I recently swapped a 4th gen rear end into my 84 Z28. I have noticed a whining or humming when I am coasting above about 30 mph. The sound is not present under acceleration or at low neighborhood speeds. I thought it was the axle bearings, so I changed them. But, the sound is still there. Could it have something to do with the crush sleve? What else could it be?

 

U-joints

 

I would look at the easy things first.

 

the U joints on the yoke?

 

Yes sir on the drive line.

 

what can I do to fix the U-joints?

 

I did have a small leak coming from the middle of the yoke around the nut.

 

And the drive shaft is the same. I didn't have the noise prior to the rear end swap.

 

Did you pull the cover off the differential cover and look. See if there is metal flakes in the oil.

 

yes and they looked great. I replaced the gasket and fluid with Royal Purple. So significant shavings and the teeth looked fine.

 

Is this differential a posi? if so you need to use the posi additive with your oil.

 

yes it is a posi, but you don't need additive w/Royal Purple. A few weeks ago I had some conventional gear oil and some posi additive and it still made the noise. Could the crush sleeve on the pinion be an issue? again, the leak comes from the pinion nut area and I already changed the front seal. When I took off the yoke I did not change the crush sleeve. i just market the nut and yoke and put it back to the same spot.

 

Gear pattern may not have been set up correctly. There is a drive pattern where the pinion to ring gear teeth touch under power and there is a coast pattern under coasting.

 

It might be your pre-load on the pinion, did you follow the recommended procedure for removing and installing your yoke.

 

Nope, how do you set the pre-load? Can you do it with the rear end still on the car?

 

Well the procedure starts when you remove the yoke nut to start with. We must of missed that step. How tight did you crank the yoke nut down.

 

just back to the origional line. I marked it prior to taking it off.

 

Can I change it out for a spacer instead?

 

I only removed the nut and the yoke during the seal change. i don't think I messed with the pre-load during the seal change. Can I fix by just replacing the crush sleve?

 

If you tightened to the original mark you should have the correct pre-load.

 

ok, then what could be making the noise?

 

I don't know for sure without being there. Could the pinion bearing be worn out? How many miles on the donor car?

 

idk, junk yard part

 

is there a way to check the pinion bearing while on the car? or do I have to take out the differential to check it?

 

A sucking noise from not reading or responding to suggestions already made.

 

A factory service manual would help you. If you don't mind reading.