heya all.

New development in my 1990 Fairlane.

Driving along te M4 motorway Lwr mountains to Parrammatta this morning, usual trip about 50kms.
Picked up my usual passenger 1/2 way..

Busier than normal stop start traffic,
about 80% of the way there, i started noticing my brake pedal was going further to the floor on application.
Pumping it up , no probs., by the time i was 90% the wway there each time i touched the pedal it felt like it went to the floor, pumping it up ok.

Parked it, chcked the ground at the wheels for leaks , opened the bonnet , checked Master , no evidence of leaks on the booster, still full... did my day at work , rang around for a S/H master Cylinder (selling car in two weeks,, just bought a 98 Concorde) booked in for Sat am.

After work get in the car , brakes are fine.. not a problem as usual , usual start & Stop traffic on the way home in peak hour , turn off to drop off my mate.. just then , pedal slowly gets worse, pumping it up ok , till his place a few blocks away from the Motorway, Pedal starts going to the floor , pumping it up ok.
Spent to mins with him chattin , took off, getting out of the suburb towards the motorway , same thing , bad pedal.

Got on the motorway ,, headed towards the mountains.. driving well behind traffic , (much lighter traffic now) touched the brakes about 10 mins later.. FINE.

All the way home uninterrupted , no stop/ start traffic .. brakes fine.

I am thinking HEAT, stuffed fluid..
thinking that when in stop start traffic , discs calipers pads heating , transeffering heat to the fluid.. fluid stuffed.. No pedal.

At worst pedal amost goes to the floor , but one or two pumps and its fine.

So , driving along the motorway later on .. no traffic , did the brakes cool enough and my normal braking was restored?

I have had the car for 5 years, changed my own pads in that time , never had a Flush N bleed.

IS THIS the issue? Should i get a flush n bleed?

Could it be the Master?
Although with my foot on the pedal lightly sitting at the lights, the pedal doesnt move.

This mornng driving to work the traffic wasnt as bad, and being mindful , i allowed much more room behind cars and was able to use the brakes fairly gently.
By the time i got to work i dont think the pedal changed , maybe a little.

I am thinking 5 year old brake fluid needs to be changed?

my ea did that when i was in peak hour traffic heading up the cumberland highway,,scared the crap out of me,,,I've heard that a possible fix for this is a v8 double diaphragm booster.

still yet to try it.

The brake master cyl can bypass inside, when worn out. You should change brakefluid every 12 months, regardless of K's.
I would be replacing the master cyl. and change the fluid.
You may need to look at the calipers too, seized slides and/or pistons sticking.

Turned out to be the master.

I'd still change the fluid anyway if I were you.. you don't want to be skimping on brakes.

Here's the thing with hydraulics, one little bit of crap can completely disable your brakes, full stop.

Cleanliness is the only cure and by this I mean flushing is a good start. At the very least it will hopefully move that bit of dirt away from the master cylinder and further up the system.

A better approach is remove master cyl, clean thoroughly including side circuits, replace rubbers and check for marks in bores.

Put back and flush system. Go around a couple of times after initial bleed.

After this you could find the problem reoccurs intermittently.

Other option, buy new master cylinder and then have system flushed.
This is quicker but dearer.