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MG MGA - clutch won't bleed

I am working on a 1957 MGA 1500 which has MGA 1600 front disk brakes, and I am using silicone brake fluid. The car has the standard MGA clutch assembly, and all of the brake and clutch pieces and lines are new. I have been trying for weeks to bleed the clutch. I have read and tried everything in the archives, but no joy. The clutch is not fully disengaging the transmission from the engine, so the gears grind and won’t shift.

Here is what happens when using the old-fashioned tube-in-a-jar method:

1. Give the clutch pedal 10 slow pumps and then hold it down. (I have also done steps 1 and 2 with only one pump and then hold-down. Results are the same for 1 pump or 10 pumps.)
2. Open the bleed screw on the slave cylinder. Many bubbles come out. Close bleed screw and let up on clutch pedal.
3. Wait 1 minute and repeat the above steps for 12 times. Bubbles always come out in the jar. (I also have repeated steps 1 and 2 for 12 times without waiting one minute. Same result: always some bubbles.) I can see that fluid is flowing slowly from the master cyl. into the jar. The clutch pedal gets harder during this operation, but it still is spongy.
4. Move on to the slave cylinder. Open bleed screw and compress the slave piston all the way in. Many large bubbles come out.
5. Close bleed screw and release slave cylinder piston.
6. Wait 1 minute and repeat the above steps 4 and 5 for 12 times. Many bubbles always come out in the jar. (I also have done this 12 times without waiting a minute between compressions.) I can see that fluid is slowly flowing into the jar from the master cylinder.
7. Return to the clutch pedal, which now feels softer than it did before work on the slave cylinder.

In desperation, I attached a pressure bleeder to the clutch slave cyl. bleed screw to try bleeding the system in reverse. I pumped it up to its maximum (30 pounds) and opened the slave cyl. bleed screw. I expected a gush of fluid back through the master cylinder, but nothing happened, even leaving the pressure on for 10 minutes. Fluid could not pushed from the slave cyl back through the master cylinder.

I have repeated this whole process on 5-6 different days, with exactly the same results. Is air coming into the system as fast as I squeeze it out? All fittings are tight and I can see no fluid leaks anywhere.

I am bewlidered and would greatly appreciate suggestions on what to do next.

Thanks in advance, Mike

M.E. Whalen

You have a master cylinder problem. You should be able to push fluid backward with very little pressure. I do the clutch reverse bleeding with a trigger pump oil can.

My best guess is that you have a master cylinder piston that will not return far enough to allow fluid to return to the reservoir.

During normal bleeding procedure, the main seal in the master cylinder may not be working like a check valve as it should. When the master cylinder piston returns it may be pulling fluid back up the pipe with enough force to suck air in paste the slave cylinder seal cup. This can happen with a freshly rebuilt master cylinder and a weak old slave cylinder. Sometimes installing a new pressure cup in the slave cylinder may fix this problem. If not, then you may be in for disassembling the master cylinder to discover what may be awry.
Barney Gaylord

Barney is an expert but I have had the same problem. What I did was take the slave cylinder off and hold it in my hand with the bleeder screw upright. Bleed in the normal way until the bubbles stop.
Barry Bahnisch

Check the clutch pedal rod adjustment. Make sure it is allowing the master to return fully. Usually not too much of a problem on the clutch side. You can gravity bleed the system by putting a hose on to drain into a clear jar. Open the bleeder until fluid drips. Then let it drip for awhile, making sure you keep the reservoir topped up. After a couple of ounces, close everything up and try the pedal. It should have a better feel. Leave it overnight then check for leaks then bleed again normally.

Let us know how you made out.
C.R. Tyrell

Mike did you resolve this and if so what did you do? bob
bk bob

This thread was discussed between 30/01/2014 and 15/02/2014

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