Diagnosing brake issues

[aus jd 2703]

the GT Four boys will know ive been having brake issues for the past week, which is a problem as it is my daily and im borrowing cars to get to work atm.
i need some help to diagnose whats wrong, here is what happended:

track day at queensland raceway did 5 lots of 5 laps and progressively the pedal got longer and longer....
drove the car home, long pedal but some brakes at the end but not enough to lock up (no abs).

so pulled in the shed checked the pads (glazed and cracked) sanded the glazing off cleaned the discs (new pads and disc ordered, project mu HC+ and slotted RDA are the best i could find).

and then went to do a fluid flush. used a syringe to draw out fluid from the master. refilled with new fluid. and bled as normal. starting furtherest from the master. slight pressure on pedal open nipple, foot to floor, close nipple release and pump it up.
now i have a worse pedal than before.

symptoms at the moment are. hard pedal after a few pumps with engine off,
soon as engine is on pedal goes soft and almost to the floor.
front calipers you can see flex and move with engine moving and pressing on the brake.
tried bleeding with engine on and off, also taped the calipers with a hammer to 'shake out and bubble' not more air in the fluid. put about 1L through so far last 500ml no air.
replaced old oem lines with new HEL lines... no change....

i had the front calipers and master rebuilt no more than 18months ago when i had a similar issue...
ive ordered New pads rotors all round, has new brake fluid and new braided lines...
what could it be? how can i diagnose if it is or isnt the master?
thanks guys, just need it on the road ASAP.

[japlish]

I fear your booster is dead buddy?? where in qld are you as i have good contacts for brake stuff all over brissy.....

[DX20VT]

I have had a few issues with bleeding brakes beforeand here are a couple of things to try.

When you release the pedal from the floor back up each time after the nipple is closed,
bring the pedal back slowly, take about 5 seconds oor more to get the pedal back up.
If you come back up too fast and the seals in the master cyl are soft, they will let air in from the pushrod.
If this has happened it may take a bit to get the air through and out, but should notice a difference pretty quickly.

Also try pump the pedal up, foot right off the pedal, open the nipple then slam the pedal down hard and fast,
close the nipple and draw the pedal back slowly. Pump it up and repeat. and the the last time hold pressure onbefore you open the nipple like normal.

[aus jd 2703]

south side of brisbane....
how do you diagnose a booster completely?

[lexsmaz]

It doesnt sound like the booster is dead to me, as its doing its job of increasing pedal assist to the callipers etc .. The only way of checking a booster is to pump the pedal with the engine off to deplete the air out of the booster & then push down on the pedal & start up the car, if its working ok the pedal will drop in height when the engine starts as yours does, but if the brakes are dodgy it just helps to show up other faults in the system ..

It sounds like the m/cyl could be at fault especially as you said it got worse when you bled it .. With the wheels off the ground & the brakes applied do all the wheels actually lock up .. Also check to make sure none of the brake flex line are balloning when the brakes are applied ..

[4th surf]

Your Master Cylinder is by-passing. Replace it with a new one. I should be able to find you a part no for it somewhere even if it means an e-mail back home and supply from there. Drop me a PM to remind me and I will need full frame and model numbers from the car as there is a change part the way thru production

[dumbass]

Best way to diagnose this is to get 4 brake line crimps or vies grips

Get someone to sit in car and test brakes when they are bad

Then u clamp off one of the rear lines then get friend to pres brakes
U clamp and unclamp rear line and see if it gets better or worse
Leave it clamped in the end
Then goto next wheel
Clamp it on and off see if it makes it better
Then leave it clamped

One undo this for all 4 wheels
U should find that some wheels makes the pedal much better
Well that's the wheel with problem

If u have clamped all 4 wheels and it's still bad then u have air in your master cylinder
Or you have stuffed master cylinder

[TERRA Operative]

Have you cycled the ABS pump to bleed it of air? I know with my Levin, you had to bleed it twice to do it fully.

Bleed as per normal, then cycle the ABS pump (either at the diagnostics port, or on road) then bleed the system again.

[aus jd 2703]

ok to answer all questions and comments.
cant clamp brake lines as the HEL braidedlines and i really dont want to ruin them. (brand new), but before i put them on, clamping one (either didnt matter which) improved the peddle to near perfect. figure that out, clamp the front left good peddle release it poor peddle, clamp the right with the left still free and you get a good peddle...
booster works as ive done as you say start the motor and the peddle moves to the floor.
no ABS to worry about.
as for master, trying to decide. can get mine rebuilt (non genuine) $185 and done now, genuine rebuild kit $195 3 weeks (not really an option due to time) or a new master of ebay for $220 but non genuine, got a 205 master in the shed but suspect they are to different.
it can be only be one of 3 things (i think atleast) the master as most of you say, the P valve (pretty long shot) and maybe the pads as i noticed they were worn on weird angle, so maybe the pads being pushed straight is causing the long peddle? not sure

i have ordered project mu HC+ pads from japan and they should arrive soon, so ill test that and then get a new master (Ebay). and pray it works....... if not burn the car lol

[andrew_mx83]

Put $30 supercrap pads in til proper ones arrive?


Been there, done that chasing my tail with soft brakes after a track day no matter how many times we bled it..... original pads were toast even after scuffing the glazing off.

[aus jd 2703]

thanks but i have a borrowed car for this week so id rather wait then waste more money.
has any one had any experience with HC+ pads? good bad?

[allencr]

...noticed they were worn on weird angle, so maybe the pads being pushed straight is causing the long peddle? not sure

I'm sure that contributes a lot, if not all, to a long pedal, especially if you didn't put them back in the same place.