brakes working except pass. side front!?!

[MarkSanne]

Yesterday I changed the front brake pads for new ones. Everything seemed perfect, until I was ready for a testdrive. The brake pedal felt supersoft. I haven't done anything with the brake fluid (except opening up the brake fluid canister before pushing back the brake-calipers/cylinders). The drivers side works good, both rear brakes too, except for the front passenger side brake which does nothing?! I can pump but no fluid comes out?! I've checked the hose, the hardline the goes onto the (I think) ABS distribution unit (all hardlines are connected to this one, FR, FL, RR, RL, S & P).

I've tried bleeding (sucking) the faulty side with one of those compressor-fed things that look a bit like a plant-water-pistol. I even tried forcing the fluid from the brake bluid canister by modifiying the top lid and putting almost 2 bar pressure on it. No joy what so ever.

I'm completely lost now and I really need to get it working by tomorrow... any ideas anyone?!

[Davezj]

are your brakes standard factory VR4 or brembo.
sounds like a blockage in a pipe or a piston is stuck, or a slide bolt stuck or broken, or a blockage in the bias valve.
can you push the pistons back on the caplier that is faulty
and can you slide the pad carrier back and forth on the slide bolts.

lots of question but need to be sure before you continue.

[MarkSanne]

are your brakes standard factory VR4 or brembo.

Standard factory vr4

sounds like a blockage in a pipe or a piston is stuck, or a slide bolt stuck or broken, or a blockage in the bias valve.

can you push the pistons back on the caplier that is faulty

yes, and I'd seen the brake fluid level rise when I did that. I did it gently by the way.

and can you slide the pad carrier back and forth on the slide bolts.

Yes, no problem, quite smoothly.

Thanks Dave, I'm hoping you might give me some clues where to look as I'm out

[Davezj]

so some sort of blockage in the pipe would be my guess,
if you can make up a temperary pipe or get someone to make one you could replace the existing pipe and check it that way.

better still disconnect pipe at caliper banjo union on back of it, see if you get fluid from there, when pump brake peddle, if not then,
you could remove suspect pipe from bias valve and see if fluid can be pumped from there, then you know the blockage is in the pipe to the caliper at some point. if not then,
it is probably a blockage in the bias valve which is mounter on the engine bay bulkhead kind of below brake servo and towards the middle car.

can you still move the pistons, eg pull them back out of the caliper.

if you are diconnecting brake pipe unions they can get stuck fast and you may end up rounding off the nuts, use a little WD40 (is flamable) get a blow tourch and heat the joint up (nuts) for 30 seconds then they should come undone, don't set fire to anything major.

[MarkSanne]

Well... been investigating and trying everything I could think of with the help of a friend (a mechanic) but we couldn't fix it. We narrowed it down to the master brake cylinder. Although we took it out, checked and cleaned it thoroughly and actually it looked perfect, the first 'chamber' (the one closest to the firewall so to speak) doesn't seem to be delivering any pressure no matter what we tried...

We also inspected and tested every single metal brakeline, tested (roughly) the inner workings of the ABS pump and all seemed well. Just getting brake fluid out of the first master brake cylinder chamber... So I think I'll try to find a replacement asap and see how it goes from there... If anyone has one: please let me know! Shipping to the Netherlands is not expensive nor troublesome And ofcourse I'm willing to pay a good price!

[The Vee]

Sounds like one of the pistons in the master cylinder is not returning. Does sometimes happen after fitting new pads, after the caliper pistons have been pushed back for the new pads you will get pedal travel to floor to get the pistons firm on the pad again. Problem occurs when the master cylinder piston travels much further than normal and sticks rather than returning for the next pump of the pedal. Sometimes a careful knock on the master cylinder with a hammer will shock it back. I take it the fluid level never went too low as for some reason Mitsi Master Cylinders can be right pigs to bleed through.

[Davezj]

so the initial diagnosis of only one corner having an issue was wrong and it was one complete circuit that was faulty. which is a front left back right combination or a front right rear lft combination that had the issue.
am i right in thinking the master cylinder is split into 2 circuits front and back, and these individual circuits run one front back pair and the other runs the other front back pair.

[The Vee]

Don't think his initial diagnosis is wrong, but looks like he's worked back to the master cylinder. Of course with that it may even be the piston seal is worn / split. Like all these things often a process of elimination

[Davezj]

I know, i was just backing up my initial diaganosis, given the information that was available at the time.
i don't like giving people incorrect advice.
but when your diagnising a fault it can be hard to tell some in text exactly what you mean and get the entire situation explained in it's entirety.
which is why i tend to waffle on, and on and on a bit.
LOL!

[Wodjno]

I know, i was just backing up my initial diaganosis, given the information that was available at the time.
i don't like giving people incorrect advice.
but when your diagnising a fault it can be hard to tell some in text exactly what you mean and get the entire situation explained in it's entirety.
which is why i tend to waffle on, and on and on a bit.
LOL!

Barry.. Can we have Waffle smiley please, especially for Dave.. Nearest we got is the Nag Smiley

[MarkSanne]

Anyway: your help and thinking along is much appreciated y'all!

And indeed: my initial diagnosis was wrong... the right rear brake didn't bleed trough. But it still functioned enough as a brake to fool me... after trying to bleed it, it was apparent it didn't work correctly too. Which makes sense as the left-front and right rear are on the same brake-'group'.

[MarkSanne]

Just to update this: a new master brake cylinder did the trick!