Mullin Motorsports

Hi, I've got a 2007 Z51 w/6spd auto. I noticed a strange creaking/growling noise when backing slowly out of my driveway. I thought it could be rear tires scrubbing. Could it be posi plates chattering?

There is no noise in forward gears, at any speed..

Dave

STANG KILLA SS

growling is often the discription of wheel bearings going out

extrapilot

Check the rear axle nuts also, a lot of reports that they come loose and make a creaking noise.
There is a TSB on this issue.

Mullin Motorsports

Thanks for the tips. I'll give it all a visual check out on the lift. Anyone know the correct procedure to find out if wheel bearings are shot, other than what we do on a front end, i.e.move the wheels in and out top to bottom, with no spring load?

Is there a web link to a Tech Bulletin on axle nut problems and/or torque specs?

As I stated, there's no noise whatsoever when in drive, only when backing and turning. Any other suggestions? U-joints, or CV joints maybe? I'm not familiar with the design and mechanical components in a C-6. I have put together a few C-3 rear axle assemblies, but I know they're nowhere near the same.

This is the same C-6 that had the trans re-programmed so 1-2 shift are really hard in drive. I guess it's possible that the constant hard shifts negatively affected CV joints or some other components.

Ring and pinion sound perfect. Brakes are perfect too. When I shift manually in Sport, and start in 2nd gear, the shifts are far more tame.

Dave

extrapilot

How many miles are on the car?
And yes, it could also be the rear diff clutch disc noise, if your hearing it while turning.
Give the nuts a torque of about 140 ft lbs. as a check. If they are loose, take the nuts off, clean the threads and re-install with red loctite thread sealer.
You have to do a check here about the TSB for the axle nuts, as there are different ones depending on the year, but like I said before I think that 140 is a safe torque.
I have read about a TSB having a new value of 160 ft lbs, but people have reported broken shafts with that higher torque, so don't do that.
As stated in a previous post, wheel bearing will generally sound off with a rumbling noise, and on higher mileage cars.

extrapilot

I remember reading about the hard shifting that was programed in your tranny by the PO.
I would think that could contribute to loosening things up a bit and maybe give the harmonic balancer a good workout, and BTW, if you read anything about our HB's, they are really poorly constructed, something I would be concerned about with that quick shifting feature.

Mullin Motorsports

It's got 50 K miles on it. I imagine that the rear axle posi unit has it's own source of fluid, like any other rear axle. It seems unlikely that it would share fluid with the trans. Or does it?

It's my experience that a chattering posi can be helped out by an oil change, (along with proper additives). Anyone got any experience with this on a C-6?

Dave

extrapilot

You are right, not a shared fluid, and many have had this problem, and yes a change will help if not eliminate the chattering.
Most like to us the GM LS rear diff oil.
50k is not much for the bearings, unless the car was subjected to adverse climates before your ownership.

Mullin Motorsports

I've seen some post on Harmonic Balancers going bad, what's up with that? We're talking about the units o the front of the crank shaft right? How is that affected by hard shifting? Are they separating, and causing a vibration in the drive line?

Dave

extrapilot

You'll get a ton of reply's here on this issue, as they are just not bonded together very well, and along with the under-hood heat, that doesn't help IMO.
If the stock one goes, there are usually replaced with a good after market one, like ATI.
IMO, shifting hard will create more testing of that bonding issue I spoke of and if it's on the weak side and think about all that inertia change that it needs to tolerate.
Hope this make sense to you, and again, this is my mechanical opinion.

Mullin Motorsports

Makes sense.. Can't hurt to check it out. Many older (meaning 70's etc.) GM bonded harmonic balancers have spun, so this is not news to me. Been around a while, LOL

We use an ATI on our race car. it's a nice piece. Even the best race balancers have a time limit on them before they must be checked out.

We just got this car, so I'm sure that I'll find some little stuff to fix. I wasn't to concerned about the 50K miles as it appeared to be very well maintained with good records, and it was affordable. It still drives like a Super Car should.

Now that I'm reading all the various high tech issues that can crop up, I'm almost wishing that I bought an older low tech C-3 (early 70's) like the previous five that I owned, but let's face it.....none of them were as good as this. What a great car in stock form!

BTW the car was in Florida first then only nice weather northern Indiana car. So happy a super **** guy owned it up north.

Dave

extrapilot

I never owned a c3 put have been behind the wheel of them a few times driving cars to auction from NJ to PA.
The C6 is so much a better car I feel, no regrets of ownership here from buying a used one in November of 2013 and making it a daily driver, 14K to 51K as of today.
Lot of smiles per miles..

codyc24

has the car been sitting for winter months and now making the noise? At my chevy dealer we take all the vettes once a week and do slow figure 8's in the parking lot to cycle the fluid around in the rear diff. Also if the fluid has never been changed at 50k then it def is a good idea to have that serviced. Here's what GM recommends for fluid

"SAE 75W-90 Synthetic Axle Lubricant (GM Part No. U.S. 89021677, in Canada 89021678) meeting GM Specification 9986115. With a complete drain and refill, add 4.7 ounces (140 ml), or 6.8 ounces (200  ml) for ZO6 Models, of Limited-Slip Axle Lubricant Additive (GM Part No. U.S. 1052358, in Canada 992694) where required"

rkj427

The attachments contain more than enough of the information you asked for................

John Harry

That is not correct. Since about 2009 GM has recommended Dexron LS Gear Oil 75W-90, part #88862624. No additive is required or recommended with it.

Mullin Motorsports

Now that I've done some research and based on my own experience, I'm confident that I have posi clutch chatter. I read all 7 pages of posts on this subject from 2010.

https://www.corvetteforum.com/forums...ing-noise.html

It seems that there were many opinions on which oil is better to replace the OEM fluid, Dexron LS vs Amsoil SD w additive..

Has the Amsoil Severe Duty Rear end oil and their additive proven better in the long term, over the GM Dexron LS, or are they about the same?

BTW....RJK427, Thanks for the links. They're invaluable.

Dave

Runsonboost

I also have an 07 z51 A6, with around 50k miles lol. I noticed the growling pulling out of the garage too. I thought maybe it was just a little exhaust drone, but haven't ruled out the diff. I'm going to change it out with the Dexron LS fluid since it's easy to find and not terribly expensive.

John Harry

Your research may have found many opinions, but I bet 90% of people on the Forum would say to use the Dexron.