Topic: rear end clunk
in Forum: C3 Driveline Components
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Former Member
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camas, WA - USA
Joined: 9/21/2006
Posts: 6
Vette(s): 1974 t-top 454 #'s matching engine,ugly light green color to be repainted original corvette orange at a later date
Hi everyone!I'm new to the corvette world with my first,a 74 454 that appears to be original except for paint.My problem is that whenever you put the car in reverse ,there is a clunk sound coming from the rear end area.Any ideas?I know NOTHING about corvette rear end/suspension systems.Thanks!Also,when viewed from behind the car, the rear tires sit at an angle with the tops further inward than the bottoms.Could this be that the spring is worn out?Thanks again!
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Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20215
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Welcome to the Shark Tank, first off!!! 
A "clunk" in the rear when putting in gear can be a few things. First would be the front differential mount bushing. It is a rubber/steel mount that holds the front of the diff. to the chassis.
When the rubber deteriorates, it allows the diff. to flip up/down, as you put it in gear, or even sometimes when you first take off, or slow down(on-off the gas quickly). They are replacable fairly easily.
Second, you could have u-joints in the driveshaft, or either/both of the half shafts worn/damaged, that could cause a clunk noise. (There is also a possibility of the half shaft flanges being loose on the stub shafts. This is not a common issue, and doubtfull that it is your noise...just info for you.)
Finally, you could have wear in the ring/pinion gears in the differential. This usually manifests itself as a growling, or whine noise while driving, but can also make a clunking noise, depending on what may actually be worn.
My bet is the front diff. mount.
Pt.# 582122 "Front Carrier Mount Kit"Adams' Apple 2006-10-06 07:55:32
A "clunk" in the rear when putting in gear can be a few things. First would be the front differential mount bushing. It is a rubber/steel mount that holds the front of the diff. to the chassis.
When the rubber deteriorates, it allows the diff. to flip up/down, as you put it in gear, or even sometimes when you first take off, or slow down(on-off the gas quickly). They are replacable fairly easily.
Second, you could have u-joints in the driveshaft, or either/both of the half shafts worn/damaged, that could cause a clunk noise. (There is also a possibility of the half shaft flanges being loose on the stub shafts. This is not a common issue, and doubtfull that it is your noise...just info for you.
)
Finally, you could have wear in the ring/pinion gears in the differential. This usually manifests itself as a growling, or whine noise while driving, but can also make a clunking noise, depending on what may actually be worn.
My bet is the front diff. mount.
Pt.# 582122 "Front Carrier Mount Kit"Joel Adams
C3VR Lifetime Member #56 
My Link 
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Former Member
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camas, WA - USA
Joined: 9/21/2006
Posts: 6
Vette(s): 1974 t-top 454 #'s matching engine,ugly light green color to be repainted original corvette orange at a later date
Thanks for replying guys!It sounds to me like it probably is that front diff mount.I'll try that first as that's probably something fairly easy and affordable(besides I like easy and affordable!
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but we're glad you did .Now we can help you fix itFormer Member
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Lutz, FL - USA
Joined: 9/21/2006
Posts: 4
Vette(s): 72 Big Block Coupe 2nd Owner
92 Convertible 2nd Owner
Lots of previous and all Manuals!
The fun starts when all 4 are sliding!!!
Ok, everyone helped on the clunk and I agree with the front mount.
As for the tires camber. There are two eccentric bolts on the mount just below the diff. If these are at about 2 (left) and 10 (right) and the spring is towards the flat side, it is shot. If not, jack up the car and use jack stands, mark the eccentric washer/bolt with a sharpee (so you know where you started), loosen the nut and move bolts inward a small amount and retighten. Drive car forward and backward to settle suspension. I use a level with 2 sockets taped to it so that I'm only on the rim. Check for level and redo until vertical. This is the garage floor alignment. Now if you run out of room to pull the tires in, you need a new spring (easy to change). A short term fix is to use large washers between the nut at the bottom of the spring bolt and the spring to raise the rear of the car. If you change the spring, change the outboard spring bolts!!!
I had one of these nuts fail from age on a 64 Vette and it was WAY TOO Exciting and that was in my front yard so it was slow.
Joel
The fun starts when all 4 are sliding! (long before it was called drifting)
Former Member
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Willow Grove, PA - USA
Joined: 10/27/2006
Posts: 232
Vette(s): 1974 Stingray Coupe LS4 454 Dark Brown Metallic with Deluxe Saddle interior
MY 454 equipped car has the same sound, I just chalked it up to having so many u-joints and having the big block.... guess Ill take a closer look.
the poop of it is, during the summer, I had it at a corvette shop to have the rear suspention worked on and said to them to change what ever needs changed as I did not have my garage built yet.....
I've got the same noise, a clunk when shifting the car into D or R. It also has a noticeable squat when transferring gears from P. Sounds like it just could be that front diff. mount, guess I have another new part to add to my wish list 
Former Member
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camas, WA - USA
Joined: 9/21/2006
Posts: 6
Vette(s): 1974 t-top 454 #'s matching engine,ugly light green color to be repainted original corvette orange at a later date
Thanks joel for the reply.I'll try some of your suggestions when I get home as I am out on the road right now.
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20215
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
[QUOTE=PSU 98] I've got the same noise, a clunk when shifting the car into D or R. It also has a noticeable squat when transferring gears from P. Sounds like it just could be that front diff. mount, guess I have another new part to add to my wish list [/QUOTE]
Independant rear suspensions do the squat when put in Drive. This is normal. If you put it in reverse, it will raise up a bit. A clunk noise when putting into gear can be the mount, u-joint(s), bushing wear, etc. Just have to put it up, and check each area carefully.
[/QUOTE]
Independant rear suspensions do the squat when put in Drive. This is normal. If you put it in reverse, it will raise up a bit. A clunk noise when putting into gear can be the mount, u-joint(s), bushing wear, etc. Just have to put it up, and check each area carefully.
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
in Forum: C3 Driveline Components
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