I just picked up a 3.42 axle out of a 91 formula. Is there any way to check the condition of the differential while its out of the car? The gears look good and the bearings seem fine but I would hate to install it and find out the diff is shot.

 

As long as there are no stress fractures and the wear pattern is consistent then the gear set will be fin.

 

Yeah, the gears look good, its the posi itself I'm wanting to check.

 

visual inspection of springs and clutches is about all you can do, no way to really test it

 

I am assuming this is an Auburn Gear unit. The only way to check these is to dissassemble them and look at the clutches and friction plates. I think you need a special tool to compress the springs to get the diff apart, but I have never done it myself. I would suggest you install new carrier bearings however, the inner race could be damaged and you wont be able to see it. I just experienced this with the Auburn posi I am putting in my truck. It is used and the bearings looked ok, but I replaced them anyway. To get the old bearings off I cut the cages off and then used a hammer and chisel to knock the inner races off. The inner races were not in very good shape. The hardness had worn off of them and they had started to pit. Installing new bearings is pretty cheap insurance.

 

This is an excerpt from the GM service manual & it assumes the axle is installed in the car. You would have to find a way to lock the pinion shaft from turning & also one wheel


If the vehicle is equipped with an automatic transmission, place the transmission range selector lever in PARK with the parking brake lever released. If the vehicle is equipped with a manual transmission, place the vehicle in gear.
Raise both of the rear tires and wheels off the floor. Refer to Lifting and Jacking the Vehicle in General Information.



Install the J 21579 , the 12.7 x 330.0 mm (1/2 x 13 in) adapter from the J 2619-01 (1), and a torque wrench (2).
Measure the torque required in order to rotate one tire and wheel. The torque should measure between 169-305 N·m (125-225 lb ft).
Place the automatic transmission range selector level in NEUTRAL.
Lower one rear tire and wheel to the ground.
Measure the torque required in order to rotate the raised tire and wheel. The torque should measure between 58-91 N·m (43-67 lb ft).
Install the tire and the wheel. Refer to Wheel Installation in Tires and Wheels.
Replace the differential case if any of the above measurements do not fall within specifications.

 

Sorry got busy at work & had to end this before I got a chance to explain. The adpater they are talking about is basically a flange that attaches to the wheel studs with a 1/2" female drive for a beam style torque wrench. Lock the pinion by putting in park or bolting a bar to the pinion flange if the axle is out of the car. basically what they are saying is the posi is supposed to slip when a certain amount of torque is applied. Too much or too little & the diff is bad.