Confirmation about clutch fluid...

[HarryM1BYT]

Every hydraulic system has to have some sort of vent in the master cylinder, above the level of the fluid. Large commercial/ industrial hydraulic units have a vent often sealed with a drying filter.

The top of the 75's brake master cylinder has a vent in it, to allow air in surely? If it didn't, then as the brake pads wore down the fluid in the cylinder would be under a slight vacuum.

Modern motorcycles which use hydraulics for clutch or brakes, use a similar semi-sealed system. Mine uses hydraulics for both F&R brakes and the clutch.

The cover of the master cylinders have a diaphram which forms a seal between fluid and air, but yet allow the fluid level to fall. The top covers have an vent to allow air in above the diaphram. The seal is like a shallow rubber bellows. That pretty much describes the idea behind the seal in the clutch master cylinder of the 75's clutch.

[Mike V]

Update: I removed the cover above the pedals to inspect the clutch master cylinder. Here is what I found:

A light trace of something dripping down. I couldnt take a pic as my sister has borrowed the camera. But here is a mock up..



What do you guys think? Is it possible the clutch has leaked slightly or is this just the remnants of some lubricant used on the piston?

[HarryM1BYT]

The only way to prove it is a leak, is to dry it all off thoroughly and see if more fluid appears. Did you check the fluid level in the cylinder? you can't really check it except by putting a finger down into the cylinder.

Some suggest it makes the pedal easier to operate, if some lubricant is sprayed around the area of the pivot - hopefully your 'leak' might just be where someone has attempted to lubricate it.

[Mike V]

Originally Posted by HarryM1BYT

The only way to prove it is a leak, is to dry it all off thoroughly and see if more fluid appears. Did you check the fluid level in the cylinder? you can't really check it except by putting a finger down into the cylinder.

Some suggest it makes the pedal easier to operate, if some lubricant is sprayed around the area of the pivot - hopefully your 'leak' might just be where someone has attempted to lubricate it.

Im hoping so Harry. I couldnt check the level on the side and didnt want to open it and put any fingers in. Like you say Il clean it and see how I go. Theres a chance someone has tried something before as one of the screws was missing from the panel above the pedals.

[COLVERT]

Originally Posted by Phil

Just my opinion but I wouldn't snip the seal down, I agree that it is too big but it serves a purpose to seal the system from the atmosphere.
Brake fluid is hygroscopic so absorbs water, if the brake fluid absorbs water it won't do what it is meant to.
The idea of the big seal is to allow the drop and rise of brake fluid in the reservoir without creating pressure or vacuum when the pedal is depressed. Hence there is a vent hole drilled in the reservoir cap.

The reason people talk about water absorbtion in the brake fluid being detrimental is because if it reaches the brake calipers it can possibly be turned to steam with total brake loss. OUCH !!! However moisture in the clutch fluid is hardly worth bothering about because the system runs almost COLD. ie. it doesn't need changing.
Once the clutch system starts to leak topping up is hardly worth the trouble because the leak is due to wear and no amount of topping up will make THAT go away.

Colvert.

[COLVERT]

Originally Posted by Mike V

Update: I removed the cover above the pedals to inspect the clutch master cylinder. Here is what I found:

A light trace of something dripping down. I couldnt take a pic as my sister has borrowed the camera. But here is a mock up..



What do you guys think? Is it possible the clutch has leaked slightly or is this just the remnants of some lubricant used on the piston?

There are two seals. The one that operates the clutch and the other one which seals the operating rod to the inside of the car. The rod seal is the one that has gone.If the other seal has gone then you will not be able to operate the clutch.


Colvert.

[T-Cut]

I have been told that the clutch reservoir cap has a vent hole in it. I'm slightly surprised, because I have always assumed that the internal 'condom' gizmo was to allow the fluid to maintain its equilibrium pressure by allowing the condom to expand and contract. If that's not the case, and the cap does indeed have a vent hole, then why on Earth did they fit it?

TC

[HarryM1BYT]

Originally Posted by T-Cut

I have been told that the clutch reservoir cap has a vent hole in it. I'm slightly surprised, because I have always assumed that the internal 'condom' gizmo was to allow the fluid to maintain its equilibrium pressure by allowing the condom to expand and contract. If that's not the case, and the cap does indeed have a vent hole, then why on Earth did they fit it?

TC

To be absolutely honest, I just assumed that there had to be a vent in the cap - I didn't actually think to confirm it. As already said, the diaphram/condom is there just to prevent the air from getting to the fluid and thus allowing the moisture from the air into the fluid.

There really has to be a vent, otherwise temperature variations and small amounts of fluid loss would cause enough pressure to cause it not work.

My bikes front brake and clutch levers each have a master cyclinder mounted on the handlebars. The cylinders are a little smaller than a 10 pack of ciggarettes, laid flat down and cast from alloy. The side upper most is removable for topping up etc.. Directly under the cover is a bellows like flexible diaphram to keeping the air away from the fluid, which is able to expand into the master cylinder as the fluid level changes. Above the diaphram is vented to the atmosphere by breather which zig-zags its way out to a vent - to prevent dirt and wet getting in. The diaphram not only keeps the air and fluid apart in the bikes master cylinder, but prevents fluid loss directly from the master cylinder vent due to the crazy angles the shallow master cylinder is put through whilst riding the bike. To check or top it up, you have to turn the steering to level each cylinder.

[drewbie]

I think the seal is just that, so that it can be sold as a sealed for life part and kept in store without the risk of fliud leaking from it. I removed and replaced it with an 'o' ring, i bleed thru new fluid yearly using a pressure bleeder and keep the level 10mm below the top of the reservoir using a simple dipstick made from a bit of wire. This clean fluid i believe helps protect the seals in both the slave and master from faliure.

[COLVERT]

Originally Posted by drewbie

I think the seal is just that, so that it can be sold as a sealed for life part and kept in store without the risk of fliud leaking from it. I removed and replaced it with an 'o' ring, i bleed thru new fluid yearly using a pressure bleeder and keep the level 10mm below the top of the reservoir using a simple dipstick made from a bit of wire. This clean fluid i believe helps protect the seals in both the slave and master from faliure.

Clean fluid sounds like a good idea but may I ask you a question ??
Changing the fluid presupposes that the old fluid is dirty.
If it is dirty then where did the dirt come from in a sealed system ?
I guess the only place could be the seals wearing away.
If this is so then changing the fluid will not make the seals new again, just clean and worn. Clean fluid will leak past worn seals just as easily dirty fluid !!!
I think having to perform that contortionist act to replace the old fluid will afford very little gain and a great deal of sprain !! Lol.




Colvert.