slipping noise

[woodwright]

Although this thread has to do with a 70 suburban, the issues it having aren't suburban related and theres more traffic here.

Anyway, I'm looking at a 70 c10 suburban. It has a 402/400, and a posi rear. I'm not sure of the ratio. When you accelerate, theres a loud vibration noise coming from the back. Imagine sliding a heavy steel desk across concrete. And it feels like a clutch slipping. And it gets worse as it warms up. Any ideas?

[woodwright]

What does it sound like when the pinion bearings are going and the pinion is climbing the ring gear?

[swamp rat]

Not sure what it sounds like personally i'd describe it as a wherring sound, but if i was you i'd crawl under the thing and see if you can wiggle the pinion shaft side to side or up and down, which would indicate bad bearings, bad bearings would allow the pinion to move affecting the contact pattern

[woodwright]

It definitely sounds more like sliding a BIG steel desk across concrete. Or metal on metal......sorta. I had my transmission guy drive it, and he thought maybe a slip yoke on the driveline was binding up. That just doesn't sound right to me.

[swamp rat]

Well, jack the back end up and put it on jack stands, unbolt the U joint and remove the drive line and inspect the slip yoke and U joint while there. Block one wheel and spin the other and have a listen for unusual noises and try and pinpoint where its coming from, then block the other wheel and do the same on the other side, make sure you are listening for any noise at both the wheel hubs and differential.