Hey guys,
I've got an '89 GMC Sierra 2500 short cab, long box. The transmission has gotten pretty screwy lately. It started when I was coming to a stop from exiting the express way. It felt like the brakes grabbed when I was very close to a stop. After the light turned green I tried going and the truck wouldn't move. I gave it a little more gas and I heard/felt a BANG and it started moving. While moving though it sounded as if I had stones in my differential. I stopped looked at everything but couldn't see anything visually. I started driving again and it moved but that sound persisted and drive felt rough up until I hit about 15 MPH and then it shut up, until I slowed down and it happened all over again. Come to find out the sound is coming from the transmission. It does the "grinding thing" when in reverse and forward. When thrown into neutral at a dead stop it makes a sound like chunks in a vaccum cleaner. It's locked up twice after the first time and giving it some heavy throttle breaks it loose. When it's locked up, even if the transmission is in neutral you can't move the truck unless you put the TC in neutral. I'm not driving it now, but I want to know it anybody has any ideas as to what happened. The transmission only has 19K on it since it was rebuilt. It's a TH400 by the way. Any help would be greatly appreciated!

I have a 90 GMC K1500 and the chain in the transfer case is streached and I am pulling the transfer case this weekend.

I wonder it your chain snapped? If you jack up the rear, with the tranny is neutral, rotate the rear driveshaft and listen to see if you hear a noise and where it is coming from.

Also if you put the transfer case is 4 wheel high, does the front drive shaft spin freely? Both drive shafts should move together unless the chain is broken.

//2000CAYukon

So basically, if the trucks up on stands and it's in 4 wheel, but only the back wheels are moving when in drive I've pin pointed it to the transfer case... right?

So basically, if the trucks up on stands and it's in 4 wheel, but only the back wheels are moving when in drive I've pin pointed it to the transfer case... right?

Yep. I bet you the chain snapped in the transfer case. In my case, I can hear the chain scraping in the case when I am in 2wd and rotate the rear drive shaft.

Will know more tomorrow when I drop the transfer case.

//2000CAYukon

I'll look into it as soon as my Caprice gets out of the garage (the nest day or so). The chain snapping makes sense too, only a day before this happened I accidently got the truck stuck in the mud tring to get an S10 out of a creek. That must've put just enough strain on the chain to make it go.

I'll look into it as soon as my Caprice gets out of the garage (the nest day or so). The chain snapping makes sense too, only a day before this happened I accidently got the truck stuck in the mud tring to get an S10 out of a creek. That must've put just enough strain on the chain to make it go.

What year Caprice? I like the 94 - 96 ones with the LT1!!

I buddy of mine who use to be a service manager at a local shop told me the chain streaching is real common on our trucks.

Post back after you figure out what it is.

//2000CAYukon

After pulling my transfer case apart and looking at the chain, I doubt that yours snapped. The chain is pretty big but I guess it is possible.

I am thinking that maybe the snapring for the rear output shaft bearing broke and that is causing all of the noise and lack of 4x4 to the front drive shaft.

//2000CAYukon

As far as I know 4x4 still works, but I haven't checked that yet. Today after work the truck's going into the garage and I'll find out more then. I tried pushing it in yesterday but it;s locked up again, so I'll jump start it tonight and see if the engine's power will break it lose again.
What year Caprice? I like the 94 - 96 ones with the LT1!!

Mine's an '84. It was in the garage because I was swapping the 305 out for a lightly built 350 I was working on. The 350 that just went in had a .3" lift cam, roller tipped rockers, flat topped pistons, 63cc 2.02 heads, 10.5:1 compression and a performer intake. Even though I'm babying it for the first 500 miles it's a HUGE power difference from the 305. The car reached 100 already at 1/2 throttle where the 305 took a good mile at WOT to get there (no exaggeration!)

As far as I know 4x4 still works, but I haven't checked that yet. Today after work the truck's going into the garage and I'll find out more then. I tried pushing it in yesterday but it;s locked up again, so I'll jump start it tonight and see if the engine's power will break it lose again.


If the snap ring broke, breaking it loose can damage the transfer case. You could pull the rear drive shaft, drain the transfer case and remove the tail shaft housing (4 bolts) and you will know if it is a broken snap ring or not.


Mine's an '84. It was in the garage because I was swapping the 305 out for a lightly built 350 I was working on. The 350 that just went in had a .3" lift cam, roller tipped rockers, flat topped pistons, 63cc 2.02 heads, 10.5:1 compression and a performer intake. Even though I'm babying it for the first 500 miles it's a HUGE power difference from the 305. The car reached 100 already at 1/2 throttle where the 305 took a good mile at WOT to get there (no exaggeration!)

That 350 should really wake up that Boxy. Hope things work out well for both the Caprice and the truck.

//2000CAYukon

Any update on what was the cause of the problem?

//2000CAYukon

ive had those same symptoms on my truck and i pulled the cover off my ten bolt diff. to find that my spider gears where shreaded...have you cracked open your differential cover yet???