Can corregations somehow allow brake fluid to become airated?

Two things can cause the problem, insufficient freeplay between the master cylinder piston and the actuating pushrod on the brake pedal, (doesn't sound like this is the case this time) and worn master cylinder seals/bore.
Personally I'd be getting it checked professionally unless you are very familiar with brake systems especially on modern vehicles with ABS etc.

GN,

The possible cause of brake fade, having to push the brake pedal twice to have a good feel, might just be front wheel bearings.

If the bearings are not tight and the vehicle goes over corrugations the front wheel move from side to side.
It does not have to be much but it will move the brake pads out from the disc and two application of the brakes are required to stop the vehicle. The first push of the brake pedal pushes the pads in and the second then applies the brakes.

To check the wheel bearings, jack one front wheel off the ground, crab the tyre top and the bottom and move the tyre in and out. If there is movement the wheel bearings need adjusting.

Wayne

I had this same thing happen to me while driving on bad corrugated roads a few years back in my old GQ

I have had them checked by a few brake machanics and there was nothing wrong with them.

I also had Old man emu shockers at the time and i don't think much of them either , you get what you pay for.

I do believe it does make them airatioin.

The front pads might be knocking the pistons back, is the pedal soft but then okay after being pumped a couple of times or is it soft until they cool down ? Rhys.

I was talking to a mechanic mate about this just 3 days ago while fishing, he adjusted my wheel bearing after a similar thing about 3 months ago, this helped a little, we then drained the fluid and it fixed the problem.

Our conversation was about the fluid itself, brake fluid absorbs water and the more water it absorbs, the more the fluid aerates over corrugations, this in turn creates brake fade.

My advice is change the fluid first and see if that makes a difference.

Cheers Steve.

GN,

My experience and a little story to boot:

You say that the pedal comes back after a few pumps. I had this on the 80 series a few years ago when the mrs and I were on a trip from Melbourne-Fraser-Cameron Corner-Melbourne.

For a few days after we got to Qld, driving for an hour or so up the highway, you come into a town and no brakes. After one or two pumps, no problems. I dropped in to see a mate in Bundaberg and we bled the brakes. Seemed a little better, but was not sure.

After driving for an hour the next day on the start of the leg into Outback Qld and NSW, I slowed down to allow a Combi in front of me to turn right. After I accellerated to 100kmh, and changed from 4th to 5th, let the clutch out and put the foot down again, the motor went staight to redline (and beyond) and there was an almighty noise of metal on metal scrapping. Took my foot off the gas, was still in 5th gear, but no drive. Threw it into neutral, put on the brakes and pulled up on the side of the road. Thought at this stage I had a blown clutch, gearbox or transfer case.

Anway tried all gears, foward, reverse, high, low range and no problems. All very very strange. No noise, car was perfect again ... hmmm. Pulled over onto a side road and got the mrs to drive along slowly. No noise .... It was when she went to turn around, I heard a strange noise from the front left wheel. Almost dark, but I jacked it up and pulled off the LHS front wheel and revealed the cause of the faded brake and temporary loss of drive. The nut and locking nut that pulls the wheel bearing up tight had undone themselves right out and this allowed the drive plate at the end of the stub axle to move so far out that the spline on the axle no longer drove the plate. As it is a full time 4wd, all drive was sent to this side of the front axle and hence the redline and crapped dacks.

The only thing that stopped the wheel coming off was the calliper holding the disc from moving any further out. This was the noise that I heard ... the disc scraping on the calliper.

The thread for the bearing nuts was stripped and I was having a bastard of a time trying to get the nuts back on. It was dark by now, I am covered in grease, starving and the mrs is getting eaten alive by mozzies, but i would not let her sit in the car while it was jacked up and my head was in the wheel well, so I am not in the good books.

No cars had gone past and I could see she was working up to giving me a good serve. A 4wd finally comes around the corner on my 40th attempt to get the nut to take up. Works out he is a diesel mechanic with a 70 series ute and 80 series cruiser and the big bearing nut socket that I needed. We limped to his place about 2km up the road, got there about 8pm.

He and his wife invited us to stay, we had our first hot shower in about a week, fed us and we shared many beers and travel stories. The next day, I stripped the hub down, she drove us into Bundaberg for new bearing kit and parts and dropped by his workshop and picked up a thread file. We were all packed up and back on the road about 10am.

Moral of the story .... country people are great, always carry a thread file and you should check your wheel bearings as you don't know when a wheel is likely to go spearing off into the sunset by itself.

Wazza.

G`Day G N,, Have you found the problem yet? Is your vehicle a 60 Series diesel with the 2H engine? If so I may have the answer to your problem. Will wait for a response before I go into it though. Regards...Nav.

i had a gq patrol with same problem found brake pads were worn and moved away disk when on corrigations. replaced pads problem fixed.
have a nice day
al

Hi GN
I don't think the fluid is aerating it is just the disk pads being pushed back as suggested by loose wheel bearings or just the vibrations can cause the pads to push back, and when you apply the brake the master cylinder has to take up the slack first.

My 60 series did the same thing on big corrugations so I used to just touch the brakes every so often to take up the slack.

Thank you very much to all the replys
I finaly got a bit of time to have an investigation and yes the wheel bearing are far too loose. I am surprised as they were serviced not so long ago but just goes to show.
Also the pads are down too so its sounds this may of made it even worse.
kind regards
GN