Front disc overheating and causing vibration
Discussion
After about 10 miles at speed I'm picking up vibration and lots of pulsation in the brake pedal. It is sometimes so pronounced I have to slow down. I thought I had a flat tire one time, but now I know it's the disc. I've taken temp readings and the passenger side is much hotter than the driver side disc.
A few times I've just really pressed the brake pedal hard and the vibration oddly goes away. Strange, eh?
Today I pulled the wheel off and pulled out the pads, etc. and I really didn't see anything out of the usual. The link opens a series of photos and it will take a few moments for them to all load (please be patient). Any tips will be appreciated!
Regards from Nashville,
Dogsharks
http://www.network54.com/Forum/message?forumid=426130&messageid=1126987073
http://www.network54.com/Forum/message?forumid=426130&messageid=1126987073
A few times I've just really pressed the brake pedal hard and the vibration oddly goes away. Strange, eh?
Today I pulled the wheel off and pulled out the pads, etc. and I really didn't see anything out of the usual. The link opens a series of photos and it will take a few moments for them to all load (please be patient). Any tips will be appreciated!
Regards from Nashville,
Dogsharks
http://www.network54.com/Forum/message?forumid=426130&messageid=1126987073
http://www.network54.com/Forum/message?forumid=426130&messageid=1126987073
Hi Dogsharks,
That is the oddest thing. From the pictures there is surface rust showing on the lower half of the disk, and the top portion is shiny. I'm not sure whether this is a feature of the picture, or if it actually looks like that.
From your description, I would be looking at the wheel bearing/stub axle rather than the disk and pad. Your description of the vibration going away when you apply the brakes makes me suspect that it's something in this area.
Have you checked the runout on the disk? That's the first place to check if you think that you have a problem with the disk.
I hope that this has given you food for thought, although we all know how hard it is to diagnose a fault over the internet. It's only slightly easier than trying to do it over the phone
Cheers
James
That is the oddest thing. From the pictures there is surface rust showing on the lower half of the disk, and the top portion is shiny. I'm not sure whether this is a feature of the picture, or if it actually looks like that.
From your description, I would be looking at the wheel bearing/stub axle rather than the disk and pad. Your description of the vibration going away when you apply the brakes makes me suspect that it's something in this area.
Have you checked the runout on the disk? That's the first place to check if you think that you have a problem with the disk.
I hope that this has given you food for thought, although we all know how hard it is to diagnose a fault over the internet. It's only slightly easier than trying to do it over the phone
Cheers
James
I think James was closest.
It looks like new pads have been fitted to reasonably well worn discs. The discs have developed a curve on their face (check this with a metal straight edge) and the new pads are only contacting in the 12mm band near the hub (see the bit that's a darker colour). You can also see evidence of this on the pad face.
Because all of the braking is going through this tiny area, the heat being produced is way off the scale and the disc is, at best, giving Disc Thickness Variance (the surface goes corrugated as the heat loss over internal webs is less than that between webs) or the disc is warping under the heat. If the frequency of the pulsing is one per revolution then its warping, if its a higher frequency, even at low speeds, its DTV.
Your options would be...
1) Get the discs reground so that the surfaces are flat.
2) Get new discs
If you do go for option one and the discs have warped, they will continue to warp when they get very hot, like on a track day. For road use they should be fine.
After getting the discs machined or replaced, sand the pad faces flat before fitting them or you will generate the same problem but from the pads' concave faces.
Its vital to bed new pads in before using them in anger. This does two things.
1) It helps them form to any irregularity in disc surface flatness, without generating excess heat.
2) It ensures an even coating of pad resin on the disc, which is vital for even, judder free braking.
It looks like new pads have been fitted to reasonably well worn discs. The discs have developed a curve on their face (check this with a metal straight edge) and the new pads are only contacting in the 12mm band near the hub (see the bit that's a darker colour). You can also see evidence of this on the pad face.
Because all of the braking is going through this tiny area, the heat being produced is way off the scale and the disc is, at best, giving Disc Thickness Variance (the surface goes corrugated as the heat loss over internal webs is less than that between webs) or the disc is warping under the heat. If the frequency of the pulsing is one per revolution then its warping, if its a higher frequency, even at low speeds, its DTV.
Your options would be...
1) Get the discs reground so that the surfaces are flat.
2) Get new discs
If you do go for option one and the discs have warped, they will continue to warp when they get very hot, like on a track day. For road use they should be fine.
After getting the discs machined or replaced, sand the pad faces flat before fitting them or you will generate the same problem but from the pads' concave faces.
Its vital to bed new pads in before using them in anger. This does two things.
1) It helps them form to any irregularity in disc surface flatness, without generating excess heat.
2) It ensures an even coating of pad resin on the disc, which is vital for even, judder free braking.
THANKS FOR THE COMMENTS GUYS, but one thing I need to correct, is the "rust" on that disc. That an illusion that shows up on the photo only. Rest assured, that disc is uniformly polished all the way around.
If there is a bearing runout problem, I should be able to tell by tugging on the wheel especially if the car is up on a lift.
keep those cards and letters coming in.
Regards, Dogsharks
If there is a bearing runout problem, I should be able to tell by tugging on the wheel especially if the car is up on a lift.
keep those cards and letters coming in.
Regards, Dogsharks
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