Chicagoland MG Club: Tech Tips

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  Chicagoland MG Club:Tech Tips

Late Model MGB, 1975-1980

On 7/27/2014, Allan Thompson wrote: "Wondering if anyone has a suggestion as to what may be the cause of the brake servo on my 1977 MGB appearing to come on late and stick. When I press the brake pedal and the car slows to a stop, the servo appears to become 'active' taking some pressure off the brake pedal and 'clamping' the brakes on for a brief period. Has anyone experience of this phenomenon"?

To which Paul Hunt replied:
"Not uncommon. The air valve on the remote servo sticks which prevents the vacuum on one side of the diaphragm from filling, and that keeps pressure on the fluid downstream of the servo. My roadster has done it for years intermittently, in hot weather, usually a tap of the brake pedal releases it. But a pal's was so severe while away touring we had to disconnect the vacuum hose from the servo and plug it with a spare spark plug. Some say lubricating the air valve with silicone grease fixes it, others point to the installation instructions for the after-market Lockheed servo that shows the servo fitted with the air-valve pointing downwards instead of upwards as the factory fitted it, yet more say the air valve needs to be removed and it's cylinder polished with fine wet and dry".

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