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MG MGA - slipping clutch

Hello, I need help with a slipping clutch on the TYPE 9 5 SPEED. It only has 2000 miles on new clutch disc,but does not slip until car is run for about 30 min.I did no
t replace the pressure plate on new engine.THANK YOU JOHN
John Gordon

No freeplay at master cyl
R J Brown

Did you replace the clutch disc? A worn clutch disc will slip (too thin). Otherwise you may have oil on the clutch disc, most commonly due to crankshaft rear seal leak. This much oil would leave a puddle where you park. Also noted, no free play in the master cylinder push rod can cause clutch slip.
Barney Gaylord

RJ,1/2 in.of freeplay at M.C. BARNEY, clutch slips only after car is warm,
John Gordon

That is too much free play at the master cylinder.
Set as per the Workshop Manual.
However, this will not be your problem.

Mick
M F Anderson

John,
So it will pass a stall test (stall) when cold and fail (slip and keep running) when run for 30 minutes?

Ralph
L Poupard

Thank-you,, Ralph,I ran this new clutch for 2000 mi..IT should not be slipping.I am trying to avoid taking out the engine if I'm not sure what the cure is. LONG WINTER AHEAD!!!JOHN
Thank-you
for the input,Mick, I will adjust length of play.
John Gordon

Next time it slips, reach underneath and see if you can push the slave cylinder back a bit. Only thing holding the slave cylinder from retracting is (supposed to be) a very light spring inside the cylinder. If you can't push it back with your fingers, you have a hydraulic problem in the master cylinder obstruction fluid return, or perhaps a collapsed hose. If you can push it back with your fingers, then the slipping is something awry inside the bell housing,and the engine will have to come out for clutch inspection and repair.
Barney Gaylord

Thanks BARNEY, I always read your site first. That's where I got the balls to do the restoration myself. What worries me,is why does it not slip right from the start? JOHN [CAN'T PUSH IN SLAVE]
John Gordon

If you have an obstructed system that is not allowing the fluid to return to the master cylinder freely, then when everything warms up the fluid in the system expands causing the slave cylinder to put pressure against the throwout bearing and thus causing your clutch to slip. Just my 2 cents worth thrown in with the others.
Ed Bell

If you can't push in the slave, the fluid is being wrongly restricted from returning to the master cylinder.

You have a fixed amount of fluid in the circuit between master cylinder piston and slave cylinder piston. In operation, when pressing and releasing the clutch pedal the same fluid simply flows back and forth between master and slave with (almost) no fluid exchange to the reservoir. The reservoir is there to accommodate thermal expansion and any loss of fluid over time.

If the master piston and seal are not allowing fluid to return to the reservoir, then thermal expansion of fluid in the line and slave cylinder will cause residual pressure in the circuit that will prevent the slave piston from returning all the way to original rest position. Therefore it works when cool but slips when hot.

Next test it to open the slave bleed nipple and see if you can press the slave piston back some, allowing some fluid to escape. If the slave still does not move, then the slave piston is stuck, and out likely need to replace the slave cylinder. If this works, then the obstruction is farther up stream. Pump the pedal until the clutch works again.

Then crack the steel line open farther upstream, either at the input end of the hose or at the master cylinder connection. This will make a mess, so be ready to deal with spilled fluid. If opening the line between pipe and hose does not allow the slave to be pushed back, then you have a clogged hose. If that works but opening the line at the master cylinder does not allow the slave to be pushed back, then you have a clogged pipe (look for a kink in the pipe). If hose and pipe are clear, then the obstruction is inside the master cylinder. Maybe order a repacking kit before you take it apart, as it may be as simple as a rolled over seal edge.
Barney Gaylord

This thread was discussed between 07/11/2011 and 08/11/2011

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