Rear end noise...?

[robh77L48]

I'm starting to freak out here, guys.

Under heavy acceleration in a medium-hard left turn, I hear a rattling clacking sound from what sounds to be the left rear wheel well. I'm thinking it could be a loose U-joint or a spindle/bearing/bushing problem in the rear trailing arm assembly. Anybody got any other ideas what it may be?

 

[John Kuzman]

Positraction clutch pack? Rear differential side yoke end play?

 

[GTR1999]

could be any of those items, also check the PB shoes for a broken spring.

 

[81 Corvette]

hard to tell with that description, but boy wonder at gm decided the best way to build the rear suspension was to use the drive train as part of the support

this causes the side yokes on teh diff. to grind down on the inside of the diff.

without hearing more, it could be as simple as changing the diff fluid, u joints or parking break. Could also involve an entire rear end rebuild

 

[robh77L48]

Fair enough to all replies, but from what I hear, it sounds way too far to the outside of the car to be a differential noise (hence why I didn't mention ring and pinion or posi problems.)

I also rebuilt all four corners worth of brakes less than a month ago using sleeved calipers, brand new rotors, fresh pads and new hoses and stainless lines. I checked all of the parking brake stuff when I redid the brakes and everything checked out just fine at the time.

I spoke with my boss, who happens to be a factory-trained GM tech, and his immediate guess (which I've noticed has been wrong nearly as often as it's right) was U-joints.

If the noise IS cause by the U-joints, what kind of damage can a completely destroyed U-joint do? And how much work are they to change?

 

[wishuwerehere82]

They are not too bad to do. Just unbolt the straps that holds the U-joints in place on both ends. Then take the whole shaft to your workbench. The retaining clips that hold the joints in will have to be removed and then press the bearing caps out with a dowel in a vise. Clean the shaft bearing mount surfaces up with a scotchbrite pad before putting in new ones.
You don't want to let it go too long. A snapped U-joint can punch a hole in the bottom of your Vette if an outside one goes, and it sounds like that's where yours is.

 

[robh77L48]

Fantastic. Thanks for the help, WUWH.

*edit out part number question*

In case anyone else is interested, I've gone so far as to compile a list of NAPA's offerings as far as U-joints go for C3s. Here it is:

NAPA U-joints
NAPA Part # Price Description
----------- ----- -----------
NUJ 2100213 11.49 Standard NAPA U-joint @ trans OR Rear Axle (AT)
NUJ 2151203 26.49 Hi. Perf NAPA U-joint @ trans OR Rear Axle (AT)
NUJ 2100153 11.49 Standard NAPA U-joint @ trans OR Rear Axle (MT)
NUJ 2150153 18.99 Hi. Perf NAPA U-joint @ trans OR Rear Axle (MT)
BK. 6755176 4.29 .Balkamp Snap Rings
BK. 6755195 5.49 .Balkamp U-bolt Kit

(Please ignore the erroneous periods after the BK and Balkamp portions of the text, they were needed to force the forum software to properly align the text, as it refuses to allow double-spaces in the middle of my message. They are not part of the actual part number used when ordering from NAPA.)

 

[GTR1999]

You might be able to do a driveshaft joint in a vise but I think you'll find the 1/2 shafts much harder. You can cut them out with a torch,clean the yoke bore with emery cloth and then assemble in a vise. If you use a press you will have to bolt the flange to a plate or you'll bend and wreck it.

 

[81 Corvette]

a shot u joint can do a lot of damage. if the half shaft starts spinning while only connected to one end, bye bye fiberglass.

it can also bust the flanges on teh shaft. My folks just went thru this on a drive shaft. the u joint froze up completly and busted out one side of the drive shaft flange

 

[Ol'Scratch]

Rear end noise

Hello Folks!!
I also have a "Scrscrscrscr" noise from my rear-end (yeah..dollars escaping from my wallet) when you are in the null zone between accelerate and decelarete. I was told "U-Joints"...had them replaced and guess what...the noise was still there. Some of the joints were so bad that the joint shaft that the caps ride on were longitudally divited from the needle bearings. And dry as a bone. My next question...since now the are singing the wheel bearing tune... If I jack her up and take the wheel in my hands and try to move it either vertically or horizontally...should I get any play? If so...how much? Or does a sloppy wheel mean bearings?... :confused

Thanks for your time
Fred from Columbia City
Bright Red 81 Coupe

 

[wishuwerehere82]

Fred,

You shouldn't have any movement side to side with your bearings. A little up and down movement can mean that your trailing arm bushings are dry. A little is a lot on rear bearings, since they are shimmed from .001" - .005" tolerance depending on how good the person is that's doing them.
Your bearings may be shot, or your rear spindle, or both.
Your parking brake could also be the cause of the screscre noise too. Start by checking the play on the wheel side to side. You need special tools to remove the bearings and shims to get them back in right. Leave it to a professional.
There are a lot of shops that will rebuild your whole trailing arm assembly or swap it with a new one.