Time to ask the Oracle (that would you guys) regarding a complete brake failure. Underwear having been changed, the symptoms are these:
Driving along, went to apply brakes, pedal went to the floor. I thought I may have felt a small - very small - amount of brake action and pedal resistance, but ... thank heavens for J gates and handbrakes (especially having one for each hand)!
Back at the house, checked driveway after a 5 minute park, but no fluid on ground. (of course, that may have stopped dripping during the hour drive)
Checked reservoir: level is normal. No signs of fluid anywhere under the hood.
No messages flagged (except the handbrake warning whilst driving).
Please, could anyone point me in the right direct to troubleshoot this? Thanks

 

How long since the brake fluid has been changed? Have you tried bleeding the brakes? That’s the first thing I would do, if they don’t pump up I would then be looking at the master cylinder and see if it is pumping fluid out, Can’t say I have heard of a complete bake fail without a reason (like pounding around a track and boiling the fluid, don’t ask)

 

That’s rare! Sudden Complete brake failure at all 4 wheels! I would suspect fluid leak - must be gushing somewhere, bad bleed nipples failure second, then master cylinder (but wouldn’t get 100percent failure) then hydraulic line failure. Heard about a problem where bad brake lines can swell so you loose pressure .... but at all 4 wheels!

 

“I would suspect fluid leak - must be gushing.” Quote
OP states no fluid on the ground and reservoir level correct, thats why I’m suspecting the M/c

 

A failed cup in the brake master cylinder can result in sudden brake failure. I have also had an abs module failure that caused an immediate and total loss of brakes in an xjs, fortunately at a very low speed.

You do not need to see fluid on the ground to have suffered total brake failure.

 

Is the pedal still going to the floor ? With the car running and not running ? I'd pull a wheel and crack open the bleed nipple and have someone pump the pedal, but it sounds like a complete master cylinder failure, which would be very strange since there are two circuits to eliminate this very problem. Very curious, very curious indeed.

 

With symptoms like you describe, check that the brake pedal pivot pin has not failed. If the pin falls out, the pedal will go to the floor but the rest of the system will be normal.

 

Thanks. I would imagine that the pedal pivot is rather hard to see, and I haven't managed to get a look at it., but wouldn't the pedal either be all floppy or jammed up if the pivot failed? The action of the pedal is smooth, and goes down to the floor in a normal arc. The pressure without the engine is weak, but there is uniform resistance all the way down, such as might be expected if there are return springs on the pedal and / or inside the booster. One can push the pedal to the floor by hand, without massive effort. With the engine running, of course it is that much easier.
With the engine off, there is a squishy / squeaky sort of a noise that comes from the brake (presumably) ABS / distribution manifold block up by the power steering reservoir, when the brake pedal is pushed to the floor.
I think I will do a bleed, starting at the DS front etc., tomorrow, and see if anything changes. It is still hard to see how the brakes went from normal to zero with no apparent loss of fluid. That implies either no piston pressure from the M/C or no fluid. The fluid in the reservoir is slightly disturbed by operating the pedal, but no level change can be detected. The pedal isn't able to 'pump up' the system either.

 

When my xjs lost brakes, a valve cup (very tiny) in the abs block had flipped/inverted which caused the fluid to bypass directly back to the reservoir. I would think that a failed stuck valve in your unit could cause a similar problem.

I have no experience with the x100 system so I'm not saying that it is a probable cause. Just another thing to look at.

 

Atlastajag1, please let us know the end of the story, if/when you can !