Sticking brake issue - Testing the adjustment

[fulvia888]

Well - that's all the easy checks exhausted  - and guess what 6 miles and the brakes applied - rock solid - waited 1/2 hr for them to release and drove back home - Time for the master cylinder to come off to expose the servo push rod, which appears to be the favoured cause  . First time taking off the cylinder, looks pretty straightforward, if perhaps potentially a little messy.
May get the cylinder tested whilst it's off, and will be looking for that rod  not to be flush as I'm looking a clear culprit. Am away for a few days so perhaps will get to it next week.

[nistri]

With high underbonnet temp, internal components of the master cylinder might distort and block the normal operation. Moreover, it is not rare to find out that the internals had been refitted incorrectly.

[Neil]

On a S2 car no.15 on the diagram is the critical item to adjust correctly, there is no pedal box adjustment of the rod in side the car as Tim pointed out.

[fulvia888]

Master cylinder off this afternoon, was hoping to find the servo pushrod protruding beyond the casing - Unfortunately not - it's absolutely level - touching my straight edge.
Was wondering if there was value to winding it back a couple of mm with the case ?  has that approach worked for anyone or is level with the case absolutely the right set up.
Although no apparent leaks from the MC  rear seal am beginning now to think of sending the MC off to Omicron to  be tested.
The struggle continues

[Scott]

Whilst things are pointing to this being a master cylinder issues let me just introduce a possibility that I suffered quite some years back ... that of brake line internals collapsing.

Whilst all outward signs were that the brake lines were fine the constriction caused by collapsed internals was the root cause of a sticking brakes issue.

In your situation I'm reading that brakes are fine but after not very long they stick on; wait for a while and everything is okay. Could a situation exist where hydraulic pressure is enough to apply brakes but collapsed internals prevent fluid release back from the on situation (at least until you've waited long enough for fluid to seeps back)? Realising this is unlikely if all brakes stick on but that's worth questioning / double checking if the MC angle is seemingly drawing a blank.

[lancialulu]

Master cylinder off this afternoon, was hoping to find the servo pushrod protruding beyond the casing - Unfortunately not - it's absolutely level - touching my straight edge.
Was wondering if there was value to winding it back a couple of mm with the case ?  has that approach worked for anyone or is level with the case absolutely the right set up.
Although no apparent leaks from the MC  rear seal am beginning now to think of sending the MC off to Omicron to  be tested.
The struggle continues

if you adjust only one turn will be enough

[fulvia888]

Just tried and one turn seems to equate to just over 1mm , and also seems despite there being more thread visible the max I can screw back in .... so I'll reassemble , bleed and give it a go - Fingers crossed - Thanks

[lancialulu]

Just tried and one turn seems to equate to just over 1mm , and also seems despite there being more thread visible the max I can screw back in .... so I'll reassemble , bleed and give it a go - Fingers crossed - Thanks

when  the brakes stick on is it all 4 or just the fronts or just one??

[fulvia888]

All 4 wheels lock up.

[neil-yaj396]

There was mention at the Yorkshire Meet Up yesterday of a non-return valve in the vacuum pipe that feeds the servo from the manifold? This can apparently seize and cause binding. One of our Fulvia members also has this issue......

[Wangler]

There was mention at the Yorkshire Meet Up yesterday of a non-return valve in the vacuum pipe that feeds the servo from the manifold? This can apparently seize and cause binding. One of our Fulvia members also has this issue......

Easy enough to remove to check and if necessary replace.

Thinking about the problem, the only thing that's outside your control that's a variable capable of affecting the 4 callipers when the car's being driven is the brake servo valve. There's not much to go wrong with it because it's so simple, but after a few decades who knows.

[fulvia888]

Tentative positive news - Servo pushrod wound in a turn , reassembled , bleed , which went quite smoothly, took it out for  a run , the trip to Liskeard and back , which on the last two occasions we failed to make it without needing 1/2hr stop  to allow the brakes to unseize - well it was positively uneventful no phantom braking. Looking forward to pushing out on a longer run at the weekend and lets see. Appreciated  the input and advise... Fingers still crossed