Another Diff gearing question
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Registered User
Joined: Oct 2011
Posts: 164
From: Seattle
Another Diff gearing question
We started working on the master list for my brothers 70 S car yesterday.
We pulled the motor/trans leaving the 12 bolt open rearend in place to see what we were working with. I cleaned the diff off to get some numbers and found that someone had literally taken a grinder and ground the the numbers off. The question is:
Is there a way to figure out the gearing by revolutions of axle to the shaft mount, or pulling the cover and counting teeth? It's seems like a silly question, and I looked through the threads but couldn't find anything.
Soooo...Thanks ahead of time Fellas
We pulled the motor/trans leaving the 12 bolt open rearend in place to see what we were working with. I cleaned the diff off to get some numbers and found that someone had literally taken a grinder and ground the the numbers off. The question is:
Is there a way to figure out the gearing by revolutions of axle to the shaft mount, or pulling the cover and counting teeth? It's seems like a silly question, and I looked through the threads but couldn't find anything.
Soooo...Thanks ahead of time Fellas
Registered User
Joined: Apr 2011
Posts: 2,703
The most accurate method is to pull the cover and count the teeth of the ring gear and divide that by the number of teeth on the pinion gear. That will give you the exact ratio.
An alternate method is to lift the back drive wheel off the ground (for a posi rear end lift both) and rotate the wheel 2 times (1 time for a posi) while counting the number of driveshaft revolutions. That should get you close to a known ratio, IE 2.7 = 2.73, 3 = 3.08, 3.2 = 3.23, 3.4 = 3.42, etc.
An alternate method is to lift the back drive wheel off the ground (for a posi rear end lift both) and rotate the wheel 2 times (1 time for a posi) while counting the number of driveshaft revolutions. That should get you close to a known ratio, IE 2.7 = 2.73, 3 = 3.08, 3.2 = 3.23, 3.4 = 3.42, etc.
Old(s) Fart
Joined: Mar 2007
Posts: 50,539
From: Northern VA
The most accurate method is to pull the cover and count the teeth of the ring gear and divide that by the number of teeth on the pinion gear. That will give you the exact ratio.
An alternate method is to lift the back drive wheel off the ground (for a posi rear end lift both) and rotate the wheel 2 times (1 time for a posi) while counting the number of driveshaft revolutions. That should get you close to a known ratio, IE 2.7 = 2.73, 3 = 3.08, 3.2 = 3.23, 3.4 = 3.42, etc.
An alternate method is to lift the back drive wheel off the ground (for a posi rear end lift both) and rotate the wheel 2 times (1 time for a posi) while counting the number of driveshaft revolutions. That should get you close to a known ratio, IE 2.7 = 2.73, 3 = 3.08, 3.2 = 3.23, 3.4 = 3.42, etc.
Registered User
Joined: Jul 2006
Posts: 1,824
From: Richfield, Oh
Olds 12 bolt or most rear ends
If you remove the cover almost every GM ring gear has the part number and ring and pinion tooth count along with the date on the outer diameter of the ring and even on the flat head of tghe pinion gear.
So removing the rear cover would be the best method here as ratios get close like 3.23 3.08 3.42 etc.
KNOWing exacting what you have first will help in the plan of the rebuild and or build of the rear.
OPENing the rear will alos give you the CONDITION of the rear end also WHICH is again a huge sway factor in rebuilding or just out right buying a new rear.
OPEN THE REAR.
Jim
J D
So removing the rear cover would be the best method here as ratios get close like 3.23 3.08 3.42 etc.
KNOWing exacting what you have first will help in the plan of the rebuild and or build of the rear.
OPENing the rear will alos give you the CONDITION of the rear end also WHICH is again a huge sway factor in rebuilding or just out right buying a new rear.
OPEN THE REAR.
Jim
J D
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