Brake issues - standard setup - advice please.

[orangecurry]

So - the fluid level is good, no leaks. Car has been unused for months.

(Innuendo hazard ahead)

Engine off, the pedal will go hard, and stay hard.

Start engine, with foot on the pedal, and the pedal immediately drops an inch or so, and is difficult to get hard, but the brakes do work.

Engine off, the pedal will go hard, and stay hard.

...and repeat.

Don't think there is air in the system - what is the most likely problem?
Servo or master cylinder please?

The hose from the engine head to the servo looks ok, but where it attaches to the servo is quite 'moveable'.... but I'd have thought if there was a leak there, I couldn't get the pedal hard at all?

Thanks!

[flybynite]

I know you have a standard setup but the same principles apply. Haven you had a read through this for ideas?

viewtopic.php?f=2&t=281928

[martauto]

I know you have a standard setup but the same principles apply. Haven you had a read through this for ideas?

viewtopic.php?f=2&t=281928

You beat me to it mate !!
There Must be something in this topic to help you.

Mart.

[orangecurry]

...yes - thanks - read through that.

Bit like treacle wading, but wasn't it a leak at a caliper?


I've just been out to check the pipes from TB to servo, which seem fine, and the pedal is still rock hard, hours later.

Doesn't that rule out any leaks? Because the 'system' is still pressurised?

I'm trying to make sure I understand the basic priniciples.

[flybynite]

It was more the fault finding that went on rather than the result that I thought would be useful.

So if you have pedal and you can push further with engine running then your assistance is working. Hard pedal with engine running is knackered assistance. Not the problem here.

If pedal keeps going down then there is either

1. Air in the system (have you bled the brakes? air gets past seals especially when not in use)

2. If you are sure you are pumping fluid and not air or water (when was fluid last changed?) then it must be going somewhere, Either a leak somewhere (as in the linked thread) or getting past the master cylinder back into the reservoir.

So
1. Check for leaks, it won't be big, you can spit more than is needed to cause a problem.
2. Bleed the brakes and while you are at it run some fresh fluid through. Clean thoroughly and dry
3. Check for leaks again. particularly round caliper pistons and bleed nipples
4. If problem still there, replace mater cylinder.

[onthames]

If it does turn out to be master cylinder I can fully rebuild them (saves you a bit as extremely pricey from BMW)
https://www.cclassics.com/services/brakes

[orangecurry]

Thanks both. I thought the symptoms might say 'it is exactly this...' and I wouldn't have to get dirty - must be getting lazy in my old age.

Will bleed the system and report back - thanks!