Transmission or Rear Diff

[JustinC]

So Today I was driving through a parking lot and all of a sudden my 03
Yukon started jerking real bad and barely going. Put it in park and then drive
again and it didnt want to go anywhere. I had to rev up the engine to get it to
even move and when it did it was jerking alot. My first thought was the
transmission was going out. Tried to put it into low gears to see if it would
move (its an automatic so I tried 3 first) and no matter what gear I put it into I
had the same issue. Thinking it was the transmission I put it into reverse to
see if I still had that gear and was able to drive it backwards a good ways to
back it into a parking spot with no issues. Another motorists near by came
over to check on me and when describing the issue and when trying second
gear he heard and saw what it was doing. He thought it might be the rear
end because the noise seemed to be coming from the rear. When looking
under the car it seemed to be leaking fluid around the diff where the drive
shaft is attached. Another symptom is that when putting the car in neutral it
will not roll, which also makes me think the rear end is locked up. But what I
cant figure out is that if the rear end is locked up why would it be able to
drive in reverse with seemingly no issue. Wouldnt it have the same issue in
reverse? But if its the transmission then why when I put it in neutral will it not
roll? Any help or tips to help diagnose would be appreciated.

 

[wjburken]

So Today I was driving through a parking lot and all of a sudden my 03
Yukon started jerking real bad and barely going. Put it in park and then drive
again and it didnt want to go anywhere. I had to rev up the engine to get it to
even move and when it did it was jerking alot. My first thought was the
transmission was going out. Tried to put it into low gears to see if it would
move (its an automatic so I tried 3 first) and no matter what gear I put it into I
had the same issue. Thinking it was the transmission I put it into reverse to
see if I still had that gear and was able to drive it backwards a good ways to
back it into a parking spot with no issues. Another motorists near by came
over to check on me and when describing the issue and when trying second
gear he heard and saw what it was doing. He thought it might be the rear
end because the noise seemed to be coming from the rear. When looking
under the car it seemed to be leaking fluid around the diff where the drive
shaft is attached. Another symptom is that when putting the car in neutral it
will not roll, which also makes me think the rear end is locked up. But what I
cant figure out is that if the rear end is locked up why would it be able to
drive in reverse with seemingly no issue. Wouldnt it have the same issue in
reverse? But if its the transmission then why when I put it in neutral will it not
roll? Any help or tips to help diagnose would be appreciated.

Where is the vehicle now?

A quick check would be to pull the cover off the differential and take a look.

 

[drakon543]

well the rear diff is just gear to gear and depending on the gearing type its either posi, limited slip, or full float. all the symptoms point to your transmission to me. how many miles are on your truck and has the transmission ever been serviced. when a transmission goes its either just going to completely stop functioning or you going to lose most of any movement and features. it sounds like you have some blow by in your valve body in the transmission and its not allowing it to engage fully or disengage fully. only reason reverse still works is its run differently then any forward gears or neutral. if you have too much blow by on your pistons it might not allow everything to disengage properly so neutral wont work correctly either. the chance the rear end is causing your problems isnt impossible just alot more likely its the transmission.

 

[rockola1971]

Transfer case or planetary in transmission is grenaded. Pull your driveshaft and that will rule out the transmission and Tcase and validate your rearend is trashed.

 

[JustinC]

Thanks guys. To answer some of the questions the truck has 280k on it and I bought it used with around 230k and only know I have never serviced the transmission. Its still at a parking lot and will need to be towed, hence why I was trying to figure out what was wrong with it. If it was the rear end I feel fairly confident I could do that work here at the house but if its transmission I would probably feel more confident having a transmission shop do that work. It sounds like I should go ahead and have it towed to a buddies that does transmission work and just have him rule out the rear end before he replaces it as it sounds like it is most likely the transmission.

 

[drakon543]

best to rule everything out so your not wasting money but it does seem like a trans to me

 

[rockola1971]

Reach up and feel around the top side of Tcase and see if you can feel any large holes where they arent suppose to be and if there is a large chain poking out. This actually happened to my wifes Tahoe a few years back and it was because the chain got too loose and was rubbing. The symptom was clanking noise and tahoe would move a foot or so and then it was like it was against a brick wall until you accelerated alot then eventually it would overcome it and go another 6-10ft and do it all over again. With lots of loud popping, clanking and banging.

If your tranny planetary is grenaded then a total teardown will be required since the planetary is at the vary back side of the tranny and everything has to be removed from the front (except the valve body).