other wheel will rotate backwards. If you take it out of gear, the other wheel could either rotate forward, backward or not at all, depending on what the drive shaft does.

knight37128

You have a 3.36

stratplus

Try these calculators, this is how I figured out what I have.

http://www.angelfire.com/fl/procrastination/rear.html

http://www.idavette.net/tech/ratioc.htm

66since71

Be very careful comparing the tach and speedo to compute rear axle ratio. All that comparison tells you is what speedometer gear you have in the transmission.

You are on the right track comparing revolutions of the drive shaft and the wheel.

Cliff63

What is the stamp @ 6 o'clock on the rear housing? Great info.

Thanks, Cliff

cramus

I'll put her up on blocks tomorrow and see if I can read the stamping. To close under their laying on my back with these 50 year old eyes.

Kensmith

Forgot to tell you, you have to X2 for non-posi. Sorry!

stratplus

Yes you are correct. After I posted the ratio calculator I should have said that I had to follow another car to get an accurate speed reading, and double checked the tack. I was reading 10 mph to slow. So if your rpm or speedometer is off the ratio calc will not yield the correct number. I changed the speedo gear, retested it with another car, then found it was perfect, and then used the ratio calc to get the final ratio.

ssgnco

or....if you have a GPS navigator (Tom-Tom, in my case), you can display your speed directly and use it to get the ratio. If your speeds are correct, 3.36 is your ratio.

If you are going to use the wheel/driveshaft rotation method, I would use 10 revolutions so that you can see the difference between 1.54 (3.08) and 1.68 (3.36) more clearly.

cramus

I checked the rear end #'s on my 64 today, it was tough to make them out but I think this is what was stamped.
AR 2 5 65
Looks like it is a 65 3:08 if the gears are still the original

AZDoug

One tire turn isn't that exact. Turn the tire ten times and figure out how many times the drive shaft went around. You have either a 3.08 or 3.3x gear set.

If you do ten tire turns, the drive shaft will go about 15 1/2 turns for a 3.08 and about 17 for a 3.3x.

Doug