Loss of brake fluid / loss of pressure on brake pedal

[hightop ratty]

I've had an issue with the brakes on our 1984 2.1 petrol - brakes have passed mot last 2 years (& had new hand brake cables a couple of years ago / new back plates, front caliper & bits & bobs).
The issue is pedal sometimes goes almost straight down without resistance (scary moments), other times there's pressure but can lose it (but never enough to lose brakes), & press on the pedal - it can lose pressure (sometimes, not always) - memory tells me it started happening after the front caliper was changed, but can't be sure as my memory isn't what it used to be - marriage & kid have put paid to that LOL .
Never seemed to be any fluid loss over the last 2 years approx.
This morning - red light is on & fluid level on minimum (brakes still working) - but don't want to take any chances.
Van is going into garage on Tuesday to investigate the brake fade, but any ideas (i'm changing the rear pipe in the engine bay for a silicon one as the old one looks past its best - probably the original - was 1/2 hoping it was this until the loss of fluid today).

[captain Byrne]

Does this happen when you've travelled a distance or from cold. They could be overheating.

[California Dreamin]

Loss of brake fluid, so there is your first indicator..it must be going somewhere, therefore, you shod have evidence. So 1) is it leaking at the pedal indicating either the brake OR clutch master cylinders have failed (yes, the clutch also shares the same fluid reservoir. 2) there is a slim chance but not unheard of, that the master cylinder is leaking into the brake servo. 3) the clutch is leaking at the slave cylinder (gearbox end) however, your symptoms don't point to this. 4) one of your rear wheel cylinders is leaking (visibly wet back plate and inside wheel rim) 5) leaking flexible hose or failing corroded brake pipe. Also..something you said..are you sure that one of the front caliper pistons isn't seizing causing an overheating brake which can BOIL the fluid causing something called vapourlock (symptom is pedal to the floor)...lots of things to check....hope this helps.

[hightop ratty]

All from cold & can't see any leaks (externally on the floor) - I haven't taken anything off or crawled around underneath.
I'd learn't to live with the sudden losses, one of the quirks - LOL (not funny I know, as it could be dangerous), but with no other symptoms (& have been up & down some very very steep hills)
Would like to get to the bottom of it, as I can only pull the "its fine love, there's nothing wrong with the van look" for so long
Garage have never changed the fluid in the 10 years i've owned it (to my knowledge), but might have when doing the calipers etc.

[California Dreamin]

From cold (therefore, not the fluid boiling) intermittent would indicate that it isn't just air in the system (that would require pumping several times each time the brakes are applied. I have seen it where the master cylinder seals turn inside out and a new master cylinder would be my best guess at this stage. What did you mean when you said silicon pipe replacement? Do you mean braided flexo's
Martin

[California Dreamin]

From cold (therefore, not the fluid boiling) intermittent would indicate that it isn't just air in the system (that would require pumping several times each time the brakes are applied) I have seen it where the master cylinder seals turn inside out and a new master cylinder would be my best guess at this stage. What did you mean when you said silicon pipe replacement? Do you mean braided flexi's?
Martin