Brake Issues

[whoneedsbitumen]

In the last 2 weeks or there abouts the brake pedal in my HJ75 has
slowly started to get softer, nothng to serious but enough to notice.
Today on a trip out to the beach we took the freshwater track out to Double island, if anyone doesnt know it its about 15-20km of single lane sandy rutted track, i noticed that after being in H4 for a while that the pedal nearly went to the floor a few times.
The thing that has me stumped is that after driving a while the pedal comes back to about half.
Took it easy on the way out,got onto the bitumen drive down the road and my pedal is back to full again.
I noticed driving back into town tonight after a few corners etc that it starts to get soft again nearly down to the floor.
Its a standard 1hz 1990 trayback, standard sus height just runnin 33's,
the brake fluid leval is just below the full line.

Anyone had anythign like this happen before?
What should i look for when i go and get under it tomorrow?

[whoneedsbitumen]

Just went for a drive to go wash it, 1 minute the brakes will be fine no problems at all next time you touch the brakes the pedal will go down to halfway next time it will be fine for a while thewn it will go to the floor, seems to be no back brakes as i locked the fronts commin up to a set of lights

Heaps of fluid seems to be no leaks anywhere that i can see front pads have enough.

Anyone????

[Ol'40]

Its a process of elimination, do the simple bit first.
Bleed the whole system, then try it out....
If no joy, check your rear wheel cylinders for free operation, and go on from there....

Good luck

[NiftyNev]

Master cylinder seals are probably kaput.

Nev

[g35me]

Possible the rear proportioning valve, they can make the brake pedal feel very unpredictable. That how I had my accident that wrote off my 80 series.

[dow50r]

First off shake all 4 wheels and see if the bearings on the front wheels are loose...this will cause this sort of thing. If all is ok there, jack up the wheels and try spinning them, brake, spin again looking for hard to turn wheels indicating frozen pistons in callipers, check all hoses for bulging when someones foot is on brake. Lastly bleed all fluids...looking for air coming out...but the symptoms dont point to air, as it would be thesame all the time with air... If you cant find any of these symptoms, its most probably the master cylinder

[Andre]

I had similar erratic pedal movement. After the mechanic replaced the master cylinder with no luck it turned out that the front wheel bearings were stuffed.
The excessive bearing play caused the disc to push the brake pistons back into the bores and when you apply brakes it needed to travel more than normal to make up the distance that the pistons moved in.