brake issues..finally sorted

[weldore]

when im sat at traffic lights or on a junction and i'm just holding the brakes to stop the van moving..not pushing..after about 10 secs the brake peddle slowly drops about an inch then it goes hard ,but if i take my foot off and put it back on it returns to normal..for about 10 secs and does it again.do you think i have a leak in the vaccum or is this symptoms of a krackered servo?

theres no sign of brake fluid anywhere either

cheers...dave.

[Nicola&Tony]

If there's no leak to worry about, how long is it since the brake fluid was drained and replaced?

Wheel cylinders aren't leaking?

Tony

[weldore]

when i got the van in august i had to replace the brake flexipipes to the front then after that i replaced the drivers side rear backplate so theres 3 of the brakes that were bled so its fairly recent ..the only one that hasnt been touched is the rear pass side
oh also i had the top off the dash and its not gone down

[HarryMann]

No, that symptom is probably the vacuum servo itself

[pockets]

I recently had exactly the same problem myself, turned out to be the brake master cylinder, What happens is that brake fluid leaks past the seals hence the sinking pedal after 10 seconds or so. Check your brake fluid level again, if you are not losing any fluid then my money is on the master cylinder and if you are losing fluid and the master cylinder appears free from leaks then it could be your rear wheel cylinders.

A dodgy brake servo would give different symptoms would it not? like a heavier pedal from lack of assistance?

[weldore]

is this gonna be a dashboard off deal?

i was thinking with the peddle dropping then going hard, it still has peddle travel but its harder,so wouldnt this be the vacuum giving up until i am pushing without assistance

[Red Westie]

Really don't mean to put anyone down here but I'm afraid some really poor information is being handed out.
If you read weldore's posts again he states several things:
The brake fluid is not going down
The pedal goes hard and sinks slightly after 10 seconds
Whilst I cannot give a definate diagnosis there are certain things you can be sure of;

He is loosing the vacuum in the servo (that's a fact) if the statements are accurate.
The reason for this is unfortunately less clear..it could be one of several things ie;
The one way valve in the vacuum pipe could be faulty.
The vacuum pipe itself may be holed
The diaphram may be punctured in the servo
The vacuum pump maybe faulty (Diesel only)
The vacuum pipe or unions could be blocked or loose (carbon build up in inlet manifold for instance) although I'm not sure of the specific layout

How can I be certain that the rear wheel cylinders or master cylinder are not leaking...easy, the fluid is not goimg down.
How can I be sure the master cylinder seals haven't failed internally..the symptom would be a progressive creeping of the pedal under load...not after 10 seconds as stated.
I hope this makes things a little clearer.
Martin

[lloyd]

Really don't mean to put anyone down here but I'm afraid some really poor information is being handed out.
If you read weldore's posts again he states several things:

You might want to read what weldore actually posted mate.

i'm just holding the brakes to stop the van moving..not pushing..after about 10 secs the brake peddle slowly drops about an inch then it goes hard ,but if i take my foot off and put it back on it returns to normal..for about 10 secs and does it again.

theres no sign of brake fluid anywhere either

Does not state fluid is not going down. He states "theres no sign of brake fluid anywhere either". Big difference to saying fluid level is full.... and we don't know that reservoir is still full.
Most likely is servo itself... but could be master cylinder slipping fluid back into reservoir... might be a leak, but not probable.
Don't think it's one way vacuum valve as would be no vacuum when "take foot off and put it back on" peddle to make servo work. It appears he still has vacuum.
Same applies for vacuum piping and several other of your possibles.

weldore, try pushing brake pedal without starting engine and seem if it does same. Do it several times to bleed of vacuum and see if pedal still still drops. If it doesn't , it's probably servo. If it still does, it's probably master cylinder .. That's assuming fluid level is not dropping.

Red Westie has some good points, but make sure fluid is not going down first, then chase the vacuum for possible leaks, but I'm pretty sure it's servo too.

Have a great Boxing day everyone!

[weldore]

gonna have a look later today.thanks for all the sugestions im gonna check everything and leave the master cylinder till last...ill let you know ..cheers again and have a blurry boxing day

[jason k]

when i got the van in august i had to replace the brake flexipipes to the front then after that i replaced the drivers side rear backplate so theres 3 of the brakes that were bled so its fairly recent ..the only one that hasnt been touched is the rear pass side
oh also i had the top off the dash and its not gone down

um we may all not be reading things eh lloyd!!!

have a great boxing day chaps!!!

[Red Westie]

I think the answer to the problem lies in the statement about 10 seconds and then the pedal goes hard and sinks.
The Servo has reserve vacuum for several brake applications but more importantly whilst the engine is running there should be suficient NEW vacuum being produced to NOT allow the vacuum in the servo to 'run out'.
Hence the suggestions around a leak, a blockage or a faulty one way valve (or if a diesel..a poorly vacuum pump not producing enough vacuum at idle)
Martin

[lloyd]

Jason, Missed second post

Sorry RW, I need to wake up before reading forum. If piping/reservoir system has vacuum leak (looses vacuum), how can releasing petal and depressing get servo/boost back? Seems there would be no vacuum to activate servo in first place. If servo is leaking, when you release petal and depress you get new vacuum into servo... until it leaks down again.. Well actually it leaks air into vacuum, not out, but you get my meaning.

[weldore]

well gents.....looks like eddie is playing mind games with me.i went to test it out today and pumped the brakes b4 i started the engine and it was hard at the top,started the engine and i got the servo drop on the peddle..as it should be...correct me if im wrong tho...so i kept pressure on it and ..erm...it didnt drop! so i repeated it a few times and it looks like he has sorted himself out,im thinking i might call him herbie!
but this was not tested while driving as he is in a bit of a state with the interior stuff im doing,but ive took note of all your sugestions and hopefully the interior will be finished over the hols and i get a ride out b4 going back to work.once again thanks for the help ,this forum is invaluble to a diy mechanic and fingers crossed he behaves himself.
cheers..dave

[skell]

might be the vacuum pump then , mine occasionally doesn't produce enough vacuum, but is ok most of the time, only ever have not enough vacuum at idle though...

[weldore]

has this ever caused you problems?,mine has never been without braking but it concerns me if im going down a hill and i lose braking