Strange rear klunk
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Pro
Joined: Apr 2006
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From: Norwalk CT and Boynton Beach FL
Strange rear klunk
I have a 75 convertible. From a dead stop, when I just begin to take off and the nose of the car begins to lift, I get a Klunk from the rear and sounds like it is coming from the drivers side. This doesn't happen every time and I usually have to drive the car awhile , come to a red light and then when I bagin to take off and the nose of the car lifts I hear a Klunk --- sounds like metal on metal. But if I immediately stop and then try to duplicate the motion --- it wil not klunk again. It's not the same kind of klunk you get from a bad or loose U-joint but a higher sounding klunk. Initially, it sounded like a loose caliper that was moving but I checked both rear calipers out and they are secure. I 've crawled under the car and tightened every bolt I could see and nothing seemed to be loose? Anybody have and ideas here? This has been going on now for two years and it's starting to get to me.
Intermediate
Joined: Jul 2006
Posts: 41
Likes: 0
From: Manakau City Auckland
Maybe one of the following.....
Manual or auto ??
-Worn or loose front mount on diff
-Worn spline on rear of trans or front of diff
-Worn or loose crown wheel on carrier in diff
-A U joint on one of the drive shafts that is hard to see although has been checked
-A worn spline along with a loose nut on one of the trailing arm axle shafts
Suggest taking off both rear drive shafts to properly check the UJ,s and the axles.
Mine had a very worn and bent spline on one axle along with a loose nut, this came from taking off very quickly at times (if you know what I mean)
Manual or auto ??
-Worn or loose front mount on diff
-Worn spline on rear of trans or front of diff
-Worn or loose crown wheel on carrier in diff
-A U joint on one of the drive shafts that is hard to see although has been checked
-A worn spline along with a loose nut on one of the trailing arm axle shafts
Suggest taking off both rear drive shafts to properly check the UJ,s and the axles.
Mine had a very worn and bent spline on one axle along with a loose nut, this came from taking off very quickly at times (if you know what I mean)
Burning Brakes
Joined: Dec 2005
Posts: 1,179
Likes: 100
From: cranford nj
had the same problem on my 71 after driving around awhile i would hear a clunk and some times not. Drain the rear put in new fluid and additive go to a parking lot and do tight figure 8's for 10 min and you should be good to go.
Thread Starter
Pro
Joined: Apr 2006
Posts: 647
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From: Norwalk CT and Boynton Beach FL
Originally Posted by blue by you
had the same problem on my 71 after driving around awhile i would hear a clunk and some times not. Drain the rear put in new fluid and additive go to a parking lot and do tight figure 8's for 10 min and you should be good to go.
This is easy to do so I will give it a try first. I hope no one sees me doing figure 8's in the parking lot for 10 minutes as they will probably call the mental institution and have me hauled away.
Thanks
Thread Starter
Pro
Joined: Apr 2006
Posts: 647
Likes: 22
From: Norwalk CT and Boynton Beach FL
Originally Posted by Tony S
Maybe one of the following.....
Manual or auto ??
-Worn or loose front mount on diff
-Worn spline on rear of trans or front of diff
-Worn or loose crown wheel on carrier in diff
-A U joint on one of the drive shafts that is hard to see although has been checked
-A worn spline along with a loose nut on one of the trailing arm axle shafts
Suggest taking off both rear drive shafts to properly check the UJ,s and the axles.
Mine had a very worn and bent spline on one axle along with a loose nut, this came from taking off very quickly at times (if you know what I mean)
Manual or auto ??
-Worn or loose front mount on diff
-Worn spline on rear of trans or front of diff
-Worn or loose crown wheel on carrier in diff
-A U joint on one of the drive shafts that is hard to see although has been checked
-A worn spline along with a loose nut on one of the trailing arm axle shafts
Suggest taking off both rear drive shafts to properly check the UJ,s and the axles.
Mine had a very worn and bent spline on one axle along with a loose nut, this came from taking off very quickly at times (if you know what I mean)
My trans is auto ---- if that makes any difference. Much of what you suggested is over my head in terms of competency so I will do some reading up on this stuff and in the end may just take it to my local mechanic with your list of possible causes and discuss with him when I feel more knowledgable about this stuff. The problem is that I can't always duplicate the klunk but it seems to ALWAYS happen when I come off of a highway run of a few miles, get to the off ramp stop sign and them take off from there. Thanks for your ideas as to where the problem might be.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Could it be something like the vent door in cargo area back wall?-its vacumn operated-----something in the gas tank?----something in the areas behind the rear speakers?----power antenna swinging back? ---something in the jack compartment?
Le Mans Master
Joined: Nov 2001
Posts: 8,806
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From: LONG ISLAND
2025 C3 ('68-'73) of the Year Finalist - Unmodified
2024 C3 of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
Originally Posted by happiedazs
I have a 75 convertible. From a dead stop, when I just begin to take off and the nose of the car begins to lift, I get a Klunk from the rear and sounds like it is coming from the drivers side. This doesn't happen every time and I usually have to drive the car awhile , come to a red light and then when I bagin to take off and the nose of the car lifts I hear a Klunk --- sounds like metal on metal. But if I immediately stop and then try to duplicate the motion --- it wil not klunk again. It's not the same kind of klunk you get from a bad or loose U-joint but a higher sounding klunk. Initially, it sounded like a loose caliper that was moving but I checked both rear calipers out and they are secure. I 've crawled under the car and tightened every bolt I could see and nothing seemed to be loose? Anybody have and ideas here? This has been going on now for two years and it's starting to get to me.
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
There is a bushing at the front of the differential that wears out or gets loose after time. It's called the front carrier mount in this photo. If it's loose, the bolt tends to separate when you take off and come back together when you stop - and makes a clunk. Have you checked this? 
Differential link
Differential link
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Le Mans Master
Joined: Nov 2001
Posts: 8,806
Likes: 1,945
From: LONG ISLAND
2025 C3 ('68-'73) of the Year Finalist - Unmodified
2024 C3 of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
Originally Posted by Z-man
There is a bushing at the front of the differential that wears out or gets loose after time. It's called the front carrier mount in this photo. If it's loose, the bolt tends to separate when you take off and come back together when you stop - and makes a clunk. Have you checked this?
Differential link
Differential link
NOTHING NADA ZILCH IS EVER EASY..........!!!!
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
Originally Posted by 427SIXPACK
HARD TO REPLACE ? WHATS INVOLVED ? I'LL TRY IT.......IF NOT TO INSANE............BUT EVERYTHING ON MY 68 IS JUST THAT.....INSANE
NOTHING NADA ZILCH IS EVER EASY..........!!!!
NOTHING NADA ZILCH IS EVER EASY..........!!!!
If it needs to be replaced, you remove the bolt and replace with the upper and lower cushions. About a 3 on a scale of 10.
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
Originally Posted by 427SIXPACK
HARD TO REPLACE ? WHATS INVOLVED ? I'LL TRY IT.......IF NOT TO INSANE............BUT EVERYTHING ON MY 68 IS JUST THAT.....INSANE
NOTHING NADA ZILCH IS EVER EASY..........!!!!
NOTHING NADA ZILCH IS EVER EASY..........!!!!
Le Mans Master
Joined: Nov 2001
Posts: 8,806
Likes: 1,945
From: LONG ISLAND
2025 C3 ('68-'73) of the Year Finalist - Unmodified
2024 C3 of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
Originally Posted by DWncchs
427 the bushing is 2 part as has been said.You can see the lower easily and most of the time that one looks good.The upper is hard to see,you have to stick your fingers up and around and feel it.The upper is the one I find bad most of the time.
Thread Starter
Pro
Joined: Apr 2006
Posts: 647
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From: Norwalk CT and Boynton Beach FL
Originally Posted by Z-man
There is a bushing at the front of the differential that wears out or gets loose after time. It's called the front carrier mount in this photo. If it's loose, the bolt tends to separate when you take off and come back together when you stop - and makes a clunk. Have you checked this?
Differential link
Differential link
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
Originally Posted by happiedazs
I've checked and tightened the front carrier mount bolt/bushing. That's not it
Thread Starter
Pro
Joined: Apr 2006
Posts: 647
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From: Norwalk CT and Boynton Beach FL
Originally Posted by Z-man
Hmmm....you've checked most of the common stuff. Could it be parts of the parking brake catching or moving around??
Melting Slicks
Joined: May 1999
Posts: 2,897
Likes: 0
From: Moon Township PA
Originally Posted by happiedazs
I've checked and tightened the front carrier mount bolt/bushing. That's not it