Groan in rear end of C4

[c4rick]

I have developed a groan sound in the rear end of my 1992 Coupe. It is most notable when accelerating from stop. It goes away in a few seconds after accelerating. Don't notice it when accelerating at highway speed or on braking. A Corvette technician suggested it could be either the tires or rear wheel bearings. I just got new tires in January so that was not the problem. Any ideas for what this could be? Am I doing further damage by driving the car? Your help is appreciated.

Rick J. ;help

 

[78SilvAnniv]

Damage?

...well the groan is not normal and it could be causing undue wear and tear on whatever is not performing its duty.

My 78 had a rear end groan that turned out to be worn side yokes.
It would moan and groan (felt/sounded like the rear gears were binding up) at acceleration from a stop and when going around corners at slow speeds. My problem was so severe we needed to change out the rear end along with the side yokes.

Mechanics I was taking the 78 to were not able to diagnose the problem correctly. They thought it was an alignment issue. They did replace my rear tires after they said the 4th alignment fixed the problem and the new tires were chewed up within a month.

Check for excessive inner rear tire tread wear. I think you can also check for play in the side yokes by lifting the rear and trying to rock the wheel when holding it at 3 and 9 and also at 12 and 6.
If this is incorrect, would someone please post and correct?
Heidi

 

[paintdaddy]

On the early c4s they had a Factory groan due to the abs system .Somewhere in the late 80s or ealy 90s they fixed the groan because that was one of the customer complaints of the early cars.Whatever it was that they changed may have went bad in your car.My 88 does exactly that,it groans from a dead stop,but it usually only happens after its been sitting over night.Does this sound the same as what your experiencing?If so check it out.

 

[78SilvAnniv]

So...

...is this something that the C4s only need grease, maybe?
That would be nice to have a simple and quick fix!
H

 

[paintdaddy]

...is this something that the C4s only need grease, maybe?

Not if its the abs ,I would have to hear it to know for sure.

 

[c4rick]

Groan Continues

I had my wheels aligned when I got the new tires in January. It was not the alignment that was causing the problem since the groan is still there. I haven't driven the car enough on the new tires to see if there is inner tire wear. (I deliberately keep the mileage down. The car is not a daily driver.) Not being mechanically inclined, would the side yokes involve the wheel bearings? How big of a repair is replacing the side yokes? Thanks.

Rick J. :confused

 

[paintdaddy]

The side yoaks make a clicking sound when they go bad.If it was the bearings I think it would be a constant groan any time you were moving.You said it isnt noticeable when you speed up so I dont think thats it.I never claimed to be a mechanic so I could be wrong.If it was me I think Id replace the wheel bearings first and see if that does the trick.

 

[vader86]

Id check the bearings, mine were making a groan/creak noise and they were done.

If you replace the bearings, go ahead and replace the U-joints.

 

[slashnick]

vader,

the groan/creak you describe, was it like a sets of clicks just before you come to a complete stop and as you start from a dead stop? mine recently started doing this. i was told about a month ago that my bearings were starting to go out. this was based on the fact that there was very minor side-to-side play in the read wheels when jacked up. i checked again the other day, and there is no more play than there was a month or so ago. could this still be the bearings?

-matt

 

[vader86]

That sounds more like the U-joints than the bearing. U-joints almost always make a clicking sound, or cause a jolt when you put it in gear or D.

 

[slashnick]

i had the u joints checked, they were fine.

 

[c4rick]

The groan sound I have is just that, a groan sound. There are no clicks that I can hear. I really hear the groan when backing out of a parking space, stopping, and then start to accelerate from stop. No groan when accelerating at highway speed or when braking. The groan only lasts for a few seconds and then stops. There may be some groan when rounding corners but not a whole lot. Based on the comments in this thread it looks like it might be the rear wheel bearings. How expensive is this to fix, especially if I include the u joint?

 

[Hotred94]

I have two vettes--an 87 and a 94--and they both moan exactly the same. In the morning after a cold night, I back out of the driveway and as soon as I hit the street and start turning, they moan through the turn. Then, that is the last time they moan for the rest of the day no matter what kind of driving I do. I think it is the differential clutch. They get cold and they stick together, but as soon as they are pulled apart in the morning by turning into the street, they're freed up and don't make any more noise. I know my groans are not from wheel bearings or tires or u joints because I changed them all on the 87 and it stills makes the same noise.

That's my experience with groans.

 

[vader86]

I had a shop do the bearings and the U-joints on the halfshaft and driveshaft, i believe it cost me about $600.

Most of that was labor.

 

[vettepilot]

One of the problems that the C4s were experiencing was the lubricant in the differential. Try changing the diff. fluid, and make certain to add the GM posi-trac additive when re-filling.
The clutch plates in the posi unit had/have a tendency to produce noises ranging from a "groan" like you describe to a chatter or clunking noise.
Without actually hearing your noise it's difficult to trouble shoot over the internet, but your description of the noise makes me believe that is the problem. It's also the least expensive to take care of.
The C4s didn't have as many problems as the C3s did in respect to the wheel bearings, that's not to say they didn't have any problems, just didn't seem as prevalent.
Anyway, that's the route I would take first, (changing the fluid) then drive about 10 to 20 miles it to allow the GM additive to work into the clutch plates. It may take more miles than that, but you should begoin to notice a differance in the sound or lack of sound in about 20 miles, if that was what was causing the noise.
vettepilot

 

[c4rick]

Groan is not continuous

It sounds like the differential fluid might be place to start. The groan is not continuous when driving but I do have it throughout the day, especially when backing up and accelerating forward from stop. This virtually always causes the groan. If the fluid is not the problem, then I guess I will have to move on to the wheel bearings and U-joint. :eyerole

 

[first]

I have a groan but only when I start backing up.I read, and I believe on this site that for my year 91 6-speed this is normal.If I were to change the differential fluid do I add the the GM posi-trac additive when re-filling.I guess my question is how do I know if I have posi-trac.or do all vettes have it.

 

[Tuna]

I can't remember getting a 'groan' from my 92 but I remember that it was much quieter to drive after having the rear bearing replaced.

I'd suggest having the diff fluid checked as you had already surmised. While you're doing that, check the wheel bearings and U-joints for looseness. If the bearings are going bad, they could be the groan. My experience with the U-joints is that they start clicking as you roll to a stop or as you start off.

 

[vettepilot]

first,
All the C4s and C5s have posi-traction, I can't recall without looking it up just when all Vettes recieved the posi-traction rear diff. as standard.
vettepilot

 

[first]

Thanks Vettepilot. Since I am only just beginning with my Vette experience any info is helpful.I thought I would change all the fluids soon just because I don’t know if they ever were.