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I have a 1974 C3 and have a loud klunk when I let out the clutch or let on and off the gas. I dont know it it can be rear control arm bushings, or something in the meatball? All the u joints on drive shaft and half shafts are new. Need some help on what to look for? Thanks
Mrvettenick,
I can not wiggle the driveshaft side to side or up and down where it meets the differential. Is there a better way to check it? It almost feels like there is slack in the gears, or the whole rear end is moving fore and aft when you let on and off the gas pedal. Very strange...
It takes more than hand power to move the diff. I would look under the car while both sides of the rear is on stands while someone ;lets up on the clutch. I'm sure you'll find out quickly where that clunk is coming from. I wouldn't drive it until you know where it's coming from.
Good advice. When the car is off the ground, the rear wheels hang at a pretty steep angle. I'm not sure the axles and u joints were designed to run at that angle?
Good advice. When the car is off the ground, the rear wheels hang at a pretty steep angle. I'm not sure the axles and u joints were designed to run at that angle?
All you want to do is put a load on the drivetrain. You won't be going fast enough or long enough to create any issue.
Good advice. When the car is off the ground, the rear wheels hang at a pretty steep angle. I'm not sure the axles and u joints were designed to run at that angle?
They are not. If you need to turn the rear wheels while off the ground you need to support both trailing arms and reduce the angle otherwise you will risk binding up the u-joints of the half-shafts.
You should be able to do a visual of the differential snubber mounts. Try using a large screw driver and pry down the mount. Also check the transmission and motor mounts. Check the trailing arm bushings and shims as well as the shocks. Jerry
Thanks Tampa Jerry. What is the proper way to check the trailing arm bushings. Those are what I am suspect of (and also maybe the snubber bushing). The engine and tranny mounts are good. Thanks for your help..
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Originally Posted by captng1
Thanks Tampa Jerry. What is the proper way to check the trailing arm bushings. Those are what I am suspect of (and also maybe the snubber bushing).
With the trailing arm installed on the car it's difficult to tell if the bushings are good or not.
If the bushings are bad the rear of the car will seem to move sideways as you accelerate and the rear will move the other way as you decelerate.
Thanks Peterbuilt,
I have a klunking noise and feel when I let on and off the gas. It feels like there is slop in the drivetrain somehow. It feels more like a fore and aft motion than side to side. I was suspect of trailing arm bushings, but will have a look at the snubber bushing...
my 68s clunk was actually from the rear cross member sunbreo bushings. i drove in a vette that had a bad pinon snubber bushing and the clunk sounded like the floor being hit.
You can check the trailing arm bushings and shims visually and also with a prybar. With a strong light, look inside the pocket on the frame where the trailing arm attaches to the frame. You should see little to no side to side movement. The bushings should not be cracked or falling apart. You should not be able to easily move the shims. My bet is on the snubber bushings. Do not replace with poly. They are too thin. Jerry
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
My clunk was a combination of these after installing new u joints on the driveshaft and half shafts and driving it about 100 miles
broken snubber mount
loose caps on half shafts
loose caps on driveshaft
after tighten them and welding up and reinforcing the snubber mount I bought new grade 8 bolts and nuts, with a little extra length for secondary lock nuts. The shoulder was too long and event though they were "tight" the bolts were not pinching the snubber mount to the differential enough and an occasional clunk would occur on harder acceleration or heavy downshifting. Adding a few extra washers as shims under the nuts and a second nut as a locking nut eliminated all clunking on my last drive with a few hard accelerations, no clutch drops though.
thought it was a hair line crack then with a light it looked worse
I unbolted this and that piece landed on my face
stitch welded it inside and out ground the weld flat internally and mostly flat on the outside added angle iron onto the bottom and inside a and a small plate on the outside. I reinforced both the left and right sides. Added grade 8 washers to all the mounting holes and welded them inplace test fit on another rear end before welding on the washers
The newer model mounts have a thick piece of steel tack welded to reinforce the holes, but there is only a few welds
Last edited by Rescue Rogers; May 24, 2021 at 09:46 AM.
Drive Train Klunk
