Engine running = crap brakes?

Today I changed the pad on my GSi (Early Calibra turbo calipers with 4 stud 285mm discs) - got both calipers off, found that the nearside one had a seized piston, took piston out, cleaned it up, checked the rubber seal (it was ok), put it back in and it moved as freely as it should.

Put new GM pads in, reattched calipers, decided to renew brake fluid because afaik it's not been done.
Opened front OS bleed nipple and pumped fluid out, took union joint off the NS caliper (Bleed nipple has broken) and pumped out the remaining fluid from there.
Put new Dot4 fluid in, pumped it through all 4 corners and pedal still went to the floor, thinking that maybe air might be trapped in the master cylinder we bled from where the solid lines join the master cylinder aswell - tried peddle for feel and it was fine - started engine and it went to the floor :evil:
Bled all 4 corners again and the master cylinder unions again (no air from any of them) and once again it was ok with the engine off but when it was running it was w@nk and went almost to the floor. I've adjusted the brake pedal up as much as possible to get as much of a peddle as I can and it has worked but the brakes are worse than before I started.

Any ideas on what to so next? I'm going to take the NS caliper off next week (my next days off) to try and replace the bleed nipple just so I can get it bled properly - but failing that any ideas?
:roll:

Sounds like the master cylinder could be playing up? Other than that i havent a cluee?

Keith

Yeah Keith i'm also thinking something is up with the Master Cylinder and / or Servo.
I don't wanna change either of them if it doesn't solve the problem, I'd rather know what it was first to save me buying both (and another caliper if I mess it up trying to get the remains of the bleed nipple out.....)
:roll:

Your brakes would feel fine with the engine off coz they dont work when the engines not runnin-coz of the servo.
I made that mistake when i was queing down this hill, decided to switch my engine off to save petrol (v.long queue) and then nearly went into the back of the car in front :oops:

they do work but they aren't servo assisted. You just have to press harder when the engine is off to achieve the same braking effect.

But the pedal should not go to the floor when the engine is running. I doubt it's the servo. When they go, the diaphram splits so when you depress the pedal you get a hissing sound where the vacuum pipe is sucking air in from the atmosphere.

Sorry if thats not any help

i wouldn't touch anything until you've fitted a new bleed nipple and bled it properly.

bleeding from the union won't expel air from the caliper

Quote:

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Originally Posted by rusty

But the pedal should not go to the floor when the engine is running. I doubt it's the servo. When they go, the diaphram splits so when you depress the pedal you get a hissing sound where the vacuum pipe is sucking air in from the atmosphere.

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Thats what that noise is!!!
cheers!

try it with the engine runing bleed it all out see if it works

Quote:

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Originally Posted by novaforever

try it with the engine runing bleed it all out see if it works

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Done that already......
:?

I'll be trying to sort he bleed nipple next week and see where it goes from there.

The brakes havent been bled right - hence they don't work. You'll have to get the bleed nipple fixed as bleeding it from anywhere else only lets air INTO the system, not out of it.

How exactly is the pedal adjustment performed? I need to do mine and Haynes manual is useless on the subject!

Alan

its adjusted up the back of the pedal. theres a small adjuster screw that you can err adjust, lol

rodgerq

Got the broken bleed nipple out and put a new on in - bled the calipers and the master cylinder again and it's still the same - ordered a new master cylinder to see if that cures it.

nova_rally - It's not that hard and similiar to how RogerQ stated above:

01 - Slide drivers seat back as far as possible.
02 - Get in the footwell and look under dash at the brake pedal arm.
03 - You'll see near the top of the arm there is a pin sliding through a bracket onto the arm.
04 - On the other end of that pin there is a spring arm and a clip - remove both of them.
05 - Push pin out.
06 - You should now be able to remove the U shaped bracket off the pedal arm.
07 - You'll notice the U shape bracket is on a thread rod and tightened up by a 15mm nut.
08 - Loosen the nut and the U bracket can now be turned up or down the thread.
09 - To udjust up turn the U bracket towards the end of the threaded rod, to Loosen turn it the other way.
10 - A small turn makes a big difference so try and do it in half turn measures - do it too much and your brakes will bind, if that happens then just loosen it a touch.
11 - Refitting is a reversal of removal ;)
12 - Take it for a test and adjust as required.

Ok, just bookmarked this gonna go play with the pedal tomorrow. Brakes are sticking again atm though, gonna have to regrease the sliders! :evil:

Before you go messing with the master cylinder bleed it from the nipples only, not using a pressurised bleeder or anything like that, just the good old fashioned way as described in Haynes manual. If that fails check all the brake pipes and joins for leaks.

a Mates master Cylinder is currently leaking fluid into the brake servo, giving absolutely awful brakes (obviously)... might be worth checking as well.

Alan

Quote:

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Originally Posted by nova_rally

Ok, just bookmarked this gonna go play with the pedal tomorrow. Brakes are sticking again atm though, gonna have to regrease the sliders! :evil:

Before you go messing with the master cylinder bleed it from the nipples only, not using a pressurised bleeder or anything like that, just the good old fashioned way as described in Haynes manual. If that fails check all the brake pipes and joins for leaks.

a Mates master Cylinder is currently leaking fluid into the brake servo, giving absolutely awful brakes (obviously)... might be worth checking as well.

Alan

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They have been bled from the nipples into a normal (non pressurised) container using 2 people.
There seems to be no leaking as the fluid level has stayed the same.
I think it came from when I pumped all the old fluid out of the system so I could renew it - I probably knackered the master cylinder seals by pushing it further that it normally travels - At least that's the theory!!
:o

very possible mate

rodgerq

Quote:

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Originally Posted by "Jules

I probably knackered the master cylinder seals by pushing it further that it normally travels - At least that's the theory!!
:o

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Or there might have been a bit of crap in there that knacked a seal when you pumped the fluid out. Just a thought Jules

I'll find out tomorrow when I change the master cylinder - By god it better solve the bloody problem!!
:x