................. one piston has come out of cylinder and damage to the handbrake mechanism.

..................., amazed at the difference when 50% of the braking was lost and also by how much the pedal dropped.

If a piston has indeed come out of the wheel cylinder, then you've lost 100% of your braking (as there is no hydraulic pressure whatsoever in the system), which is why the pedal hit the floor.

It happened to me one a long time ago and it's not nice!

For many years (at least since 1970) hydraulic brake systems have been split into two circuits, so the brakes on at least two wheels work after seals fail on one wheel.

I had a rear cylinder fail on a MkIII Cortina, the front brakes still worked as normal.

(I did have total failures on a 1950 MG and a 1957 Ford Prefect, not fun in either case)

I wonder if the auto adjuster mechanism had seized, possibly due to the soaking in mud and anything else it must get on construction sites.

Would have thought a vehicle in such use would have been under a rough service maintenance schedule not far off the sort of schedule lorries are under, ie 6 weekly inspections or sooner for vehicles on rough service.

For this pick up i don't mean the modern method of peering in the general direction of the brakes and squirting brake cleaner about, i mean pulling out the pads, removing the drums every few months and inspecting things correctly and lubing properly on reassembly.

Looking up the parts details for that truck the rear wheel slave cylinders are bolted on to the backplate, so difficult to see how the cylinder came loose, unless Loos Han Doo was on the axle line that day in Thailand.

Had brakes fail on a fire engine once. Coming down a steep hill full tilt, rapidly approaching a T junction...applied firm pressure to the brake pedal and nowt. Turned to the officer in charge and just said "no brakes". Didn't really have time to try changing down through gears (automatic) or pulling on the handbrake, but shot out into the main road (which was generally busy but on this occasion turned out to be totally empty of traffic).

Same thing happened to several other drivers in the same machine, all of whom avoided serious consequences through luck or better reactions than me.

It might have been brake "fade" because it happened to a lesser extent on one occasion after a long run to a fire call, when the brakes were red hot and we were approaching red traffic lights. Fortunately on that occasion I had a good line of sight on all entrances to the junction and all other drivers gave way.

But naturally, I digress.