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MG MGA - Pumping brake pedal

I know that this has been covered many times and I've read most of the archives, but I'm looking for devine intervention here on my 60 Coupe resoration. I need help. Everything is new, new master cylinder, new brake lines, new lockheed wheel cylinders, rebuilt front calipers. I've checked all fitings and fixed all leeks and seeps. I've bled the brakes at least 10 times. I've used the conventional 2 person method, the mitivac and the easi-bleed. The easi-bleed is the easiest. I put 1 gallon of new castrol LMA fluid through the system and the pedal still pumps. The brake pedal is 1" from the floor so you can drive the car on the road. Pumping the brakes brings the pedal up another inch or so. Could there be a problem withe the master cylinder which was a brand new lockheed and still in the original wrapping.

I'm at wits end and need some new ideas.

Many thanks,

Andy 60 Coupe
Andy Preston

There are many possible reasons. You have to try them one at a time.
I will start with the first one.
Check the pushrod clearance at the master cylinder.



Mick
M F Anderson

Andy,
Think about the mechanics of a brake system. It's pretty simple. When you press the pedal the master cylinder moves a certain amount and a certain amount of fluid is dispensed. This amount of fluid moves the caliper pistons and slave cylinder pistons. If the pistons move far enough, contact with the rotors and drums occurs and no further movement is possible. You have a "hard" pedal. If you have to "pump" to get a hard pedal (doesn't drift down) you either are not dispensing enough fluid (bad MC), you have too much mechanical clearance (bad adjustment or worn linkages) or there is compression (caused by air). If you don't get a "hard pedal" (drifts down) there is a leak somewhere (external or internal). Could be a wheel cylinder, could be the master cylinder.
Good luck,
Gerry
G T Foster

Andy,

Be sure that you have adjusted the brake shoes on each wheel before bleeding the system. There are two adjusters on the front drums and one on each of the rear drums.

Adjust each wheel up tight (so it will not turn), then back off a click or two so the drum will spin without any noticable drag.

If the brake shoes have not been adjusted the MC can only push wheel brake cylinders out so far which may correspond to your low brake pedal.

Also be sure that your new MC is for an MGA and is not the smaller bore for a Sprite/midget. The smaller MC would require a longer throw for the MGA brakes. I don't recall the dimensions for each kind. Try searching the archives.

John
jjb Backman

Andy,
You probably already know this, however, there are two bleed screws on each caliper. One on the inside, one on the outside. While you can sometimes get away with bleeding just the outside one, to be sure, bleed both. I usually do the inside then the outside.
Regards,
Gerry
G T Foster

Also make sure the bleed screws are at the top!
Neil McGurk

For what it's worth, I had a simular problem with an early seventies motor bike, it drove me insane. The problem, too much travel in the pads. Cure, packed out the pads by shiming behind. Result happyness !
S Sherry

This thread was discussed between 21/04/2009 and 22/04/2009

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