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MG MGA - Brake servo issue

I have just fitted a brake servo to my A. When I start the engine the brakes are applied (not touching the brake peddle)? Not sure what I have done wrong - any help would be appreciated.
F Watson

If its a PBR VH44--the hydraulic pipes need reversing.
The outlet pipe is at the end of the cylinder. Easy to mix-up.
I.W. Cowen.

The servo is a TT3949. I am sure it is connected correctly - the only issue might be the angle of installation of the unit? When I start the engine the brakes lock on and after a minute they are free again.
F Watson

Frank, The servo can only put pressure into the system if either the air valve is open or you have leak to atmosphere at the back of unit. The air valve is lifted to allow atmospheric pressure to the rear "can" of the unit by the movement of a small piston, under the diaphragm, being moved by the increase in hydraulic pressure when you put your foot on the pedal. If it is opening the valve without the hydraulic pressure, that piston may be stuck open., this is quite common on old units (and some of the rubbish new units). Try disconnecting the vacuum pipe and blanking off the manifold off-take. This should solve the problem temporarily, show the fault and give you un-servo'd brakes.
Leaks can be past the air valve rubbers, a split rubber hose between the valve and rear can, a badly seated diaphragm between the two halve of the unit or a slack compression band between the two halves.
Allan Reeling

Come on Mr Watson, We all take great pleasure in offering our, sometimes, pearls of wisdom, but we also like the feedback on the issues posted!
Allan Reeling

So sorry. I have sent for a new air intake kit as that seems to be the issue.
Thank you all for your help which made me focus on this area.
Go Well
Frank Watson
F Watson

This thread was discussed between 22/10/2017 and 01/11/2017

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This thread is from the archive. The Live MG MGA BBS is active now.