Brake mystery

[mac123yre]

Please help folks! I have a brake problem, new callipers new disks & pads new flex hoses new master cylinder, but the front drivers side brake keeps locking, it starts driving great for the first few mins then the travel on the peddle reduces until I have total Lock.
Lift the wheel of ground and release the bleed nipple and the wheel frees up. I am totally lost as I have got rid of all the air.
Any help would be great chaps

[blaineuk]

have you checked for kinks in pipes and hoses, sounds like fluid not returning from cailiper.

[taz turbo]

What type of hoses have you used, rubber or aeroquip style? I have heard of rubber hoses failing internally and acting as a one way valve, also heard of new rubber hoses doing the same.

You could swap the hoses left to right, see if the fault moves with the hose.

Regards,

Chris.

[GreenV8S]

Follow the hose back to the solid pipework and crack the union at the far end of the pipe to release the pressure. If that cures the symptoms you know it's not the hose, more likely the master cylinder. That should affect both sides equally, but if the other calliper was faulty then you wouldn't see the same symptoms ...

[andybloggs260@ho]

id aim for the hose internals causin one way valve had it happen on lots of memebers vehicles ive been called out to easy way to check just put old hose bcak on bleed up brakes and see how it drives id bet problem cured

[GreenV8S]

andybloggs260@ho said:

id aim for the hose internals causin one way valve had it happen on lots of memebers vehicles ive been called out to easy way to check just put old hose bcak on bleed up brakes and see how it drives id bet problem cured

Much much easier way to check is to simply crack a union somewhere between the hose and the m/c. No need to muck about changing hoses and bleeding etc.

[mac123yre]

Thanks Chaps will try hoses they are all new but will try it thanks for the help

[mac123yre]

.Have now moved the brake pipes and it seems all front wheels lock up after 10mins is it possible that it may be to much pressure in the reservoir, as the master cylinder is new

[blaineuk]

it could be that there is a problem with the master cylinder, and it is not allowing fluid back into the resavoir.

[mac123yre]

how can i check this as the cylinder was new a few days ago?

[andybloggs260@ho]

daft question why did you replace the master cylinder ? was old one faulty if not put it back on and try if you check allong the lines to see where presure is held then that will give you the answer to the problem as its obviously not calipers or flexi's work you way back up towards the master and hopefully solve your mystery

[GreenV8S]

mac123yre said:

.Have now moved the brake pipes and it seems all front wheels lock up after 10mins is it possible that it may be to much pressure in the reservoir, as the master cylinder is new

The master cylinder being new makes it more likely that it is wrong adjusted. It is the master cylinder that holds pressure, not the reservoir.

If the brakes unlock when you slacken the union at the master cylinder then the master cylinder is the cause of the problem. That could be because it is faulty (worn, gunged up etc) or because the pushrod is set too tight. Being new makes the first issue less likely and the second one much more likely.

[blaineuk]

ater ready greenv8s's post i would agree thet the push rod is adjusted wrong.as he said undo the bolts holding master cylinder to servo and see if that cures it.

[350zwelgje]

There is adjustment (a nut on the operating rod) to set it correctly on the master cylinder (it needs just that little bit of play). If no play (or less!) it could cause your symptoms.

How did you setup the new one? As I assume it needs adjustment as the standard setting is unknown and adapting to the wedge type of play/operation is always required.

Rob

[mac123yre]

I damaged the old master when tried to bleed the brakes so bought a new one and a pressure bleed system, can the push rod on the master cylinder be adjusted if so how, just want to say thanks for all the help chaps

[blaineuk]

if you remove the master cylinder ant get someone to press the brake pedal you will see the adjustable rod.

[mac123yre]

That make sense that it could be this as the car had the same problem when I got it, but just thought I could cur it by replacing the lot, thanks I will try that.

To reduce the pressure do I screw it in or out?

Also my expansion tank has more leaks than MI5 can you tell me what car it is of so I can get a replacement

[blaineuk]

needs to be screwed in , best way is to make sure the master cylinder will bolt up without the rod from touching it.

it is a bit of a trial and error job rod out to much brakes bind, to little and you have to much pedal travel.

good luck.

the expansion tank is off a capri i think.

[mac123yre]

thanks blaineuk

[mac123yre]

Have now tried the lot new cylinder new callipers disks pads and changed the flexi pipes twice, am now on braided hoses, and still the master cylinder not letting the fluid back, I have adjusted the travel on the servo unit to stop bind but still no luck, I have come to the end of my mechanical knowledge any ideas?