C3 Rear axle noise.

[CharlieB]

I have recently purchased a 1977 C3. I had a good test drive noticing one slight judder in the axle when moving forward.
However on the 70 mile drive back home the noise when starting from junctions became horrible. Knocking, graunching and judder. It smoothed out when the speed had built up and there was no vibration in normal driving, (difficult to hear if there is any noise over the magnificent sound of the exhaust).
The car has been well maintained with new rear wheel bearings, universal joints on the drive shafts, shock absorbers and bushes. It had not been run for some months.
Does anyone have any experience of this? Would fresh oil in the differential cure the problem.
Any suggestions would be appreciated.
CharlieB

 

[kentvette]

The first thing to do is to change the diff fluid. Don't be tempted to go down any other route except that prescribed by Chevy - ie, use 90 diff oil and the GM Limited Slip Diff additive. The consensus now seems to be two bottles of additive. You'll need to pump out the diff as there is no drain plug. Then add the additive and top up to the fill plug with gear oil. Then take the car to an empty car park etc and do about 12 gentle figures of eight, to get the fluid bedded into the clutches.

 

[CharlieB]

Thanks, I'll try that and let you know the outcome.

 

[Corvetteville]

I used one of these to pump out the diff. Worked a treat.

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[kentvette]

I used one of these to pump out the diff. Worked a treat.

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Yes, I have something similar.
I'd say to Charlie to be careful about using the pump to re-fill the diff - it'll fill it quickly and cause a messy overflow!

 

[Corvetteville]

I used the pump to empty only. It was pretty gunked up with old oil.

 

[BigVet]

PM sent.

 

[CharlieB]

Update on axle noise. Its gone!!!!
I changed the oil in the back axle using Lucas 80-90 and two bottles of GM limited slip diff additive.
12 or so figure of eights ensured a smooth take off at junctions when doing the road test.
Thanks Kentvette for the good advice.
Charlie.

 

[James Vette]

I have recently purchased a 1977 C3. I had a good test drive noticing one slight judder in the axle when moving forward.
However on the 70 mile drive back home the noise when starting from junctions became horrible. Knocking, graunching and judder. It smoothed out when the speed had built up and there was no vibration in normal driving, (difficult to hear if there is any noise over the magnificent sound of the exhaust).
The car has been well maintained with new rear wheel bearings, universal joints on the drive shafts, shock absorbers and bushes. It had not been run for some months.
Does anyone have any experience of this? Would fresh oil in the differential cure the problem.
Any suggestions would be appreciated.
CharlieB

Post some photos!

 

[kentvette]

Update on axle noise. Its gone!!!!
I changed the oil in the back axle using Lucas 80-90 and two bottles of GM limited slip diff additive.
12 or so figure of eights ensured a smooth take off at junctions when doing the road test.
Thanks Kentvette for the good advice.
Charlie.

Glad it worked out!

 

[Chuffer]

Lucky you got away with that one CharlieB and no more damage done !

 

[Mr. Cricket]

Result! I bought a 1.5 ltr syringe to do mine rather than a pump

 

[kentvette]

Lucky you got away with that one CharlieB and no more damage done !

He was! But, 9 times out of 10, that's all it needs. Unless you're the 10th, like me, and it "explodes" 300 miles from home! A long, gentle drive back on the straightest Autoroute we could find!

 

[Chuffer]

Been there and done that ! I must have been number 9 & 1/2 ! I was a mere 100 miles from home and nursed it northwards up the A34 and A43 with it sounding more and more like a bag of spanners and negotiating the few roundabouts encountered very gingerly . Ended up needing a complete new diff .