brake issue, problem diagnosis

ive go a fault with the brakes on my red na .

the problem;

ive got a very soft long pedal. it will stop the car but its not great.

what ive done so far;

obviously i did the usual full bleed. and with the car off the pedal pumped up hard no problems. as soon a i started the car the pedal goes soft again ??? . so i flushed the system , repalced all the fluid and did a leak test . no leaks fresh fluid and re bled . again turn the key and she goes soft.

i then tried bleeding the system with the engine on but it wouldn pump up. ive been through atleast 15lts of dot 4 and nothing .

my thaughts;

im thining the master cylinder maby faulty. if it was a goosed servo id have a harder pedal , if the seals in the master cylinder are seeping maybe the assistance of the servo is allowing fluid back past the piston?

what do you all think ?

no other suggestions

Yeah, it will be master brake cylinder most likely, or some air stuck around ABS unit if you have one.

no abs. cant be any air in the system now its been mega bled an fully drained twice. i think its woryth trying a new master . if not atleast ill have a spare

If it still has rubber brake hoses clamp them all off and see what happens. If the pedal is OK then it's air in a caliper or a seized caliper moving on it's brackets. Release each clamp in turn to see which one(s). If it's the MC try taking the pistons out and giving it all a good clean in brake cleaner and blow out the body with compressed air, grease with correct red brake hydraulics grease and put back together, you can have a proper look at the seals for wear or damage, and the bore of the body whilst it's in bits. Better if you fit a seal kit, but that costs money

ok thanks chris ..,

just did this and the results.

with all hoses clamped i got a hard pedal . so that eliminales the master cylinder.

with the rears off still hard. so they are fine .

now the confusly bit.

if i remove the front left i have a smi hard normal feeling pedal. if i remove the frot right with the left camped it feels the same . if i remove both pedal goes to the floor . ill get the calipers off now and dig deeper . maybe both fronts are shafted ? lets see

STOP! (Pardon the pun!). Before taking them off get a helper to press the brake hard or as hard as the sponginess allows, and watch if the caliper is flexing on seized sliders. Even a bit of flex will give a very bad pedal, a lot will give hardly any pedal at all. In normal usage the pedal travel only moves the pistons ten to twenty thousandths of an inch.

I've just texted Craig to stop him from removing them to try this new fault find.

lol cheers guys , ill get someone in now

I've just texted Craig to stop him from removing them to try this new fault find.

Thanks, that was very nice of you

he will be acquiring a turbo for me so need to help him out where i can

Your his brother from another mother at the moment then

ok so . there is no movement in the calipers on the sliders. i have removed the calipers cleand them up. no seeping on them and all pistons are free. sliders are free and fine . greased everything , put it all back on with more fresh fluid ( this is getting expensive) and .........

its still the bloddy same . i checked all the rubber hoses for bulges ect but they are fine .

think im going to need to start replacing bits

mint set of J spec fronts for sale with oooOOOooo sexy painted calipers and machined discs 150.

Are they standard J-Spec front calipers? Have you tried letting them gravity bleed? To do that open both caliper bleed nipples about two full turns, leave the cap off the MC reservoir and keep it well topped up. Fluid will start dripping out of the nipples after a bit, let about half a MC reservoir full of fluid drip out, then close the nipples and see what happens. There's not much if anything that can happen internally in the calipers to give this sort of problem. It's usually your bleeding technique

my technique has never had complaints befor . oh you mean bleeding ( still got the jokes)

its the same way ive allways bled brakes . one in on the pedal me on the nipples (gigady)

ill try the gravity bleed and see how that goes , thanks again chris

Another trick is to lever the caliper pistons back into the calipers as far as they will go. That reduces the internal volume to virtually nothing, so less space for air to get trapped. If you do it slowly, with the nipple open you may even see any trapped air being expelled. I think that about exhausts my repertoire of tricks of the trade on brake bleeding

superb . one again thanks again for your time chris . ill try everything a few more times and if i get no joy ill have a hissy fit then buy new parts

puzzling me though. it has to be to do with the front calipers . with them clamped the pedal is solid

Don't shout........ But, the nipples are at the top, aren't they? I have seen people put calipers on upside down, or on the wrong side, which is often possible and has the same effect. Not sure if you can do that with J-Spec fronts.

yea they are up top. not going to shout , ive done sillyer things

Try vaccum bleeding them, always worked for me + you can do it on your own

after more time testing everything over and over and bleeding over and over i decided to check the plunger on the pedal and noticed the adjuster is wound as far out as it can go? not sure why ( only picked the car up last week )

so i wound it out about 1cm and hey presto i have a pedal and wheels that lock up if you step on it . why would someonr wind the plunger all the way out ?

To alter the pedal height perhaps? But what it would have also done is closed off the bleed back hole in the master cylinder, which would certainly do odd things

Here's the factory brake service manual for you, it gives pedal height set up figures:

BRAKE_SYSTEM.pdf

thats magic , getting somewhere now thanks

hope its sorted now dude???