Master Cylinder Causing Problems?

[commievid 8]

I apologise thoroughly if this has been answered before, but most of my search combinations are all pointing at usual suspects which I'm sure I've singled out.

 

Been battling the brakes for absolutely ages now, and now they're getting worse. Before, the front left was sticking, and one way to sort this out was to swap the pads over, which seemed to help bizarrely. But only for a while.

 

Now the fronts are sticking quite regularly, with the pedal getting very firm being the indication. Obvious signs are the car not rolling downhill, much more effort to accelerate, and of course bloomin' hot brakes (smoking yesterday). I swapped the front left with another refurbed caliper over the weekend. All four were replaced half a year ago.

 

I've thoroughly cleaned the slider pins, they look fine, they move with no issue, red rubber grease to lubricate. The caliper pistons push back in nice and easily, and hard brake lines replaced and HEL braided lines to the calipers.

 

However, yesterday when bleeding the brakes (pressure bleed via Eezibleed), I noticed that the rear right wasn't pushing out any fluid. The fluid was only coming out when the pedal was pushed and only when pushed.

 

Is it this caliper that's the issue, or is it, now that I'm guessing, the master cylinder? This was one of the first things I replaced, but I am guessing I must have bodged the installation, or damaged it since. I've read that pushing the brake pedal in too far could mess up the seals inside and I fear that's what I've done. Could the seals inside maybe prevent the brakes from backing off, causing them to act like they are half-engaged?

 

The usual suspects are being crossed off, as I've cleaned the sliders, replaced the calipers (one corner twice), using new lines and braided hoses, and probably used 3+ litres of brake fluid to flush multiple times.

 

One thing I wanted to do in the summer was to remove the ABS compensators, but with no confidence in the fronts it's becoming a bit exasperating as I don't want to continue if the fundementals aren't working.

[welshpug 1,646]

Sounds like a sticking servo or master cylinder.

[Anthony 1,002]

Check the clearance between the MC and the rod inside the servo.

 

If that's too tight you'll get issues with the brakes binding as it's effectively like you're gently resting your foot on the pedal. It would normally do the same on both sides though, not just one.

 

It's normally OK on replacement standard MC's but I know that it does occasionally cause issues when using different MC's like 406.

 

Other thing that can cause problems on a single side is a brake hose that's collapsed internally, as it ends up acting like a one way valve.

[Weser 30]

Other thing that can cause problems on a single side is a brake hose that's collapsed internally, as it ends up acting like a one way valve.

I have had this and cause my brakes to stick on another car. I know you have changed the flexible hoses on the calipers but what about the ones on the rear beam?

[commievid 8]

OK, replaced the master cylinder, still had the rear right not come out initially; played with the rear compensator (ABS one) and then started to come alive, few more taps to the compensator and now seems fine. Bled through a litre of brake fluid, will leave it for tomorrow to give it a drive. Really sick of these rear compensators now.

 

Quite difficult to check the clearance of the pushrod with a GTI6 engine in there, but it looked around the 22mm mark, and I think its between 22.2 and 22.4, so I think its fine. Haven't changed the master cylinder spec, so fingers crossed thats not it.

 

Is it possible for braided hoses to collapse in the same manner as rubber ones? If so, then thats one other possibility. I have another set of front disc and pads to use as the absolute final thing that hasn't been changed, should none of this have worked.

 

To be honest I haven't changed the hoses that go around the rear beam. Quite frankly too afraid in case something goes wrong and I'm left with no backup plan. My intent was to change out those ABS compensators for standard 1.9 ones and replumb the brake lines to suit, and I'll put the braided hoses on then.