sudden total transmission failure

[mstaake415]

1996 GMC Yukon, 5.7 v8, 4L60e automatic, push button 4x4

Leaving work, back out of parking space, put it in drive, get about 10ft before there is a loud bang and clunking noise, and the truck stops. Engine just revs like its in neutral.

Had a coworker give me a ride home and I'll be taking the bus to work today, but before work I'll have some time to poke at it.

I'm thinking either the transmission output shaft failed, the transfer case failed, or the diff failed. When I get back to work I'm going to try putting it in 4wd (I don't think my 4hi works but 4lo does I think) which will rule out rear diff.

Any thoughts beyond that besides buying a new truck? I don't have the money to replace either the transmission or the truck.

Thanks

 

[livingez_123]

An easy way to rule out the rear diff is to set the parking brake, put it in gear and look under the truck to see if the driveline is turning, if it is, then you have a broken diff, that's a fairly easy fix. If it doesn't turn, give it a little gas and see if you can find any noise coming from the TC. if all of that fails, lock the front hubs, put it in 4wd and see if it moves. If it doesn't, then it could be a broken trans output shaft or TC input shaft. Does the truck go into reverse? if it does backwards, then it's in the trans.

 

[mstaake415]

Replaced rear end (the old diff was completely wrecked, broken twisted chunks of metal and gear sections).

Now the truck drives but only in Reverse, and when the shifter is in 2 or 1. When in (D) or 3 it acts like it's in neutral.

We're thinking the forward sprag was damaged when the rear end failed. This transmission was already not in great condition (light slipping can be observed when accelerating especially on the highway) and the shock of the rear end blowing up must have been the tipping point.

Now, my question is can I drive the truck back and forth to my part time job, or should I take the bus until I come up with another vehicle? It's about 5 miles of city driving in stop and go traffic? I drove it home today (we finally finished putting the new rear end on behind the warehouse of where I work) and it was not an enjoyable experience. It makes an abnormal noise even in 1st & 2nd gear and has much less acceleration than it should, and I smelled something nasty the whole time (transmission killing itself?) I totally babied it but I'm wondering if it can continue to drive like this. I checked the trans fluid when I got home and it smells very burnt already.

 

[chaingun427]

That's weird, does it go straight to acting like it's in neutral when it's in 3 or D?

I'd think that if it drives up until the 3rd gear shift it would be either the 3/4 clutch pack as you observed was already slipping, or possibly the apply piston is shot

if your forward sprag was damaged you shouldn't have 1/2 either. Try using this page and chart to help narrow it down a bit. http://sethirdgen.org/tranny.htm

You're probably better off rebuilding it than trying to drive it right now, otherwise you risk permanent failure and the loss of the ability to rebuild it at all.