Disco 200Tdi Brake pedal creep

I am unsure about the UK models but the air con on my 200tdi needs a vacuum to change airflow direction, the slightest leak stops the system working however, my brake servo still works if I press the pedal once. If I repeat to quickly and the vacuum is leaking then the servo runs out of vacuum and the pedal goes solid.

The general method of testing the servo is:

Engine off, pump brake pedal about 5/6 times to empty (fill) the servo, now with a firm and steady pressure start the engine, within seconds the pedal should be pulled towards the floor.

Also to check the vacuum pump pull the pipe of that goes to the servo and put you finger over it with the engine running the vacuum should try to suck your finger inwards indicating some vacuum. There is proper test equipment available but this should give you a indication if all is not well.

Hope this help

regards

Dave

Dave 2000 said:

I have seen this on a couple of cars not just Disco's, when the pistons are pushed back into the caliper fluid rushes back into the master cylinder and disturbs the sediment in the reservoir.

This can then get trapped in the seals/bore of the master cylinder allowing fluid to get past the seals and move back into the reservior. To discount calipers ect try clamping off each caliper with a BRAKE PIPE clamp!!

Sorry for shouting I must have seen to many molegrips being used without some form of padding.

This problem can also occur after routine brake fluid changes.

If the servo was faulty the pedal would be very hard to push down and would disguise the pedal creep engine on or off.

Add that to the other comments made and you are sure to find the fault.

Make sure you come back with the remedy it will help others at a later date.

regards

Dave

Click to expand...

Hi guys
Sorry to raise an old thread - but no resolution to the excessive brake pedal travel issue was posted and i now have this problem with my 1997 300tdi.

As Dave posted - my fault arose after a pad change and i'm thinking that i've disturbed the seals in the master cylinder. Is my only option to replace the master cylinder or can i take it off strip it down and clean it out?

I've bled the brakes (engine running as the car has abs) until i'd done a complete fluid change, i've also checked all the flexis for bulging and have removed and re-seated all the pads checking brake pistons at the same time no loss of fluid and no servo leaks. Symptoms are that the car stops ok but brake pedal travel is excessive (worse than before i replaced all the pads which were well down) - however a second press of the pedal and pedal travel is normal.

Cheers
Andy

ANDY-C said:

Hi guys
Sorry to raise an old thread - but no resolution to the excessive brake pedal travel issue was posted and i now have this problem with my 1997 300tdi.

As Dave posted - my fault arose after a pad change and i'm thinking that i've disturbed the seals in the master cylinder. Is my only option to replace the master cylinder or can i take it off strip it down and clean it out?

I've bled the brakes (engine running as the car has abs) until i'd done a complete fluid change, i've also checked all the flexis for bulging and have removed and re-seated all the pads checking brake pistons at the same time no loss of fluid and no servo leaks. Symptoms are that the car stops ok but brake pedal travel is excessive (worse than before i replaced all the pads which were well down) - however a second press of the pedal and pedal travel is normal.

Cheers
Andy

Click to expand...

The symptoms suggest that the flow of brake fluid from the reservoir into the master cylinder, is not taking place as it should.

This suggests that the Master Cylinder seals may have expanded a little, which causes one main seal to close or partially close the fluid passage too soon. That is almost always caused by contamination with mineral oil, as in fuel, diesel being about the worst.

Another possibility is that the brake master cylinder is not returning fully when the brakes are released (sticky master cylinder pistons and seals) or because the brake pedal is not returning FULLY UP every time you take your foot off it, or even the servo not returning fully.
There MUST be clearance (just a little will be fine) between the servo push-rod and the dished end of the master cylinder main piston or the fluid will not flow into the master cylinder, and you will have to "pump it up" as they say.

Brakes ... you need some.

did you change discs and pads or just pads,and how many miles have you done on the new pads,it could just be your pads needing to bed in properly...

hi i have had this happen on a car when pads were done that one of the seals in the master cylinder were pushed back the wrong direction causing a loss of pressure from master cylinder only fix was to reseal master cylinder or replace it

Thanks for the replies guys. Looks like i'll be replacing the master cylinder or can they be stripped and re-built with new seals? Anyone know?

Cheers
Andy

ANDY-C said:

Thanks for the replies guys. Looks like i'll be replacing the master cylinder or can they be stripped and re-built with new seals? Anyone know?

Cheers
Andy

Click to expand...

They are easy enough to strip clean and rebuild if you can get the seals kit.
A recon unit would be as easy.

CharlesY

buy a new one they never reseal 100% nowadays ,one way to check master cylinder is that usually when seals go the will push fluid/air back into reservoir making it splash