[screwloose]

Hi everyone
I have a brake issue with my Sierra.
If I leave it sitting around for a while the first time you press the pedal it goes to the floor.
After you press it once or twice it's back to normal.
There is fluid in the reservoir and no visible leaks.
Thanks

[youda]

there is a leak somewhere, probly in the wheel cylinders in your brake drums. I'd look there first

[Scrawny]

It's bypassing in the master cylinder. If you're sure that there's no air in the system then replace the master cylinder

[sstteevvee]

Really need more info too, i.e what year, drums all round or rear only? If its an early model it could be something simple like the shoes need adjusting.

[royce]

how long is 'sitting around for a while'?

[ZookZilla96]

mine is doing the same thing an i think it could have something to do with the proportioning valve because mine if i put another 150kgs over the rear the brakes are perfect!

[screwloose]

It's disk front drum rear. By a while I mean an hour or so.
I bleed the brakes a couple of times to check for air getting in. If the brakes where leaking I would notice. It lives in the shed at the moment on a concrete floor. Still building