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MG MGA - Clutch problems again

A few months ago I inquired about my clutch not engaging therefore the disc slipped. Barney, as well as others,suggested possibly the flex line that attaches to the slave cylinder might be swollen from age. When I removed the flex line and slave cylinder I noticed the seal, in the cylinder, was twisted sideways and jammed. I removed the seal and replaced it with a new one. I also cleaned (honed) the cylinder before replacing it. I replaced the flex line with a new stainless braided one as well. Then I bled the system well. I was able to make a couple of test trips (20 miles or so) with no problems. Yesterday we were one our way to a car show and the clutch began to slip. We had the car brought back home on a flat bed wrecker. After a night of sleepless anger about what had happened, I re-bled the system several times again and everything works fine for now.

Is it possible that I didn't bleed it enough the last time (not today)? I probably did it 10 - 12 times until no more air came out. Will air in the line cause the pressure plate to not engage fully?
Joe Wiley

You may have to bite the bullet and replace the clutch.
If you are getting full throw at the slave cylinder and your clutch is still slipping that is the next step.

Rich
Rich McKIe

Rich

After bleeding the slave cylinder I now have "full throw" again. In other words the clutch is fully engaged. Maybe I wasn't clear. Is it possible for a small amount of air, which might have remained in the line, cause the slave to not fully retract? Once the air was bled this morning the clutch fully engages. I've never had this happen before in 45+ years of owning and restoring these cars.

Joe
Joe Wiley

Joe,

From what I understand of your question, my answer would be no, it is not possible for air in the system to cause clutch slip. The effect of a poorly bled system would be the opposite, i.e a binding clutch, resulting in crunching gear changes!

Maybe a piece of the old rubber tubing jammed in the slave cylinder unions/clutch pipe could cause slip by restricting the flow of fluid when you release the clutch, but not air.

Normally the clutch bleeds easily, so I would look at the cylinder piston again. The clutch friction plate is the other most likely candidate for a slipping clutch, if the slave cylinder piston is free to return.

Neil
Neil McGurk

The master cylinder pushrod(s) need a small amount of clearance when at rest. If the master pushrod is adjusted too long the master cylinder piston cannot retract all the way. That can lead to fluid not being released back into the reservoir at rest, which can cause residual pressure in the line and may prevent the clutch from engaging (especially with thermal expansion of the fluid).

Check adjustment of the master pushrod first. It should wiggle a tiny bit when at rest. You should also be able to press the pedal down a short distance (1/8 to 1/4 inch) with one finger before you feel the take up of force required to start moving the master piston.

If you are having residual pressure it the line, next time you may encounter clutch slip pull over and open the slave bleed nipple to relieve the pressure. If that eliminates the problem, then look for a problem with the master cylinder (considering you have already replaced the hose).

Some years ago there was a problem with new master seal cups being too long and blocking the fluid return hole when at rest. Solution was to install two paper gaskets for the end plate and cut holes in the gaskets to allow the pistons to retract a bit more before hitting the end plate. I have not heard of this problem occurring in the past 10 years or so, but perhaps there may be another batch of bad seal cups.








Barney Gaylord

Joe
When you bleed the system it is best to secure the slave cylinder fully home. This gives the smallest amount of volume of fluid in the cylinder and hence also the smallest chance to have air in it.
I saw that on bleeding the fork moved a bit and even when no air was coming out the bleed pipe the pedal did not move the fork enough. On securing the fork with some strong wire I could succesfully bleed the system.
In terms of air making the clutch slip I think it should not be possible unless air is in the slave and it expands on heating enough to operate the clutch. You could test this by seeing if the fork goes from loose when not operated (there should be some free play, not under load at rest) to tight. A quick waggle under the car should soon tell (note the use of technical terms - Waggle = move side to side!!)

Hope that helps

Neil
Neil Purves

This thread was discussed between 07/10/2007 and 08/10/2007

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