70 LT1 411 gears vibration/ noise

[Dennis D.]

I had felt a vibration when starting from a hill or making a turn.
Put the rear up on Ramps and found the large rubber cushion on the differential bracket was so loose, I could rotate it by hand. Also the bolt was installed with the nut on top which I believe is upside down. Tightened to spec, test drive, appeared good.

Out to a local show and noticed it was still there on a hill start. Nothing leaking, shaft joints all appear fine. Ideas?

[Mark E.]

Re: 70 LT1 411 gears vibration/ noise

The typical symptom of a bad snubber cushion is a thump or clunk when launching or going from reverse to drive.

Things to check for a vibration under load or while turning:
- Wheels properly mounted and not bent
- Worn half-shaft joints
- Worn u-joints
- Worn or improperly adjusted wheel bearings/hub

If it's sensitive to engine load it's probably the rear suspension or drive train, but also check the front suspension and tires (out of round; tread separation).

[Timothy B.]

Re: 70 LT1 411 gears vibration/ noise

Dennis,

The bushing is two pieces, the large bottom you refer to and the top half above the frame. The top portion usually is the bad piece so get it up again and remove the top bushing to have a look.

There are two part #'s for the bushings and the top is easier to find then the bottom.

[Dennis D.]

Re: 70 LT1 411 gears vibration/ noise

Thanks Mark.
Been trying to think what the noise sounds like. Sort of sounds like tire slip, but more grinding like. Lasted for a second, and stops

[Dennis D.]

Re: 70 LT1 411 gears vibration/ noise

Thanks Tim.would you think that installing the bolt from the bottom would hinder torquing? My AIM show the bolt installed from the top.

[Timothy B.]

Re: 70 LT1 411 gears vibration/ noise

Dennis,

Make sure the thick washers are in place (top and bottom) the exposed threaded end may interfere with something so I would install the long bolt in the factory direction.

It's tight but you can fish it in place then swing the mounting bracket up and install the lower half and torque per factory specs.

[Mark E.]

Re: 70 LT1 411 gears vibration/ noise

Thanks Mark.
Been trying to think what the noise sounds like. Sort of sounds like tire slip, but more grinding like. Lasted for a second, and stops

Another possibility: Posi-traction unit. I would check the other things first.

[E B.]

[Dennis D.]

Re: 70 LT1 411 gears vibration/ noise

I posted a reply the other day to Ed. Dont know what happened.

Went for a 1/2 hour drive around town. Stop and go, up hill, turn, etc.
Nothing. No symptoms at all.
Usually I go for highway drives. That when I get the noise.

I am planning on changing the diff fluid. Figure it cant hurt, and I dont know when it was last serviced.

[E B.]

Re: 70 LT1 411 gears vibration/ noise

Dennis, received answer in junk mail? Tryin to fix. I had same problem on our Honeymoon driving a 1979. Long straight driving slung lubrication from the discs and sounded like rear end was going to fall out on turns Corvette buddy said go ahead and drive it and change when back home.
Like new after the new lubricants changed. Ed

[Dennis D.]

Re: 70 LT1 411 gears vibration/ noise

Soon as I set up my kwik lift the fluids will be changed.
(warmed up first of course )