OK, just to stir the pot on this one a little bit...
I can't speak precisely for the MGB on this one, but on my Midget and my
BMW 2002 (disk front, drum rear, vaguely similar in distant ways to the MG
system), the brake pedal feel is surprisingly dependent on rear brake
adjustment. If the shoes are even a little bit loose, the pedal will need
to be "pumped up."
If you haven't flushed your brake system in the last 12 months, do that
first - yearly brake fluid flushes are the equivalent of 3000-mile oil
changes: a little more often than you absolutely NEED...but why chance
Ulix mentioned two other common causes: wheel bearings and/or warped
front rotors. Any one or combination of these things can be the cause.
Here's my recommended procedure, based on cost (pity me, the poor college
Adjust rear brakes - if it's like the Midget it will take an hour - two,
tops, and it's absolutely FREE.
Flush entire brake system - Will cost perhaps two or three pints of fluid,
max. Hey, why not flush the clutch hydraulics while you have an open
fluid can and a pedal-pumper? Do the brakes first; the clutch is easier
to depress, so the pedal-pumper will prefer to do it last.
Check the front wheel bearings and rotor runout. Does the car shimmy
under hard braking? If not, rotor warpage probably isn't enough to cause
your problem. How much play do you have in your wheel bearings?
One thing I'm fairly confident it isn't is the master cylinder. The
classic master cylinder failure mode is not an initial-soggy thing, but
rather a situation where the brakes feel fine when driving, but sitting
at a stoplight the pedal will ever-so-slowly sink to the floor under the
weight of your foot.
Please make sure you get the rear brakes adjusted properly and
less-than-1-year-old fluid in the lines before you spend money on parts
you may not need.
On Tue, 27 Feb 1996, john peloquin wrote:
> Sure sounds like air in the brake lines to me. Bleed 'em!
> John Peloquin
> On Tue, 27 Feb 1996, The Warped Goat wrote:
> > I have a 1968 MGB with a strange brake problem. They work fine, it's just
> > [description of classic soggy-brakes-itis]
> > Benjy Edwards.