What rear end gears do I have?

[RogerDodger]

I have a 74 with an 8-1/4 rear end. If I turn the rear wheel 1 complete turn the driveshaft turns 1-1/3 times. I expected it would turn more. Something tells me this is geared for the road. I expect to upgrade at some point. Still have a lot of other things to do first.

[no318]

When the open differential is spinning, one wheel turns and the carrier rotates around the pinions which makes it turn 1/2 as many turns. 1.33 x 2 = 2.66.  So, I would assume that it is a 2.76.  That is a pretty common highway gear.

[RogerDodger]

That makes sense. I did have just one wheel turning. Thanks.

[moparguy01]

I have a 74 with an 8-1/4 rear end. If I turn the rear wheel 1 complete turn the driveshaft turns 1-1/3 times. I expected it would turn more. Something tells me this is geared for the road. I expect to upgrade at some point. Still have a lot of other things to do first.

Count your turns again. I GUARANTEE your number is not right.  a 1 1/3 turn on the driveshaft with 1 complete turn of the rear wheel wouldnt move the car very good. thats only 1.33:1 and nobody ever made a gear for a automobile that low to my knowledge. Although AMC DID make a 2.08.

Mark the driveshaft with something more visible. the shaft turns AWFUL fast so you really have to watch it close. chances are you have something like a 3.23 if you think there was a 1/3 in there somewhere. but your gonna need to spin it again.

[RogerDodger]

I'll check tonight with both rear wheels in the air.

[RogerDodger]

Yes. It is dedfinetly 1-1/3 on the driveshaft to 1 on the wheel. Doesn't matter if its with both wheels up or one. I expected it would have 2.76 gears. I just didn't know how to check it.

[moparguy01]

maybe try marking the wheel and turning the yoke? cause that cant be right.

[firefighter3931]

maybe try marking the wheel and turning the yoke? cause that cant be right.

Russ, you're assuming this diff had a suregrip in it. The proper way to check for a gear ratio on an "open" rear end is to have 1 rear wheel on the ground and the other elevated. Then perform the test as outlined above ; 1 tire rotation & count the u-joint revolutions.


Ron

[deputycrawford]

My 69 383 2bbl came with an open 2:76. it was a common rear end.

[Chryco Psycho]

with 1 wheel blocked count the driveshaft revolutions for the turning wheel to go around twice , if you still get 1.3 for 1 revolution you have 2.7 gears

[andy74]

my 72s 8 1/4 had 2.76s,pretty common  ratio in the 70s,the 3.55 swap made a huge difference in launch manners

[RogerDodger]

Thanks everyone. I think it is 2.76. I just didn't understand how to come up with it.

[TylerCharger69]

It's definately a 2:76....very common gear.

[Steve P.]

WELL I THINK