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MG MGB Technical - Sticking brakes

I have recently a 1959 MGA which has a servo fitted. My brakes stick on slightly but free after a few seconds. Have had it suggested that this is caused by the use of silicone brake fluid which does not lubricate some valve in the servo. The master cylinder was recently overhauled apparently to try to cure the prob.I intend to replace the rear brake hose to start and change to normal DOT4 fluid. I ask MGB owners because they have servos.
H L Davy

Sound like a rubber brake hose acting as a one way valve. Replace front & rear and bleed system. That seems to work 90% of the time.
Luigi

This is a common one which I suffer on both my Bs which both have silicon fluid. This I believe is part of the problem but can be solved.

Your car will have a Lockheed remote servo with the air valve on top. A small air bubble collects under the reaction piston and must be eliminated to get proper brake release. Remove the air valve and then undo the three screws which hold the base plate on until only a couple of threads are holding. Depress the brake pedal GENTLY and by finger only. This will push the piston partly out and lift the plate. Remove the three screws, the plate and then lift out the small reaction piston.

Place a "dod" of silicn grease down the piston hole and replace the piston and all other parts. Bleed the brakes out of the ns front only and the problem should have disappeared.
Iain MacKintosh

My roadster has always suffered from this and my V8 never, but a friends V8 did. All have the same servo arrangement and not silicone fluid. Chris at Octarine has said that rotating the servo so that the air valve is no longer at the top cured it for him.
Paul Hunt

If you do replace the silicone with DOT4 be sure you get every trace of the silicone out. If not, the silicone will interact with the DOT4 and form a "jelly" out of the fluid. This also causes the brakes to drag. Best to disassemble everything for a good cleaning and purge the lines.

Don't ask me how I know this.
Edd Weninger

Thanks guys for fascinating replies. Iain/Paul you have the definitive answer but I can't even see the servo because its stuck somewhere behind the RH front wing. Since the problem is not severe I will try Luigis method first. Ed - I have Texaco DOT 4 fluid which specifically says it will mix with DOT 5.
Hugh Davy

This thread was discussed between 28/04/2005 and 29/04/2005

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