rock hard brake pedal!

Hi All seasons greetings to one and all; now to the point I finally got my 2000 Tc running even stats in this weather! but one issue still remains a problem, I've swapped out the master brake cylinder some time ago but I've had it out recently seems to be ok , piston moves, and I've changed the servo for a new one but the brake pedal does not move one millimeter it appears out before starting the engine and with the vacum pipe taken off where it connects to the carbs but once connected the pedal feels rock solid. the brakes appears to be off and I've bleed the system, but I can't work out what would cause this anyone have any ideas??
 
If it's the same rock hard pedal regardless of whether the engine is running or not it's either the servo vacuum hose collapsed, or the replacement servo has the same fault as the previous one.
 
With no vacuum assistance, the pedal will indeed be rock hard. The air control piston needs to travel freely within its cylinder and there must be no air leaks between the air control valve's white plastic cover and the steel lower section and between that lower section and where it attaches to the slave cylinder.

Ron.
 
Also inspect the check valves Kevin for correct operation. With the engine running, air is drawn out of the vacuum chamber, so the valves need to allow this to happen.

Ron.
 
kevinchown wrote,...
Check valves? where the h*ll are those!

Hi Kevin,

Where the vacuum hose meets with the booster (servo) vacuum chamber and the engine. You'll see a white plug with a rubber seal on the booster, that is a check valve. It is one way valve that allows air to be drawn out of the chamber. Test it for correct operation, you'll be able to draw air through it in the right direction if it is working properly. Same applies to the check valve on the engine, which is quite different in design on the V8, not sure what one looks like on the 4 pot.

Ron.
 
Hi Thanks for the help so fat but problem persists, I've now installed a new non return valve and vacuum hose and still the brake pedal barely moves, no brakes aply its as if nothing is getting through the servo! With the servo removed the brake pedal is free I'm also having trouble bleeding the system, when the nipples arre open barely any fluild can be drawn through, whether this is related I don't now. [I've one of these vacuum bleed kits which supposed to mean you can bleed the sysyem on your own!] but with the nipple open on the caliper nearest the brake pedal I can pump fluid out. My only thought so far are seized cylinders in the clapiers but I'm being told its not likely. Any thoughts would be welcome??????
 
I'm very surprised you managed to source a new non return valve! Or do you mean the simple brass one on the inlet manifold?

This is almost certain to be a servo issue. My instinct would be simply to remove it and return it to whence it came for a proper overhaul. It should not have been sold as a new servo in this condition.

Alternatively, if by new, you mean 2nd hand but new to the car, then first port of call is a full servo overhaul. And that should include the air valve located within the white plastic mushroom where the vacuum hose attaches. It might be worth getting an overhaul kit for the air valve first, as it is the most likely location of your defect - it's not just a simple non return valve, it's quite complex inside.

Chris
 
Hi Kevin,

I assume when you say that the pedal barely moves, that the engine is running? If you purchased the booster (servo) as a reconditioned item, then I would return it and have them test it for correct operation.

The pistons within the front calipers barely move at all during brake applications. In what condition are the rubber boots? Are they soft and flexible or dry and cracked? Even if the latter, that still won't prevent the calipers from functioning as they are only there to prevent ingress of dust and moisture.

Ron.
 
Hi All The servo is a recondition unit purchased from a P6 supplier, the pedal is rock hard with the engine running, if that helps!
 
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