My brakes seem to be disappearing...
When I first start the car, the brake pedal travels all the way to the bottom and there is very little braking action. After a couple of "pumps" it returns to normal; full braking without excessive pedal travel.
If I don't use the brakes for a while, it happens again. If I've been on the motorway for example and come off at a slip road then I have to give the brakes a couple of "pumps" before they work properly.
For obvious reasons this is dangerous and needs sorting ASAP, so rather than taking everything apart, I'm reaching out to you wonderful people for the most likely cause of the problem.

Air in the lines is my first get it bled.

Check the full braking system for leaks, every wheel, Flexi hoses, all pipe joins , master cylinder (look up above the brake pedal with a torch). Nothing found? Bleed the brakes and moniter like your life depends on it.
Still no good? Replace the master with a quality item.
Do the leak checks with someone pressing the pedal hard and pumping it if it goes soft.
No smut implied.

Glyn D said:

My brakes seem to be disappearing...
When I first start the car, the brake pedal travels all the way to the bottom and there is very little braking action. After a couple of "pumps" it returns to normal; full braking without excessive pedal travel.
If I don't use the brakes for a while, it happens again. If I've been on the motorway for example and come off at a slip road then I have to give the brakes a couple of "pumps" before they work properly.
For obvious reasons this is dangerous and needs sorting ASAP, so rather than taking everything apart, I'm reaching out to you wonderful people for the most likely cause of the problem.

Click to expand...

Master seals would be my money.

And to add....fluid level is ok yes?

Yes, fluid levels OK.
I imagine it's probably a different problem but... when my foot is on the brake (when driving), I can feel the pedal lift my foot up and down, only about 10mm or so (probably less), and seems to change with the speed of the wheels.
My guess would be wheel bearings or a warped disc but figured it was worth mentioning in case it helps to pinpoint the problem.

Possibly the caliper pistons are being pushed back by a warped disc which would cause a spongy pedal on next application.
Better get that sorted.

I'm thinking master seals too. You can disconnect the servo and carefully bend the pipework back to the point where you can remove the servo - any fluid visible at the back of the master means the seals have failed. If the master cylinder bore is still in good nick (no worn lips) you can just change the seals for a new genuine set, much cheaper than a new master. I wouldn't bother with a "Blue Box" master replacement cylinder, it's one of those parts where it's worth paying for genuine items.

Glyn D said:

Yes, fluid levels OK.
I imagine it's probably a different problem but... when my foot is on the brake (when driving), I can feel the pedal lift my foot up and down, only about 10mm or so (probably less), and seems to change with the speed of the wheels.
My guess would be wheel bearings or a warped disc but figured it was worth mentioning in case it helps to pinpoint the problem.

Click to expand...

This sounds like you have multiple issues, the most serious of which is the lack of braking and soft pedal, which I am fairly certain will be a master cylinder issue - based on what you have told us, if that was happening to me, there would be no question about it, I would be ordering a new master or seal kit now.

The pulsating is positive feedback via the hydraulic system, as noted above probably being caused by a warped disc(s) or shot bearing. Both of these things can be easily diagnosed - even jacking up each corner and spinning the wheel could give you a fairly reliable diagnoses - a wobble on the wheel would be indicative of a bearing and if you spin it and feel it bind at one point then ease off for the rest of the rotation that is probably a warped disc (although this is not foolproof) - at that you could remove the wheel and take a steel rule to the face of the disc - turn it 90° at a time and lay the rule across the face, you are looking for a relative high or low spot.

The description of the pumping of brakes etc. sounds like a master seal issue - arguably, if the warped disc was so bad that it was pushing the pistons back far enough, it could therefore require additional fluid to get the pads back to where they need to be, making the whole system feel a bit soft - but that would take a hell'uva warped disc to push the pads back far enough and to displace so much fluid as to cause soft braking to a point you need to pump the system back up each time - it also wouldn't explain why it was like that first thing.

Little experiment. When you next park, or indeed nip out and do this tonight, with the engine running, go out and press the brake pedal, pump it up if need be so it feels "normal". Then switch off the vehicle and leave it well alone - don't move it even an inch. Then the following morning see how your brake pedal feels. If it has gone soft then you can rule our a warped disc pushing back the pistons.