Sanity check on trouble changing gear..

[andy willi]

replace the lot and buy genuine LUK master and slave .

andy

ps dont buy luk repset comes with valio pressure plate not good .

andy

[COLVERT]

Brian.

Quick question. There is a hole leading down from the reservoir to the part of the master cylinder that houses the piston. With no pressure on the clutch pedal fluid can flow freely back and forth through this hole thus allowing the clutch to fully engage. As the piston moves forward this through hole is closed off. Pressure builds up in the pipework and the clutch disengages.

Is this the hole you suggest is getting blocked and thus maintaining pressure in the slave cylinder ?-----------Phew, long question.

[marinabrian]

Originally Posted by andy willi

replace the lot and buy genuine LUK master and slave .

andy

ps dont buy luk repset comes with valio pressure plate not good .

andy

Last one I bought had LUK, printed on the friction material, and stamped on the pressure plate, not Valeo

In any case it was a considerable improvement over the rubbish National clutch it replaced, where the splined centre had parted company from the rest of the driven plate, strangely enough it had a Freelander LUK slave fitted too

Brian

[marinabrian]

Originally Posted by COLVERT

Brian.

Quick question. There is a hole leading down from the reservoir to the part of the master cylinder that houses the piston. With no pressure on the clutch pedal fluid can flow freely back and forth through this hole thus allowing the clutch to fully engage. As the piston moves forward this through hole is closed off. Pressure builds up in the pipework and the clutch disengages.

Is this the hole you suggest is getting blocked and thus maintaining pressure in the slave cylinder ?-----------Phew, long question.

Hi John, the make up valve for the master reservoir is located on the end of the piston, and takes the form of a spring loaded poppet valve.

The returning fluid displaced from the slave when the diaphragm springs of the pressure plate compresses the slave, returns up the pipework to the master cylinder, moving the poppet valve from it's spring loaded seat, and travelling up the centre of the piston exiting through the hole pictured below, and back into the master cylinder reservoir through the hole in the bottom of the reservoir.



Blockages in this part of the circuit lead to varying bite point, the slave cylinder not releasing fully as you describe, and of course can be remedied easily by careful cleaning.

It is amazing that prior to purchasing a new master cylinder for upward of £150, that anyone with any mechanical savvy whatsoever wouldn't investigate why this was happening.

However Ross has said that the clevis on the end of the master cylinder piston pushrod is worn, and rightly points out that replacement is the best course of action for him in this case, and I totally agree

Brian

[HarryM1BYT]

Originally Posted by marinabrian

However Ross has said that the clevis on the end of the master cylinder piston pushrod is worn, and rightly points out that replacement is the best course of action for him in this case, and I totally agree

Brian

The eye or clevis on my MC was also worn oval with use, so I guess it was the original. It seemed to cause a lot of lost motion as the pedal was pressed down and the pedal had to be pressed down hard to the floor when in brief traffic stops. Which was why I swapped it for the TAZU Mk II, which let me down out in the sticks and was replaced with the standard Rover part - both replacement MC's fixed the lost motion in the clevis nicely.

Even a small amount of wear there, is amplified by the leverage of the pedal.

[COLVERT]

Brian.

Thank you for going to all that trouble to give me an answer.---


Though why the fluid under pressure in the slave cylinder doesn't flow back through that valve when you push the pedal down beats me.

Something else must be happening that I can't grasp.---



PS.. I thought that the small valve at the end of the piston operated in the opposite way to the way you suggest in order to make sure that the part of the cylinder in front of the piston was always full of fluid.

It shut under pressure as the clutch pedal was pushed down. If it didn't close you could not generate the pressure required to disengage the clutch. ( Signed-------Puzzled in France. Lol. )