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MG MGB Technical - Slave Cylinder/Clutch Question

I have a 74 chrome bumber mgb roadster. When the clutch was pushed in and the car was in gear, the gears would engage without letting the clutch out. It would take it 5-10 seconds, but eventually the car would start to roll forward. Other than that, I had no problems with the clutch and it changed gears just fine.

I looked under the car and the clutch hose was rotting and leaking, so I replaced the clutch hose and slave cylinder this weekend. I removed the solenoid so I could work where the metal pipe and rubber hose connect. I cut the old rubber hose off close to the metal pipe and used a 13/16 deep socket to remove the nut that connects it to the metal pipe.

I've got everything back on and tightened up, but something's not right. When the slave cylinder is not connected to the pushrod, I can manually move the pushrod back and forth with no problem. When I connect the slave cylinder to the pushrod and attach the slave to the bellhousing, the rod is fully extended when the clutch pedal is up. I would think that when the clutch pedal is up, the pushrod should be pulled back into the slave cylinder, and when the pedal is pushed, then the slave pushed the rod out, thus disengaging the clutch. Why is the pushrod fully extended when the clutch pedal is not pushed in??? Does it just need to be bled more??? Does the clutch have a spring that makes the pushrod go back into the slave, or is it the hydraulics that pull the pushrod back into the slave??? I've checked and I don't have any leaks.
TBP Thom Patrick

Thom, If I understand your description of the problem it sounds like you have some internal clutch problems.
The clutch lever pushes the push rod into the slave cylinder. The throwout bearing and driven plate dermines how far the rod is pushed. There is no spring. Excessive wear of the throwout bearing and the driven plate could cause the problem. You can do some more bleeding, manually pushing the push rod in when you bleed will help, bleeding MG clutch hydraulics can be difficult. Let us know if you have more questions. Good luck, Clifton
Clifton Gordon

There is a spring, in fact two, one in the master, one in the slave. For example, if your brake pedal rod is adjusted to be too long, and there is not enough space for the internal plunger to return to allow fluid back, then the brakes will bind. ( maybe the same for the clutch ). As Clifton points out the best thing to check is that the slave pin is fully in by releasing the bleeder on the slave and pushing it back, note these new cylinders can be very tight, and need some force to push them back in. Also make sure the pin is through the end cap of the slave, and is resting on the metal plunger behind.
Tatty

When the slave cylinder is not on the pushrod you will only be able to move the arm in its free travel - ie as far back as the clutch itself will allow, there is no way you can exert enough pressure on that arm to actually operate the clutch.

When you fit the slave cylinder and bleed it, it will push the rod back to take out all play in the system.

Get someone to operate the clutch pedal while you watch underneath - the rod should move backwards by about 1/2 inch or so.

It is working normally if this is happening - only rebleed if you get less tha 1/2 inch movement or the engagement point of the clutch with the engine running is too close to the floor.
Chris Betson

As Chris notes, there should be very little, if any, movement in the assembled clutch system. The pressure of the springs on the pressure plate push the throwout bearing backwards, but not sufficiently to create any slop in the system. On three cars, with working clutch systems, I only measure about 3/8" of push rod movement. None of them have any problem in shifting, nor do they creep forwardward with the clutch disengaged. That, to me, is the final definition of a properly working system. While you are working on the system, also examine the pushrods on the master cylinder and slave cylinder. They can become oval over a period of years and cause problems of insufficient travel. The clevis pins, which connect the brake pedal to the MC pushrod and the slave cylinder pushrod to the clutch fork should also be examined for wear. It is possible for a properly working hydraulic system to not work if these parts have excessive wear. Les
Les Bengtson

Thanx Chris...your right on. I thought I was pushing the clutch in by hand, but I was only seeing the free play in the clutch lever. After I bled the system, then the pushrod would extend about 1/2 inch and retract like it was supposed to. Only problem now is the gears still engage after 5-10 seconds with the clutch pedal pushed down to the floor. Would air in the clutch line be the cause of this, or should I go ahead and replace the clutch master?
Thom Patrick

My advice is to replace the clutch master and drink beer.
Scott Rodriguez

Most likely a bad seal in the master cylinder letting the fluid leak past - pull the cylinder and examine the bore - if OK then fit a seal kit - if not fit a new cylinder.
Chris Betson

This thread was discussed between 10/02/2003 and 11/02/2003

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