hi i was just wondering if any one could help i have a vetra (2001) 2.2 auto the front brakes get so hot that you are unable to touch the WHEEL for more than a few seconds i belive the pads are sticking on but here is where it gets complicated i have already changed the hoses / calipers / and master cylinder and still the problem persits the rear brakes are fine there is no pulling under braking but after one hour the fronts are so hot it afects the pads and they scream like you would not belive
Without seeing the car it'll be difficult to help I think. Brakes getting hot is normal to some extent, especially on an auto but the screaming isn't normal unless it's usual "normal" brake squeal. It could be you've got really crappy pads on there or there's some wheel bearing problems or something else entirely!
I had this same problem about a year ago with the brakes on a Suzuki. On just one front wheel, the disc brakes would overheat so bad the wheel would lock up. It happened at random and it happened several times. I consulted the gurus on the Usenet, none of which had answers that helped me [ That should not be interpreted as unhelpful, to the contrary there were lost of posts and lots of theories ]
The thing that really puzzled me, and still does, is what stops the pads from rubbing on the disc, when the hydraulic pressure is removed. The best story I heard was that the minute run out of the disc was enough to push the pads back and away from the disc ----- well, it sounded good anyway.
You said brakes, plural, which sounds to me like the hydraulic pressure isn't reducing to zero, when you take your foot off the pedal [ you're not a foot dragger are you? You do take your foot completely OFF the pedal? ]
OK. Enough. My solution, suggested by an 'old hand', was to take some of the material off the pads. That way the clearance, pads to disk, was increased. Sure enough the problem went away.
In retrospect, I may have caused my problem, I think I bought after market pads. Maybe I should have bought genuine Suzuki parts [ But, OH the cost! ] John Hewitt, Malaga, Spain
If you think back to high-school physics, this isn't too hard to understand. According to the Coulomb friction model, the friction (braking) force F, the force perpendicular to the pads N, and the coefficient of friction between the pads and the disc, u are related as follows:
F = uN
If you look at this formula, no run out is required, as when the force that is applied to the pads is zero (i.e. hydraulic pressure is zero) so will be the friction force. This is the case *even* when the pads and disc are touching. In reality there will more than likely be some run out on the discs, which will mean that the pads will be pushed out and only end up touching the disc at one point during the disc rotation, but this isn't the reason that the braking force goes to zero.
If you still have a problem believing this, think about a race car with carbon discs - as the car races the discs are rapidly worn away by the pads, removing any run-out that may be present every time the car brakes for a corner!
That's my thinking too. Of course if the pads are too thick for the calipers then that can't happen. *Sometimes* with new discs and new pads that can happen to some extent but you'd also have a tough time fitting them.
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