New driver, first MOT question

Over by there

Finding a good garage is a mare. Once found though they are a godsend.

Regards the screen wash, I believe it is still an offence if found empty (no points).

Chance of getting caught though....nil?

car-man

I assure you that brake discs do actually warp or "bend" If you put a dial guage on a bent "warped" disc you will see quite a difference in how out of line or true they are.
You get the shudder because the disc are actually wobbling.

Matt_C

Absolutely right.

It comes from the build up of pad material on the disc. It's not the disc itself that's bent. The wobble effect is the centrifugal force of the uneven disc rotating in a clamping caliper.


I suspect to the OP, if your car is constantly "warping" discs (it's not, it's just that's what everyone calls the effect) then your calipers are the problem. I have the same problem with my car currently - the off-side front caliper is "sticky" so it keeps a small amount of pressure causing the pads to stay in contact with the disc. Not enough to apply braking force, but enough to a) prematurely wear the pads and b) build up deposits on the disc, giving the "warped" effect. What happens is when you brake down from a speed to a stop, both the disc and pad heat up, and when you stop with your foot still on the brake, a small mount of pad material is "burned" into the disc (it's not actually burned in, that's just the best way to describe it). This creates and uneven surface on the disc, making it wobble or judder under breaking. Under normal use, this excess pad material is removed during the next braking application, but when your pads constantly touch the disc it builds and builds and it never removed, giving the indication of warped discs. It's why they feel great after new discs are fitted (usually with new pads) then not too long after the same effect comes back.

My first port of call would be to have the slider pins on the caliper carriers changed. Simple, easy, inexpensive job. Anyone with a basic socket set and a jack can do it on the driveway in an hour or so (less if it's not your first time). If that doesn't solve it, then you'll want to look at the caliper itself. Calipers do fail, just so happens it's a common fault on my car. I've already had new discs and pads - problem came back. New sliders - problem came back. Pads on drivers side wore much quicker than passenger side, good indication it's only that caliper, but to be sure I'll change both before, or during, it's next service in a couple months.

car-man

This is a brake manufacturers take on warped discs, it mentions that the discs are wobbling.
As I mentioned, new discs and pads should be bed in properly and the run out checked using a dial gauge. Perhaps bent was an unfortunate term, the other term I used was out of true which is correct.
Brake Judder | Delphi Auto Parts

mjn

Stop-Tech know a thing or two about braking

The Myth of Warped Brake Disks - Interesting Read from Stoptech

A good read.