How to tell the difference between a bad rotor or wheel bearing?
10-06-2008, 03:54 PM
#1
Le Mans Master
Thread Starter
How to tell the difference between a bad rotor or wheel bearing?
Title says most of it. I have a vibration under high speed braking. It is not noticeable on the street, only under threshold braking at 100mph+. I was could swear I felt it at the peak of an elevated turn where the car got light. Outside of braking, I don't fell any general sloppyness. I had a bearing fail on my once and it made noise. I don't hear a noise this time. I originally thought for sure it was the rotor, as I didn't bed the pad properly, but now I am not so sure.
Any easy way to tell if it is the rotor glazed or if it is a bearing? Or do I just have to go through process of elimination? I guess I would always use the rotor again, if it didn't turn out to be the rotor. Just posting to see if I am missing the obvious before I start tearing things apart?
Any easy way to tell if it is the rotor glazed or if it is a bearing? Or do I just have to go through process of elimination? I guess I would always use the rotor again, if it didn't turn out to be the rotor. Just posting to see if I am missing the obvious before I start tearing things apart?
10-06-2008, 04:14 PM
#2
Burning Brakes
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St. Jude Donor '08-'09-'10
I had bad shudder at the end of a track day and first thought I lost some wheel weights.
- Problem was still there on street tires and I then removed the calipers, checked all pads and cleaned the rotors with break cleaner; slight change.
- I tried pulling/pushing the tire at 12/6-o'clock but I could not feel any play.
Turning the front rotors fixed it. (stock)
My 2c.
/Nik
- Problem was still there on street tires and I then removed the calipers, checked all pads and cleaned the rotors with break cleaner; slight change.
- I tried pulling/pushing the tire at 12/6-o'clock but I could not feel any play.
Turning the front rotors fixed it. (stock)
My 2c.
/Nik
10-06-2008, 04:54 PM
#3
Tech Contributor
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Sometimes the rotor will thump quite badly just before it cracks. I had one that started thumping in the middle of one session at the Glen and when I inspected it I didn't see anything. During the next session it started thumping very badly and upon inspection I could see a little ridge running from the center of the pad area to the edge of the rotor. I let the car cool down for about 20 minutes and that little ridge turned into a full blown crack.
Bill
Bill
10-06-2008, 04:58 PM
#4
Melting Slicks
Sometimes the rotor will thump quite badly just before it cracks. I had one that started thumping in the middle of one session at the Glen and when I inspected it I didn't see anything. During the next session it started thumping very badly and upon inspection I could see a little ridge running from the center of the pad area to the edge of the rotor. I let the car cool down for about 20 minutes and that little ridge turned into a full blown crack.
Bill
Bill
yep........ Same experience.Jim
10-06-2008, 05:08 PM
#5
Instructor
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Had the right front rotor do the same. Third session of the day I noticed slight thump under braking from 125 on the straight at Roebling. Session four it got worse showing in other places, after cool down and drive home it was a full blown crack across the rotor.
10-06-2008, 05:15 PM
#6
Drifting
Sometimes the rotor will thump quite badly just before it cracks. I had one that started thumping in the middle of one session at the Glen and when I inspected it I didn't see anything. During the next session it started thumping very badly and upon inspection I could see a little ridge running from the center of the pad area to the edge of the rotor. I let the car cool down for about 20 minutes and that little ridge turned into a full blown crack.
Bill
Bill
10-06-2008, 05:47 PM
#7
Le Mans Master
Thread Starter
This is different. I have had that thump, several times. The rotors are almost brand new (2 day). The only explanation...if it was the rotor, was that I did not bed the rotor in correctly, as I had to change the rotor at the race track in between hot sessions, and simply went out a ran a full session, with no regard for proper bedding. But I can't see not properly bedding in a new rotor actually causing an issue such as vibration??? I have not bed in pad/rotors properly before due to circumstance (at the track) and have not had such a vibration.
I guess I will just have to change the rotor in question and give it a shot. Problem is that I can't get it to happen on the street under 100mph and I am not going to break laws to test a mechanical problem.
I only had one bearing go bad and it was easy to pick out...would a bad bearing only cause problem under say heavy braking, but no where else?
I guess I will just have to change the rotor in question and give it a shot. Problem is that I can't get it to happen on the street under 100mph and I am not going to break laws to test a mechanical problem.
I only had one bearing go bad and it was easy to pick out...would a bad bearing only cause problem under say heavy braking, but no where else?
Last edited by 95jersey; 10-06-2008 at 05:53 PM.
10-07-2008, 11:01 AM
#8
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This is different. I have had that thump, several times. The rotors are almost brand new (2 day). The only explanation...if it was the rotor, was that I did not bed the rotor in correctly, as I had to change the rotor at the race track in between hot sessions, and simply went out a ran a full session, with no regard for proper bedding. But I can't see not properly bedding in a new rotor actually causing an issue such as vibration??? I have not bed in pad/rotors properly before due to circumstance (at the track) and have not had such a vibration.
I guess I will just have to change the rotor in question and give it a shot. Problem is that I can't get it to happen on the street under 100mph and I am not going to break laws to test a mechanical problem.
I only had one bearing go bad and it was easy to pick out...would a bad bearing only cause problem under say heavy braking, but no where else?
I guess I will just have to change the rotor in question and give it a shot. Problem is that I can't get it to happen on the street under 100mph and I am not going to break laws to test a mechanical problem.
I only had one bearing go bad and it was easy to pick out...would a bad bearing only cause problem under say heavy braking, but no where else?
10-07-2008, 11:14 AM
#9
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If you are running a track alignment check the inside edges of your front tires, you may be cording causing a bad vibration in heavy braking. Happened to me at NJMP a couple of weeks ago.
10-07-2008, 12:05 PM
#10
Le Mans Master
Thread Starter
Tires are brand new. I actually did cord that last set in the inside, but no vibration. It's not like it happens at high speed and the tires are unbalanced. I can do 150mph and no problem.
I am going to change the rotor this week and look over the entire front suspension. If it happens at my next track event, then it's got to be a bearing.
I am going to change the rotor this week and look over the entire front suspension. If it happens at my next track event, then it's got to be a bearing.
10-07-2008, 12:22 PM
#11
Melting Slicks
I had new NAPA rotors with maybe 2 weekends on them.
I went to get gas the 2nd morning at the track and then drove to the grid with no problems. Pulling out of the grid onto the track I got on the brakes a little to warm them up and I felt a flutter in the car. Nothing when I let off the brakes. I thought I might have corded a tire (as these were pretty used up) or I ran over something when going to get gas and a tire was goind down.
I had to drive 3 miles around the track to get back to the pits. I asked someone to look over my car - thinking it was a tire. He said they all looked ok so I went back out. The flutter became less the hotter the brakes got but it was always there when I got on the brakes. It wasn't a shudder and I couldn't really feel it through the steering wheel.
I ran one more session with the car doing the same thing. I probably shouldn't have but I didn't see anything "obviously" wrong between sessions and there weren't any strange noises or wobbly tires when I pulled/pushed on them.
After lunch I looked at the brakes and found a huge crack from center to outside edge of left front rotor. Lots of small cracks in both front rotors.
I'd pull the rotors and check for cracks. You might have one on the inside that is hard to see. It might not be bad enough to feel under street driving conditions but shows up on the track.
I went to get gas the 2nd morning at the track and then drove to the grid with no problems. Pulling out of the grid onto the track I got on the brakes a little to warm them up and I felt a flutter in the car. Nothing when I let off the brakes. I thought I might have corded a tire (as these were pretty used up) or I ran over something when going to get gas and a tire was goind down.
I had to drive 3 miles around the track to get back to the pits. I asked someone to look over my car - thinking it was a tire. He said they all looked ok so I went back out. The flutter became less the hotter the brakes got but it was always there when I got on the brakes. It wasn't a shudder and I couldn't really feel it through the steering wheel.
I ran one more session with the car doing the same thing. I probably shouldn't have but I didn't see anything "obviously" wrong between sessions and there weren't any strange noises or wobbly tires when I pulled/pushed on them.
After lunch I looked at the brakes and found a huge crack from center to outside edge of left front rotor. Lots of small cracks in both front rotors.
I'd pull the rotors and check for cracks. You might have one on the inside that is hard to see. It might not be bad enough to feel under street driving conditions but shows up on the track.
