Mike J Youngquist

Hi all. My 1990 corvette automatic is making a weird grinding metal rubbing noise when I’m in reverse. It almost sounds like a brake pad grinding on the rotor. If I pull out of a parking space and start to back out I hear this metal rubbing sound. Then if I put it in drive and when I’m first gear I hear it again when I start moving forward for about the first 10 feet then it’s gone only while at slow speed in 1st. It’s more prominent in reverse. It sounds like brake rubbing but when I brake while driving it doesn’t make the noise at all. Sounds like it’s coming from the rear. Could it be the brakes? If so why only in reverse or 1st and no other times. Confused. Hoping it’s nothing major. Any input will be greatly appreciated. Thanks

Steve Garrett

Moved for your convenience....

Kevova

Have you had brake pads checked?

Mike J Youngquist

No. They seem to be working fine. Don’t grind st all when I come to a stop while regular driving. Could it still be the brakes? Is it possible just to do that when in reverse? I’m hoping it’s not my planetary gear.

hcbph

In addition to your brake pads have you checked that your parking brake is fully released? It could also be something like a caliper hanging up, see that before in other cars.

Mike J Youngquist

No I have not. Would that only make noise in reverse and 1st with those 2 things? How would I heck the parking break? Sorry I’m not too mechanically inclined lol.

arbee

Check your rotors! It won't take long to see if you have metal on metal contact from the pads.

Kevova

Well you have to start somewhere. Rust edge of wear surface of rotor can set up a noise. Noise in front or rear? There is a washer at rear hub which can cause a noise. From the transmission sunshell splines starting to strip.

Mike J Youngquist

Coming from the rear I believe. What are sunshell splines!

Mike J Youngquist

Nevermind just looked it up. I hope it’s not that. Can’t afford a tranny rebuild. It’s not a growl it’s like a metal rubbing sound. Now that I think about it if I brake I can sometimes make it louder or sometimes it stops the sound. But when starting to move in 1st it has no affect.

65Z01

Sounds like it's time to pull the rear wheels and check rotors for wear/pad binding and possible caliper issues.

Mike J Youngquist

I hope that’s all it is. I’m worried about my planetary gear now after a reply above. It’s real weird. Like I said I hear it in reverse more. And it louder when I’m backing out and turning the wheel. I hear noise from the rear anyway at low speeds almost sounds like exhaust rubbing but it speeds up and slows down with the car. I’m at a loss. U joints?? Wheel bearing? The wheel is solid when it’s jacked up. But I do notice a couple of small lines being worn on the rotor. I hear the metal rubbing sound in reverse and when taking off from reverse until like 5 to 10 miles an hour then it goes away. Also if car is warmed up it doesn’t do it as bad.

Mike J Youngquist

I noticed a grooved area on the passenger rear rotor. Where I believe the noise is coming from. On the second pic is from the driver rear. It doesn’t have that groove. Could this be an issue?

Drivers side. No grooved are on top.

hcbph

Nope. That's where the manufacturer balanced the rotors. Simple process (if you have the equipment) to remove a little material where needed to put them in balance.
try with the wheels off and the car supported, turn the rotors and see if you hear something. Also be sure to check the back sides of the rotors also for damage. My money is still on the problem being calipers or brake pads related.

Mike J Youngquist

Ok. It doesn’t sound like the planetary gear to you? Based on description or anything?

arbee

From your description above, I would suspect some component in the differential. Backing up would cause the pinion to act on the coast side of the ring gear. Also, you say it is louder when turning, suggesting the posi clutches are in play. When is the last time you checked the oil level?

Mdarnold00

My '87 has exactly the same issue. Sometimes it happens in reverse, sometimes when starting out in D, but always one or the other. Only happens at low speed and goes away after 10 - 15 feet as mentioned. Did you ever find the cause?

Paul Workman

I (and others) suggest you inspect your brakes - including the parking brake. Commiserating about it ISN'T going to fix the problem. It is nearly impossible (?) to pinpoint the issue from a description on the internet alone. At some point ya have to leave the keyboard alone and get your fingers dirty, OK?

Mdarnold00

I assure you, my hands have gotten dirty. Here's what I've done so far to try and isolate the issue.

• Changed rear rotors and pads
• New half shaft u joints
• Raised the rear end off the ground to isolate (no issues in forward or reverse when lifted and there's no weight on the back end)
• Removed parking brake shoes to eliminate any possible interference

None of these made any difference, so, like the OP, I'm unfortunately leaning toward the differential. The car's in storage now, but I plan to do a rear diff fluid change come spring, since I have no idea when or if it's ever been changed.