Confirmation about clutch fluid...

[COLVERT]

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

T-Cut, Sir. Not having actually seen one of these gizmos, could you tell me if it is actually sealed with a volume of air inside it ??
If so then I think the way you described it's function is correct.


Colvert.

[Phil]

The condom type thing is there to allow the fluid to rise and fall. It also completely seals the fluid from air. The cap has a hole in it to allow the expansion and retraction of the condom.
At least that's what I thought but Harry has other experience.

[drewbie]

Originally Posted by COLVERT

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.

The blackening of the fluid is mainly caused by the reaction of the fluid with aluminum. Best to use a brand name of dot 4.

[FrenchMike]

Hi,

You want to know why black dirt:

Here the state of my slave seal after 70 Kmiles

Pic14.jpg

Mike

[T-Cut]

Indeed, the black contamination typically found in old fluid is rubber particles from the pressure seal on the piston. The relatively short life of these units is definitely associated with deterioration of the seal material. One might argue that flushing the debris away using a new fluid charge on a regular basis can only improve its chances of a longer service life.

TC

[HarryM1BYT]

Originally Posted by Phil

The condom type thing is there to allow the fluid to rise and fall. It also completely seals the fluid from air. The cap has a hole in it to allow the expansion and retraction of the condom.
At least that's what I thought but Harry has other experience.

No, No....

I was suggesting that there MUST be an air vent in the lid to allow for expansion and contraction. I said '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.'

I said '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.'

T-Cut suggested he hadn't realised it was vented.

Phil said 'Hi, I am more than likely wrong but I can't think of any brake or clutch circuit with a vent to the atmosphere on any model? '

[T-Cut]

The cap vent is primarily to allow air to replace the displaced fluid volume during the pressure cycle. As the slave piston returns, the volume of fluid in the reservoir recovers and air then leaves the headspace. The brake master cylinder is similarly vented. If the clutch reservoir condom is indeed a flexible diaphragm (which seems unlikely from what I've seen), then the fluid level fall/rise would be balanced by an inflation/deflation of the diaphragm without need of a vent. However, I believe (from what I've read) that the condom is of rigid plastic construction, so it's purpose remains a mystery (to me anyway). Maybe my undertanding of its construction is wrong?

TC

[Phil]

I will post some pics in a minute..

[Phil]

As promised..

[HarryM1BYT]

The diaphram/condom thingummy is very flexible. As you can see from the photos, with the condom in place it takes up a lot of room in the cylinder, it does no leave very much room fluid - most of the fluid is displaced as the condom is put back into the cylinder. I spent ages trying to work out how to refit the condom in a compressed form, so that it wouldn't displace so much fluid - in the end I gave up and simply cut the condom down.

I think, simply fitting something (a disc) a touch smaller than the internal diameter of the cylinder, which would float on the fluid - would be as good a method of preventing moisture absorbtion from the air. The less surface area between the interface between fluid and air, the slower will be the moisture absorbtion.