We went down to Brindabilla and Koscziusko National Parks over the Australia Day period and suffered a partial brake failure on the second day. Took two days to get out and to civilisation so not easy to get help.
Anyway, the problem was that when applying the brakes (of course on a very steep downhill low range hill) the pedal went to the floor. If you pumped it, the brakes worked, but eventually the pedal went back to the floor. Once down, a check showed no loss of brake fluid. The next day it was a lot better so we put it down to perhaps contaminated brake fluid (water or air). However, it soon returned the same, so it was certainly not overheating. Still no loss of brake fluid. A check of the booster showed correct vacuum.
We limped to Cooma eventually where we finally found a mechanic (most were closed even though a working day). Guess what, when they looked at it everything worked perfectly. We drove around town, refuelled and all was okay. We contemplated returning to finish the trip (and meet back up with our friends) but decided to drive back to Sydney.
Sure enough, brakes ended up back as before. Not too bad on the Hume as no real need to stop, but had to use a lot of care going through Canberra and then into Sydney (picked the route we less need to stop!).
Now back at home still cannot work out the problem, obviously a brake booster problem from what I can assess (and reading my Prado service and repair manual). Any ideas before I take it to the mechanics?