lose of brake pedal pressure

Check your wheel bearings.

If they are loose the "wobble" allows the disk rotors to push the pistons back in slightly, when you brake the majority of the first push is used pushing the pistons back onto the rotors. Once that is OK the brake pedal pressure will come back OK as you appear to be finding.

Hi Al,
Had this happen to me on a trip to Cape York. Tab washer on the front wheel bearing was not bent over after fitting lockers. So check your wheel bearings,maybe loose.
Regards
John

I have had 3 gq's which have all done what you say,,,,even did it on not so bad corrugations..... My mates rb30 gq did it also/.....
I have had 2 diesels and one efi 4.2...

wheels bearings sounds like a issue , or stuffed master cylinder

A stuffed master cylinderis the likely cause, had an old troopy that used to do exactly that, changed the master cylinder and no more problem.
What happens I suspect is that with the pedal and master cylinder piston wobbling around that the fluid bleeds past the tired seals on the piston, never leaked out past the back seal though.

This is a normal issue with GQs on corrigations.

Its the pads being pushed away from the disc by the viabrations. Ask at any Nissan club, and they will all know. When you go for the stoppers it takes a few pumps to push them back to the disc

I agree with TRUCKSTER. I travelled Oz in 99 in a 96 model GQ and this happened while travelling along the Gibb River Road. At camp that night I assumed it was prolly wheel bearings so pulled it apart to check only to find them both OK. I re-assembeled the car and kept going with the problem still occuring and me being careful. When we arrived in Darwin I took it to Niossan and was advised it was caused with low (not dangerously low) pads and was common on all the fleet vehicles they service and that pads were changed every service. Anyway just take care on the dirt. I finally fixed the issue........I bought an 80!!