How to determining the ratio of a rear end??

[Ken K.]

How to determining the ratio of a rear end??

I have my original 1959 differential out of the car. I believe it is the stock NON-posi 3.70:1 rear end. Without opening the case, how can I determine if the 3.70 gears are still installed?
I tried to mark the axles and drive shaft flange and then turn the wheel and count the turns. Something is not correct. I'm only coming up with 1.80 or so (less then two) turns. I'm I doing something wrong? With a NON-posi rearend, I made sure that one of the axle did not turn during the test. Do I need to multiply by 2 to get the correct ratio?
Any suggestions? Thanks

[Tom S.]

Re: How to determining the ratio of a rear end??

ken go to www.angalfire.com That will help you out! Tom

[Tom S.]

Re: How to determining the ratio of a rear end??

ken go to www.angalfire.com That will help you out! Tom

[Duke W.]

Re: How to determining the ratio of a rear end??

If you turn the input axle yoke both axles may turn equally, but this is not always the case with an open diff.

If you hold one axle stationary the free axle should turn double or half the amount - I forgot which, but your 1.8 number is half and would indicate a 3.55, which is tough to tell from a 3.70 because they are only about 4% apart, so it's best do the count as accurately as possible and do it two or three times with consistancy before you draw the final conclusion.

Duke

[Duke W.]

Re: How to determining the ratio of a rear end??

If you turn the input axle yoke both axles may turn equally, but this is not always the case with an open diff.

If you hold one axle stationary the free axle should turn double or half the amount - I forgot which, but your 1.8 number is half and would indicate a 3.55, which is tough to tell from a 3.70 because they are only about 4% apart, so it's best do the count as accurately as possible and do it two or three times with consistancy before you draw the final conclusion.

Duke

[Albert P.]

Re: How to determining the ratio of a rear end??

If you could count the teeth on both the pinion and ring gear and divide the number of pinion teeth by the number of ring gear teeth I think that will give you the ratio.

[Albert P.]

Re: How to determining the ratio of a rear end??

If you could count the teeth on both the pinion and ring gear and divide the number of pinion teeth by the number of ring gear teeth I think that will give you the ratio.

[Ken K.]

Re: How to determining the ratio of a rear end??

I realy don't want to open up the case to check the number of teeth. I just thought someone would know the proper way to turn and count a NON-post rear-end to figure out the ratio.
Thanks

[Ken K.]

Re: How to determining the ratio of a rear end??

I realy don't want to open up the case to check the number of teeth. I just thought someone would know the proper way to turn and count a NON-post rear-end to figure out the ratio.
Thanks

[Verle R.]

Re: How to determining the ratio of a rear end??

Do as Duke suggested, several times and you should get close.

If one axle does not turn, yes, multiply by two.

Verle

[Verle R.]

Re: How to determining the ratio of a rear end??

Do as Duke suggested, several times and you should get close.

If one axle does not turn, yes, multiply by two.

Verle

[Rod K.]

Re: How to determining the ratio of a rear end??

As Duke indicated, if you have one wheel blocked, the free wheel will rotate at twice the normal ratio relative to the drive shaft. So you're expecting 3.7 drive shaft revs per wheel rev. Dividing by 2 gives you 1.85. Looks like you're in the ballpark, but as Duke said, it could still be a 3.55.

Best way would be to mark a tire at the contact spot on the floor with both wheels down, also mark the driveshaft someplace where you can get a precise point location relative to the frame for instance, or even rig a pointer to the shaft then mark the shaft at the pointer, then roll the car forward one complete wheel rev counting the shaft revs. I know you have to dive under the car, but this is the most accurate way I can think of. You should be able to differentiate between about 3-1/2 and 3-3/4 fairly accurately.

Hope this helps.

[Rod K.]

Re: How to determining the ratio of a rear end??

As Duke indicated, if you have one wheel blocked, the free wheel will rotate at twice the normal ratio relative to the drive shaft. So you're expecting 3.7 drive shaft revs per wheel rev. Dividing by 2 gives you 1.85. Looks like you're in the ballpark, but as Duke said, it could still be a 3.55.

Best way would be to mark a tire at the contact spot on the floor with both wheels down, also mark the driveshaft someplace where you can get a precise point location relative to the frame for instance, or even rig a pointer to the shaft then mark the shaft at the pointer, then roll the car forward one complete wheel rev counting the shaft revs. I know you have to dive under the car, but this is the most accurate way I can think of. You should be able to differentiate between about 3-1/2 and 3-3/4 fairly accurately.

Hope this helps.

[Erich C.]

Re: How to determining the ratio of a rear end??

Does the diff still have the metal tag on one of the studs. It was on the stud at the 2 o'clock position from the factory. A 3.55 tag is fully round, 3.70 tag has a triangular cut out ( looks like pac-man ). The tags are repo'd go the website of C.C , Paragon, etc. They have pictures of the tags in their catalogs.

[Erich C.]

Re: How to determining the ratio of a rear end??

Does the diff still have the metal tag on one of the studs. It was on the stud at the 2 o'clock position from the factory. A 3.55 tag is fully round, 3.70 tag has a triangular cut out ( looks like pac-man ). The tags are repo'd go the website of C.C , Paragon, etc. They have pictures of the tags in their catalogs.