hard brake peddle sometimes in the GTR

[7HEAVN]

Noticed lately a couple of times while cruising along at relatively low speed and go to pull the car up I loose peddle pressure as in the peddle goes hard on me which certainly catches my attention . Only happens in a blue moon though but what could be causing this ?.

[RB30-POWER]

what do you mean, you mean you lose vacuum assistance so it's hard or a mechanical problem not allowing you to press the pedal/jambed brakes etc?

[7HEAVN]

It would be more like loosing the vacuum assistance as I can depress the peddle but it does go hard and have trouble pulling the car up .

[260DET]

Faulty one way vacuum valve?

[RB30-POWER]

yeah to try and confirm, turn car off, press brake pedal a couple of times, you should have assistance for a couple of presses, but by the third it will be out of vacuum and go hard.

if you have no assistance after you first turn the car off, the valve would be the fault.

fairly sure the gtr has a balance tube picking up vacuum from each inlet runner, don't really think this would be any problem just thought i would mention.

if the oneway valve didn't fix the problem it could be a leaking booster, not real common but.

also if you have massive cams the engine might not develop much vacuum at idle and only builds up vacuum under deceleration, so if your stopped for a while and deplet the storage in the booster you might need to wait until you next decelrate again to build some vacuum up. (vacuum is higher under deceleration)

[7HEAVN]

Took someone for a test drive the other night gave it the goods through 2nd and 3rd and then on the brakes hard to pull her up then coasted ,then back onto the brakes to turn off into a car park and the peddle went hard on me . Will get it looked at anyhow because it's not fun and has neally caught me out a couple of times .

[GTSBoysShadow]

Booster could definitely be dead/dying. I had to do one on my R32 some years ago. They are getting old enough, and the guys who rebuilt the booster said they do them for Skylines semi-regularly.

Although the behaviour does sound a lot like a faulty valve.