406oc.co.uk

Could any of you check your brake servo to see how it compares?
How long is the vacuum retained after turning the engine off?
On my previous 405 diesel, it would still be there days after, but with this one it's always gone the following day.
I have checked the non return valve and can't hear any hissing from the servo.
Could you see if your vacuum is still there after 24 hours (or longer) please.
Cheers.

The vacuum is provided by a small vac pump on the right hand end of the camshaft.

So, what you're saying is that your 405 could sit for 2 days, you jump back in, and the brake servo would still have vacuum BEFORE you start the engine? I don't think I've ever needed to try this but I know that every car I've had will lose it's vacuum after 3 or 4 pumps of the brake pedal with engine off... the pedal then goes rock solid.

You can test that the vac is working by getting the pedal to go solid - then start the engine with your foot on the brake..which should slowly sink down a bit.

You would be having more trouble if the pedal was going hard whilst driving about...indicating a vac leak somewhere.

I remember being able to defeat the vac system on the HDi where, with the engine running, I could get the pedal to go solid by pumping it a few times and the Vac was struggling to keep up. It seems Diesel vac systems are a bit slower than petrols to me.

Petrols have a much bigger pump

The Volvo's got an electric vacuum pump, don't know why

Of course! - Forced induction - the inlet has positive pressure in it so I guess it needs vacuum from somewhere else. That's funny, it's never occurred to me before

And once again I forgot to try my brakes before I started the engine, sorry MrBean

Hi, Thanks for replies.
Yes, I'm trying to find the reason for the difference between my previous diesel 405 and this one, and to discover a fault if there is one.
I park on the road outside which has a slight incline down. Spaces are at a premium, so the following day I jump in the car and let it roll a car's length to be outside my house, without starting the engine. I have to push on the brake pedal very hard as no vacuum is there from the day before.
When I did this with the diesel 405, there would still be vacuum even after days.
Yes, as soon as the engine starts, vacuum is there and the brakes are fine. If the vacuum goes so soon though, I guess if the engine ever cut out, there would be no brakes very quickly!
So, could I ask Diesel HDI owners to do a test.
Before starting the following day, try the brake pedal to see if it's hard to press (no vacuum).
Thanks again.

The vacuum is held in by a one way valve at the master cylinder. they occasionally leak air the wrong way which doesnt matter when engine is running. when mine leaked it did so immediately when engine stopped running. i could hear the hum as the vacuum sucked air through the solenoid valve for EGR and turbo. they are very easy remove and test. just trace the pipe from vac pump to master cylinder . the assembly it enters containd the one way valve. Just pull it out of cylinder and see if you can blow through towards cylinder end.

Mike

steve_earwig wrote:Petrols have a much bigger pump