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MG MGB Technical - no brakes

I have my first MG, a 78 roadster, I have worked on lots of cars in the past but this one has me stumped. I put on new brake calipers,and repair kit and new shoes on the rear. I can't get brakes. I have been bleeding them for three days now. No bubbles, just clear fluid. Still no brakes. I can pump them up and get some brakes, but it is unsafe to drive. I am beginning to suspect the master cylinder. Oh yea I have looked for leaks, there are none.
Help
Jerry

Sure sounds like the seals are gone in the master cylinder.
The brakes could feel very low if the rears are not adjusted,
but you would still get some pedal resistance.

The fact that pumping helps does suggest the MC. Probably
best to replace it rather than attempt a rebuild if its really
old. Also consider replacing the rear cylinders and hoses
unless they're fairly recent.
Ronald

Can we safely assume that you have adjusted the rear brakes?
George B.

I did adjust the rear brakes, Twice. I appreciate the response. I hope the MC is not too difficult to repair, and/or locate a replacement. This is my next step in this project.
Jerry Hopkins

Okay, I got the master cylinder off the car, and discovered the pressure differential sensor is not on the cylinder. It appears the sensor has been removed for some time. Is this part critical?
Jerry

Jerry,
You certainly need the switch as it stops the "shuttle" or piston in the pressure differential cylinder from returning when one half of the system fails. Otherwise the piston in the pressure differential switch just "floats" and you lose fluid from the good half.
On the other hand, you must remove or at least screw out the switch before bleeding the system, otherwise you cannot bleed the system properly and the shuttle will not centralize after bleeding.
The switch also works the brake warning light to tell you that half your brakes are not working. The switches are hard to find new in OZ, but, presumably Moss in the US will sell them. Make sure you get the right one for your model as there are at least two different switches, but most pommie cars of that era had the same or similar setup.
Hope you get the MC to work.
Happy MGing
Greg
Greg Taplin

The other thing is that bleeding is often not straight-forward on the MGB. Others have their own methods but I find normal pumping with the nipple oopen doesn't get rid off all the air. On both mine after initial flow bleeding I have to get someone to really stand on the pedal while I rapidly open and close the nipple on each front caliper in turn. That *always' gets another 'lump' of air out and cures the low pedal and 'pumping up' situation.
Paul Hunt

This thread was discussed between 15/08/2002 and 16/08/2002

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