Brake Booster and Check Valve

[Mpgeslak]

I am trying to diagnose what is causing my brakes to be very soft with limited stopping power.  Brake Pads are new and my assumption is the Callipers are not getting much brake fluid pressure.

Having searched the forum I will be replacing the Master Cylinder and the Flexible Hoses as I don't their age (the master cylinder shows a great deal of rust) and it seems this is likely cause.   

In addition, I think I may have a leak in the Booster.  I have the situation I have read in posts in the forum about the RPM increasing when applying the brakes, and mine is increasing about 300 RPM when I apply the brakes.   The thing that seems strange is I don't seem to have a check valve in the car.   There is a single hose between the Separator and the Manifold, I assume this is a problem?  Could it be causing the RPM to rise? 

Any thoughts would be appreciated.

[Mpgeslak]

An update on my situation:

I read in my Workshop Manual that the check valve can be in the connector pipe coming off of the Booster and I found a similar reference in the forum.  I removed the pipe and no check valve was present.  Have concluded that there is none, not sure why this is the case but have ordered a check valve and will install this weekend. 

Not sure the impact of not having the check valve and the functioning of the booster.

Any thoughts are welcome

[stickandrudderman]

Increased RPM when depressing brake pedal is a sure sign of a failed booster.

[Mpgeslak]

Thanks for the response, much appreciated

Any thought on what impact not having a check valve installed would have on the Booster and could it cause the RPM or other issues?

[Pawel66]

Not sure what exactly happens when you do not have it at all, but when I installed it by mistake in the wrong direction, I had no brakes. I mean: very heavy brakes, you have to really press it to get any response. Can kill yourself...

Please look at the picture to install the check valve in the correct direction.

I have a little increase in rpm when I press the brakes pedal - maybe by 50rpms but then they drop immediately when I keep the pedal pressed. When I had failed booster, the increase was much higher and permanent.

I would install the check valve and see what happens.

[Mpgeslak]

Thanks Pawel.

I have ordered the Check Valve,  Brake Hoses, and a Master Cylinder and will install on Saturday.  I am hoping this solves my problems. 

Will report back.

[Minerva]

No check valve would give no storage of vacuum, so if the engine stalled you would at once have a hard pedal,  also I would think that the servo power would fluctuate depending on inlet manifold vacuum, i.e. open throttle would have poor assistance.

[Berggreen]

Not sure what exactly happens when you do not have it at all, but when I installed it by mistake in the wrong direction, I had no brakes. I mean: very heavy brakes, you have to really press it to get any response. Can kill yourself...

Please look at the picture to install the check valve in the correct direction.

I have a little increase in rpm when I press the brakes pedal - maybe by 50rpms but then they drop immediately when I keep the pedal pressed. When I had failed booster, the increase was much higher and permanent.

I would install the check valve and see what happens.

Hi Pawel

I just changed the check valve and I got in doubt, if I installed it in the correct direction.

See pictures. I have it with the arrow pointing from the brake booster to the manifold. Is that correct?

Thanx,

Christian

[Pawel66]

I think the other way .
Flow needs to go towards manifold - air is sucked out.

[Berggreen]

I think the other way .
Flow needs to go towards manifold - air is sucked out.

Hmmm isn’t that what the arrow on the check valve indicates, when it is pointing towards the manifold, as I have mounted it now?

[Pawel66]

Yes, to the manifold - must have misread you, sorry.

[Berggreen]

Yes, to the manifold - must have misread you, sorry.

Great, thanx Pawel!

This was also how the old check valve was pointing. But I was unsure if it at all worked as it broke up, when I tried to remove it, and as the vacuum line has been taken off a couple of times by several workshops, there is no guarantee that they had put it back correctly.

Cheers,

Christian

[Pawel66]

It is, actually, shaped in a way that points flow direction. Still, whenever this line was disconnected for whatever reason, I learned to put gear in with caution...