My dodgey brakes

[Cemesis]

I'm still having problems with my brakes. It was fine for ages ( a week) and then the rain came down today and it was really bad. I go to brake and the brake pedal stops and won't go down, there is a grinding noise and almost no breaking and if you push it really hard it will finally go down. At first I thought it was the ABS because it was slippery but it isn't because it can occur as soon as you touch the pedal before any breaking really occurs and when it happens you loose almost all braking. It can be really bad with me frantically trying to stop the car.

It used to be only when I braked while steering and the revs would always drop down to 500rpm ish but today it would (sometimes) just do it in a straight line and the revs would be fine. It only ever does it at low speeds (less than 15mph) no matter what the conditions are.

HELP!!!!!!

The car is a GTE 16v H-reg.

[Orbital]

Ummm a very strange problem when you replaced the disks and pads did you replace the rubber pipes? if not check them and make sure they are not hocked on anything or got any other problems.
Have you taken a look at the pedel it could be jamming there. the brake light switch is under the pedel and if that is not going in it will stop the pedel from working.

[Andy.free]

Bad servo, or restricted vacume pipe maybe? This doesnt account for the grinding though. By the sound of it, it sounds like something is fowling something. I wouldnt drive it til you sort it mate!!

[Cemesis]

I just replaced the pads and discs and looking through the wheel the discs look fine.

I don't feel happy driving it but its only 5 miles to work tomorrow. I havn't looked under the pedal yet but it is like the piston under the brake pedal is getting stuck and then suddenly becomes free. I'll look tomorrow and give an update.

[Trevor]

Well I think this is more and more starting to look like a poorly performing servo unit.

The test you did proved that it was working, but not how well it was working. The fact that this is always at low revs is a bit of a give-away.

You did check the one-way valve in the vacuum pipe?

Can you remove a fuse or relay to switch off the ABS to see if it is that?

[Cemesis]

Thought of that, I removed the fuse yesterday and it did it regardless. The AMS warning light has never come one either. I didn't check the one way valve. Where is that?

I'm going to have the brake fluid checked tomorrow and will go through any pipes I can find.

Slow progress.

How much is a new servo unit and is it the large black flatish drum thing just infront of the steering wheel in the engine bay?

[Trevor]

Yep the thing the brake master cylinder is fixed to. There will be a pipe connecting it to the inlet manifold to it. In the pipe will be a bit plugged into it. That is the one way valve. you should be able to suck through it one way from the manifold side, and not the other.