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MG MGA - No brakes and out of time

I'm leaving for GT-30 in Mackinaw in three days so this is a big problem. My master cylinder was on its way out and in need of a rebuild. It would have been the second rebuild in a year so I decided it was time for a new unit. I went with a brass re-sleeved unit from Apple hydraulics. This is a 1600, by the way. They sent the bare MC and I rebuilt it with a kit from Moss. Upon installation in the car, I find that I cannot sufficiently bleed the brakes. I've read dozens of archive threads on this and I'm all out of ideas. I'm using an EZ-bleed system hooked up to an air compressor at 20psi. I have used this exact same technique a dozen times and have never had a problem bleeding the brakes. I have bled the system five times so far. I have worked the wheel cylinders by hand to expel all the air. I have cut away the front plate gasket to ensure that the piston can travel all the way forward. I have cleared the vent holes with a piece of wire. I have ensured that the piston is indeed traveling all the way forward so that it clears the vent hole (A-Antics tech tip manual). I have worked the brake pedal with the EZ-bleed pressurized. I have run out of ideas. There is nowhere else air can possibly be hiding. The pedal goes all the way to the floor with no resistance, unless it is pumped rapidly four or five times. Then the pedal will travel halfway to the floor and hold firm. As far as I can tell the clutch seems to be working fine. I can't believe that there is a problem with the resleeved unit, but you never know. Tomorrow I'm going to hone the old MC unit and rebuild it with the rebuild parts that are currently in the resleeved unit. Maybe that will tell me something. As for right now, I'm stumped and possibly unable to take my car to Mackinaw, which really bums me out.

mark
Mark J Michalak

Don't forget to check rear brake adjusters,... have you tried running a bleeding hose from each brake line to the clutch slave bleeder to keep the fluid in the system. As you know it is a very simple system. Good luck and hope to see you there.
JEFF BECKER

Mark,

Your approach is logical. A few thoughts:

After you pumped up the brakes, did you get the brake lights to come on? If not, you might have collected air below the switch. Did they come on with "normal" foot pressure? Also are you bleeding the rears first? Do you get a solid stream of fluid out of the bleeder discharge? If all of the above are affirmative, I would concentrate on the M/C.

Don
'60 MGA-1600
Don Tremblay

I think you will find that this is a problem with the piston seals of the MC. I had the same problem, and cured it by replacing the outer seal. I had to reuse an old inner one -the new seal kits were too big for my MC, causing the piston to bind in the bore. The old seal had failed (17 years old) and was failing to keep pressure in the system. Fortunately I only had the problem on the clutch, but the principle of operation at the MC is identical.

Also try adding a second gasket at the front plate.

Setting the rear adjusters will also help if you have too much travel in the system. Also check that you have got only marginal free play at the MC pushrods from the pedal.

Then try bleeding in reverse order (ie shortest line first), and see if that makes any difference.

Jeff's comment puzzles me: The clutch is a seperate system, just sharing the same reservoir, so whether it works is irrelevant. Connecting the two at the bleed nipples to "keep the fluid in the system" is just going to blow air into your clutch hydraulics, making the whole job a lot more difficult. I would not recommend this, particularly as it will also blow any crap from the old lines into the reservoir too.
dominic clancy

Mark,
In a effort to leave no stone unturned, did you verify the bore size on the MC from Apple? Stock bores are .875 (7/8 in.). Did they possibly install oversize sleeves?

Regards,
GTF
G T Foster

Mark - I believe GT has got a valid point, and it goes back to your original post which says, "They sent the bare MC and I rebuilt it with a kit from Moss." These kits are available in both 7/8" and 3/4" sizes, and the difference is not very obvious when looking at them by eye, though the cups are usually marked onthe inside as to size.

Your symptoms are exactly what would happen with cups that are just skimming the walls of the bore. A few QUICK pushes, and you build up some pressure, and the cups are pushed against the walls, while a normal push just allows the fluid to seep around the edges.

Very curious - please let us know what you find - - Alec
Alec Darnall

OK, there are a few new ideas that I haven't thought of and I will give them a try. Jeff, I'm familiar with reverse bleeding the clutch using a line from the caliper to the slave cylinder, but not bleeding all of the brakes into the slave bleeder. Can you explain what benefit this would have? I would really hope that Apple would be competent enought to send me the proper size cylinder bores, but you never know. I'll have to measure when I take it out of the car today. Also, when I ordered the parts from Moss, there is no stipulation as to 7/8" or 3/4" bore, at least on their webpage. So I can only assume that the seals are the right size but again, I will double check when it comes apart. Don, I will check my brake lights today. Can you tell me how to bleed the air from under the switch? I've been bleeding the rears first, will reversing the bleed order really do anything for me?

Thanks for all your input.

Mark
Mark

Mark,
Did you make it to the GT? If you did, you're there now and probably can't respond. Whether you did or not we're still curious to hear what the problem was.

GTF
G T Foster

mark; check that the hole that allows fluid to flow from the reservior into the cylinder bore is open. If everything seems find try reverse bleeding; Inject brake fluid into the bleed nipple. This makes sense as the fluid is pushing air up. Be sure to lower the level of fluid in the m/c first. Most auto stores have this new style of bleeder that will move fluids both ways. good luck, Bill
w.g cook

Hello again eveybody. I did indeed make the GT. The problem turned out not to be the M/C after all. Apparently there was a very large pocket of air trapped somewhere in the system. I took apart the M/C and rebuilt it a couple times to ensure everything was assembled right. Then I bled it until there was no more air coming out of the bleeders. However there was still a very soft pedal. So I took apart the rear brakes and worked the wheel cylinders by hand. I opened the bleeder very slightly and the worked the cylinder until a few air bubbles appeared. Then I would open the bleeder all the way and a collection of bubbles would come out. The fluid would then appear solid until I worked the wheel cylinder again, then more bubbles would be drawn out of the system. Eventually I pumped the wheel cyldinder until I could do it 20 times without seeing air, on each wheel. That took about an hour. Then I adjusted the rear brakes, and adjuster the pedal rods so that they were tight. This allowed me anough pressure to slow the car with the first pump of the brakes, and stop with the second. I then drove it this way to Mackinaw. The next morning, I bled the rear brakes once each the old fashioned way, with one person pumping the brakes, then re-adjusted the pedal rods and the rear brakes. The result was a firm pedal, but still with about 1/2 inch of squish. At the end of the week, afetr about 600 miles, I again re-adjusted the rear brakes and the result was a perfectly firm pedal. So it appears a combination of driving and adjusting solved the problem. Thanks to all who offered advice.

Mark
Mark J Michalak

Mark,

What do you mean by "adjusted the pedal rods so that they were tight?" Do you mean the master cylinder pushrod?
This must have a slight clearance when the brakes are off, or your brakes will bind.

Mick
Mick Anderson

Yes, I had adjusted the pushrods so that they were without the recommended clearance but if you keep reading you'll see that I re-adjusted them after the brakes firmed up. They are now adjusted with 1/8" of play.
Mark

This thread was discussed between 10/07/2005 and 18/07/2005

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