Front brakes binding

[marcus]

Just took my Mk 2 1985 1.8 GTL for MOT and it failed on 3 minor items that are easily rectified and one puzzling one... the front brakes are binding.

They're weren't binding on the way to the test centre and hadn't been binding before that, I'm guessing that in standing on them hard for the brake something has gone wrong - I could really feel them dragging on the drive back from the centre and the pedal has gone rock-hard.

The tester thinks if I take the pads out and withdraw, clean and lubricate the pistons all should be well but before I do, has anyone got any thoughts on this?

[hyperdrinky]

Testers have to stamp hard on the brakes during an MOT. If you're a conservative driver they may have pushed the calliper onto a rough part of the calliper slider which is causing them to bind.

An overhaul is definitely on the cards. As he said, check the piston but also check the calliper sliders for rust (the sliders are underneath the little rubber boots, one top and one bottom, connecting the calliper to the cradle).

Does anyone know if you can still get brake piston boot/seal kits these days? I think they made them illegal on newer cars due to health and safety fears (Grr!)

Hyperdrinky

[marcus]

I was wondering about the sliders... my worry was the master cylinder was implicated because both sides are binding equally (ie the car doesn't pull to either side).

Is it possible to inspect the sliders without dismantling the caliper?

Can the sliders be smoothed off (or should they be replaced) if they are rough?

[marcus]

Re repair kits, I phoned up my local branch of GSF in North London today and was told repair kits had been discontinued.

[PeteGLi]

Repair kits are available from here

http://brakesint.co.uk/brake_hydraulics.html

[marcus]

Thanks for the tip re repair kits, good to know they can still be obtained - there were only two ads in Practical Classics, both for British makes only (I'm sure that years ago there were many more ads for brake parts eg from Norton Servos and others...).

[marcus]

Just found the following too:

http://www.brakepartssuperstore.org.uk/ ... 12890.html

[marcus]

Despite having changed pads and discs before, I couldn't get my head around how the caliper assembly fits together from the Haynes diagrams, nor could I work out how the slide bolts work, or how it all comes apart and goes back together... but found some videos on YouTube, a four part guide to disassembling a caliper and unseizing a seized slide bolt and putting it all back together.

It relates to a '98 Jetta but it all looks pretty similar and really helped me understand how it all fits together (and the guy is quite entertaining with it...):

Part 1: http://www.youtube.com/watch?v=wSW0kMZl0AE covers removal
Part 2: http://www.youtube.com/watch?v=8b59R93_xM0 covers disassembly
Part 3: http://www.youtube.com/watch?v=YtwNNKj1tfI covers repair and reassembly
Part 4: http://www.youtube.com/watch?v=4CVyOJE0quo covers reinstallation

[Nate]

just have a quick check the tester didn't leave a torch or something on the link from the pedal to the master cylinder that is fouling and making it stick

[marcus]

Good tip but no such luck - was almost convinced it was the guide bolts, but took it all apart today and they seem fine...

Something was clearly sticking though, because the calipers weren't parallel to the discs - which would have been consistent with sticking guide bolts - and the pads are worn more at one end than the other. The difference is only about 1mm but was very noticeable visually.

I think maybe the pistons were sticking near the end of their travel and the MOT was just that bit too much - I'll need to pull the calipers apart at some point and either overhaul or replace them.

For the time being, I replaced the pads and discs, which I was going to do anyway, on the assumption that since the pads were worn down by 2-3mm each (ie 4-6mm the pair), and the discs by at least 2mm, that the new components would mean the pistons would have to travel 6-8mm less and therefore would be less likely to reach the 'sticking zone'.

I'll find out tomorrow, when I finish off and take it for a test drive...

[marcus]

Duh! When I said the calipers weren't parallel to the discs I meant the pads - for the calipers to be non-parallel some serious distortion of the carrier or hub assembly would be needed...

[marcus]

Well, I was wrong in a big way...

The car passed its MOT and I drove it 50 miles out to Essex, and intermittently the binding seemed to recur a little in the first few miles but I kept my speed down to 50MPH and all seemed well, no binding, brakes fine, pedal feel back to normal (ie a bit soft). When I inspected the discs and pads through the spokes of the alloys, all looked well.

Six miles into my return journey, the binding returned badly at about 45MPH as I accelerated onto the A12 and the car started to slow down. I reduced speed and changed down to keep going, knowing there was a service area a couple of hundred metres further along. As I pulled into the service area, white smoke began billowing from the front wheels. When I got out, both discs were glowing red hot (I mean actually glowing red).

Got the car back to London on the back of an flatbed recovery truck, first time I've used my AA membership in six years. The brakes were no longer seized by the time I got back and was able to park it normally.

Clearly, the pads will be ruined, but I'm hoping I haven't warped or cracked the discs - they're brand new Brembo Max grooved vented discs which I fitted only a week ago. The previous discs were vented but not grooved.

What else is likely to have been damaged by the excess heat? I'm guessing the seals must be suspect now (even assuming the calipers weren't at fault in the first place), the flexible hoses and the brake fluid.

What about the master cylinder and the wheel bearings?

I still don't know the cause of the binding - I'll take the calipers apart though their condition may no longer be as it was prior to this incident.

I read somewhere that flexi hoses can collapse internally, resulting in a one-way valve effect, but I'm sceptical about either hoses or calipers as a cause, as both brakes were binding equally (there was no steering pull, and both discs were glowing an equal shade of red), and it seems unlikely that the same fault could have occurred simultaneously and equally on in the same compenent on both sides.

Could the master cylinder have been the culprit?

Any thoughts much appreciated.

[bensspares]

marcus,

it sounds like the mastercylinder/brake servo to me.somehow its jamming,maybe an internal seal is causing the internal piston to jam.if both brakes are jamming on its nothing to do with the pipes or flexys as for both to jam it is almost certainly the mastercylinder.i may be wrong but its the most logical explination in my mind.

hope this helps

ben

[marcus]

Cheers for this, it does seem to make more sense it's one component further upstream, rather than two at the business end.

[bensspares]

here's a realy stupid question but,

were the breaks binding before you swopped the discs and pads ???????????????????????????????????????????????????????????????????????????????????????????????????????.