Light scraping/grinding noise, not speed proportional

[DecalService]

Hello folks,

I posted this once in the Facebook forum, but figured I should probably stop asking for mechanical advice there simply because one of the functions of a forum is to preserve the questions and answers.

I initially thought I had solved the noise issue by 80%, but as it turns out I was sadly mistaken. I was riding with the windows down and just couldn't notice it. I figured if anything, it would make the sound louder because I thought it was coming from the front passenger brakes. Either that, or fixing the brakes caused a reduction in noise but not completely.

my '89 C3-equipped XR has a scraping/grinding noise, almost like air rushing through a pipe, sounds like coming from under the seats/passenger side/under gear shift. It is NOT speed dependent or proportional - it comes on at around 5mph and vanishes completely, instantly, below that speed. Noise stays exactly the same from ~3mph onwards. At about 65 you can't hear it any longer, probably due to other noises covering it up.

Car is pretty and was bought on eBay not long ago. It was owned by a purportedly precise and careful guy recently who is an XR enthusiast. Aside from the condition of the front brakes, the car was delivered as expected. Below is what I've done so far:

*Spin wheels by hand while jacked up and check front brakes - rusted badly and scraping. Changed pads, caliper and rotor. Wheel spins silently now.
*Checked wheel bearings, carrier hub. They are essentially new and tight. Look like less than 5k miles on them at most.
*Drove at speed of 55mph, placed car in neutral - noise did not change one bit.
*Check center support bearing and guibo - minimal play.
*Car drives pretty much perfectly other than noise. No pulling, no shift delays, no slipping.

I'm at a loss. Should I jack the back end up and put it in drive to check? I really don't want to have my wife push the car in neutral while it's off to check to see if the noise is there, but if I'm all out of options, I just might have to.

I come from daily driving a W124, so maybe I'm just really sensitive to noises? I mean, that Benz was crazy quiet.

I appreciate any and all help and apologies for the long post

[DecalService]

So if anyone was following this or the FB post, and for the sake of wrapping up the issue for posterity, I jacked up the rear completely and put her in drive. The noise still exists but the more I listened to it I just can't tell if I'm being too sensitive about it or not. Havent driven a C3 in almost 20 years. Plus, there is BARELY any noise suppression beneath the shifter assembly, it's just an ultra thin layer of sheet rubber which I can pretty much poke my finger through, and I just came from driving a W124 daily, which was quiet as all heck. I guess I can conclude that since the C3 is shifting all gears as it should and fluid looks good, I can chalk it up to normal operating noise from an older design transmission. Gonna try to dynamat it a bit and see what happens. I just have to scrutinize a car more heavily before pulling the trigger, and drive it myself and decide if certain things will bug ME since I'll be driving it. Either way, thanks to everyone who helped, at least new brakes quieted it down significantly. Cheers!

[eaton53]

All I can say is mine doesn't make any noises like that.
It hates going 55, hunts for gears like crazy. Fortunately that's not the speed limit now... it would not have been tolerable back in the day.

[taylor0987]

Could it be the speedometer cable?

[Ed Lijewski]

All I can say is mine doesn't make any noises like that.
It hates going 55, hunts for gears like crazy. Fortunately that's not the speed limit now... it would not have been tolerable back in the day.

The gear hunting may indicate the downshift cable is improperly adjusted.

YMMV

[eaton53]

All I can say is mine doesn't make any noises like that.
It hates going 55, hunts for gears like crazy. Fortunately that's not the speed limit now... it would not have been tolerable back in the day.

The gear hunting may indicate the downshift cable is improperly adjusted.

YMMV

How difficult is the adjustment?
I get my routine maintenance done in the spring. I can have my mechanic look at it.

[reddy2300]

See if you can get it up on a lift, running, in gear and see if a mechanics stethoscope can isolate the sound. Noises from these drivelines are not normal. Could be the CSB, as well.

Btw, just because a part "looks new and feels tight" doesn't mean it's not at fault.

Best bet: Switch to a manual trans.

[Ed Lijewski]

All I can say is mine doesn't make any noises like that.
It hates going 55, hunts for gears like crazy. Fortunately that's not the speed limit now... it would not have been tolerable back in the day.

The gear hunting may indicate the downshift cable is improperly adjusted.

YMMV

How difficult is the adjustment?
I get my routine maintenance done in the spring. I can have my mechanic look at it.

Per the Service Manual it's straightforward (do you have the S.M.?).

YMMV.

[eaton53]

The gear hunting may indicate the downshift cable is improperly adjusted.

YMMV

How difficult is the adjustment?
I get my routine maintenance done in the spring. I can have my mechanic look at it.

Per the Service Manual it's straightforward (do you have the S.M.?).

YMMV.

I have Mike's CD just in case.
My mechanic is pretty familiar with the car, it's likely he'll know what to do when I ask him to look at it.

[DecalService]

Could someone explain to me what the planetary gears in transmission are doing when car is coasting in neutral? Are the spinning, or is only the output and input shafts spinning? I'm trying to rule out the transmission. But, again, the noise comes on at 5mph and stays the same even at high speed. No change in pitch or frequency.

I appreciate all the replies, as far as I can tell, the CSB is okay, BUT... I checked by jacking up the rear and putting car in drive to check noises. I am surmising that with tires down and driving under load, it makes sense that parts are more stressed and may cause noise. Spinning rear tires by hand while rear is jacked up doesn't reveal any noises, but with car jacked up and in drive I do hear it while inside the car. It's just not as loud.

I guess I'm trying to say that I've hunted for the noise using a variety of methods. I'm still on the hunt.

Car drives great, shifts correctly, no vibration, goes straight, stops, etc, but noise is still there. Sounds like air being forced through a baffled tube or something. I'm saying "grinding" for lack of a better term, perhaps "abrasion" or "constant turbulence" is a more apt description.

I already have an '86 Rapido 5-speed, and I bought another C3 on purpose. For one, my first XR was auto, and also sometimes you just wanna cruise and not do any work, ya know? I think that seller claimed C3 was rebuilt 40k miles ago. Not exactly yesterday, but not THAT old.

[DecalService]

All I can say is mine doesn't make any noises like that.
It hates going 55, hunts for gears like crazy. Fortunately that's not the speed limit now... it would not have been tolerable back in the day.

Mine shifts just fine, doesn't hunt, but it hates going 30mph. It's almost impossible. It's natural tendency is 35 which is not good for the city I live in. 30mph is enforced BIG TIME. I have to be extra careful. But, with that said, my 5-speed is also prone to want to avoid 30mph.

[eaton53]

All I can say is mine doesn't make any noises like that.
It hates going 55, hunts for gears like crazy. Fortunately that's not the speed limit now... it would not have been tolerable back in the day.

Mine shifts just fine, doesn't hunt, but it hates going 30mph. It's almost impossible. It's natural tendency is 35 which is not good for the city I live in. 30mph is enforced BIG TIME. I have to be extra careful. But, with that said, my 5-speed is also prone to want to avoid 30mph.

I am definitely going to look into getting mine adjusted. I'd be very happy with a small improvement.
If the C3 happens to blow up someday, it will not be rebuilt. I'll switch to Mike's 4-speed auto and make it invisible to all but the most astute.