I have a dana 60 under a car. it has been shortened and rebuilt.

I put the car in reverse and it tries to move. in neutral it unloads like it should. in drive it rocks forward then nothing. just free revs.

I blocked the wheels and looked under the car with it in drive and a friend on the brakes. the driveshaft was spinning, we rev it the DS spins faster the car won't move.

I pulled the diff cover and had it on the wheels, started the car and put it in gear. the diff is rotating like you expect to see it... except the wheels are not moving.

I pulled the axles and there is a TON of spline engagement. I can barely spin the driveshaft in neutral wheels on the ground and the car off, but i can get it to rotate.

So this means the diff is bad?????


Help

Also- is this a stock differential unit?

Yes it is broken, take it apart to find out what is broken

Sounds like the posi is missing some plates or it was not assembled correctly
That is the good early Dana 60 clutch type posi
If you are able to work on it yourself, rebuild the posi, check the current backlash and then remove the posi with the ring gear on it and mark the two halfs of the posi case before taking it apart to inspect it so you can reassemble it with the cases aligned properly. All the stock Dana 60 clutch type posi have two beveled clutch drive plates, the rest are flat I don't remember which way the curved plate install, towards the ring gear or towards the axles tubes Buy or borrow a good 1967 to 1971 B body FSM and use it for your information on that unit and how to repair it properly
maybe it is something really stupid like the wrong clutch plates in the posi unit for the axle splines
I remember being told years ago to remove the bevel plate and used a straight plate instead to help reducing friction in high gear for a drag race only rear end, the one thing you had to do after backing up was to make the car go forward 5 or 6 inches minimum to reload the friction plates before getting on the throttle hard
IHTHs
Mark the caps also so they go back on the proper side installed correctly

Like said above, somebody left one, two or all disc plates out.

Is this a fresh job? Or is this something that broke?
How do you know there is a ton of axle engagement?
Do the axles rotate by hand? Can they be rotated independently of each other?

Looking at the pin, it's not sitting in the bore very tight. It also looks like the pin is flattened out on the bottom. Doesn't look right to me?

Is the housing offset? Is the right axle in the left side of the housing? That would be the only thing that makes sense to me. This would cause the car to “try” to move. That condition would be relying solely on the single side diff clutches to drive the car. The clutches are not enough to drive the car. It needs both axles to engage the side/ spiders. Also of note, the spider pin rides on a ramp that increases clutch application, assuming both axles are loaded against the diff case.

I pulled the axels out and can see the oil line on the spline. it is 1 5/8" engagement.
This was a "fresh job" almost 15 years ago. it has been sitting. the shop is no longer and the guy moved out of state. he was very reputable chassis builder. Lots of cars running around he built. I'd chalk this up to an mistake.
with the wheels on, and off the ground and the trans in neutral the drive shaft will spin both wheels.


I won't be able to touch it for a few days, but ill pull it out and part and post up a few more pictures.

That’s a terrible “mistake”.

I'm not clear on what would cause a rear end to act like that but it seems to be either broken or else it was put together wrong. Not sure how come it wasn't noticed for the past 15 years. Wasn't the car ever driven after the rear end was worked on? Usually the car has to be moved around the shop or driven on a trailer or something.

Even if it had no clutches in it, it should still move...or am I missing something?

Cover off? Stick the axles in and try to rotate the rear with a bar stuck in the studs. Gotta have the wrong size axles in it or the teeth cleaned off of a spider gear.

The fact that it tries to move, tells me that only one axle is engaged in the side gears. This would allow the clutches to slip enough to seem like it wants to move the car, but not quite be able to. It’s the only explanation that makes sense to me. If the clutches /plates weren’t in there, the cross pin would be flopping around. In the pic, the cross pin is sitting on the ramp as it should. I have to assume that the clutches are there based on that picture.

My bet is an early suregrip unit with 2 piece side gears and the axle is only in far enough to get the clutch plate, but not the gear that engages the spider/ pinion gears. It happens a lot at chassis shops that do not know danas are offset, they measure the short side and order axles, exact symptoms you describe. Late clutch type diffs had one piece side gears so they could "slide" by with that kinda work. I did a trans for a guy, car would not move on the ground after narrowing the rear, of course blamed the trans, nope, one axle too short, by a bigshot chassis shop.

i got home earlier than anticipated today so i was able to get a little more done.

I shoved both axles in the housing with the diff in, there is a good mount of spline angagement. With the brakes off and the trans in neutral i spun the driveshaft and both axles spin. if i spin one axle the other one moves too. it works as it is supposed to by hand.

The axles are not equal length. Driver side axle is 19 7/8 pass side is 17 5/8". or close to that.

The chassis guy is a mopar guy, he ran mopars for years and years.

I pulled the diff out and have it on my work table. I will hopefully pull it apart tomorrow after work.

The car went to the chassis shop, came home and sat in the garage a bare shell for the last 15 years. I decided to get it going for my uncle. All he has to do is pay for parts, im donating all my labor.

I loaded it on my trailer with my winch and had 3 guys help me get it into my driveway. this was the first attempt for it to move under its own power.

Even with destroyed plates, input in should result in rpm out.

If you have input in as as far as driveshaft speed and nothing out, it's much worse than any diff clutch. Even completely open would result in outside shaft rpm....

what style unit it this?

I've got a sneaking suspicion this unit wasn't rebuilt!

yea its bad

Are the side gears 1 or 2 piece? Doctor diff has a kit to fix that