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Discussion Starter · #1 ·
I have a 1974 C3 and have a loud klunk when I let out the clutch or let on and off the gas. I don't know if it can be rear control arm bushings, or something in the meatball? It almost feels like the whole rear end is moving fore and aft when I let on and off the gas. Very strange. All the u joints on drive shaft and half shafts are new. Need some help on what to look for? Thanks
 

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Check the rear snubber that is at the front of the differential on top. The rubber bushing gets worn out. Or, could be u-joints.
 

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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 don't know if it can be rear control arm bushings, or something in the meatball? It almost feels like the whole rear end is moving fore and aft when I let on and off the gas. Very strange. All the u joints on drive shaft and half shafts are new. Need some help on what to look for? Thanks
With the description you gave I would bet on the rubber bushing on the front of the swing arm. If they are original the rubber may have rotted away.
103967
 

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Get it on a lift where the wheels are free and get you or a qualifed mechanic underneath to look and listen
 

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Discussion Starter · #7 · (Edited)
Get it on a lift where the wheels are free and get you or a qualifed mechanic underneath to look and listen
Thanks The Torch,
You can not turn the axles with rear wheels off the ground without jacking up the trailing arms, or the u joints on the half shafts will bind. I will try and accommodate that,,,
 

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Thanks Zimmej51,
I was suspect of those. You really cant see the bushings. Is there a way to properly check them?
I don't know of a method other than a good visual inspection. If they are original, there is a good chance they are rotten. There are actually several things that can cause klunks and scrapes with the rear suspension. As Torch said, I'd start by getting the car on a lift and do a visual inspection of everything with the engine off, then with it running in gear, being very careful obviously. Remember that the klunk may not be anything in the suspension at all. Be thorough in your inspection. Don't guess, try to find the problem.

The C3 rear suspension system isn't inherently troublesome, but does require more maintenance than a traditional rear suspension setup. If your 74 has never had the trailing arms rebuilt, it is way overdue. Bearing failure in one of your trailing arms is something you don't want.

Let us know what you find, or don't find!
 

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I don't know of a method other than a good visual inspection. If they are original, there is a good chance they are rotten. There are actually several things that can cause klunks and scrapes with the rear suspension. As Torch said, I'd start by getting the car on a lift and do a visual inspection of everything with the engine off, then with it running in gear, being very careful obviously. Remember that the klunk may not be anything in the suspension at all. Be thorough in your inspection. Don't guess, try to find the problem.

The C3 rear suspension system isn't inherently troublesome, but does require more maintenance than a traditional rear suspension setup. If your 74 has never had the trailing arms rebuilt, it is way overdue. Bearing failure in one of your trailing arms is something you don't want.

Let us know what you find, or don't find!
Just remembered, another possibility could be the transmission mount. I once traced an elusive clunk (not on a Corvette) to a broken transmission mount.
 

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Discussion Starter · #10 ·
I don't know of a method other than a good visual inspection. If they are original, there is a good chance they are rotten. There are actually several things that can cause klunks and scrapes with the rear suspension. As Torch said, I'd start by getting the car on a lift and do a visual inspection of everything with the engine off, then with it running in gear, being very careful obviously. Remember that the klunk may not be anything in the suspension at all. Be thorough in your inspection. Don't guess, try to find the problem.

The C3 rear suspension system isn't inherently troublesome, but does require more maintenance than a traditional rear suspension setup. If your 74 has never had the trailing arms rebuilt, it is way overdue. Bearing failure in one of your trailing arms is something you don't want.

Let us know what you find, or don't find!
Thanks Zimmej51,
I got under the car to find that the snubber bushing is good, the trailing arm bushings are shot, as well as the strut rod bushings. Not looking forward to trying to get those trailing arms off. I know they are a MF! My passenger side trailing arm has a bend in it. Is it supposed to be that way? Also the drivers side trailing arm appears to have been welded. See attached pics.
 

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Captng1 I'd say a rear rebuild is in your immediate future. I can't say for sure about the bend in the passenger side TA. Likewise, the welds from the factory are usually pretty rough. In your photo something looks a little out of whack but I can't be sure. Given the apparent condition of the bushings I would plan on a total rebuild of all the rear suspension components. I have found that applying lots of Blaster (penetrating oil) all over the TA mount in the frame will greatly aid in removing the bolt. I have a small pneumatic hammer that knocks them right out. Be sure and note the shim packs, when putting everything back in it will give you a starting point.

Voice of experience here: Replacing the TA bushings can be challenging without the proper tools. The same holds true for the spindle bearings. The clearance dimensions on the spindle bearings are a bit critical and is hard to set without the proper tools. I have done all this stuff several times in the past with homemade tools and correct tools. Either way, for someone that doesn't do this every day this is one area that I recommend contracting out. I chose to use VTechCorvette and am happy with the service. I had both TA's and the differential rebuilt, also switched to a 3:54 ratio gearset. VTechCorvette will send you the boxes to ship them in. I'm sure there are other services around that are good too. And don't forget all those u-joints!

Keep us posted!
 

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Discussion Starter · #12 ·
Captng1 I'd say a rear rebuild is in your immediate future. I can't say for sure about the bend in the passenger side TA. Likewise, the welds from the factory are usually pretty rough. In your photo something looks a little out of whack but I can't be sure. Given the apparent condition of the bushings I would plan on a total rebuild of all the rear suspension components. I have found that applying lots of Blaster (penetrating oil) all over the TA mount in the frame will greatly aid in removing the bolt. I have a small pneumatic hammer that knocks them right out. Be sure and note the shim packs, when putting everything back in it will give you a starting point.

Voice of experience here: Replacing the TA bushings can be challenging without the proper tools. The same holds true for the spindle bearings. The clearance dimensions on the spindle bearings are a bit critical and is hard to set without the proper tools. I have done all this stuff several times in the past with homemade tools and correct tools. Either way, for someone that doesn't do this every day this is one area that I recommend contracting out. I chose to use VTechCorvette and am happy with the service. I had both TA's and the differential rebuilt, also switched to a 3:54 ratio gearset. VTechCorvette will send you the boxes to ship them in. I'm sure there are other services around that are good too. And don't forget all those u-joints!

Keep us posted!
Thanks Zimmej51 for the good advice. I have already done all of the u joints :)
What are your thoughts on adjustable strut rods? They seem to be better than the original cam type adjusters...
103980
 

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Thanks Zimmej51 for the good advice. I have already done all of the u joints :)
What are your thoughts on adjustable strut rods? They seem to be better than the original cam type adjusters... View attachment 103980
I definitely would go with the adjustable strut rods if you have to replace the originals. Adjustment is a lot easier and more accurate.
 

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Discussion Starter · #14 ·
I definitely would go with the adjustable strut rods if you have to replace the originals. Adjustment is a lot easier and more accurate.
I dont "Have" to replace the originals. Just the bushings. I beleive they are pressed in which seems like a pain in the ass to replace. Maybe easier just to go with the adjustables?
 

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I dont "Have" to replace the originals. Just the bushings. I beleive they are pressed in which seems like a pain in the ass to replace. Maybe easier just to go with the adjustables?
Yep. The bushings aren't difficult to replace if you have access to a press, but since you are there you might as well do the upgrade.
 

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Looking over your pictures it appears some repairs have been made to them and yes one arm appears bent. The arms are over lapped stitch welded c channel and they rot in between the seams. Many times alignment shops will attempt to bend the arms since removing 40 year old toe shims is not often easy to do. I suspect your arms are in need of replacement but you won't know until you get them out and check them.
I rebuilt 100's of these so if you have any questions just send me an email- [email protected] and I will answer your questions.
If the IRS and differential are original and untouched you should also check the axle end play in the diff as 74's had soft axles. Since it looks like someone has been working on the parts in the past who knows what you will find. Most of the issues I find with arms and diff's are caused by previous people not experienced with these cars, they may be good general mechanics but no so good corvette mechanics.
Gary
 
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