Brake dramas

Bushbasher · 15-11-2008, 09:59 AM

Just fitted new discs and pads to the wagon (AUII) and now the bloody pedal has gone all spongy and goes to the floor, I'm guessing I have blown a seal out or something while pushing the pistons back into the calipers cos nothing else makes sense. It wasn't till I had finished and bled the brakes that I realised I hadn't taken the top off the master cylinder and removed some of the fluid to make room for the back flow of fluid. So what would most likely be the problem, master cylinder seal or is there a valve somewhere in the system to do with the ABS perhaps that may now be stuck open? I can't let the missus loose with the wagon again till it's sorted cos it don't pull up real well at the moment. Any pointers or clues would be greatly appreciated.

Cheers
Bushbasher

EvilChief · 15-11-2008, 10:12 AM

is there fluid at the calipers coming out? (ie behind the pads). if thats the case its a good chance you may have damaged a piston seal while pushing back in. BTW how did u push them back in? if there is no fluid behind the pads, id just rebleed the brakes once more to double check that there is no air (ie pedal pressure bleed).

taking the top off or no will not blow a seal, there are breather hohles in bother the rubber membrane and the plactic cover through which fluid could hjave escaped.

EDIT: if you have pedal pressure bled it in the first place, did u push the pedal all the way to the floor? if thats the case you may have damaged the seals in the master cylinder and its now bypassing fluid from primary to secondary chamber or to the reflow valve

Mr Hardware · 15-11-2008, 10:36 AM

...and thats why i never touch brakes myself. I'll do just about anything on a car, but never brakes.
Also, is it just the case that they need a good bedding in?

Bushbasher · 15-11-2008, 11:05 AM

Quote:

Originally Posted by EvilChief

is there fluid at the calipers coming out? (ie behind the pads). if thats the case its a good chance you may have damaged a piston seal while pushing back in. BTW how did u push them back in? if there is no fluid behind the pads, id just rebleed the brakes once more to double check that there is no air (ie pedal pressure bleed).

taking the top off or no will not blow a seal, there are breather hohles in bother the rubber membrane and the plactic cover through which fluid could hjave escaped.

EDIT: if you have pedal pressure bled it in the first place, did u push the pedal all the way to the floor? if thats the case you may have damaged the seals in the master cylinder and its now bypassing fluid from primary to secondary chamber or to the reflow valve

Here's what I did ( and there's no fluid leak at the caliper). I used multigrips to push the pistons back in one at a time cos the grips weren't big enough to get over the old pad as well if it was in place. Once the new pads were in I took the car out to bed the brakes and had a spongy pedal. I came back and this morning bled the brakes thinking there must be air in there but it made no difference. Also, I noticed my handbrake has suddenly got very sad and pulls all the way up now . Don't know if it's related but there ya go. Oh, btw, I only changed the fronts , haven't touched the rears.

Bushbasher

Mr Hardware · 15-11-2008, 11:32 AM

handbrake should have absolutely nothing to do with this if you haven't touched the rear brakes. the handbrake operates on a giant cable with handbrake shoes inside the rear hub.

Bolly · 15-11-2008, 12:59 PM

Sounds like Master Cylinder.....With an old master cyl. Because they only travel a small distance, crap gets built up in the unused part of the cylinder which sits dormant right next to the seals, So if you bleed the brakes using the master cylinder, the seals are forced to go in the crapy part of the cylinder which damages the seals which lead to brake fluid by passing the seals.
A good way to test your master cylinder is to start the engine and let it idle then firmly apply even pressure for 5 minutes and see if the pedal slowly drops to the floor..
If you already have a low pedal just pump the brakes until the pedal builds up then hold firmly and see if the pedal drops...Replacing the master Cylinder should solve your problem..
With old m/Cyl i always pressure bleed using a air compressor..
Cheers

waggaclint · 15-11-2008, 06:16 PM

sound like you havnt bled the system (rear&front) properly to me....

Bushbasher · 16-11-2008, 07:54 PM

Thanks guys for the replys, much appreciated.
Bolly, the master cylinder failure sounds reasonable especially as the old fluid was all but black and full of crud and the old pads were fairly well down to within the last 4mm of material.

waggaclint, I flushed nearly a 1/2 a litre of fluid through each caliper till it was running clean and clear again and that was after I syphoned off all the old crappy fluid from the master cylinder and filled it with clean fluid before I started. There is definitely no air in the front lines and I haven't yet done the rears so don't know how ther could possably be air in the rear lines. I will do the rears when I put some new alloys on next week......after I cure the brake problem. I think I might pull the front wheels again in the morning and double check the calipers before I rip out the master cylinder though.

Thanks again guys,
Cheers
Bushbasher