Technical Punto brake problem

[pooroldcodger]

Hi all.
I've got a problem on the Mk2 8v Punto brakes. When you are coming up to a stop, you can feel as though you are actually braking, letting off, braking , letting off so the car lurches and doesn't stop smoothly. Coming to a stop off a motorway is much worse because of the speed.
I jacked the car up, and turned the wheel by hand, and you can feel that the resistance gets more and less on each rotation, so I am thinking maybe the disc is warped or something (pads and discs replaced last summer onky about 5k miles ago).
So I took the pads out today, and cleaned them up, and they look fine. I put the pads back in, rotated the disc by hand and the problem has gone!
But then I pump the brake pedal, and return the wheel by hand again, and the problem has come back.
Any ideas?

 

[malty123]

flexible hose to the caliper could be perished/ damaged, i had a similar problem where the caliper wasnt releasing properly, replaced the hose and all was fine

good luck

 

[pooroldcodger]

flexible hose to the caliper could be perished/ damaged, i had a similar problem where the caliper wasnt releasing properly, replaced the hose and all was fine

good luck

Thanks for the idea. It looks ok, but I didn't look too closely at it.
I will have a closer look.

 

[malty123]

Thanks for the idea. It looks ok, but I didn't look too closely at it.
I will have a closer look.

mine was perished on the inside so nothing was obvious visually,

i unscrewed the bleed nipple on the caliper to let out the pressure and the brake released..

 

[pooroldcodger]

Mine doesn't seem as extreme as that. You can still rotate the disc easily with your hand, but it just seems to hit soem resistance once every rotation. So when you are braking, this is translating itself into uneven brake pressure, which makes it feel like you are letting the brakes on and off when youn are coming to a stop.

 

[malty123]

Mine doesn't seem as extreme as that. You can still rotate the disc easily with your hand, but it just seems to hit soem resistance once every rotation. So when you are braking, this is translating itself into uneven brake pressure, which makes it feel like you are letting the brakes on and off when youn are coming to a stop.

sounds more like a warped disc

 

[pooroldcodger]

That was my first thought, but when I take the pads out, and then put them back in, the wheel spins ok, but once I have pressed the brake pedal and then try to turn the wheel again, it won't turn evenly.There is uneven friction.

 

[bredsticz]

Is there a lip on the disc at all? I know they weren't long since replaced but that was my problem and it was the brake pad, once the pedal had been pushed. Getting jammed in the groove of the disc

 

[pooroldcodger]

Is there a lip on the disc at all? I know they weren't long since replaced but that was my problem and it was the brake pad, once the pedal had been pushed. Getting jammed in the groove of the disc

Not that I could notice to be honest.
How did you solve it? New disc?

 

[red]

If there is a lip of rust, you can just scrape that off (e.g. hold chisel against rim while turning hub). Check also for rust in guides for pads. Scrape out and apply a smear of copper grease.

If necessary you could measure the runout of the disk (to see whether warped) but you'd need a dial gauge for that.

red.

 

[pooroldcodger]

I will check for the rust problem. I don't have a dial gauge for run out, but what about if I just put something solid (like an axle stand) virtually touching the disc, and then turn it? At least I will be able to see if the gap between the disc and the axle stand is changing or staying the same. Will that work?

 

[DaveMcT]

Dirt under a disc is also likely. Take the caliper off and look under the disc.

 

[pooroldcodger]

Ok thanks. I will try that.

 

[pooroldcodger]

sounds more like a warped disc

Just to wrap this one up, it was a warped disc.Thanks everybody.

 

[DaveMcT]

Make sure the new disc is running true. If its on a slight wobble it will overheat and warp like the old one. My front brake recently stuck on after replacing pads and discs. I took it apart and made sure the pads weren't sticking in their grooves and its been fine since.

Releasing the pressure by undoing the bleed nipple is pathopnemonic for a blocked hose. Id it was the piston seals or seized pads any pressure release would have no obvious effect.