VAC pump (HDi) verses petrol brakes

[Welly]

Can someone with a HDi check this for me please......

With the engine at tickover, pump the brake pedal, after several times the pedal goes solid (like there's no servo assistance) keep the pressure on and the pedal slowly sinks down a bit as the VAC recovers.

Mine does this, and I am beginning to think the VAC pump is not quite running as it should, I'm also getting variable performance at times and this will also point to the VAC pump not operating the Turbo wastegate properly.

As I remember, with a petrol engine you can pump the brakes as many times as you want with the engine running and the pedal won't go solid on you.

See if you can try it and let me know?

Cheers

Welly

[jameslxdt]

As I remember, with a petrol engine you can pump the brakes as many times as you want with the engine running and the pedal won't go solid on you.

this is because a petrol engine at idle has an infinite supply of vacuum, a vacuum pump can only supply as much as fast as its running, so try the same test but hold the revs up to about 2,000 rpm,
but its normal for the pedal to go hard after a few pumps
the minimum test to for the mot is as follows,
with the engine switched off, vigorously but slowly pump the brake pedal approximatley 5 times, the pedal should go hard, keep the pedal depressed and start the engine, after arround 10 seconds the pedal should become soft again, if it doesnt it will fail the mot

i wouldnt worry about it welton, my old diesel had 180,000 miles and the vac pump was a bit lazy but the brakes on that thing were amazing, better than my petrol 406 i have now