Noticed this on both my Z's and was wondering if it's a thing on all of them or just a problem on both mine (unlikely I'd have thought).

Basically it's that on first press, the first bit of travel on the brake pedal dosen't do much, but if you release and then press again it's much better.

Feels like the knock back that you can get from warped disks where it forces the pads away so you have to pump them back out.

My disks are fine and it's a bit worse with R34 callipars, presumably as the pistons are bigger volume so need more fluid moved to contact the disk again?

Any ideas??

Was thinking of putting residual pressure valves on the brake lines to hold a few PSI on the callipars and hold them closer to the disks.

I think it a Z thing.

 

If I press the brake lightly and then press really hard the brakes work really well. If I press the brakes hard from the start, it really bad.

 

But I do have the same thing as you. Press the brake the 2nd time round and it feels better.

 

Stuart

John I read an interesting feature in the workshop mag i receive, and it explained the current elctronic brake assist systems that are coming on line in new cars.

 

It is very clever and would be the answer for what you mentioned, basically sensors monitor the air gap between the disc and pad, a second sensor reads accelerator lift of speed so as to anticipate a braking maneuver, in turn the system instantly moves the pistons ( not sure how) a fraction so the pad is as close to the disc as can be without appling any brakes, of course this means that when you do apply the brakes there is instant feel with no travel to take up! clever or what?

 

The system does more!..using the same system that operates the rain sensative wipers it calculates how wet the disc`s may be and the same sequence occurs intermittently to clear the disc of surface water automatically as you drive..without you even knowing it.

 

Jeff

You will know of it when you pads only last 2 weeks ;)

Master cylinder/servo/air in the system

So it's not just me then :(

Don't think it's air or master cyl, as 2nd time if static you can hold the pedal and it goes absolutely solid, no release at all.

Saw that article too, but the bit on electric only steering was scary!

 

has anyone tried the residual pressure valves??

Try pumping the brakes hard with the engine off, and then keep the pressure on the brakes and start the engine. If it stays hard the servo isnt getting a vacuum, so is leaking.

Probably ;)

Have the brakes been bled recently? changed the fluid?

Yeah, I've tried all that stuff, there dosen't seem to be anything particularly wrong, just think it's the way the brakes are on these.

Disconnecting the ABS helps a little, may try making up some bypass pipes for it and see if that cures it.

Other poss is slight wheel bearing wear that allows the disc ands hub to move enough to knock the pads back. You'd notice this effect most after turning on full lock as that puts a high sideways stress on the wheel.