Diff test issue

[Drewski]

Hi everyone,

So I'm replacing the brakes on my CJ and decided it'd be a good time to do the ole 'spin the wheel, count the driveshaft revolution' test to determine my gear ratio.

Well I spun one of the rear wheels and the drive shaft spun around but...the other wheel didn't spin at all. Odd. It should spin the opposite way as I'm quite sure I have an open diff on the AMC20 . So I spun the other rear wheel and got the same result. What could be causing this?

Side note. I locked the front hubs and did the same test w/the front wheels. Spinning my right front caused the driveshaft and left front wheel to rotate (backwards for the wheel...open diff). Spinning the left front wheel, drive shaft rotated but my right front did not spin the opposite way as it should. Strange.

 

[Torxhead]

Yeah that does not sound right. If you have the rear two piece axles, the rear hub could have come loose from the axle. Removing the rear drums could check for this. Also look up converting to the one piece axles if you don't have these installed. If the hubs are still fixed to the axles, try removing the rear axle inspection plate to check the operation there.

 

[mstar]

I know all the regulars will ring in on this so I will just say what you experienced is perfectly normal.

 

[IOPort51]

what happens when you spin the driveshaft??

 

[Drewski]

Spinning the driveshaft resulted in both wheels turning forward.

 

[gert]

It should normally spin the other wheel in the opposite direction. How ever the quick test to see if you have a suregrip or locker is to raise one wheel off the ground and spin it, which means it is possible for one wheel to be stationary while the other spins. I believe it is time to change the fluid on your axles to be safe. While you are at it you can read the gear and tooth count stamped on the ring gears This way you will know what the condition of your axles are and youve got some preventative maintenance out of the way

 

[mstar]

Spinning the driveshaft resulted in both wheels turning forward.

again to confirm your finding that would be normal.

 

[IOPort51]

Pull the cover, it is overdue for new gear lube anyway.

 

[Torxhead]

Spinning the driveshaft resulted in both wheels turning forward.

This statement indicates a locker or Limited slip rear diff. A rear diff cover removal for inspection would help here.

 

[Hedgehog]

Lots of seemingly conflicting information here.

- Turning the drive shaft should have both wheels turning together.

- Turn one wheel and the other going in reverse should indicate an open differential.

- Turn one wheel and the other turns in the same direction means some sort of locking device in the differential.

- Not sure what turning one wheel with the other not responding means. Sounds like a problem to me.

- Your oil more than likely needs replacing and there is no factory drain plug. The cover needs to come off.