But steam isnorman wrote:Like I said first up .... water in the brake fluid. water is not compressible.....Jon and Kay wrote:Ok, so I have a 10 tonne MH, Auto Tranny, four speed, Pacbrake that decreases revs by 500rpm, but auto tranny does not lock.
From Cooma to Bega, down Brown Mtn, using the pacbrake, all was good to the bottom (quite a long steep decent) until we reached the last 200m. The brake pedal went soft , for top half, then hard. Second push on pedal was hard to the top.Later when the brakes had not been used for a time, the brakes worked as usual, hard on first press.
Yesterday crossing Melbourne from Port Albert to Geelong , under brakes as stop and go on highway, all good until bottom of Westgate bridge, when again the brake pedal went soft on top half, then solid. Two presses and brakes were good to the top of pedal.
Brake fluid changed one year ago (dot 3).
What may be going on?
The problem could be in either half of the split system, there is a valve that must see balanced pressure between both halves of the systems, if it does not the valve will be forced into a position that will block the half of the system with the least resistance, this stops the pedal going to the floor and half the brake system functions, a quick stab of the pedal will give a full pedal feel, but only half of the system will be operating.When the brakes are not used for a while, the next operation of the pedal could shift the valve back to the central position and both halves of the system function.
The fact the pedal does not remain spongy after a partial failure makes water boiling to steam and causing 1 half of system to become in operative less likely to be the only problem, I think there is more than one problem.
The next issue is, the shuttle valve that protects against a total system failure because by one half of the system has a trip pin that should hold the shuttle valve against the failed system shut off and should cause a brake fail warning light to appear on the dash, this appears to be non functional and this should be rectified as soon as possible along with the full system flush and clean. This unit lives in the side of the master cyl, most commonly a pink colour plastic upper body with a 2 wire plug attached.
