1978BackToLife

Thanks in advance for taking the time to offer any advice.

Have had some noise from the rear end in the past on this 1978, and it just got a whole lot worse - see video below.

It's an inconsistent problem - The noise almost always happens when I slam on the gas and put the car under a strong load. However, some times it'll happen on light acceleration, or as I'm exiting the freeway and braking to a stop without touching the gas. If I throw it into neutral, it will go away.

Wanted to see if you could identify what this sound could be? Ultimately, I'm hoping someone may have some advice on what to begin to look for and how to check it, to start ruling stuff out (possibly what topics I should search for on these forums). Unfortunately I don't have the money to drop it off at a shop and have them go wild on it. I'm not a master mechanic, but pretty handy at figuring things out.

As a history, I heard some grabbing and what was believed to be rear differential chatter a while back. Then one day the noise got as bad as the video. I've since changed the differential fluid with Lucas 85w140 and 2 GM additive bottles, and it didn't change a thing. Here's the video link if the embedded video isn't working:

forman

sounds like a bearing

forman

put the car on a jack and see if you can move the wheels left , right ,up and down with out spinning the wheel check for play

GTR1999

I would get the car in the air and check from wheel to wheel. Check for play in the rear bearings, grab a wheel stud and see if you can push/pull it - if there is play then it's at least 003" or more. Could be a broken parking brake spring or shoe dragging. You can see if the rear rotors still have the rivets in place or not- that will tell you if anyone has been into them. You might be able to spin the wheel and hear a ticking noise.

Check the u-joints for play and look for rust at the caps.

The 77 -79 diffs had cheap ring gear bolts, to save a penny they went to flanged head bolts without a lock washer or loctite on them, they often backed out and will either shear off or lock up the diff. If you can't find anything outside the diff you might be better off dropping the diff and pulling the cover for a look. If all is good you can install new ARP RG bolts with loctite and that will take care of that. The 71-79 posi clutches were not good but they should not come out of the case if broken.

Chicago Bob

stub axle bolts hitting differential?

drwet

Get under there and look for something that's moveable that shouldn't be. I would start with the front of the differential. There is a rubber mount there that might have deteriorated and is permitting the differential to move excessively with acceleration/deceleration.

gkull

Your differential might need to go in a dumpster

GM installed yokes made of soft metal. The ends ware out to the point where the flange starts grinding the outside of the case away

I had to replace my 79 diff before it even had 50K miles

Chicago Bob

George, why not just install new yokes/stub axles?

Mine are hitting the diff. and I've purchased new stubs....nothing has been removed/inspected yet. Hope I didn't jump the gun and now have a spare set of axles.

GTR1999

If your axles are hitting the case the tips have worn down close to .200", that will mean grit in the gear oil. If they have not faced off the 1/8" lip at the seal then you're still good, if they cut into the seal then the bore may be too shallow and the cost to machine, sleeve, and install would be more then just replacing the housing.

If you bought new axles they are most likely imports, if rebuilt may still be usa. I would advise you check them if you can find someone with an old spider. Many times they come in and have issues, other times they fit well.

replacing axles will help cut down on axle endplay but you really have to check the posi when you have the cover off. Axle end play comes from 3 areas within the diff.

gkull

if the yokes are grinding the diff case exterior away you have a terrific amount of metal in the gear oil Mine were worn past the c-clips. The bearings and posi unit were toast. My gears looked polished. So any way I ordered a new rear end from mid America and they didn't want to give me the $450 core charge because of the worn outer case

it was shipped without the yokes and I bought the super yokes for something like $300 each.

ezobens

The noise to me sounds light and tinny like brake shoes dragging or something hitting the brake shroud or bad U-Joints. Bearings and axle noises tend to be more of a growl than a squeak.

Have you lifted both wheels off the ground and spun the wheels to see if you can re-create the sound?

Personally, my money is on something external (brakes or U-Joint) vs inside the diff.
Just my .02

calwldlife

sound does have a brake shield ting to it.

time to jack car and work your way in.
shake wheel for trail bearing play
shake in and out for side yoke
grab shaft for u joint
pull cover for diffy

wer2xu

2nd calwldlife, that is a thin metal type of sound...something rubbing brake shield.

for the love of god please don't drive with the door open and holding your phone out there...and even worse, no portrait mode unless you are taking a portrait.

Big2Bird

Sound like a broken brake spring to me as well. Just dig in and look.

calwldlife

i seconded EZO

leadfoot4

Maybe something has loosened in the e-brake mechanism.....

1978BackToLife

Thanks very much for all the responses. I've got a few great places to start, and will grab a couple pictures / videos once it's lifted up.

scrappy76

3rd calwldlife. Would start out at the wheel and work inward. If you have play in your stub bearings, its possible something is rubbing when you are loading it up or hitting the brake.

fishslayer143

sounds just like a dry worn out old U-Joint to me

1978BackToLife