940 Clutch Master New seals

[jlawler]

So I'm putting in new seals on the Master Clutch cylinder from the spares car
The two seals on the piston, rubber boot and new circlip are obvious but I have this spare seal in the pack and no idea what it is for. Can anybody give me a pointer?

[360beast]

Looks like a bit like a bleed nipple cover

[Laird Scooby]

I agree with Luke on this, it looks very like a bleed nipple cover.

Before you fit your nice new seals back into the bore of the cylinder, don't forget to clean/polish it. Couple of methods, one is get some fine emery tape and an old bolt, long enough to go all the way into the cylinder while leaving enough outside to go in a drill chuck.
Cut a slot in the end of the bolt deep enough to slide the emery tape in, fold the tape so it's about twice the diameter of the bore in length with the two ends in the middle. This will be a bit like a figure 8 if viewed from the side with the two ends in the middle - slide this into the slot so you have two loops of emery tape, one each side of the bolt.

Now you can fit the bolt into a drill, feed it into the cylinder and switch on, moving the bolt in and out to get even coverage.
Don't overdo it, just enough to get it clean, bright and shiny uniformly down the length of the bore.

Clean it out with a volatile solvent such as meths, carb or brake cleaner to ensure no abrasive material remains. Give it another dose of the cleaner and set the cylinder upright, bore entry hole down to drain and dry.

Then do the smear of rubber grease on the seals, slide the piston in and reassemble.

[jlawler]

Hi
Thanks for the pointers. I have some 2000 grit paper and give it a go.

That rubber piece isn’t a bleed nipple cover as there is a hole in the middle.

Can’t see where it might go. Looking online at other suppliers of the kit they show it too. I wondered were there any variants on these master cylinders that might use it?

Also why don’t they give you a replacement for the check valve seal on the end of the plastic piston. I know it doesn’t get the wear like the sliding seals but if your going to all this trouble it would be nice to swap it.

[Laird Scooby]

I hope you don't mean sandpaper/wet'n'dry paper? Not a good idea as there is a much higher chance some grains of abrasive could come off and remain lodged in the bore, scoring the bore and new seals.

Worth investing a bit in some proper fine emery tape.

As for other variants of the clutch cylinder, easiest way of finding out is to check the listings online, should be an "Application List" somewhere on it and that should give you an idea.

As for the check valve seal, you've more or less answered your own question - if it doesn't wear, why replace it?