mchristyuk
Junior Member
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If you're suffering from an inconsistent brake pedal that has a habit of going hard and/or a strange whistling from the brake pedal area under acceleration (positive boost) then read on..
Modern cars utilise vacuum power to give power assistance to the brake pedal. Without it you'd need much stronger leg muscles to get your car to a halt as effectively! The vacuum is generated in the air intake system of your engine, as it sucks air in it creates a vacuum. This vacuum sucks air out of your brake servo to provide assistance to your leg efforts.
To protect against any positive air pressure and to keep the vacuum in the servo most cars feature a one way valve on the servo.
Early Maserati 3200's had exactly this set up.
However in a turbo car such as the 3200 you have a lot of positive pressure in the plenum under acceleration. Whilst a one way valve will stop this filling the booster with air, the problem arrises that there won't be any vacuum in the servo when you jump off the throttle on to the brakes until the positive air pressure has all been dumped by the turbo dump valves. This could give an unassisted heavy pedal for a moment until the vacuum has built up.
To fix this Maserati soon added a “Kaiser Valve†(in Maserati speak) to the brake vacuum line. This device splits the line and provides a second vacuum feed from the air filter housing. Therefore under “boost†conditions the vacuum created in the air filter box is utilised. The one way valve in the Kaiser Valve feed line ensure that no positive pressure can come up this line.
Item 6 in the diagram below is the Kaiser Valve. The one way valve is item 2.
The VW/Audi group and older BMW's used almost identical parts on a number of their cars and called them “Suction Jet Pumps†and they do exactly the same thing and are there for exactly the same reason. Below is a picture of the VW/Audi part.
The problem however is that these valves are a bit rubbish and they break (Both the Kaiser Valve and the one way in the feed line).
This wouldn't be the end of the world, except when Maserati installed the Kaiser Valve they removed the original one way valve from the brake servo itself. Therefore you can get positive air pressure coming from the plenum and/or the air filter housing back in to your servo, removing power assistance and making your brake pedal go hard.
If yours has died (or you think it's died) you have two options. Revert to the simpler original setup without the Kaiser valve, or buy a VW/Audi equivalent (Maserati originals seem to be getting hard to get). If you revert to the original setup you will need to replace the brake booster valve to include a one way valve or place an after market one way valve between the plenum and the booster.
If you go for the VW/Audi part be warned that the nipples can be a bit larger and therefore require more effort to get them into the pipework. Also some of them integrate the one way valve from the air box into them.
This job can be tackled by anybody with a Philips head screw driver to undo the jubilee clips. However be warned that the Kaiser valve is buried down the back of the engine and you will graze your knuckles and curse & swear whilst doing it! Also if you don't have a pipe coming from the front of your left hand air filter housing then the chances are you don't have a Kaiser Valve anyway... but always best to check down the back of the engine just in case..
Modern cars utilise vacuum power to give power assistance to the brake pedal. Without it you'd need much stronger leg muscles to get your car to a halt as effectively! The vacuum is generated in the air intake system of your engine, as it sucks air in it creates a vacuum. This vacuum sucks air out of your brake servo to provide assistance to your leg efforts.
To protect against any positive air pressure and to keep the vacuum in the servo most cars feature a one way valve on the servo.
Early Maserati 3200's had exactly this set up.
However in a turbo car such as the 3200 you have a lot of positive pressure in the plenum under acceleration. Whilst a one way valve will stop this filling the booster with air, the problem arrises that there won't be any vacuum in the servo when you jump off the throttle on to the brakes until the positive air pressure has all been dumped by the turbo dump valves. This could give an unassisted heavy pedal for a moment until the vacuum has built up.
To fix this Maserati soon added a “Kaiser Valve†(in Maserati speak) to the brake vacuum line. This device splits the line and provides a second vacuum feed from the air filter housing. Therefore under “boost†conditions the vacuum created in the air filter box is utilised. The one way valve in the Kaiser Valve feed line ensure that no positive pressure can come up this line.
Item 6 in the diagram below is the Kaiser Valve. The one way valve is item 2.
The VW/Audi group and older BMW's used almost identical parts on a number of their cars and called them “Suction Jet Pumps†and they do exactly the same thing and are there for exactly the same reason. Below is a picture of the VW/Audi part.
The problem however is that these valves are a bit rubbish and they break (Both the Kaiser Valve and the one way in the feed line).
This wouldn't be the end of the world, except when Maserati installed the Kaiser Valve they removed the original one way valve from the brake servo itself. Therefore you can get positive air pressure coming from the plenum and/or the air filter housing back in to your servo, removing power assistance and making your brake pedal go hard.
If yours has died (or you think it's died) you have two options. Revert to the simpler original setup without the Kaiser valve, or buy a VW/Audi equivalent (Maserati originals seem to be getting hard to get). If you revert to the original setup you will need to replace the brake booster valve to include a one way valve or place an after market one way valve between the plenum and the booster.
If you go for the VW/Audi part be warned that the nipples can be a bit larger and therefore require more effort to get them into the pipework. Also some of them integrate the one way valve from the air box into them.
This job can be tackled by anybody with a Philips head screw driver to undo the jubilee clips. However be warned that the Kaiser valve is buried down the back of the engine and you will graze your knuckles and curse & swear whilst doing it! Also if you don't have a pipe coming from the front of your left hand air filter housing then the chances are you don't have a Kaiser Valve anyway... but always best to check down the back of the engine just in case..