MG Car Repair: clutch, clutch pedal, dot 4

Question
I purchased a 1980 mgb just a little over a year ago. Owner stated that the slave was bad. I honed the slave, put in a kit and bled the system. Clutch worked fine. Had car for a 700 mile run in July, no problems. Early August, on a drive one hour long, the transmission wouldn't shift out of 4th. Stopped, put into first and it wouldn't shift out. After a few minutes wait it shifted fine. Later that same day, same thing. Fluid level is full. Can't seem to figure it out. Help

Answer
Hi Lee,

You need to note the feel of the clutch pedal when it is not operating correctly. The pedal should have about an inch of free play then be firm to push and feel about the same firmness all the way to the floor.

Another test is to pump up the clutch pedal and put the pedal all the way to the floor and put it in gear and let the clutch out slowly and note how far from the floor the car starts to move. Then depress the clutch pedal, put it in gear again and hold it on the floor for a minute of two and then slowly let it up and note how far off the floor it starts to move the car again. A master cylinder can go bad it two ways. It can leak which is easy to see but it can also only leak past the main seal in the master and thus not leak out side of the cylinder but only leak past the piston inside. Thus no loss of fluid.

From what you tell me it is quite possible that the master cylinder is also going bad as most of the time when a slave it is bad the master is close behind it. In the dealerships we refused to do one without the other.

Another factor is sometimes a car can have "new-old stock" in either kits or cylinders which would have seals with natural rubber in them and then use old stock of DOT 3 brake fluid which would eat up natural rubber. Also there may be some aftermarket seals still out there that are natural rubber even though the newer fluids tend not to eat them up as much. To play it safe we always used DOT 4 fluid.

Howard