Pedal to the metal.

[boatdog]

hi all is it not worth bleeding brakes first, if a jab works but steady pressure sinks to the floor i would say air in the system, what happens if you pump brakes do they work?

[Pepperami]

If i pump the brakes they are fine. I have nipped up the brake pipes on the rear as these were the last to be worked on.

[Ian Hulley]

OK, 1st things 1st ...

Do you have a leak ? Because from the sound of your latest staement it sounds like you have air in the system .... which implies you have a leak. You need to bleed the system properly ( all 4 bleed nipples AND the crutch).

There is no specific test for the master cylinder in either the Haynes or the Bentley, they show you how to reseal your existing one but not how to tell if it's fooked in't first place. However if you've no leaks (checking the rear cylinders and have someone press the pedal hard and make sure you haven't got a bulging flexy ) after having bled the system and the pedal still goes to the floor and requires pumping up then the master cylinder would be my first port of call.

Ian

[Pepperami]

Cheers Ian. I will round up one of the usual suspects to help me bleed the system as first port of call. If that fails i will just replace the master cylinder. Again thanks for your help. Tony.

[Ian Hulley]

Cheers Ian. I will round up one of the usual suspects to help me bleed the system as first port of call. If that fails i will just replace the master cylinder. Again thanks for your help. Tony.

Worth checking for a duff flexy, these have been known to go, IIRC Matt had one go.

Ian.

[Pepperami]

Will check em. I have braided flexi's on the fronts so they should be ok.

[Ian Hulley]

Will check em. I have braided flexi's on the fronts so they should be ok.

There's flexys on't back too ya know

[Pepperami]

Will check em. I have braided flexi's on the fronts so they should be ok.

There's flexys on't back too ya know

Yes i know there are flexi's on the rears also

[boatdog]

Always worth checking the simple things first if you worked on the pipes you will have air in them especially if you changed brake hoses, i disagree with the no test for a bad master cylinder, normally if you apply gentle pressure to brake pedal and you can get it to the floor it shows either air or knacked master (presuming you have checked and your not losing fluid somewhere) but if you "pump" the pedal and get pressure its air, so between the two tests you can work out which it is. hope that makes sense.

[72BUG]

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 !

Just read this with interest as my van has just developed spongy brakes (nothing for half the pedal on first touch but then ok after pumping) and I also have a knackered front wheel bearing. The problem with the brakes started immediately after the wheel bearing went.

How / why does a knackered bearing effect the brakes (are we talking friction = heat causing vapour lock?) and once the bearing is replaced can I cure it just by bleeding them.

Cheers.

[Mr Bean]

In order to isolate the problem you would be wise to undertake the following test:
First check the brake drums/calipers for seal leaks. Then park the van over a clean bit of ideally light coloured concrete (for leaking hydraulic fluid witness) and with the engine on tickover, hold the brake pedal firmly down until it reaches the floor. With the engine running the servo multiplies your foot effort and therefore the test pressure. Do this several times and then peer underneath for brake fluid. If you can look along the brake lines and around the joints and cylinders (drums on while doing pressure test otherwise the pistons pop out and put you in more trouble) for signs of leakage. If it is an internal master cylinder fault no external leak will be apparent. Whereas if it is external to the master cylinder brake fluid will ultimately finish up on the floor or running down the underside somewhere.
As had already been said comiserations on such a miserable job at this time of year. I just snuk through an MOT with just a rear shocker to replace.
Cheers
Wolfie