Question about clutch master cylinder reservoir.

[helpme]

What purpose does the rubber bulb in there accomplish? Do they go bad? Thanks.

 

[scotts90ranger]

It is a diaphragm to take up the space the piston uses when the clutch is used, it helps keep air out of the fluid but lets the fluid move around the system. I've never seen a bad one, if there is brake fluid on the top side I would consider that bad...

 

[helpme]

What purpose does the rubber bulb in there accomplish? Do they go bad? Thanks.

Thanks. I was just wondering what it does. I've had some episodes of hard shifting. On Ebay there were a number of them sold so I was wondering if they go bad. Thanks.

 

[sgtsandman]

It also helps to keep air from getting sucked into the system if the fluid gets low for some reason. Bleeding the clutch system is not fun. Mostly because the master cylinder has to be removed in order to properly bench bleed it.

 

[helpme]

I've never seen low fluid level in there. Can't you bleed it like you do brakes? Run a hose from the bleed valve back up to the reservoir, slowly pump it and make sure the reservoir doesn't run dry? Thanks.

 

[sgtsandman]

I've never seen low fluid level in there. Can't you bleed it like you do brakes? Run a hose from the bleed valve back up to the reservoir, slowly pump it and make sure the reservoir doesn't run dry? Thanks.

If you have the setup for it sure. The fluid does turn dark over time just like the fluid in the brake system. So using fresh fluid would be better.
As long as you don’t let the reservoir run dry, you can gravity bleed it and not even use a pump.

If air does get in there, due to the orientation of the master cylinder, the only way to get the air out is the remove it so it can be oriented correctly for the air to be purged while bench bleeding.

 

[gw33gp]

I think the main function of that bulb is to slow moisture absorption into the brake fluid by acting as a barrier. I feel it also helps to prevent sloshing of the fluid which can result in some leakage at the cap.

 

[RonD]

Yes, +1 ^^^, its only purpose is to limit brake fluid and air contact to prevent the fluid from absorbing moisture from the air
The reservoir is vented so fluid in the master and slave can be replaced if there is a leak, same as Brake Master reservoir is vented


No fluid should come out of the clutch reservoir unless there is a leak in the system, so its level should be consistent over the years

Unlike brake master fluid levels which will go down a bit as brake pads and shoes wear down, and the calipers and slaves retain more fluid

The Clutch slave always opens and closes the same distance regardless of clutch disc thickness, the engage/disengage on pedal travel can change but fluid level in reservoir should stay the same, which is why you don't need as much fluid in clutch reservoir, its never "used up" and I guess the black cup could also be an "anti-slosh" device, lol, so I stand corrected

 

[helpme]

Thanks all. If you've got a leak in the slave would the level in the reservoir go down? Or would air get in the line and not necessarily come to the top? I think you could jack up the driver's side and that would facilitate getting air out doing a gravity bleed. I checked my records and this slave was put on 35,553 miles ago. The original one lasted longer than that!

 

[pjtoledo]

yes the fluid can get low thru normal usage. normal for me was over 150,000 miles on a clutch, twice.

jacking will not aid bleeding.

 

[sgtsandman]

If the fluid gets low enough, I think air will still get sucked in regardless. Either way, you are going to lose clutch function.

If and when it comes time to change the slave, make sure it’s the same brand as the one you are replacing. There is two styles of coupler and they do not interchange. Or you can just buy the whole kit with the master and slave. The master is usually already bench bled with the kit. Just make sure it states so in the description.

I couldn’t get a Motorcraft slave when mine failed. So I got the kit to make sure they would connect.

 

[RonD]

When the clutch pedal is up fluid can flow down from reservoir to the slave an out if there is a leak

Its possible for air to be "sucked in" from a leak in the slave but less likely as gravity will cause fluid to flow out of the leak

There are no "valves" in the system, its similar to the brake system
The reservoir is connected to the master cylinder via a hole that's exposed when piston is up all the way, pedal up
When you press the pedal/piston down it cuts off this hole so reservoir is cut off, and fluid is forced down the slave hose and into the slave to expand it
If there was a leak then fluid would come out faster but when pedal/piston was back up at the top fluid in the reservoir would be free to flow back into the system by gravity, and of course drip out of the leak point

The slave has a bleeder that is strategically(lol) placed at the top of the slave's fluid chamber
If you open the bleeder then fluid will gravity bleed out and any air trapped in the slave will come out first

If reservoir ever runs dry then air will be trapped in the Master, and its a pain to get out
So simple thing is NEVER let the reservoir run dry