SO, what do you think was going on here ? Just "stiction" on the outboard pistons, and they
stuck in their position due to the rubber boot and a little grime just holding them there or what ?
They would seem to have been working properly as you drove, so was it just some quirk that they hung up, all in a similar position, and only on the outboard side, when you started to take things apart ? A little Odd to say the least, but if the outboard pistons were really stuck in that position, you'd expect corroded cylinder bores, a "tide line" in the bore as well as on the piston, poor braking performance and tell-tale signs of a stuck piston on the outside of the rotors.... none of which do I think you had, correct ? So perhaps they all (outboard) assumed the position based on the line pressure, and it's all normal- it just took a little pressure to get them to move....Or am I missing something here ?
The rotors, both sides had tell-tale signs alright The outer side's were both worn right down, one side (passenger side) very bad, 14-16mm depending where you measure and the drivers side was at 19mm (See attached picture of the
passenger side)
I've measured the rear's and they are good, one at ~21.5" and the other ~22" or better
As for why they stuck out? I'm still looking for that answer, and hope to find it before I put it all back together and have it happen again.
Here's what I know:
-The flex-lines are probably (99% sure) original to the truck, they still have the paint on the nuts, as did the bolts holding the rotors ect on.
-The Pistons from all the calipers looked good, even on the severely failed side that the caliper cracked and the dust boot was near non-existent, no odd corrosion or even sand/dirt/ect behind the boots
-I haven't driven the truck in much, if any salt, in deep snow, but no salt
-One of the inner pistons
may have been stuck I say may have been because it retracted with the C-Clamp, but it did seem harder than it should have been, but i've never done a Unimogs calipers before, so who am I to know?
-The differential pressure light came on once before when I first got the truck, but I topped up the fluid and it was all good, obviously a sign I should have investigated further.
The truck developed a brake squeal after the light came on, I suspected wet pads, so I took the wheel off, and visually inspected, I didn't see anything, after going through some snow, it disappeared, I though maybe it was a rock, but it returned right before the failure, and I couldn't pour fluid in fast enough.
My thoughts on possible causes (I could be totally out to lunch here, I'm shooting in the dark)
-Truck has a 4 wheel park brake that applies air to the front brake system for winching, perhaps a valve got stuck slightly open with crud or similar and clamped the front brakes down a bit? But why only the outers? I had just finished winching a dodge the night before. however the indicator light works, and it was off after releasing the brakes. If that were the case, you'd think they'd come back out...since the brake system still has air.
-Collapsed flex line, most likely candidate IMO, new ones are sitting in a box waiting for the long weekend. Both sides though?
-I had to two foot brake to avoid a minivan turning right from the left lane, It was close, my winch cable rubbed her back tailgate on her van, locked up all 4 tires, its something to see on a mog on dry pavement, perhaps something happened there? It was shortly after (2-3 weeks I think) the differential pressure light came on and the master was low)
There are no other sign's of leaks that I can see anywhere, but when the light first came on it was the outermost master reservoir, and when the caliper failed on the passenger side, it was the innermost that was empty.
I assume the brakes are split into "Right front/left rear" and "Right Rear/Left front" system, I looked in the manual but it wasn't too clear.
:surrender:
Out of all this, oddly enough, I didn't feel the truck pull to one side at all, ever, nor hear grinding noise, there must have been grinding from the rotors, but I guess I couldn't hear it over the sound of the mog.
I know that rotor got eaten quick, because just before winter I had all 4 tires off, and a visual inspection was done of the pads, there was at least 60% remaining on the fronts, more on the rears, and the front pads were down to the metal, whatever it was that happened, happened recently, also the delivery inspection was done when I first got the truck and all was good then as well, little to no change in pad wear in the first 6000km that I owned the truck.