brake troubles

[907]

The the brakes on my fd3s have gone strange again, they did this before but over time and swapping bits over it slowly cured itself.

When pressing the pedal it goes 3/4 of the way down before starting to work. on reaplication of the brakes the pedal is firm and feels normal. If you leave it for about 7 seconds whilst either moving or stationary it goes back to being soft.

The brakes have been bled tonight and the fluid was clear and had no air.
It has recent braided hoses. The master cylinder was swapped for a second hand one 6 or so months ago when I last had the problem and this made no difference. It has race brake fluid and all the pistons move freely and smoothly.

All I can think of is that the pistons are creeping back in to the calipers a little bit but I have no idea what could cause this.

I have another brake master cylinder and servo that I could try or I could rip the ABS out.

Incidently the problem occoured afert having fitted hawk black pads to the fronts and bedded them in as per instructions and after having waited for the brakes to cool down the problem appeared.

Any ideas apreciated as I am running out of time as I have a trackday booked next week.
cheers Neil.

[bin liner]

sounds like u have done the basics...check hose on servo the one with the pill in it...cracked or split? Use standard dot 4 or if u need 5.1.....get it on the mot rollers and check brake function to see if there is a problem with brake bias  or calipers or try a pressure bleed although this is not needed really on the rex...

[M@r]{]

I\'m having a similar issue.  Ive been told about some sort of adjustment screw down by the brake pedal somewhere??

[TonyC]

The symptoms sound like the seal on the piston within the master cyliner is fault/not sealing corectly.It allows fluid to escape back around it and into the reservoir - it will pump up but then when left fluid will feed back past the piston and you have to pump it again - but there won\'t really be air in it to bleed out.

[907]

I think the master idea sounds the most feasable although I thought if that was the case it if you applied light pressure to the pedal and kept it there the pedal would slowly sink to the floor which it doesnt.
Is not the servo despite the pipe being cracked it keeps a vacum over night.


Cheers for the replys.

[907]

I swapped the master cylinder whith a spare tonight,  the problem is still there but less bad.  So tomorrow I will bypass the abs temperaraly and see if that makes a difference.

[RemarkLima]

Also you could try disconnecting the servo, and see if it happens without IYSWIM.

[clive]

This really sounds like you have air hiding in a line somewhere,

Starting from closest to the master O/S/F, get somebody to pump the pedal like mad building the pressure up hard with the nipple shut, then while they keep pushing hard let the nipple go, when the pedal goes down and spurts the fluid out do up the nipple up before they lift the pedal again so there is no chance of air going back into the system.

Hopefully this way under pressure you will push out any trapped air, hopefully.

Before now I have filled up a washer bottle and back feed fluid with the electric motor through the bleed nipple into the master to shift trapped air out of desperation!

Makes a mess though if your not very careful as it fills up the master cylinder reservoir.

The only other thing that potentially can cause what you are saying is that you have changed the back pads and the pistons have not ratcheted back out again and it\'s taking one pump to get the pistons out partially then the another to refill the expelled fluid in the calipers, one clue to this on an FD would be a hand brake that is either very high or does not work.

[907]

I have done all of the obvoius methods of bleeding that you suggest,  not treied from the wrong end though.  Its definatly not servo related .
The handbrake is dodgy and has been for a while but I havn\'t just changed the rears only the fronts and the problem only appeared after a bedding in procedure but I might try there first as they are definatly not right

[TonyC]

I once had a terible problem with a spongy pedal that felt like air trapped somewhere and I finaly got it sorted by the brutal method of getting my brother to basically stamp on the pedal with the nipple open a few times. After that it was finally a good pedal again.