R32 Gtr Hard Brake Pedal

[32 GOT U]

Hi guys,

I am just wondering if anyone has had a similar problem with their R32 GTR.....

Normal diriving, no problems, and the majority of the time it's the same when driving hard...... HOWEVER - every now and then, i'll give it a good squirt and the brakes will end up being rock solid - no assist at all!! scary stuff.... thankfully I have a brake stopper and am able to mash the pedal hard enough to stop...... The 60 seconds later it's fine again!?!?

So, has anyone else had this problem? I have replaced all the lines to the booster with speedflow, checked the one way valve inline to the booster and it seems to be functioning fine....

Any ideas?? Cheers ya all!!

[Richieb]

Hmm, not too sure here. I have to admit mine is touchy!!,, but not so it locks uncontrollably.

I did have!! a Fiat which did similar to what you describe, and it turned out to be the nearside flexible pipe that was almost blocked with some kind of black goo, this stopped the fluid retrning to release the pressure sufficienlty to be normal before i touched the brakes again, and man, did it skate to a halt on occasions, before I realised it was not completely predictable.

[Duncan]

probably the vacuum booster itself. unless you are left foot braking?

[Richieb]

Ah, I got it..!!

Air in the calipers expanding when hot!!

[32 GOT U]

hmmmm....... left foot braking....... isn't that the foot used to accelerate??

[Duncan]

no you're thinking of the other foot.

right foot controls the amount of boost. left foot controls the car's speed.

but seriously, when your foot is on the throttle there is no vacuum for the brake booster. if you are braking at the same time, once the vacuum resoviour is empty there is no vacumm assist left, and the pedal goes rock hard.

[32 GOT U]

Right, got u now..... to answer your question - no, no accel and brake at same time. And after it goes hard even when slipped into neutral at the throttle left alone the brakes remain rock hard for about a minute or so.....

PS - my guage reads 20in. vac also....

[Risking]

one way valve is probably faulty in the line that runs from the booster to the engine.

[Richieb]

Check the fluid in the system is not hygroscopic, as in absorbs water/moisture, 95 % is..!

If it has been contaminated as in left open to the atmosphere, it will absorb moisture, and, underpressure of braking, the water part in the fluid will boil, and produce steam, and pressure will build up above what you have exerted on the piston/s, and may actually force back hard enough to feel hard. Failing that, it could be low on fluid, or if fitted, the ABS pump may be in difficulty. Ususally in my experience, the seals in the master cylinder , or the bore have failed, leaving you almost pressing on the end-stop, which will feel rock-hard too.

So,

1, Fluid change. (will probably not do any harm anyway, as it is often neglected)

2, Check ABS system is ok, and functioning correctly.

3, Suspect master cylinder.

4, Blocked or damaged lines.

There, if any more ideas flash thro my head I will scribble them here.

[Duncan]

he did say he had checked the 1 way valve in the first post. I had trouble with mine a while back and it left me with no assist

[32 GOT U]

cheers guys, all good info here.... I will contiue hunting my problem!