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MG MGA - Brake servo non return adapter

Hi all,
I want to install a remote servo which I acquired recently, but I do not have an in-line non return adapter which screws onto the inlet manifold for the vacuum pipe. I have seen similar adapters on the net,(not sure if it was on this forum), but my memory fails me completely. I'll be very grateful for any info on where to buy one of these items.

F Camilleri

Check British Victoria here in the US. They have a kit by Armstrong which includes all parts needed to do this.I also belive they also carry the valve you are talking about.

Thank you Jeff. I will give them a try. I think you mean Victoria British. I don't have their full website address but should be able to find them easy enough.
F Camilleri

There are 2 types of check valves that I know of. Toyota used to use metal ones that screwed into the manifold and the hose attached to it. The other type is a plastic inline one like shown here:
Just google Brake booster check valve and you will find what you are looking for.
R J Brown

I am looking for the metal one that screws on the inlet manifold. Must have the same thread as the hole it screws into. I have seen this type somewhere on the net, but can't remember where. I'll try google and see what comes up. Tks
F Camilleri

When I installed my Lucas servo I did not fit a check valve but the system seems to work perfectly well. The check valve does not come as an essential component with the kit. Is the check valve an optional extra?
J H Cole

The reason for the check valve is to allow 2 or so stops after the engine quits. It also helps the idle when braking. Power brakes can act like a vacuum leak when applied.
I believe this is a good Toyota part # for what you want. They call it a union but I think it is the check valve 90404-51007.
R J Brown

Meant to say 'lockheed' in my post not 'lucas'. RB: are you saying that when the car is moving slowly the absence of a check valve would reduce the vacuum in the manifold and therefore the engine idle/slow run? When I asked about the check valve years ago I think I was told it was not necessary and tended to be used in high performance cars. Your point on braking - I suppose the worst scenario is that the brakes would revert to their non servo performance if the engine quits especially if its out of gear. I will try and see if I can replicate some of these effects in the car. I'd be interested to see if other members with servo's all have check valves?
J H Cole

With a remote servo the worst case scenario is not that the brakes revert to 'non-servo' performance; it really is worse - the brakes fail completely. Been there, done that, changed the underwear.

For more, see
J N Gibson

With the check valve the the booster is a vacuum tank/ resevoir. The vaccum level does not drop when the engine vacuum does. Most brake boosters will boost the brakes 2 or so times after the engine stops. Once this vacuum is used up the brakes revert to a non boosted condition.
Sitting still you can feel this occur. This is how I check the operation of a booster. #1 with engine off pump brakes to dissapate stored vacuum. The pedal should feel harder now. #2 While holding the pedal down start the car. You should feel the pedal drop a bit as the booster assists the brake effort. #3 remove foot from pedal and turn off car. #4 push the pedal 3 or 4 times feeling the change in the "hardness" of the pedal. This allows you to see boosted feel change to unboosted feel.
Without a checkvalve the vacuum source is only the intake manifold pressure. This pressure goes up and down depending on engine load. In a high load condition less assist would be avaiable to help push the brakes.
Without the check valve the booster would flow a larger volume of air into the manifold quickly. This could affect idle like a temporary vacuum leak. In this case a check valve serves as a smaller orifice that would slow the flow of air making the effect on idle less apparent.
Using a check valve keeps the brake feel consistant, reduces the affect brake application has on the idleing and allows limited booster function after a loss of vacuum.
The problem JNGibson notes is not the loss of vacuum causing a loss of brakes. If you lose vacuum like in plugged source, open hose or turned off engine,the brakes would work in an unassisted manner. What his post speaks of is a loss of braking because of a loss of brake fluid. The booster if faulty could eat/suck off brake fluid. A fluid level sensor in a modern car would light the warning light to warn of this condition. Having a booster makes regular fluid level checks more important.
R J Brown

This thread was discussed between 27/03/2010 and 01/04/2010

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