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MG MGA - New master, hoses, calipers, brakes still drag!

So the replacement master cylinder was thought to be the culprit. After having the front calipers rebuilt, new brakes hoses and all of the silicone brake fluid flushed out,got the car home and the front wire wheel hubs are smoking hot and the front brakes are dragging on the discs. WTF! I'm at my wits end...
R emgeeaa

So I just tried releasing the bolts on the cover plate a little and backed off the pushrod as well. No diff. Pumped the brakes a few times, felt the wheels drag, bled the left wheel, both wheels released. So now I will get some gasket material and try doubling the gasket behind the cover plate.
As another possibility. Is there any chance that the brass junction where the brake lines meet could be the culprit?
R emgeeaa

Re- Have you talked with Barney about his 'last resort' solution for providing a pressure relief hole?
J H Cole

I'm sure you've already checked when you doubled up on the gaskets, but ensure the large hole for the piston is indeed large enough for the piston to actually go through it. Enlarge it if needed, better too large a hole, it won't hurt. Marvin
Marvin Stuart

I did read about Barney's instructions on a reif hole. Unfortunately, I don't have access to a drill press. All hand tools here and an underground parking spot in an apt. building for a shop! So I'd have to hire a shop to do it.
Yes Marvin, I will certainly cut the hole larger when I make th enew gaskets.
So the fluid will have to be drained out before I take the front cover off, correct? It's the cover that holds the pistons in the bores?
R emgeeaa

What are the details on the new MC? I have said before that some of the currents MCs are rubbish. Even new ones can be badly made, with poorly honed bores etc. The one I finally consigned to the bin had differing diameters down the length of the bore.

I will put money on it being poorly poorly made.

Steve Gyles

It's a Lucas/TRW master.
So I tried new 2 new gaskets with plenty of clearance for the pistons. No change.
R emgeeaa

It sounds like it has been dragging with both master cylinders? How much play is there in the pedal linkage before it starts to move the master cylinder piston? I checked mine just now and grabbing the clevis at the end of the push rod I can push the rod inwards about 1/4" before it meets resistance where it would be trying to move the piston. If it has too much freeplay, maybe the piston is stuck in the bore. But...if the fronts dragged with both masters that seems to point to something else. Just for the heck of it I would remove the 4 way junction with brake light switch and have a good look and poke through all the ports. Could something be in there? Stranger things have happened. While things are disconnected I would blow through all the brake lines with compressed air, including the one from the master to the juction. Compressed air can pass through partially blocked tubes etc. like there was nothing there, so before reconnecting everything I would connect a short piece of hose to the end of each line and try blowing through the lines, looking for a blocked one. Another thought - you wouldn't have a kink or squash in the main brake line, allowing high pressure fluid through from the pedal, but not allowing the lower return pressure back.

Good Luck,

Hey Ralph, thanks for the ideas. I was questioning that brass junction. Most think there's nothing in there that could cause the blockage but you never know. I did check the lines thoroughly to make sue there wasn't a kink in the line.
Next experiment is to drill a new pessure relief hole on the master as per Barney Gaylord's instrucitons and see if that helps.
The first replacement master was found to be binding in the bore so it may be that this one is doing it as well.
R emgeeaa

I had problems with modern seals sticking and dragging in the bores because they were oversized. Bleeding became extremely difficult and I even found it helpful to open up the bores a couple thou and polish them smoother. Eventually the seals broke in and all is working now. Incidentally, the MC bled on the bench just fine but when installed, the pistons would not return properly. It was strange indeed but once properly bled, it stated working. My problem wasn't exactly the same as yours (soft pedal, no brake binding) but perhaps the seals are the culprit here as well? Good luck!
Steve S

Have you tried decanting some of the fluid in the reservoir and probing the very small compensating orifice hole with a fine piece of fuse wire to check that the cup is clearing it?
J H Cole

We'll definitely check the seals and we'll try to see if the cup is clearing the hole
R emgeeaa

This thread was discussed between 28/07/2011 and 31/07/2011

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