i need a bigger master cylinder for my mk4 escort .
my big disc's all round have made my pedal hit the floor and no there aint any air in system.

 

HAVE U DONE A REAR DISC CONVERSION USING COSSIE CALIPERS?

 

yes why?

 

Ive got the same set up and only a 23mm master cylinder and the brakes work. It may seem you have bled all the air out, but the problem is when you mount the rear calipers the bleed nipple isn't at the highest point, so you get air pockets in the calipers.

Undo the calipers, lift them so the nipples are at the highest point, and re-bleed, and i think you will find it works

Re-bleed the whole system aswell

 

as above thats why i asked!!!

the cossie rear calipers will be your problem!

undo the caliper and hold it on the disc get some one to pump the pedal while u hold the caliper with the bleed nipple at its highest point!

this is the only way to get the air out!!!!

once u have bled it nip up the bleed nipple and remount the caliper
do the same at other side and try it should be better

 

cheers for comment but i have already done this.
i have taken rear calipers off and bled them and got every last bit of air out.
still travels to the floor

 

Seriously there must be air in there mate, mine did the EXACT same thing when i fitted mine and i was stressing to the max over it, i did everything while i was trying to rememdy it and when i did this they started working.

Admittedly they aren't the best, there is a fair bit of travel in the pedal, but they work and passed the MOT, where as before the pedal hit the floor with just a hint of braking when on the floor.......

What size is your master cylinder?

 

master is 23mm from the 1.3 escort.
1.3 brakes are small front calipers and rear drums.
i have mk3 mondeo's which are big and sierra rears and it just dont work.
i have bled them so many times.
i have taken the rears off 3 times and i have pressure bled the whole system.
the rears did have air in the first time but even with the air out it didnt make much odds, as if there just aint enough fluid going through.
i am gonna go and clamp the pipes off in a min and try again.
but i did clamp the rears and it didnt make much odds at all.
coz the fronts are too big for the ammount of fluid that the 23mm one offers

 

I'm running the same master cylinder with 4 pots on the front and discs on the rear, and they work.

Bear in mind aswell even the biggest calipers AP make only need a 25mm cylinder.

Theres something about Fords and master cylinders, you look at any other make of car with similar sized brakes and the master cylinder is always a lot smaller......

 

i think 4 pots dont need as much fluid as the big mk3 mondeo calipers.
they are a better design and are so precise that they only need a small ammount of fluid to work.
the mk3 mondeo's have huge pistons that need alot of fluid to shift the piston over.
i think they might be alot better with the 25mm rst master.
if i can find one that is!!

 

Its all about surface area. The 4 pistons on mine totted up will be about the same as one large piston, but multi piston calipers apply the pressure on the pads more evenly etc.

If course try a bigger cylinder but if they dont work at all now i'd say theres something else up, that extra 2mm diameter wont make masses of difference to a pedal thats hitting the floor

 

try clamping up the flexi hoses, try the rears first , if the pedal goes hard your problem will be at the rear. Then carry out the same test for the front. This should at least show where your problem is!

CheeRS, Mike.

 

i have tried this and if i clamp off the rears then it only makes a little difference.
but its the same with the fronts too.
i think i need to clamp them diagnaly.
1 front and opposite rear as they are linked like that

 

Sorry but if you've clamped off the rear lines and it still doesn't work you've got air in them.

It's the massive surface area that the rear calipers require that ruins the pedal feel.

Clamping them off diagonally won't do anything, try clamping the fronts off and seeing what that does, because then thats effectively the same as two standard front calipers. If the pedal still hits the floor then, you've got a problem.

 

Ive clamped off the fronts and then the rears and then diagnal.
all seem to make little difference.
only when i clamp all 4 do i get firm pedal

 

If you can't even get a firm pedal with just 2 calipers in any combination there has to be air trapped.

Try clamping off 2 and then bleeding the 2 that are free.......and seeing if you can get a firm pedal.

Aswell, with the engine off pump the pedal and if it doesnt go rock hard that also shows air in the system

 

master cylinder might be shagged. if you bleed and bleed it and still get sponge then I'd say the seals are shot. It's not that you need a bigger one, just a better nick one.

 

just fitted rs turbo master cylinder.
i had to fit T pieces so i could run the 2 pipe master cylinder on my 4 pipes.
first impressions are good, seems as if the pedal is only going half way down at most.
might have solved the prob but cant tell till i drive it tomorrow.

 

is that half way down with the engine on or off?

 

engine off but it feels solid half way down and not spongy and doesnt touch the floor like b4.
i'd be happy if its like that, just as long as they work!

 

If it goes half way down with the engine off then i wouldnt expect good results, as soon as the engine is running and the servo is working i bet it sinks further. Thats exactly what mine were doing.

 

well its nearly sorted.
the pedal was hitting the floor with the standard 4 pipe 23mm master cylinder.
but now i fitted the 2 pipe rst 25mm item and brakes are actually working proving that it is the master cylinder that is the problem when fitting big brakes.
its still got a bit of travel but then the pads have got to wear in so it should get better.
note the brass T pieces splitting the pipes.

 

The pedal should really be rock hard with the engine switched off, because theres no servo assistance...

 

its harder with engine off of course but its still not perfect because of the bigger calipers.
you cant fit cossie rear calipers to a rst and then mk3 mndeo's to the front and expect it to be as it was with standard brakes on, its gonna be softer and thats obvious

 

See whats its like when you get it running, fairplay if its all good, im just not over confident, but we'll soon know

 

well it sort of stops now, lol, just need to run the brakes in and then i wont need to push the pedal hard and i probably wont notice the extra travel anyway
bit dusty but nearly done!

 

yeah, after they're worn in a bit they'll get loads better. My cossie stoppers get better every time i drive it, probly about 70% bedded in now, I've got virtually no sponge.

 

i'll get some braided lines made up too and that should take away some of the spongy