1980 rear end slack
Thread Starter
Cruising
Joined: Nov 2010
Posts: 11
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1980 rear end slack
My 1980, with auto trans, has slack in the differential when shifting to drive or reverse.
Off the ground, I can grab the wheel and move forward and backward.
I have changed all the u joints, replaced the rear end grease with limited slip, but did not put in the additive. It seems to be worse now than before the grease change. It runs fine once put into gear.
Any suggestions would be appreciated.
Off the ground, I can grab the wheel and move forward and backward.
I have changed all the u joints, replaced the rear end grease with limited slip, but did not put in the additive. It seems to be worse now than before the grease change. It runs fine once put into gear.
Any suggestions would be appreciated.
Race Director
Joined: May 2006
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What rear end fluid did you install? Are you saying you have one wheel off the ground and one wheel on the ground and you can fully turn by hand the wheel that is off the ground? Do you hear a clunk when shifting into drive or reverse, if so, have you checked for a worn front differential mounts?
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
I'd blame the front differential mount first. My 80 was acting about the same way. BTW, the mount is a real pain to install. No room to work. If you turn the driveshaft just right, you can get barely enough room to drop the bolt in place.
Thread Starter
Cruising
Joined: Nov 2010
Posts: 11
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What rear end fluid did you install? Are you saying you have one wheel off the ground and one wheel on the ground and you can fully turn by hand the wheel that is off the ground? Do you hear a clunk when shifting into drive or reverse, if so, have you checked for a worn front differential mounts?
I put valvoline gear oil with limited slip in the rear end. When I crank the car and shift it to drive or reverse, it is a brief second before the drive shaft engages the gear. Sounds that way to me.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Not saying what your problem is or solution but I would put the rear end additive in before you have some real problems, put it in and take it to a parking lot and do a few figure 8's
Thread Starter
Cruising
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This forum has been a life safer.
Burning Brakes
Joined: Sep 2012
Posts: 818
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From: coon rapids mn
check all the mounting points for the rear end ,and do check the trailing arm bushings .how many miles on the car ?you should check the shafts that come out of the rear differential ,to see how much they can move in or out .
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Le Mans Master
Joined: Jan 2003
Posts: 6,575
Likes: 1
From: Tuttle OK
Cruise-In VIII Veteran
Next time you do this job, just yank the driveshaft. It'll be much quicker, require fewer busted knuckles, and save you from having to create new cuss words. Beer consumption can remain the same.
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
LOL! I don't create cuss words as I take on some weird Corvette-related task. I just use the same old ones. Not very creative, but it serves the purpose.
Have you ever dropped the driveshaft on an 80? It's a big a pain as any other job. But I see your point. I was installing the whole batwing assembly and driveshaft as a unit, as I was told that was the best way to do it.
Have you ever dropped the driveshaft on an 80? It's a big a pain as any other job. But I see your point. I was installing the whole batwing assembly and driveshaft as a unit, as I was told that was the best way to do it.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
bobwarren,
You are kinda vague in your description in this 'slack issue'.
First off..make sure you use the GM limited slip additive in your differential.
FORWARDS and BACKWARDS means WHAT??? ROTATING the wheel...or actually being able to physically move the wheel to the front and rear...and NOT rotating it???? It MAKES A BIG difference in helping you find the issue.
Guessing that you are meaning that you can rotate it back and forwards:
You being able to ROTATE the wheel back and forth a little is normal.....but you are not saying 'how much' you can turn it....and if it is turning back and forth....ARE YOU doing this with the transmission in PARK or NEUTRAL....and are you watching the driveshaft????
You have 'back lash' value in the ring and pinion...so it will move some....and then you will have some movement in the transmission itself. SO...like I wrote above...it depends on how much.
Need some more input.
DUB
You are kinda vague in your description in this 'slack issue'.
First off..make sure you use the GM limited slip additive in your differential.
FORWARDS and BACKWARDS means WHAT??? ROTATING the wheel...or actually being able to physically move the wheel to the front and rear...and NOT rotating it???? It MAKES A BIG difference in helping you find the issue.
Guessing that you are meaning that you can rotate it back and forwards:
You being able to ROTATE the wheel back and forth a little is normal.....but you are not saying 'how much' you can turn it....and if it is turning back and forth....ARE YOU doing this with the transmission in PARK or NEUTRAL....and are you watching the driveshaft????
You have 'back lash' value in the ring and pinion...so it will move some....and then you will have some movement in the transmission itself. SO...like I wrote above...it depends on how much.
Need some more input.
DUB
Safety Car
Joined: Mar 2007
Posts: 3,652
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From: Bridgewater nj
For example; I can watch my passenger side rear wheel in the reflection of my truck. If I go from reverse to drive, I can watch my rear wheel roll forward about an inch without the car moving.
If this happens, it's most likely trailing arm bushings.
If this happens, it's most likely trailing arm bushings.
Le Mans Master
Joined: Jan 2003
Posts: 6,575
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From: Tuttle OK
Cruise-In VIII Veteran
Thread Starter
Cruising
Joined: Nov 2010
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With the 4 wheels on the ground and the engine running, I can put the trans in drive and it seems as though the main universal shaft turns about an inch or so before the wheels starts turning. It sounds like a noticeable clonk sound when this occurs.
Race Director
Joined: Apr 2009
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From: Charlotte NC
DUB