Re: oh GOD why my car?
Thread Starter
Intermediate
Joined: Jul 2014
Posts: 42
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Re: oh GOD why my car?
1979 Vette, thought I have a bad rear wheel bearing. Heard a grinding noise when movimg from a stop when making a turn, on occasion. Also hear a whomp whomp sound on occasion when making turns. Noticed this occurs when car is on the road for a little. Read could b posi low fluid. Remember mechanic topped it off 3 months ago. Called him I asked about the top off. He used regular gear oil. I am beyond upset and worried. Ok I see an additive and fluid is available on line. How do I get the old oil out without ripping the rear apart? What to do? My only car! There is no drain plug and the rear cover holds suspension components in place. I will call myself a novice. I believe this wrong fluid thing is the cause of the horrific noises I hear on occasion. They are not that bad but any noise scares me as it always costs cash I dont have!
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
If you feel it is your differential fluid...which I doubt....because the clutches would chatter and not make the sound you are describing...you can suck the fluid out with a tool and then add the GM additive with the correct gear oil.
Seeing how I can not hear what you are describing....I think you might have bearing issues in the rear or universal joint issues....and or possible parking brake shoe issues...due to broken spring making noise.
Can also be possible suspension bushing issues.....like I wrote it is hard to say.
DUB
Seeing how I can not hear what you are describing....I think you might have bearing issues in the rear or universal joint issues....and or possible parking brake shoe issues...due to broken spring making noise.
Can also be possible suspension bushing issues.....like I wrote it is hard to say.
DUB
Le Mans Master
Joined: Apr 1999
Posts: 6,134
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From: Raleigh North Carolina
1979 Vette, thought I have a bad rear wheel bearing. Heard a grinding noise when movimg from a stop when making a turn, on occasion. Also hear a whomp whomp sound on occasion when making turns. Noticed this occurs when car is on the road for a little. Read could b posi low fluid. Remember mechanic topped it off 3 months ago. Called him I asked about the top off. He used regular gear oil. I am beyond upset and worried. Ok I see an additive and fluid is available on line. How do I get the old oil out without ripping the rear apart? What to do? My only car! There is no drain plug and the rear cover holds suspension components in place. I will call myself a novice. I believe this wrong fluid thing is the cause of the horrific noises I hear on occasion. They are not that bad but any noise scares me as it always costs cash I dont have!
Pro
Joined: May 2013
Posts: 672
Likes: 31
From: Rapid City South Dakota
Unlikely diff fluid issues, I agree with DUB. There is likely some posi fluid left, it leaked out in proportion to the gear oil so if he added gear oil he likely just diluted it a little. I doubt the posi clutches are all that tight on a '79 unless it was rebuilt anyway....
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
You only need to remove the "FILL" plug (it has no 'drain' plug). Stick you little finger in there to see how far below the hole the fluid level sits. If you have some space, just put one (small) bottle of posi-fluid in it and put the plug back in. I'm sure the new gear lube the mechanic put in should be fine.
If you have no extra space for the posi-fluid, use a turkey baster to suck out about as much as you are going to put in with the posi-fluid bottle.
You have not done any damage to the differential.
If you have no extra space for the posi-fluid, use a turkey baster to suck out about as much as you are going to put in with the posi-fluid bottle.
You have not done any damage to the differential.
Thread Starter
Intermediate
Joined: Jul 2014
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I will take her to another mechanic to check it out. Just suspect the fluid as it is the wrong type and only does thos when driven for a while. Figure the rear end oil heats up at that point and then fails causing these issues. As far as parking brake goes, it does not work, possibly an issue w this as well.
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Former Vendor
Joined: Aug 2006
Posts: 76,656
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Molly's other thread described the car as driving on gravel which made me think clutches before trailing arm bearing.
Hopefully one bottle will do the trick if not then add a second.
But you all know it could be many other things causing this noise. The key is what I call duck waddle out of the corner. If you are felling this in the car with the noise then odds are it's the clutches. If not it could be a rear bearing, parking brake springs/hardware or something else.
Imho,
Willcox
Last edited by Willcox Corvette; Sep 15, 2014 at 09:20 PM.
Instructor
Joined: Nov 2008
Posts: 112
Likes: 8
My 79 was making the kind of noise you're describing. It was especially bad when I would start off very slowly. It would pop and snap and you could actually feel it through the car. I sucked out all of the old lube and added 2 bottles of GM Posi Additive then topped it off with GM Positive Traction Gear lube.
I then took the car to an empty parking lot and did some low speed figure 8's for about 15 minutes. Quite as a mouse.
One more thing. That was about 20K ago and it's still quite. My Vette was my only ride for several years just like you. I've clocked over 100K on it over the last 25 years.
Hope this helps.
I then took the car to an empty parking lot and did some low speed figure 8's for about 15 minutes. Quite as a mouse.
One more thing. That was about 20K ago and it's still quite. My Vette was my only ride for several years just like you. I've clocked over 100K on it over the last 25 years.
Hope this helps.
Melting Slicks
Joined: Apr 1999
Posts: 2,010
Likes: 3
From: Moon Twp. PA USA
1979 Vette, thought I have a bad rear wheel bearing. Heard a grinding noise when movimg from a stop when making a turn, on occasion. Also hear a whomp whomp sound on occasion when making turns. Noticed this occurs when car is on the road for a little. Read could b posi low fluid. Remember mechanic topped it off 3 months ago. Called him I asked about the top off. He used regular gear oil. I am beyond upset and worried. Ok I see an additive and fluid is available on line. How do I get the old oil out without ripping the rear apart? What to do? My only car! There is no drain plug and the rear cover holds suspension components in place. I will call myself a novice. I believe this wrong fluid thing is the cause of the horrific noises I hear on occasion. They are not that bad but any noise scares me as it always costs cash I dont have!
Did the noise start right after he added the "wrong" (regular) gear oil and how much did he add?
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,850
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I always use the GM gear oil.... but I have customers that use regular gear oil and then use the GM additive. The GM additive is of no equal in my opinion.. and this must be the same for others too because we have Ford and Beamer customers that buy the GM additive from us by the case.
Willcox
Pro
Joined: May 2013
Posts: 672
Likes: 31
From: Rapid City South Dakota
Absolutely... considering the car was in for a fluid change already. It's possible the clutches were already sticking.
Molly's other thread described the car as driving on gravel which made me think clutches before trailing arm bearing.
Hopefully one bottle will do the trick if not then add a second.
But you all know it could be many other things causing this noise. The key is what I call duck waddle out of the corner. If you are felling this in the car with the noise then odds are it's the clutches. If not it could be a rear bearing, parking brake springs/hardware or something else.
Imho,
Willcox
Molly's other thread described the car as driving on gravel which made me think clutches before trailing arm bearing.
Hopefully one bottle will do the trick if not then add a second.
But you all know it could be many other things causing this noise. The key is what I call duck waddle out of the corner. If you are felling this in the car with the noise then odds are it's the clutches. If not it could be a rear bearing, parking brake springs/hardware or something else.
Imho,
Willcox
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
The GM positraction additive is a 'friction modifier'. Without it, there is too much friction between the posi plates. A brand new [1970's] GM differential will likely do the same thing if the additive isn't included in the lube.
The brand of differential lube isn't critical (speaking of organic gear lube products); they are all very similar in their makeup and performance. But, the additive is needed to get the friction coefficient of the lube mixture to be what those clutches need.
Using synthetic differential lube may be somewhat different. I've heard (but do not have personal experience) that synthetic lube alone might work without the additive. I would be interested in knowing whether folks using synthetic lube include the GM additive...or not.
The brand of differential lube isn't critical (speaking of organic gear lube products); they are all very similar in their makeup and performance. But, the additive is needed to get the friction coefficient of the lube mixture to be what those clutches need.
Using synthetic differential lube may be somewhat different. I've heard (but do not have personal experience) that synthetic lube alone might work without the additive. I would be interested in knowing whether folks using synthetic lube include the GM additive...or not.
Last edited by 7T1vette; Sep 16, 2014 at 10:57 AM.
Pro
Joined: May 2013
Posts: 672
Likes: 31
From: Rapid City South Dakota
The GM positraction additive is a 'friction modifier'. Without it, there is too much friction between the posi plates. A brand new [1970's] GM differential will likely do the same thing if the additive isn't included in the lube.
The brand of differential lube isn't critical (speaking of organic gear lube products); they are all very similar in their makeup and performance. But, the additive is needed to get the friction coefficient of the lube mixture to be what those clutches need.
Using synthetic differential lube may be somewhat different. I've heard (but do not have personal experience) that synthetic lube alone might work without the additive. I would be interested in knowing whether folks using synthetic lube include the GM additive...or not.
The brand of differential lube isn't critical (speaking of organic gear lube products); they are all very similar in their makeup and performance. But, the additive is needed to get the friction coefficient of the lube mixture to be what those clutches need.
Using synthetic differential lube may be somewhat different. I've heard (but do not have personal experience) that synthetic lube alone might work without the additive. I would be interested in knowing whether folks using synthetic lube include the GM additive...or not.
Last edited by lurch59; Sep 16, 2014 at 11:32 AM.
Advanced
Joined: Aug 2010
Posts: 87
Likes: 0
From: Brunswick GA
I thought I was the only one crazy enough to have a C3 as my only car (going on 5 years now) 
I started hearing a similar clunking sound coming from my rear end a few months ago, especially when turning slowly around corners. I freaked out thinking my rear bearings had reached their limit. A fluid change in the diff was all it took to get rid of that. Thankfully a cheap fix (for once).
I would try this before replacing more expensive parts.
I started hearing a similar clunking sound coming from my rear end a few months ago, especially when turning slowly around corners. I freaked out thinking my rear bearings had reached their limit. A fluid change in the diff was all it took to get rid of that. Thankfully a cheap fix (for once).
I would try this before replacing more expensive parts.
Thread Starter
Intermediate
Joined: Jul 2014
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From what I remember, he used the I believe sae 80. He had the rolling gear lube canister (forgive my ignorance) he pumped it like 6 times or so if that makes sense. My thing is that it was 3 months ago, wrong fluid. I have a posi rear end and I am told there is special fluid for them. Mind you all I know about a cars rear is its the cars rear. I guess I am praying a fluid change would fix this but if symptoms sound like something else then augggggggh!
Race Director
Joined: Apr 2009
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From: Charlotte NC