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8/7/09 9:13pm - Original Message: 'Rear Diff? Noise'
KDADDY79
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Dutchess County, NY - USA

Vette(s):
White '79 Corvette. It's a driver.

Joined: 8/27/2007
Posts: 2484

   My son and I went for a nice ride today in the Vette.  The weather was perfect for some tops off driving in a C3! (High 70's - Low humidity.)

   We put around 50 country road miles on it. Nothing out of the ordinary ie...no large potholes or sudden stops.
 
   When we got home I backed it in to the driveway and for the first time I heard a scraping sound coming from the rear end. "Scrape, scrape scrape" as I rolled backwards. There was no feeling of resistance, just the noise. I rolled it forward and did not hear the noise at all. Rolled it backwards and there it was again. No delay going in to gear or anything like that.
 
   I won't have a chance to put it on a lift for a week. Any suggestions where I start looking?
 
   P.S.   My Vette is a '79 L-48 with a TH-350 trans.
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8/7/09 9:45pm - Reply: 'Rear Diff? Noise'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

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

Joined: 11/8/2003
Posts: 19457
Could be the parking brake, or a spindle bearing.
Can you have someone listen to it from outside, on both sides, to determine if the noise can be narrowed down to a particular area?


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8/7/09 10:28pm - Reply: 'Rear Diff? Noise'
KDADDY79
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Dutchess County, NY - USA

Vette(s):
White '79 Corvette. It's a driver.

Joined: 8/27/2007
Posts: 2484
Hey Joel,
The scraping noise seemed to come from the right rear.
Tomorrow I'll borrow a neighbor to give it another listen.
The Parking Brake doesn't sound too awful bad but a Spindle Bearing just plain sounds like an expensive fix.
I'll weigh in again tomorrow after some more listening.
Kevin 


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8/8/09 9:56am - Reply: 'Rear Diff? Noise'
B Woogie
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Joined: 7/7/2009
Posts: 32
Try applying the emergency brake lightly as you roll backwards, and see if the scrape noise changes. That might help pin-point the source. Seems like if it does change it, then the brakes would be the first place to investigate.
Another possibility would be the ujoints in the halfshafts. They can make scraping noises when they get dry.


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8/8/09 10:11am - Reply: 'Rear Diff? Noise'
jp75vette
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Bloomfield Hills, MI - USA

Vette(s):
1975 Corvette coupe, 4 speed manual, 383 ci 9.5:1,Edelbrock dual plane Air Gap intake, Alum Heads,Comp Cam, roller Rockers, PS,PB,Tilt

Joined: 6/29/2008
Posts: 199
I had a scraping noise on my 75 last year. it was the yoke clip in the differential had fallen off, so the yoke moved in and out of the differential and that caused the U joints on the half shafts to come in contact with other parts. Had to do a toatl differential rebuild.

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8/8/09 1:01pm - Reply: 'Rear Diff? Noise'
rraider1
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Woodland, WA - USA

Vette(s):
1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion

Joined: 10/14/2003
Posts: 1152
I beleive you can check the yokes, with the car jacked up grab the bottom and top of the rear tire and rock top to bottom if there is movement in and out the yokes are worn. Thats how mine was discovered.

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8/8/09 3:39pm - Reply: 'Rear Diff? Noise'
KDADDY79
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Dutchess County, NY - USA

Vette(s):
White '79 Corvette. It's a driver.

Joined: 8/27/2007
Posts: 2484
Me and a friend gave it another listen today.
He noticed a small clicking noise from the right rear when I first let off the brake while it was in reverse. It only made this noise when in reverse and rolling backwards but not in neutral rolling backwards. It's just one "Clickl" sound while releasing the brake followed by the "scrape, scrape, scrape" sounds after it begins to roll backwards.
I got under the car and twisted both half shafts. The passenger side half shaft has a bit more play than does the driver's side.
I'm thinkin' it's one of the U-Joints on the half shaft but I'll try rraider1"s suggestion to check the yokes too.
The E-Brake made no difference but thanks for the suggestion.
Wish me luck on this.
Kevin
 


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8/8/09 4:50pm - Reply: 'Rear Diff? Noise'
Jeffm Gold Member
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Sebago Lake, ME - USA

Vette(s):
1978 Silver Anniversary L82 4spd (M21) Red Leather. -1978 Pace Car L82 4spd (M21) 20k miles.

Joined: 2/15/2007
Posts: 962
The side yokes on my '78 were worn pretty bad with just 50k on her. One side was worn right down to the "C" clip. Much more and it would come off. I read poor metal quality those years. Only opened it cause the cover and seals leaked. Nasty looking oil with them metal grindings mixing in. Don't remember any noise in reverse. But the wife says I don't hear much anyway.

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8/8/09 8:44pm - Reply: 'Rear Diff? Noise'
KDADDY79
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Dutchess County, NY - USA

Vette(s):
White '79 Corvette. It's a driver.

Joined: 8/27/2007
Posts: 2484
And I'd have a pretty nice Vette if I was deaf, dumb and blind! LOL
Ah well! I'm lookin' forward to getting it in to the shop for an inspection by a good mechanic.
We'll see.
Kevin


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8/18/09 4:04pm - Reply: 'Rear Diff? Noise'
gellisvette Lifetime Member
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PERRYSBURG, OH - USA

Vette(s):
1975 T-Tops,Lite Custom work,Many engine mod. 700R4 trans. body is shaved,17" wheels bf goodrich g-force tires,heavy sway bars front&rear rack&pinion steering,550 slolom springs with gas shocks.

Joined: 4/23/2004
Posts: 317
Can anyone tell me just how much play there shood be in the rear yokes. I just came from Bell Tire and the guy there said this my be some of my vibration.

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8/19/09 7:10pm - Reply: 'Rear Diff? Noise'
Jeffm Gold Member
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Sebago Lake, ME - USA

Vette(s):
1978 Silver Anniversary L82 4spd (M21) Red Leather. -1978 Pace Car L82 4spd (M21) 20k miles.

Joined: 2/15/2007
Posts: 962
I replaced mine this past winter. I don't read or measure in the same language as a mechanic or machinist but from what I read and found out somewhere around an 1/8" (.o125) or a bit less is about the max. They wear out big time on the inside and you get more lateral (vertical) movement in the wheels when cornering. If they wear too much the seal shields or whatever they are called could be hitting the diff housing under corning pressure.
I'm by far no expert on this stuff so maybe someone that knows more can give you a better idea.


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8/19/09 10:05pm - Reply: 'Rear Diff? Noise'
wetvet
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Lake Oswego, OR - USA

Vette(s):
1972 Steel Cities Gray T Top. Original Owner, Original Paint and Interior. The running gear has been rebuilt after 240,000 miles.

Joined: 10/17/2003
Posts: 540
I replace all the u-joints (6) on my Vette last winter. The scraping and other drive-line noises went away after that. Make sure you get a 4 wheel alignment after you replace these and other suspension/drive-line pieces. I'm sure you will be happy with the results...the rest of the season.

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8/19/09 10:19pm - Reply: 'Rear Diff? Noise'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

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

Joined: 11/8/2003
Posts: 19457
I have never seen any published specs on the side yoke clearance/end play...not even in the factory service manuals. I think around .010"-.015" is about max(my opinion). Any more than that will effect the rear camber adjustments as the suspension moves up/down in turns/corners.

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Joel Adams
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8/20/09 5:17pm - Reply: 'Rear Diff? Noise'
gellisvette Lifetime Member
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PERRYSBURG, OH - USA

Vette(s):
1975 T-Tops,Lite Custom work,Many engine mod. 700R4 trans. body is shaved,17" wheels bf goodrich g-force tires,heavy sway bars front&rear rack&pinion steering,550 slolom springs with gas shocks.

Joined: 4/23/2004
Posts: 317
Talked with American custom ind. They said it sounds like the clutch pack in the posi-traction unit. If you drive your vette a few blocks and it starts making sounds when you turn a corner like the brakes are tying up, nine times out of ten it's the clutch pack! Metal shavings contaminate the gear lube and your done. Early C-3's it isn't very common but does happen. I'll know more when I open it up this weekend. I'll try to keep up up to speed. If you guys want?

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gellisvette


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8/20/09 7:43pm - Reply: 'Rear Diff? Noise'
Jeffm Gold Member
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Sebago Lake, ME - USA

Vette(s):
1978 Silver Anniversary L82 4spd (M21) Red Leather. -1978 Pace Car L82 4spd (M21) 20k miles.

Joined: 2/15/2007
Posts: 962
[QUOTE=gellisvette] I'll know more when I open it up this weekend. I'll try to keep up up to speed. If you guys want?[/QUOTE]

By all means. let us know what you find in there.
Mine made that chattering noise taking off from a dead stop and turning. I added some oil and posi additive and it stopped. I opened mine mainly because the cover and side seals leaked and I was doing a new spring. the oil looked like a metallic paste. New seals, side yokes, clean oil and she runs like a dream now.Big smile
Jeffm2009-08-20 17:45:27

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8/20/09 10:15pm - Reply: 'Rear Diff? Noise'
KDADDY79
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Dutchess County, NY - USA

Vette(s):
White '79 Corvette. It's a driver.

Joined: 8/27/2007
Posts: 2484
I haven't gotten mine in to the shop yet so the jury's still out.
George, please let us know how things go on yours.
Kevin
P.S.   I had good luck with the additive and a fluid change a little over a year ago.
         Hope it goes well for you.


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8/21/09 12:07pm - Reply: 'Rear Diff? Noise'
OH6A Lifetime Member
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Cadiz, KY - USA

Vette(s):
64 Convertible 73 Coupe 74 Convertible 63 Corvair Spyder Convertible

Joined: 8/26/2002
Posts: 244
My vote is that the positraction clutches are sticking.  I have had that problem.  Change the oil and that may solve the problem.  That is the easiest and the least expensive.  Not that easy to do though because there is no drain plug.  Many people put one in.  The other solution is to suck it out.  Make sure you put in a good quality positraction oil and the additive and your problem should go away.  The answer to your differential side yoke question regarding how much outward movement.  Very little!  If you can feel it, the yokes are probably worn.  A clue is if when the car is jacked up, if the top or bottom of the tire has more than 1/4" in-out movement, the yokes are worn.

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8/28/09 4:20pm - Reply: 'Rear Diff? Noise'
gellisvette Lifetime Member
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PERRYSBURG, OH - USA

Vette(s):
1975 T-Tops,Lite Custom work,Many engine mod. 700R4 trans. body is shaved,17" wheels bf goodrich g-force tires,heavy sway bars front&rear rack&pinion steering,550 slolom springs with gas shocks.

Joined: 4/23/2004
Posts: 317

Still haven't had time to open it up. But thanks for the input, I'll keep it in mind. I will let you guys know what I find.   Just got the vibration taken care of after three years and a pile of money later. The local tire man tech. has a new tire machine and he found the dad tire right off the bat and fixed it for nothing!!!!!! What a guy,,He will get all of my business and any referrals I can make. He's a real vette man. My thanks to him!!!!!Clap



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8/28/09 9:04pm - Reply: 'Rear Diff? Noise'
kstyer Lifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
Posts: 6410
Keep in mind, if the yokes are worn, that can also make the posi clutches act up.  Mine does that.  I have the new yokes in a box to go in when I get the time.

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