Turbo Woe's

[Lighty]

A leak anywhere in the vac system will cause this, the valve you are referring to is the no1cause of this issue (as seen on C5 2.2hdi,s)
The blue smoke is possibly something else, but I would sort the vac issue first.

[rookie]

Hi Lighty

Thanks for the reply.
Can the loss of vacuum in the system really apply the brakes ?
I am not doubting your wisdom, just trying to get my head round it .

Regards

[Lighty]

It won't apply the brakes. The brakes take the lions share of the vacuum , so they suffer least from a leak, due to the size of the pipes.

[BX]

I think that Citroenxm might have made a typo. In 2001 they started fitting the 2.0L 16valve engine to the eurovan family. If it is the 16valve then djadams has given you the description. Many mechanics just tie the flaps open and block the vacuum pipe (yes djadams I see that cringe). Actual butterfly valves are used in the air intake of diesels for several reasons such as NOx reduction, bypassing the intercooler, pneumatic governing and preventing the engine from jumping when it is stopping.

[rory_perrett]

Assuming it is a conventional set-up, and that is a hell of an assumption for a Citroen, then there is no direct connection between the vacuum in the servo and the brake hydraulics. Even if due to some bizarre seal failure there was a connection I can't see how this would cause the brakes to come on .

This leads me to think that it is a problem in the brake circuit. If there is a problem, possibly with the new master cylinder, that is causing the brakes to drag and heat up then that can cause the hydraulic oil to expand leading to more brake pressure, more heat, more expansion etc. if the brake fluid is past its best and had absorbed a fair bit of water or if there is air in the system especially near the wheel ends then this effect would be enhanced. I would have thought that the fluid should be newish as the whole system would/should have been completely bled when the master cylinder was changed.

If the master cylinder is retaining too high a residual pressure for too long then even with good brake fluid you may get the problem you have if sufficient heat is generated.

[rookie]

Just a quick update.

Fitted the new vacuum valve today, did not notice any appreciable difference in performance compared to just having the butterfly valves wide open all the time, but the smoke from the exhaust appeared slightly less. (or maybe it was my imagination). There is however a very slight diesel knock from the engine when driving.

Drove the car around for about half and hour with no sign of any brake binding or locking, did not have time to do any brake investigation other than to find out that BOTH rear brake cylinders are leaking, so I suppose I should really start from there and see what develops.