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MG MGB Technical - slave cylinder rubber pushing off

I have a 71 mgb and have rebuilt and honed master cylinder, rebuilt slave cylinder and reinstalled same.The slave cylinder hose was also replaced.
The problem I am having is after some driving the rubber boot has been pushed off of the slave cylinder leaving me with no clutch pedal travel. Is this a common problem? Any solutions? thanks
Kevin Donahoe

What is the condition of the clutch master and slave cylinder push rod clevis pins? It could be caused by wear in the push rods or clevis pins. The bushings in the clutch release fork could also cause the problem. It sounds like the slave cylinder piston has been pushed out of the cylinder. If non of the items mentioned are excessivly worn you probably need to pull the engine and inspect the clutch and especially the throw out bearing.

Clifton
Clifton Gordon

Did you forget to reinstall the metal retaining ring for the rubber boot?

"... the rubber boot has been pushed off of the slave cylinder leaving me with no clutch pedal travel."

Can't see how a loose rubber boot would have any effect on this. It just a cover to keep out road debris.

Is there fluid on the boot side of the slave cylinder piston?
Steve Buchina

Like Steve, if the boot is off and now the clutch doesn't work I'd say the slave has failed and the fluid has pushed the boot off. Whilst it is possible that normal operation of the clutch could push the boot off if it were perished, the boot coming off in itself wouldn't immediately affect clutch operation.

But even that doesn't tie in with all your symptoms as reported. You say you have "no clutch pedal travel". Even loss of fluid or a failure inside the bell-housing wouldn't cause this, the pedal should still move through its full travel under the control of the pedal and master return springs. But then again if the pedal spring is missing as well, maybe the master return spring on its own wouldn't return the pedal. Can you lift the pedal up by hand? If so check the fluid level, and if that is low it sounds like the slave has failed, rebuilding these, like rear brake slaves, can be a false economy. OTOH if the pedal is stuck down and you can't lift it then you need to get the pedal box off and look at the linkages for a problem.
Paul Hunt 2

It's obvious I didn't carefully read the problem. Thanks Steve and Paul.

Clifton
Clifton Gordon

Not a solution to Kevin's question but a question of my own. The boot on my slave cylinder is ripped, is this a big job to replace? I am not that mechanically inclined and hate to start something and pay to have my mistakes fixed. I have only owned the B for about a year, 74.5 RB roadster, non-od.
Bill

Bill,
Probably less than a 5 minute job, once you're under the car.

Remove cotter (split) pin.

Remove clevis pin (secures slave cylinder push rod to clutch fork arm).

Pull push rod from slave cylinder (through rubber boot).

Leverage rubber boot retaining ring from slave cylinder along with (remains of) boot.


Installation of new boot is just the reverse, but before doing so ...

Check for internal fluid leaks - cylinder should be relatively dry on boot side of piston. If brake fluid is present, piston seal is weak (or shot) and you will need to either rebuild (not difficult if cylinder bore isn't damaged) or replace your slave cylinder with a new unit.

Because your boot was torn, clean cylinder bore on boot side of internal piston. Although other products are probably better, you can lubricate exposed sides of bore with ordinary vasaline - wouldn't hurt to do the same to new boot and push rod.

Steve Buchina

Sorry but I neglected to say that all of the fluid came pouring out, I think The slave cylinder went too far and pushed it off. What could cause this? thanks
Kevin Donahoe

Kevin,
I can only think that your rebuild (slave cylinder) wasn't done properly (e.g., bore over honed or assembled wrong.

"The slave cylinder went too far and pushed it off."
Can't happen - too far, that is.

Sounds like internal bore (slave cylinder) is too far gone and a new SC is in order. Again, fluid on the boot side of piston indicates bad seal condition (boot is not a seal, it's only a cover).

Steve Buchina

Me thinks that the slave piston wasn't returning
back into the bore after pedal release and the
master cylinder kept refilling itself and expelling
fluid until the slave piston popped out.

I'm guessing maybe the slave cyl piston could be
hung up on some dirt, or there's junk in the flex
hose that's acting as a one-way valve...
Daniel Wong

The piston should only be able to be pushed out of the cylinder, and hence all the fluid escape, if the mechanical linkage between piston and pressure plate has failed in some way. On mine it was when the release bearing broke, but if yours did it immediately after refitting the slave it must be something to do with the positioning of the slave or
the linkaage from there to the arm. Either that, or when the linkage was disconnected the arm came free from its pivots, or the release bearing fell out of the arm. In either of these two cases it's probably an engine out job.
Paul Hunt 2

From Kevin:

"... have rebuilt and honed master cylinder, rebuilt slave cylinder ..."

"The slave cylinder hose was also replaced."

"The problem I am having is after some driving the rubber boot has been pushed off of the slave cylinder leaving me with no clutch pedal travel."

"I neglected to say that all of the fluid came pouring out, I think The slave cylinder went too far and pushed it off."

-------------------------------------------------

From these comments, it perhaps follows:

Slave cylinder bore has been honed and is relatively smooth (i.e., piston shouldn't be sticking).

Hose is new and master cylinder was rebuilt (i.e., debris in line is unlikely,).

Kevin is able to shift and drive normally, at least for some period of time (i.e., clutch fork, throw-out bearing, pressure plate and clutch disc are functional).

Slave cylinder only fails after some period of driving and shifting (i.e., loses function only after fluid reserve from master cylinder has bypassed (leaked) around slave cylinder seal)

As fluid collects of boot side of piston, hydraulic pressure increases with each shift and eventually pushes boot from slave cylinder with an accompanying fluid dump and shifting failure.

Steve Buchina

Thank you Steve,
I will attempt it as soon as the part arrives.
Bill
Bill

This thread was discussed between 26/07/2007 and 27/07/2007

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