s40 brake problems

[bobthecabbage]

Originally Posted by Cold Fusion

I wish I'd spotted his earlier I could have saved you a heap of trouble. The symptoms you describe are solvable in the following order, Brake master cylinder then ABS, it is usually one or the other. As a point of interest, if you take the ABS block to pieces there are a number of valves inside, one of which will be sticking, a good clean is all that is necessary to get the things working properly again. The cause of sticking valves is always dirty brake fluid...

Change the brake fluid every two years - no more problems

And don't push old fluid back up to the reservoir when you put new pads on. I say this till I'm blue in the face. Doesn't matter what you do with it just don't push it back to the reservoir!

[Clan]

Originally Posted by SYL

Not sure where you are in London?
Would appreciate if you could sort out similar problem for me if you like.
Brakes have always been okay until about 6 weeks ago when I noticed that when the engine is cold - brakes are terrible, as if nothing is happening.
However, after the idling speed drops to normal - brakes are okay.

Let me know if you can help with repair - payment of course!

The electric brake vacuum pump isnt working , it's purpose is to prevent exqctly what is happening to your brake pedal .

[pierremcalpine]

Originally Posted by SYL

Not sure where you are in London?
Would appreciate if you could sort out similar problem for me if you like.
Brakes have always been okay until about 6 weeks ago when I noticed that when the engine is cold - brakes are terrible, as if nothing is happening.
However, after the idling speed drops to normal - brakes are okay.

Let me know if you can help with repair - payment of course!

I had similar symptoms a few years back. If you do a search on the forum you'll come across a few other who have experienced same. In many cases it has to do with a brake vacuum hose that is malfunctioning. It's the one that connects to the front LHS of the manifold and then dives towards the firewall and down near the master cyclinder. It's got a sophisticated check valve assy on it and I think that's what ends up failing. Pretty scary when you get this and strangely all reverts to normal when the engine warms up!

Here is a link to the thread I reference above:
http://www.volvoforums.org.uk/showth...um+hose&page=2

[ww1dm1]

Originally Posted by Clan

The electric brake vacuum pump isnt working , it's purpose is to prevent exqctly what is happening to your brake pedal .

There is an electric brake vacuum pump? Surely not every x40 has this? And why is it needed anyways?

[bobthecabbage]

I imagine turbo petrols would need an electric pump for when the turbo is boosting.

It is worth checking the valve where the vacuum pipe attaches to the brake servo as I believe there is known issue with the plastic splitting. The split can be very hard to spot.

Certainly sounds like a possible lack of vacuum. The pedal would be very firm in this case and go soft once you had achieved a vacuum.

[Clan]

Originally Posted by ww1dm1

There is an electric brake vacuum pump? Surely not every x40 has this? And why is it needed anyways?

on autos and some manuals ... mounted under the arch near the battery ...

It is needed because on cold start the idle speed is raised to heat the catalytic converter quickly, after a minute or so it reverts to 900 rpm , whilst the throttle is open at higher rpm there is very little vacuum the manifold for the brakes . if you sit there with the ignition on pumping the brake pedal you can hear the electric pump whirring . sometimes with a small leak of vacuum the pump works full time and either wears out or burns out as it s not designed to run full time , just long enough to top up the vacuum .

[pierremcalpine]

Originally Posted by Clan

on autos and some manuals ... mounted under the arch near the battery ...

It is needed because on cold start the idle speed is raised to heat the catalytic converter quickly, after a minute or so it reverts to 900 rpm , whilst the throttle is open at higher rpm there is very little vacuum the manifold for the brakes . if you sit there with the ignition on pumping the brake pedal you can hear the electric pump whirring . sometimes with a small leak of vacuum the pump works full time and either wears out or burns out as it s not designed to run full time , just long enough to top up the vacuum .

Damn - now that's an explanation! Thank you!

[ww1dm1]

Originally Posted by bobthecabbage

I imagine turbo petrols would need an electric pump for when the turbo is boosting.

It is worth checking the valve where the vacuum pipe attaches to the brake servo as I believe there is known issue with the plastic splitting. The split can be very hard to spot.

Certainly sounds like a possible lack of vacuum. The pedal would be very firm in this case and go soft once you had achieved a vacuum.

But why would you need the brakes when the turbo is boosting? Wouldn't you step off the throttle before you brake?

Originally Posted by Clan

on autos and some manuals ... mounted under the arch near the battery ...

It is needed because on cold start the idle speed is raised to heat the catalytic converter quickly, after a minute or so it reverts to 900 rpm , whilst the throttle is open at higher rpm there is very little vacuum the manifold for the brakes . if you sit there with the ignition on pumping the brake pedal you can hear the electric pump whirring . sometimes with a small leak of vacuum the pump works full time and either wears out or burns out as it s not designed to run full time , just long enough to top up the vacuum .

Alright, though the cold start RPM on mine never really goes above 1000, I doubt much throttle is needed for that, vacuum should be fine. Though at the same time I think mine doesn't have this pump. Why only autos and some manuals? Maybe they started fitting them only on P2 and raised the cold start idle RPM?

[bobthecabbage]

Originally Posted by ww1dm1

But why would you need the brakes when the turbo is boosting? Wouldn't you step off the throttle before you brake?

Haven't you heard of left foot braking? So you can keep the throttle in to keep the turbo on boost?

[ww1dm1]

Originally Posted by bobthecabbage

Haven't you heard of left foot braking? So you can keep the throttle in to keep the turbo on boost?

Do you seriously think that Volvo added an electric vacuum pump so their compact saloon/estate owners can employ rally techniques?