Clutch Master Cylinder

[DJThom]

Hi All

I have a problem with my clutch system. On the bench, the clutch master cylinder piston can smoothly be pushed in and springs back freely. I had the cylinder reslieved and all the seals are new. I've examined the piston and bore carefully and there are no burs or signs of damage of any kind.

When I put it on the car and try to bleed the system, by the second pump the piston is sticking at the bottom, requiring removal. (not fun by the 3rd time on RHD car). Then it bench tests fine, put it back in and same problem.

I am using silicone fluid, which I am also using the brake system. Brakes are good and hard with no issues.

Any suggestions?

thx
Darren

[ppnelan]

Is the pedal box mechanism working correctly?
Is it something to do with the little valve & curved spring 'washer' at the end of the piston (from memory)? I think this allows the fluid to enter from the erservoir on the return stroke, but blocks the piston off on the down stroke - something like that...
Perhaps the sleeve is not in correctly, or has not got the holes in the correct place for fluid to enter from the reservoir?

Matthew

[DJThom]

I believe it is mechanically correct and put together properly. I should add that when I first bled it about a year ago it worked fine. I had the wrong seal in the slave, which is now fixed so there are several variables changing at the same time.

[types26/36]

Had this problem once, it was not genuine Lotus(Girling) seals I fitted even though they were supposed to be the same,fitted genuine seals and no more problems.

[Emma-Knight]

sometimes on bleeding, the piston is moved forward more than on "natural" action. (there is no hydraulic resistance) So maybe put some piece of wood or felt on the bulkhead carpet to stop the pedal before TDP position (total dead pedal...).

PS: I now use silicon on clutch with no problems so far. How long do you use it on brakes?

Anna

[SADLOTUS]

Does the piston stick if you push in with a piece of wood or big screwdriver but not the pedal mechanism? the pedal maybe putting an angle on the rod going into the cylinder. .... maybe the resleeve isn't central - (er.. can that happen?)

[DJThom]

Good suggestions, thx. I'll report back when I try to fix next week

[tbsmith]

I had a similar problem on a Europa MC. I had rebuilt it with all new seals and, thinking I was doing the right thing, I also honed the bore (just like you would hone the wheel cylinders). Bad move. The rough surface caused the pedal to stick in the down position. So you might check the bore of your sleeve to make sure it is very smooth.

Tom

[DJThom]

This is going to be a strange reply, but...

I reattached the clevis pin just to give it one more go before taking the whole thing out again. I pushed the pedal down, and it felt like the clutch was working properly. So I crawled underneath, had a friend push the pedal, and sure enough, the clutch fork is moving. I bled it again (no visible air).

I have no explanation of what happened, but I do have witnesses it wasn't working right before, so I'm pretty sure I'm not going crazy.

My question now is how much stroke should the slave cylinder have from rest to full engagement?