TDI 200 Brake Problem

Nic Bridges · Dec 13, 2008

Hi, has anyone come across this before?

With the engine not running and after a couple of presses of the brake pedal, I get a nice hard pedal with no fade.

However, with the engine running, it goes exceptionally soft and the braking efficiency seems very poor - like it's only working on the primary circuit (single pistons on the front calipers only).

I can't see any obvious leaks and the fluid level doesn't seem to have dropped.

By virtue of the pressure being good with the engine off, I'm assuming the servo is working? Could it be a problem with the vacuum pump?

Any help much appreciated

Nic

ratty · Dec 13, 2008

Nic Bridges said:
Hi, has anyone come across this before?

With the engine not running and after a couple of presses of the brake pedal, I get a nice hard pedal with no fade.

However, with the engine running, it goes exceptionally soft and the braking efficiency seems very poor - like it's only working on the primary circuit (single pistons on the front calipers only).

I can't see any obvious leaks and the fluid level doesn't seem to have dropped.

By virtue of the pressure being good with the engine off, I'm assuming the servo is working? Could it be a problem with the vacuum pump?

Any help much appreciated

Nic

With the engine off the vacuum pump will not be working to assist the brakes. The pedal will go hard.

With the engine running the vacuum pump will be assisting you so the pedal will be softer. If the pump was fecked the pedal would go solid with the engine running.

If you are definately not losing any fluid then it sounds like your brake master has failed and it's allowing the brake fluid to get past the seals.

Nic Bridges · Dec 13, 2008

Thanks for that...

If it ever stops raining I'll go and double check for leaks, before I take the master cylinder out and have a look.

Would you expect the pressure to be good with the engine off if fluid was getting round the seals?

ratty · Dec 13, 2008

Nic Bridges said:
Would you expect the pressure to be good with the engine off if fluid was getting round the seals?

YES. With the engine off you have to apply the pedal much harder to get the brakes to work. As soon as the vacuum is applied to assist you the braking becomes much easier.

Before you strip it all down check your brake pad thicknesses are ok and that the pistons aren't right out. You would expect the fluid level to drop as they wear but someone could have topped the resevoir up. You could also try bleeding the brakes first just to be sure. It does sound like brake master failure to me though.

Nic Bridges · Dec 13, 2008

Thanks again.

I'll give it all a good bleed and see if I do get any air coming out, that's a good idea and will prove that none of the calipers are leaking.

This has happened suddenly, so I doubt it's wear, it's more like something failing... master cylinder does sound the culprit, especially as it does feel like it's only the fronts working.

TDI 200 Brake Problem

Nic Bridges

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ratty

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Nic Bridges

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ratty

I'm not special I'm limited edition

Nic Bridges

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