I think its an air pressure release valve this sits on top of a small vertical tank mounted above the rear axle and is hissing all the time the truck is running the air pressure takes a long time to pressure up because of this as occasionally it does not hiss and the pressure stays good. anyone know what this is called??? and or how to remedy it. ta.

colin sykes, March 2008

Hi, I know this is an ooold thread, but I was hoping you could spread a little light onto this rubber stopper with a spring inside? Where`s this little beaty located?

Danile, October 2013

My ford cargo parking brake valve is leaking air when it is on ,can it be taken apart and repaired ?all i can imagine in it is rubber o rings ?

Ian, July 2008

Hi it was me that asked the question originally - problem now solved - - - the little valve on top of the cylinder is a safety pressure release valve which was actually fine and doing exactly ehat it should do i.e hissing all the time because there was a fault elsewhere it turned out that there is a little rubber stopper and spring in the air line going to the rear brakes this spring was very weak so the air was back feeding . I replaced this rubber and spring and hey presto problem solved.

Colin Sykes, June 2008

Normally the valve requires dismantling and cleaning out. Grease all seals etc with rubber grease. Occasionally a spring is broken which must be replaced. If this does not help try replacing the air pressure governor valve situated ontop of the engine by the compressor.

Michael Martin, May 2008

Your Cargo 0813 would have an air over hydraulic braking system.
What you describe sounds like the Parking Brake Actuator and the Quick Release Valve which is mounted on it. In an air/ hydraulic system all of the wheel cylinders are actuated by hydraulic pressure. There will be no air involved at the rear brakes - for the service braking system that is. However the parking brake is applied by a large spring and it requires air pressure to release the brake - i.e. when you move the parking brake (hand brake) lever forward in the cab, air pressure is sent to the actuator which operates the brakes via mechanical linkages. The Parking Brake Actuator looks like an inverted pudding bowl sitting on top of a soup bowl with a clamp around the middle! It's attached to the chassis rail above the rear axle. The Quick Release Valve which is mounted on the PBA could be defective or you might need to tighten some connections. Be warned: do not attempt to dismantle the actuator chamber without the correct equipment as there is a heavily loaded spring inside and people have been seriously injured while attempting to do so without following correct procedure!
The only other valve in this area - i.e. near the rear axle - is the Load Apportioning Valve (LAV) - this regulates the amount of braking effort applied to front and rear wheels in response to vehicle weight/loading. It has a spring attached to an arm and the chassis. On an air over hydraulic system this will be a fully hydraulic valve so there is no possibility of there being air hissing from it so that suggests the Quick Release Valve!
One assumes that you have 2 pressure gauges in the cab and that both gauges take time to build up together and not just one.
Hope that helps.

JD, March 2008