All The Brakes Creep On When Driving

[marksorrento205 80]

As im going along the motorway this morning I noticed the car feeling sluglish. When I touched the brake pedal a few times it went away but came back after time. Pumped again and they released. Now the car has had the front brakes (gti6) rebuilt last year, two new rear calipers, new brake lines , no compensators, a 406 m/c, s/s braided hoses, new rear discs and pads and recently (last week) flew through the mot on the brakes with no imbalance and good figures all round. When I got to work all four wheels were red hot indicating all four brakes when casuing the problem. Master cylinder or servo ???

[pablo 0]

Maybe a sticking master cylinder alright, would have to be up there if all 4 are binding.

 

maybe pop it off and make sure its seated on the servo plunger ok.

Edited December 9, 2009 by pablo

[Galifrey 1]

If they are gradually creeping on, it may be a faulty servo.

 

Sticking master cyl would normally leave them binding after pressing the pedal rather than releasing with the pedal and then gradually creeping back on.

 

Assume it hasnt got ABS?

[pablo 0]

too much vac?

 

you could disconnect and plug the pipe to the servo to test. brakes will need more of a push but will still work ok.

[Galifrey 1]

too much vac?

 

you could disconnect and plug the pipe to the servo to test. brakes will need more of a push but will still work ok.

 

There is a valve on the servo that equalises both sides of the diaphram<sp> when the brake is not operating, once pressed this valve closes and allows the vacuum to assist braking.

 

The valve could be sticking or the brake pedal not lifting properly.

 

Too much vacuum would make no difference

[marksorrento205 80]

too much vac?

 

you could disconnect and plug the pipe to the servo to test. brakes will need more of a push but will still work ok.

 

Yes they are creeping on bit by bit. Its got a gti6 engine fitted running the std gti6 servo pump from the exh cam if that is of any help?

Edited December 9, 2009 by marksorrento205

[marksorrento205 80]

There is a valve on the servo that equalises both sides of the diaphram<sp> when the brake is not operating, once pressed this valve closes and allows the vacuum to assist braking.

 

The valve could be sticking or the brake pedal not lifting properly.

 

Too much vacuum would make no difference

 

The brake pedal is fully up and the servo rod lenght is correct as I checked it the other day. The valve, is this the one that plugs into the servo and the vac pipes connect to?

[Galifrey 1]

The brake pedal is fully up and the servo rod lenght is correct as I checked it the other day. The valve, is this the one that plugs into the servo and the vac pipes connect to?

 

no, it is integral with the servo

 

http://www.kfz-tech.de/Engl/Bremskraftverst.htm

Edited December 9, 2009 by Galifrey

[Galifrey 1]

and the servo rod lenght is correct as I checked it the other day.

 

Hmm if this has recently been checked how confident are you about the info you have?

 

It could be causing the servo valve to close prematurely, or slightly, meaning everytime you lift off the throttle the servo brakes slightly?

 

Especially if it is a little sticky.

[marksorrento205 80]

Hmm if this has recently been checked how confident are you about the info you have?

 

It could be causing the servo valve to close prematurely, or slightly, meaning everytime you lift off the throttle the servo brakes slightly?

 

Especially if it is a little sticky.

 

It was reading 22.3 with a digital vernier and a digital depth gauge. If the rod was too long im guessing the servo would be slightly open? If its to short you would have long pedal travel?

[Galifrey 1]

It was reading 22.3 with a digital vernier and a digital depth gauge. If the rod was too long im guessing the servo would be slightly open? If its to short you would have long pedal travel?

 

Are we discussing the pushrod from the pedal to the servo, or servo to the master cyl?

[welshpug 1,655]

servo to M/C

 

is the gasket between M/C and servo present?

[Galifrey 1]

servo to M/C

 

is the gasket between M/C and servo present?

 

OK, ignore my confusion then

[M@tt 77]

if the rod is a little bit out or very close then you might find, as i did, that once the fluid is upto temp it expands slightly causing the brakes to bind. Mine was fine when cold but after a few mins driving braking they were starting to bind. I just wound the nut off a little bit more and that sorted it.

[Galifrey 1]

if the rod is a little bit out or very close then you might find, as i did, that once the fluid is upto temp it expands slightly causing the brakes to bind. Mine was fine when cold but after a few mins driving braking they were starting to bind. I just wound the nut off a little bit more and that sorted it.

 

Which would happen if the gasket is missing (as mei said)

[marksorrento205 80]

Yes WP the gasket is there:)

 

If the gasket is missing the rod lenght would "in theory" get longer as the spacing of the gasket wold be missing. And from what I gather, 0.1 or 0.2 mm makes all the difference. Im going to blank the servo off tonight and then sort it friday when im off work. I will try and shorten the rod and try that beofre I go into a servo change

[marksorrento205 80]

Right, had a chance to play with it today. I removed the master cylinder and re measured the rod - 22.3mm. I tried to adjust the rod but I could not find anything suitable to grip the rod whilst I wound the nut it - any suggestions?

 

Although the rod is within limits, due to the varying manufacturing tolerances, the master cylinder itself could be slightly longer or shorter from what I have read on here. This is why I want to try shortening the rod a tad to see if that helps.

 

However. When I disconnected the vac pipe from the servo and blanked the engine side off, when driving the car felt much more free wheeling and the brakes did not creep on but due to the lack of servo the brakes were sh it as expected.

 

Now would you put this down to the rod length or a knackered servo? I only ask as im getting board of bleeding the brakes and going through loads of brake fluid having the m/c off on off on etc

 

Cheers Mark

[pablo 0]

not just pull the MC out of the way? Thats what I done when swapping my servo. Didnt disconnect any pipes.

[welshpug 1,655]

not so easy with a 16v head in the way I'd imagine...

[Galifrey 1]

I am still gonna go with a knackered servo valve.

[marksorrento205 80]

As WP said, with a gti6 te room is limited to say the least. Its a misson to get the m/c off without the pipes connected. Sorrentopete has just sorted me with a replacement servo so im going to swap it over now and see what its like.