GU Brakes - what have I done wrong?

[Slug]

Guys,
Just spent the day R&R just about everything on the GU.

New slotted DBA rotors and TRW Pads.
Caliper kits front and rear.
Master was new maybe 6 months ago.

Bled the damn thing about 5 times so far (including the proportioning valve) and now the pedal is worse than before, spongy and will sink slowly to floor if you hold pressure on it.
Can't see any leaks at all.

Only thing I haven't replaced is the booster however, the pedal will go hard if you tap it a few times with the engine off and drop when started...
What have I missed before I burn the bloody thing?

Cheers
Dan

[351ciofgrunt]

the pedal will go hard if you tap it a few times with the engine off and drop when started...
What have I missed before I burn the bloody thing?

Cheers
Dan

That all sounds likes it's operating correctly, that's what the booster does.

[Lukef97]

haha sounds lile mine, i jacked up the front diff yeaterday after finaly getting the shits with a car that when braking pulld hard right and drives like nothing else. couldnt keep it straight. we found the front passenger wheel had like 40mm play, so i pilled it down and the lock washer key tab thing had stripped and the only thing holding the wheel on was the circlip on the end of the cv,

anyways maybe u need them vacume bleed. nissan cluchs need to be done like that so i have herd.

[N2O]

Spongy pedal is normal after replacing rotors and pad.
It should be ok after approx 500km.

[Yom]

If you followed the bed in procedure for the new pads then you can count them out as a possibility. The lucas/TRW pads are great in my experiences, have used them on small cars and 4wd - don't last long though (but then they also don't chew out the rotors either, you can't have everything in a pad!).

I would take a stab that you didn't touch the rear brake bias proportioning valve thing which noone ever bleeds?

Either vacuum bleed the system or get a mate to help (nothing like another set of eyes to help) and also buy a brake fluid which is a different colour to what you already have (I found some Dot 3 compatible which was blue in colour, so it scored bonus points for being pretty) and spend as long as it takes on the rear proportioning valve, rear brake calipers and then the front.

[Slug]

I would take a stab that you didn't touch the rear brake bias proportioning valve thing which noone ever bleeds?

Yeah mate,
It was a bitch of a thing but I am confident I bled it well.
I might have to simply buy some fluid and vac bleed it as you say

Cheers

[shorty4x4]

have you bleed it at the master sometimes air can make its way to master when you have disconected the lines for a while.

[Slug]

have you bleed it at the master sometimes air can make its way to master when you have disconected the lines for a while.

I can't say I did.... Is there a trick to bleeding a master?

[hiy6o]

I think what you are feeling is the new pads compressing and they will come good after a few hundred kays , as they fully bed in . Only other thing i can think of could be a bent or siezed caliper slide , but i am assuming these were checked when you did the calipers.
PS
if you hold pressure on any gu pedal they sink . does it pull up without alot of pedal pressure .

[Slug]

Calipers were kitted out as well .

Here's hoping it's the pads!

[beast of a GQ]

I reckon try bleed the master. If you have bleed everywhere else starting from back left (longest distance) and worked your way up not much else you can do. They all bleed up fine dont they. (all bleed nipples squirt out). So may as well try the master.

[kbv8ute]

Are you doing it by yourself with a bleeder kit? Have never had problems with bleeding brakes on nissan gq or gu even series 5 with abs. A incorrectly set wheel front wheel bearing can do this as the disc will sit further to the outside of the car and the caliper tries to make up the distance. Does your nissan have abs? That has to be bled too.

[Slug]

Are you doing it by yourself with a bleeder kit? Have never had problems with bleeding brakes on nissan gq or gu even series 5 with abs. A incorrectly set wheel front wheel bearing can do this as the disc will sit further to the outside of the car and the caliper tries to make up the distance. Does your nissan have abs? That has to be bled too.

The cheese and kisses on the brake pedal and me on the spanner.
I use a glass jar, length of clear tube and immerse the end in an inch or so of brake fluid... when the bubbles stop I lock off the bleeder and move on.

Pre ABS on mine.

[kbv8ute]

Really sounds like a master cylinder problem. For you to have bled the air out and have a pedal that is spongey and slowly goes right down to fire wall would seem that fluid is bypassing the piston in master cylinder or even might be the check valve in the master cylinder bleeding back. If the booster doesnt work would have a hard pedal regardless of car running. Wouldnt have vacum to assist the pedal. One way to test it is you can remove the front and rear pipes out of master cylinder and put two plugs from enzed in the holes and push the pedal will soon tell you if its the master cylinder or something further down the line. Pedal should be hard if master cylinder is good because fluid has nowhere to go is plugged.