DIY Si
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| posted on 6/3/06 at 12:02 PM |
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Mgb gt brakes
Sorry if I've put this in the wrong place, but I need some help.
Basically my '73 gt brakes have gone wrong. The system has been bled, but the pedal is none existent on the first pump, but gets firmer with
repeated pumping. However, if left for a few seconds the pedal disappears again. Am I right in thinking the master cylinder is buggered? Or could it
be a problem with the remote servo?
Swift replies if poss gents as I need the stupid old thing to get to work tomorrow!
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JAG
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| posted on 6/3/06 at 12:08 PM |
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quote:
pedal is none existent on the first pump, but gets firmer with repeated pumping
Classic sign of air in the system. Sounds like a good 'bleed' all round will sort this out.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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DIY Si
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| posted on 6/3/06 at 12:27 PM |
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Already done. Twice actually.
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mookaloid
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| posted on 6/3/06 at 12:56 PM |
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Air is getting in somewhere then. Are you used to doing this job or is it your first time?
If it is your first time then it is possible that your technique could be introducing air at some point.
If you know what you are doing then it is possible the master cylinder is shagged.
HTH
Mark
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DIY Si
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| posted on 6/3/06 at 01:01 PM |
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Been doing things like this with old cars for years. Never had a problem bleeding brakes/clutches before. If it is the master, anyone know of a cheap
source? My local factor's want £59 +vat! Not sure of that a genuine lockheed by the way.
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paulf
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| posted on 6/3/06 at 01:03 PM |
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Most likely is the master cylinder , I had the same problem on my MGB and managed to get the brakes bled but they then failed on the way to the MOT ,
turned out to be the master cylinder seals, was fine and bled first time after changing them.
Paul.
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DIY Si
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| posted on 6/3/06 at 01:08 PM |
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Is it easier to rebuild the master cylinder or just get a new one? Time is somewhat against me on this one.
Ps cheers for the help in confirming my thoughts. Always nice to know I'm not a complete wally
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britishtrident
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| posted on 6/3/06 at 01:11 PM |
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73 --- that will be single circuit with a remote servo --- Lockeheed system almost identical to the Hillman Hunter. Lockeheed remote servos are
ver reliable --( Girling ones not so).
Master cylinder failure on this type of Lockheed mastercylinder is quite common but I would expect the pedal would diasapear completely --- If the
seal has failed should be signs of fluid leaking inside the car, other failure mode is the conical spring inside the cylinder breaks at the little
end --- bad news is is dosen't come in the reapair kit however a Mini or Hillman one fits.
Either way first check the self adjusters at the back are working and haven't run back and also check the hand brake cable isn't too
tight.
However based on a lot of experience with this type of system I would I strongle suspect it is sezied piston in one of the front calipers .
[Edited on 6/3/06 by britishtrident]
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britishtrident
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| posted on 6/3/06 at 01:16 PM |
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To add it is a very easy cylinder to fit a set of seals to.
The 100% certain way of checking it is or is not the mastercylinder is to clamp off all off the flexy hoses, then if the pedal isn't solid
suspect the cylinder -- as a final test undo the pipe at the master cylinder and screw a nipples straight into the cylinder give it a quick bleed --
if the pedal isn't rock solid it isthe cylinder for sure.
[Edited on 6/3/06 by britishtrident]
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DIY Si
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| posted on 6/3/06 at 01:17 PM |
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I was really hoping this was going to be something simple! Handbrake's not too tight, if anything it needs tightening up! If it is the fronts,
what's the easiest way of freeing them up on your own? Is there a way? The car used to brake in a fairly straight line before the problem arose.
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mookaloid
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| posted on 6/3/06 at 01:21 PM |
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quote:
Originally posted by britishtrident
To add it is a very easy cylinder to fit a set of seals to.
The 100% certain way of checking it is or is not the mastercylinder is to clamp off all off the flexy hoses, then if the pedal isn't solid
suspect the cylinder -- as a final test undo the pipe at the master cylinder and screw a nipples straight into the cylinder give it a quick bleed --
if the pedal isn't rock solid it isthe cylinder for sure.
[Edited on 6/3/06 by britishtrident]
That's what I like, a proper definitive, sure fire method for diagnosis of a problem.
Much better than guessing.
Cheers
Mark
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britishtrident
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| posted on 6/3/06 at 01:22 PM |
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If it is comming from a wheel again you can clamp each of the flexy hoses to try track it down to which wheel/axle it is comming from.
Lockheed calipers aren't easy to free -- matter of getting it to move a fraction of a mm under hydraulic pressure then pushing it back, then
pumping it out again. Once it is moving fit a new caliper seal.
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DIY Si
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| posted on 6/3/06 at 01:26 PM |
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I'd like to second mookaloid's comment. Thanks for the idiot proof guide. Got to go to work now, so if there's any more advice/hints
etc please feel free! I'll be back later to check up. Thamks once agian for all the help.
Ps britshtrident, if we ever meet, I probably owe you a beer! Not the first time I've used your replies to help.
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MikeP
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| posted on 6/3/06 at 08:05 PM |
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It seems the MGB rears can trap an air bubble 'cause of the bleed location. One tip that I've tried is to use the rear brake adjusters to
lock the brakes on, forcing the pisons together - then the air has to go out the bleed. Theory is that you don't need to do the adjuster bit,
just be sure not to have the parking brake on when you bleed them - never tried that, but locking them worked well.
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