Pedal to the metal.

[Pepperami]

No not the accelerator but the brake. If i jab the brake it is initially firm but if i put pressure on the pedal for more than a couple of seconds it sinks to the floor. Any ideas as to where to look first?

I checked the brake fluid that was still full.

[Ian Hulley]

Brake master cylinder failed ? Or servo not holding pressure ?

Either way it's a crap job

Ian

[Pepperami]

Oh dear! I was hoping noone was going to say that. Cheers Ian.

[Ian Hulley]

Is the hose from the inlet manifold OK ? This creates the vacuum pressure for the servo. AND it's the cheapest/easiest thing to pray for.

Ian

[Grumpy Midget]

Al so check none of your front disc brake calipers are binding - siezed, ie fluid boil results in fluid preasure drop,
Happened to me last year coming home from the Duke, slight pedal preasure the pedal sank to the floor, Rapid pump and pressure back up,
Changed servo pipe , 1 way valve in servo pipe, Bought new brake/clutch master cylinder, Still the same checked discs, and drums after a run out.
Left my fingerprints on my nearside disc ( it was bliddy hot to mention the least)

[Pepperami]

Cheers guys i will have a look tommorrow.

[Red Westie]

If the servo fails in any way, the brake pedal goes rock solid NOT to the floor...so you can rule that one out (BTW.. it doesn't loose pressure it looses vacuum)
Like wise, if the front calipers seize it can result in 'vapour lock' caused by overheating, effectively the brake fluid boiling, which results in the pedal going to the floor BUT....only when driving not static so easy to eliminate.
Air in the brakes would be a spongy pedal...all of the time.
Then you could have a leak? but again, that should be easy to spot as the fluid level would be going down in the resevoir and you would see a wet patch somewhere under the car.
Percentage guess is the seals have failed internally in the master cylinder.
Martin

[Ian Hulley]

(BTW.. it doesn't loose pressure it looses vacuum)

Yep, I just put 'pressure' ... did say vacuum on the hose bit though sadly I think it's the seals in the cylinder too.

Looks to be TOO bad a job though

Ian

[billy739]

yep i would go with the master.the only other possibility if the pedal sinks only whilst the vehicle is in motion but not when stood still is a front wheel bearing with excessive play !

when you unbolt the master from the servo have a look in the sercvo as well as sometimes the servo can fill up with fluid over a period of time.

do the job properly , remove all the wheels with the van on axel stands and drain the fliud from all wheels

this will mean the fluid is replaced and not just a case of changing the cylinder, also this will prevent fluid leak behind the dash.

tye fluid is designed to be replaced every 3 years

[ginge]

to check the servo start the van pump the brake pedal a couple of times then turn it of leaveing your foot on the brake just like the mot man does if it goes down to the floor poss servo prob there but what you said sounds like vacum to the servo from the engine check the pipes [vacaum ones ] or a poss slave cylinder

[Red Westie]

It sounds like some members need to read up a lttle more before making comment.....no offence intended but I urge people not to comment unless they are sure of what they are saying.....brakes are not to be fooled with and advice needs to be sound.
Ever heard of the saying 'a little knowlegde is a dangerous thing'.........?
Martin

[Bowton Lad]

Several peeps have mentioned the brake servo vacuum hose. If that is holed it results in less efficient brakes with the pedal requiring extra foot pressure & it feels dead/solid. The pedal shouldn't drop to the floor.

[Pepperami]

Thankyou for the replies guys but where am i checking first?

[Ian Hulley]

Master cylinder I'm afraid.

Ian

[Pepperami]

Ian i have the instrument panel and everything off. How am i checking the master cylinder to to see if it's knact?
Or do i just replace the whole thing? Cheers Tony