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MG MGA - Clutch excessive pedal travel

Having fitted a new master cylinder as part of a whole brake system renewal, I find that I have excessive clutch pedal travel, i.e. clutch is only disengaged with pedal depressed almost to the floor. Clutch was fine previously. It's been bled thoroughly, no sign of air, and push rod adjusted for clearance.
There is one clue, the old master cylinder was 3/4" bore which I replaced with the correct 7/8" size, although I would have thought that the larger bore would have disengaged the clutch sooner rather than later, if that's got anything to do with it.
Any suggestions please?
J Houlgate

Larger bore takes more fluid to travel same distance as smaller bore, hence a lower clutch pedal.
A J Dee

The 3/4" bore unit would have long pedal travel. The 7/8" bore unit should be correct. Clutch not disengaging, or very long pedal travel, usually means the slave cylinder is not traveling far enough, which is a hydraulics problem. Get under the car and watch the slave pushrod as you have a helper depress the clutch pedal. Full pedal travel should produce at least 1/2" of travel at the slave cylinder (usually 5/8" if all is working well).

Short slave travel is commonly a result of air in the line. It might otherwise result from too much clearance at the master pushrod, too much pre-travel before the master piston moves. It might be the master piston is not returning all that way to rest against the end plate, also resulting in too much pedal pre-travel before the master piston moves).

At the slave cylinder, the bleed nipple goes in the top port on the side. For most cars the hose connection is on the end. For early production cars the hose connection was low on the side with a banjo fitting. If the bleed nipple is on the bottom or end port you will bot get all the air out of the slave cylinder.
Barney Gaylord

Sorry, i did not read your post properly. I was refering to slave cylinder.
A J Dee

I had to reverse bleed mine to get all of the air out of the clutch line. Pretty easy with a syringe to push brake fluid into the slave cylinder. You can see it bubble in the master cylinder if there's air in it.
Larry Wheeler

This thread was discussed between 14/07/2013 and 17/07/2013

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