Long brake pedal travel when car is on

[bradc]

When I drove the Turquoise VR-4 for the first time there was a lot of brake pedal travel before the brakes started to do anything. I couldn't really be bothered bleeding them so took the car up the road for a Warrant and had them bleed the brakes. There wasn't any difference in brake pedal feel. Yesterday myself and Dickytim swapped a master cylinder across from my half cut and bled the brakes again. Before the car was started brake pedal feel was superb with a very small amount of travel before the pedal got very firm. When we started the car and drove it the brake pedal travel became very long. We went for a bit of a drive to test the brakes. Because it had been standing for a year or so there was quite a bit of surface rust on the discs. After 15 or so hard brakes from 90-110 down to 30kmh or so we had smoke coming off the pads, so figured it was a good time to let the car cool down and re-bleed. The pedal feel was still crap after this drive, but that was probably due to pad fade.
After it cooled down we flushed the brakes again and the pedal feel again was excellent. As soon as we started the car the pedal became very soft and required a lot of travel to even begin to operate the brakes. Turned the car off and pumped the pedal a few times and the feeling was back again.
Pumping the pedal many times while the car is running doesn't make the pedal feel any better at all, and it is also possible to bottom out the brake pedal when the car is running.
The discs are in good condition now that the surface rust has been taken off, they don't have a lip on them at all to indicate a heap of wear. The pads also have quite a bit of meat on them. Any ideas?

 

[Guest]

well going from hard to sort with engine off to on is normal,
thats the vaccume assist kicking in.

the problem your having is eactly what i had on the ST when i fitted brembos,
( i never did solve that issue)

but the ST works fine with vr4 calipers. and the vr4 works fine with the brembos,

i would hazzard a guess at the caliper seals being tired.
or the brake bia's valve being dodgy (this was the only different part in the ST brake system i never changed)

or there could be air in the ABS Pump system? or it could be faulty??
can you get the abs to kick in???

 

[Scottie]

Isn't there a reed valve that restricts the pressure being pumped into the brake booster from leaking out? Perhaps this is not closing correctly and pressure is escaping back into the vacuum line?

 

[bradc]

There is a chance the caliper seals are screwed, especially considering the car has been standing still for so long. Wouldn't the brake fluid leak out though if that was the case? It didn't lose any fluid at all.

Didn't try the brake bias valve, but there is one on the half cut, so I could try swapping that. No idea if the abs pump is ok, I didn't try removing the abs fuse, but I couldn't get the abs to kick in anyway, even with the pedal bottomed out.

Scott - no idea! Where might it be?

 

[Scottie]

All my previous cars have had on in-line with the vacuum hose that comes from the manifold. I just checked the Legnum but it doesn't. Perhaps it works differently or has one internal with the booster.

Is the vacuum line from the manifold ok? No cracks etc?

 

[bradc]

The vacuum line is fine, no cracks or anything.

 

[VR4CE]

I has a similar problem with my car, the pedal would just sink to thew floor, basically the master cylinder wasn't holding pressure,

I went down to mitsu and ordered the new piston seals and rebuilt it, and it was perfect after that