Rear End Clunk?
08-04-2008, 04:23 PM
#1
Melting Slicks
Thread Starter
Rear End Clunk?
My '73 is currently in the shop being dyno tuned. While there I asked the mechanic to look at the auto transmisson (TH400). It was shifting fairly hard and making a clunk noise when shifting into gear from either park or neutral.
He called and said it is not the transmission but the clunk is coming from the rear end.
There are no other symptoms. There is no noise coming from the rear during either low or high speed operation. No noise or clunks during turns. Posi-trac appears to be working fine.
A search turned up two possibilities - one is that the front differential mount is loose and/or the rubber mount is in need of replacement. The other is possible loose bolts in the rear end to cross member connection.
Are there any other possibilities?
DC
He called and said it is not the transmission but the clunk is coming from the rear end.
There are no other symptoms. There is no noise coming from the rear during either low or high speed operation. No noise or clunks during turns. Posi-trac appears to be working fine.
A search turned up two possibilities - one is that the front differential mount is loose and/or the rubber mount is in need of replacement. The other is possible loose bolts in the rear end to cross member connection.
Are there any other possibilities?
DC
08-04-2008, 04:35 PM
#2
Instructor
My money is on the front mount... Makes a nasty clunk if gone or beaten up...... Did the mechanic say if the rubber bushing was still in it? It's very easy to see...
08-04-2008, 04:45 PM
#3
Race Director
Very easy to replace. 
08-04-2008, 05:48 PM
#5
Melting Slicks
Member Since: May 1999
Location: Moon Township PA
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Eddie 70 hit the nail on the head and even gave you photos.
your symptoms are classic for this type of failure. If you don't do your own work, this is a fairly straight forward repair for your mechanic. If you do your own work, this is very easy to do, just count on scraped knuckles and an hour lost. The procedure is in the GM Service Manual.
your symptoms are classic for this type of failure. If you don't do your own work, this is a fairly straight forward repair for your mechanic. If you do your own work, this is very easy to do, just count on scraped knuckles and an hour lost. The procedure is in the GM Service Manual.
08-04-2008, 07:40 PM
#6
Melting Slicks
Thread Starter
Eddie 70 hit the nail on the head and even gave you photos. your symptoms are classic for this type of failure. If you don't do your own work, this is a fairly straight forward repair for your mechanic. If you do your own work, this is very easy to do, just count on scraped knuckles and an hour lost. The procedure is in the GM Service Manual.
your symptoms are classic for this type of failure. If you don't do your own work, this is a fairly straight forward repair for your mechanic. If you do your own work, this is very easy to do, just count on scraped knuckles and an hour lost. The procedure is in the GM Service Manual.You've reminded me that I need to add the service manual to the list of stuff I want to order - thanks.
DC
08-05-2008, 11:44 AM
#8
Melting Slicks
Member Since: May 1999
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Thanks guys. I do as much of my own work as possible and this should be no problem. I'll give the mechanic a heads up in the morning and ask him to do a visual inspection to confirm.
You've reminded me that I need to add the service manual to the list of stuff I want to order - thanks.
DC
You've reminded me that I need to add the service manual to the list of stuff I want to order - thanks.
DC
I really doubt that a visual inspection will show anything for the simple reason that the only thing that can be viewed is the bolt head. For the cost of the setup, guessing around $45, it is pretty easy just to swap out the old for a new one. That rubber doughnut sits up in the front of the differential mounting point and sits between the frame and the diff nose. The GM manual gives the procedure, even telling you how to keep the nose of the diff from pivoting up, iirc.
Gary
08-05-2008, 12:55 PM
#9
Instructor
For a DIY guy, the reprinted GM Service Manual is the ONLY way to go, imo.
I really doubt that a visual inspection will show anything for the simple reason that the only thing that can be viewed is the bolt head. For the cost of the setup, guessing around $45, it is pretty easy just to swap out the old for a new one. That rubber doughnut sits up in the front of the differential mounting point and sits between the frame and the diff nose. The GM manual gives the procedure, even telling you how to keep the nose of the diff from pivoting up, iirc.
Gary
I really doubt that a visual inspection will show anything for the simple reason that the only thing that can be viewed is the bolt head. For the cost of the setup, guessing around $45, it is pretty easy just to swap out the old for a new one. That rubber doughnut sits up in the front of the differential mounting point and sits between the frame and the diff nose. The GM manual gives the procedure, even telling you how to keep the nose of the diff from pivoting up, iirc.
Gary
08-08-2008, 02:59 PM
#11
Melting Slicks
Thread Starter
Not yet. Car is still in the shop being checked and tuned. Mechanic said the front bushing and all mounting bolts are tight and in good shape. Doesn't appear to be u-joints either. He thinks its coming from inside the diff. When I get it back I'll double check everything and then will change the fluid to see if that helps. Previous owner said the rear diff is the only part of the car that did not get any attention when he restored it so maybe it's just overdue for a fluid change.
DC
DC
