MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Rebuilt brake master cyl. woes

='79 mgb roadster=
I recently pulled the MC and replaced the seals, making sure all were oriented correctly and lips not turned back when reinserted. Upon reassembly, the primary piston ass'y was a BEAR to insert, had to use clamps to get it in far enough to place the circlip.
When mounted in the car, the brake pedal travels about 1" to a rock-hard stop (emergency brake is off. btw). Opened a bleed screw on front and rear, no change in pedal behavior; hard to bleed the system with no pedal travel.
Any ideas out there? The sun is shining and I need to get this baby on the road!
Thanks!
Chris Foleen

This is why I usually buy rebuilt MC's. Found them at Advance Auto Parts for about $50.00. You have to reuse your fluid reservoir but it sure eliminates the hadaches!
william fox

Chris,

The pistons should not be a bear to insert. You should press down on it with a screw driver to hold in to put in the C-Clip.

Couple of things: did you use the AP Lockheed repair kit from Moss? VB had a no name kit in which the rear piston seals did not match up with thes one I took off the piston. I tossd that kit and used the AP Lockheed Kit (the only kit you put use on the MBC). Also the AP Lockheed kit has instructions, the no-name kit did not.

Second, the two springs of the MBC can not be put in reverse order. Reversal of order will result in the MBC misfunctioning. I believe "Black (colored spring) goes in back"

Also did you make sure you put the pistons back in the right order.

Finally, be sure to use rubber grease available from most LBC supplyn outfits to lubricate the seals before insertion (this does not prevent malfunction, but prevents premature seal wear and tear).

Hope this helps.

John D. Long
J Long

John,

Thanks for your thoughtful suggestions. I think I have the "no-name" kit you refer to - no instructions, and extra pieces which I gather are meant to work in either the early (wedge reservior) or later (square reservoir, which I have) BMC.
In the mean time, I disassembled the unit, checked *all* the seals and reassembled, making sure the springs were in the right order and the piston units also. This time I had no trouble getting enough range of motion to get the circlip in - I think I had inserted the stop pin incorrectly before.
I bench-bled the unit, re-installed it, bled the lines, and *voila* the @#$%! thing leaks around the (new) pressure failure switch! Any idea why would it do that?
Thanks!
Chris Foleen

Sounds like the shuttle piston "O" ring seals in the pressure failure switch body are kaput and are
leaking brake fluid up through the switch.

This could also be the cause of your extra 1" brake pedal travel.

A new pressure failure switch will not cure this, nor is it designed to hold back brake fluid.

The center chamber where the pressure switch screws into the brass body should always be dry.

Fortunately, renewing the seals here is a fairly straightforward operation. At least, it is much easier
than having to rebuild the brake master m/c. The caveat here is: If you goof up anything, then you're
looking at spending very big bucks to get a factory-new replacement.

It is easier to do this if you remove the assembly entirely and work on it on a bench. Unscrew the threaded end fitting and rap the body on a bench a few times to coax the piston out. Do not scratch
the piston by using bare pliers to extract it. Wrap any pliers with cloth or tape to protect the finish on
the shuttle piston.

There are 2 sets of "O" rings included in the rebuilding kit. One pair is for mid-production cars. The other pair is for late production cars. They look very similar to each other - but they're not the same. The included instructions will detail this. Wet the piston bore with brake fluid or Lockheed brake rubber seal grease when you reassemble the unit. Never install seals dry. Be sure to position the
piston switch detent in the middle of the switch body before putting it all back together.
Daniel Wong

This thread was discussed between 12/07/2002 and 14/07/2002

MG MGB Technical index

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