2G Soft Scraping Sound

[froodawg]

Wow.

I'll try and keep this brief with a little background information and current situation. I'd appreciate any and all feedback to resolve this issue.

My '97 awd tsi (w/abs) is my daily driver. Roughly a month ago, I began noticing some significant pulsation under brake. With colder weather coming, and no easy place to work on my car myself, I had a free quote given to me at a local shop. During the inspection, the mechanic takes me over to the car (currently up on the jack) and begins to spin my wheels to draw attention to a scraping sound on my driver side front wheel. He did the same on the passenger's side, with no audible noise. I was told I needed new rotors/pads and a new wheel bearing for my driver's front wheel. I was already expecting the rotors and pads, but a little shocked by the bearing. Quoted $800.

I purchased new pads/rotors and a hub assembly online for ~$200; installed them myself today in under 4 hours, three of which was spent pulling the old hub assembly (rust). I took the car for a drive to break in the pads, only to find that the scraping sound had not gone away. The pulsation is gone, and there are no other noises to speak of, even when braking.

In trying to diagnose the scraping further, I've managed to confuse myself into thinking this might be a drivetrain issue. If an awd car can't be towed by pull, how was the mechanic able to spin single tires without the others moving or locking the differential? I really need to find what's causing the scraping sound so I don't end up replacing my pads and rotors again soon.

The sound in question is similar to a pad making constant light contact on the rotor. Caliper pistons and seals look decent, caliper pins have been cleaned and greased, and the dust shield is well clear of the rotor.

 

[Dsmkauai]

Could you kindly remove the unnecessary swearing!! It's very unpleasant and has nothing to do with your problem. Anyways is the dust shield hiting the rotor anywhere? How did the caliper piston feel when pushed back in. Could be a bad/sticky caliper, and it's causing the pad to hang on the rotor alittle.

 

[farmer890]

The sound in question is similar to a pad making constant light contact on the rotor. Caliper pistons and seals look decent, caliper pins have been cleaned and greased, and the dust shield is well clear of the rotor.

He says it's clear.

So the noise didn't change places/volume? Maybe post a video.

 

[Dsmkauai]

Would still double check. Oh with the new brakes did you use new hardware or the old? I've seen the hardware sticking out alittle before and rubbing the rotor. Made a horrible scrapping noise . A video would really help. You can always put the car up on all 4's and run it in the air.

 

[froodawg]

I'm 100% certain that the dust shield is clear. I reused my old brake hardware; my local Autozone shipped the wrong kit to the store today, so I didn't have a new kit for the install. The noise doesn't change in pitch or volume, and is constant when the wheel is rotating. I would consider making a video, but I only have 2 jack stands. Would it be safe for my drivetrain to spin a single wheel?

 

[Dsmkauai]

I bet it's the hardware bro. Take the pads out and look close to see if it's pushed against the rotor in some place. Another sign would be a mark or line on the rotor where it's touching. With both front tires off the ground you can spin the tires by hand since it's a open diff. Definetly can not run the car this way.

 

[froodawg]

As long as it's alright to spin the wheel with just the front two off the ground, that'll make this a bit easier. I'm going to order a new hardware kit and try that out. Hopefully, with a few days of driving while waiting for the kit to arrive, any telltale signs will present themselves and steer me in the right direction.

On a side note, there's something that I found more curious than unsettling. At the end of the axle there's the teeth that grab the hub (splines I believe?), and immediately behind them there's another (much wider) set of teeth meant to fit to the backside of the hub assembly. If the back of the hub assembly isn't grooved for teeth, what purpose do those teeth serve?

 

[Justin Lauscher]

It's probably not safe, but I have put my car on two jackstands on its side and only the two drivers side tires were spinning. You could try it but I wouldn't advise it. Haha. Well put some WD 40 or some lube on your rotor that's making noise and that will tell you if its a sticky caliper because the sound will go away for a little bit.

 

[DogWhistle]

... and immediately behind them there's another (much wider) set of teeth meant to fit to the backside of the hub assembly. If the back of the hub assembly isn't grooved for teeth, what purpose do those teeth serve?

Those "teeth" are counting tabs for cars equipped with ABS. They might still sell axles without these, but most of the axles now, have those tabs, since they work for both ABS and non-ABS cars.

 

[Teezy]

Have you checked your splash gaurds inside the fender?

 

[froodawg]

Thank you, DogWhistle. This ABS sensor design would also help to explain the high level of corrosion behind the hub assembly. I can see that being an easy place to trap water and salt because of the counting tabs.

Teezy, the splash guards are clean and secure on my driver's side. My passenger side, not so much. Broke a couple clips when I took out my IC to clean it The sound is strictly limited to the driver's side wheel when rotating.

 

[estoyaqui30]

Froodawg, does it make the noise only when actually driving, or also when the car is up on jack stands? I'm just think and grasping at straws of what could be causing it. Thinking all of the moving parts and if it's only when the car is on the ground and driving ....I would try swapping front and rear tires.....I know it seems crazy, but I would want to replace every part that moves. I've heard of tires going defective and make creaking noises.

 

[pauleyman]

You guys are over thinking the spinning tire thing. Spinning tires by hand, even only two, is fine. I wouldnt start it and try to have two run. Real good way to knock the car off the stands

 

[froodawg]

Updated-

Snowstorm underway here, I wanted to get things checked out before the snow hit. I took off my driver's side wheel, pulled up the caliper housing, removed the pads, and replaced pad clips. With both front wheels in the air, I started rotating the hub (rotor in place, held in with nuts) to listen for change in sound. Unfortunately, I could still hear the same scraping sound. I pulled the caliper bracket and rotor, repeated, with no change. This hub didn't make any noise before I installed it, and as best I can tell, the sound isn't coming from the axle. Bummed out, and I don't have a spare hub to swap in and re-test.

 

[oneslowwdsm]

If it's not so bad, I would just rock it. You replaced everything that's moving so it shouldn't be anything safety related. My car has had a very soft scraping sound for years while moving that you can only hear when driving along side another car. I replaced everything that moves so I know it's not anything major.