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MG MGB Technical - dissapearing brake fluid

HERE'S A PROBLEM I JUST CANT SOLVE. WHILST RENOVATING MY 1970 BGT I UPRATED ALL THE BRAKING SYSTEM, NEW REAR DRUMS,SHOES SPRINGS SLAVE CYLINDERS, FLEXIBLE PIPES AND NEW UNION CONNECTOR ON AXLE.AT THE FRONT NEW DISCS, CALIPERS,green stuff PADS AND FLEXIBLE PIPES. UNDER THE BONNET NEW BRAKE AND CLUTCH MASTER CYLINDERS. FILLED THE SYSTEM WITH NEW FLUID AND USED A gunson TO BLEED, STARTING AT THE REAR N/S AND FINISHING AT THE FRONT O/S,AS PER THE BOOK.I DID THIS TWICE AND RETURNED A FIRM PEDAL. AFTER ABOUT TEN DAYS WORKING ON OTHER JOBS I CHECKED THE MASTER CYLINDER ONLY TO FIND IT VIRTUALLY EMPTY. CHECKED ALL BLEED NIPPLES AND LINES, DRUMS OFF, CHECKED SLAVES,(NO LEAKS) CHECKED DRIVERS FOOTWELL, (NO LEAK) CHECKED MASTER CYLINDER LINE CONNECTOR,(NO LEAK)AND NO LEAK IN PEDAL BOX.GOT A FRIEND WHO IS A MECHANIC BY TRADE TO HELP ME BLEED THE SYSTEM THE OLD FASHIONED WAY, MAN UNDERNEATH AND ME PUSHING THE PEDAL UP AND DOWN TO ORDER. WENT ROUND TWICE AGAIN AND AGAIN GOT A FIRM PEDAL,GREAT ALL DONE. IMAGINE MY DISMAY WHEN A WEEK LATER THE SAME THING HAPPENED AGAIN, MASTER CYLINDER ALMOST EMPTY. CHECKED AGAIN, NO LEAKS ANYWHERE!!!! IS IT POSSIBLE FOR THE FLUID AFTER BLEEDING TO SOMEHOW GET INTO THE SERVO UNIT! EVEN THOUGH NO ONE HAS TOUCHED THE PEDAL !?!?!? HELP PLEASE, AT MY WITS END


p j mayo

thats an odd one, when i rebuilt my GT i renewed all the brake system and the only problem i had was the brakes locking on and having to dab the pedal to release them.
On yours the fluid MUST be going somewhere, have you tried laying sheets of paper under the car so you know for certain if its dripping over time? If its not leaking there my next guess would be the servo, if the diaphram has a puncture then it may leak through there. When driving do you get smoke? just sometimes with a dodgy servo fluid can get sucked into the inletmanifold and burnt off.
A P New

If you have the remote servo on the bulkhead, the fluid is almost certainly in there. Read this article from the V8 Register web site - same brake hydraulics as an ordinary MGB. http://www.v8register.net/FilesV8/V8MAR09C.pdf

Either replace the servo, or remove it completely and by-pass the pipes. The brakes will work perfectly well without it. You will have to block off the vacuum hose. Do nothing and you risk being left with absolutely no brakes at a critical moment - not fun to say the least.

By the way, please don't type in capital letters, it's much harder to read.
Mike Howlett

In reply to A. New, there is no dripped fluid under the car and the car hasn't been run(still doing other jobs),its up on ramps front and rear,so can't quite understand how the fluid would even get into the remote servo, having only had pedal movement. The servo itself is only 1 year old and not had more than a hundred miles on it since fitting (by an MG garage) I have been advised to remove the rubber pipe attached to the servo and try a dip to see if the fluid in in the container having bypassed a maybe puntured diaphram. Many thanks also to Mike (sorry about the typing error)for your input. I read the article, will do the test and speak to the garage that fitted it tomorrow. Any other suggestions are more than welcome. Peter
p j mayo

Pull the vacuum pipe off the servo & poke a piece of wire in there to use for a dip stick. I'm sure you'll find the missing fluid. Barrie E
B Egerton

Peter, here's another thought. If the servo isn't the culprit, have you checked inside the car? Sometimes the master cylinder will leak and the fluid runs down behind the pedal and is absorbed by the carpet/underlay. Worth a check.
Mike Howlett

Thanks Mike, yes I checked inside the car, removing the rubber mat and carpet after not finding any leaks from the wheels or flex hoses.some puzzle this!
p j mayo

Hi Barrie, thanks for the input,took the rubber grommet off the servo put a dip stick in and ,guess what........it was bone dry. phoned the MG owners club and his opinion was that if it had gone into the servo it could be the other side of the diaphram but unless it was punctured how would it get there? Ihave bled all rouind again checked the slave cylinders and topped once moire. Here's hoping
p j mayo

Peter,I have a 1979 MGB and had the same problem. It turned out to be the master cylinder. The fluid was being sucked through the rear seal via the vacuum booster then to the intake manifold and burned out the exhaust. New Master cylinder and my white smoke at idle (highest vacuum) disappeared. Master cylinder still full.

cheers

Gary
79 MGB
gary hansen

As Gary has said the fluid is sucked into the engine and burnt, which is why you don't find any (or much) inside the servo. Remove the hose from the servo and plug it with an old spark plug (insulator end) and worm clip and drive it for a week, and see if you still get fluid loss.
P Hunt

further to my problem with the dissapearing brake fluid.... after trying all the suggestions put forward and not getting a result I once more bled the system and after getting, a firm pedal I put the pedal as far down as it would go and put a piece of timber between the pedal and the metal seat frame thus keeping the system under pressure. what did I find whilst laying under the car with an inspection lamp? fluid seeping from the Goodridge hose where it joins the calipher. no amount of force would tighten it any further. I disconnected the Goodridge flexible and removed the copper washers replacing them with new and went through the whole procedure once more. Again all I got was seepage. I contacted Goodridge who agreed with me that undue force is not needed to effect a seal, and came to the conclusion that the flex or the calipher or both were faulty. I have sent them all back for inspection,meanwhile put my old ccleaned up caliphers back on and everything is A1 and leak free. May I take this opportunity to thank everyone that offered advice,so good to feel we have a MotorinG family. Cheers Peter Mayo
p j mayo

That's a bummer, I've replaced the calipers, and hoses, on both my cars in the past and not had that problem. I've just replaced both together on a pals car, which for various reasons he isn't able to use yet. Hope he doesn't find the same thing!
Paul Hunt 2010

This thread was discussed between 23/02/2010 and 31/03/2010

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