Xantia MOT Fail "Service brake lagging in operation (no reserve hydraulic pressure)"

[Biggles]

Hi all,

Currently working on a 2001 Xantia HDi 110 I picked up recently with a view to fix it up and get through an MOT. I put the car in for an early MOT today. It failed on welding in the usual rust trap areas on the rear sill, which is pretty straight forwards, but there is also some work to be done on the breaks. It failed on the following as regards the brakes:

"Service brake lagging in operation front and rear (no reserve hydraulic pressure with engine off)". The MOT tester seemed pretty certain this was due to a bad accumulator sphere, which seemed pretty logical.

Has anyone else come across this MOT failure before? Is it really as simple potentially as replacing the accumulator sphere?

[xantia_v6]

Brake delay is always caused by air in the brakes, so a good bleeding should fix that. You must bleed the rear brakes with the suspension set to the highest setting, then you can wedge the brake pedal with a lump of wood or a toolbox and the hydraulic system will provide the pressure.

The accumulator sphere might also be weak. With the engine idling you should be able to hear the pressure regulator ticking in land out.

If the ticks are closer than 30 seconds, then the accumulator is probably dead.

[thorter]

Very likely a leaking accumulator sphere diaphragm. This is a good source of nitrogen in the hydraulic system! Fit a new accumulator before you bother to bleed the brakes.