Replacing Clutch Fluid

[Vlad Soare]

Hi,

The brake fluid should be replaced once every two years, because it absorbs water over time and its boiling point decreases. And since the same fluid is also used for the clutch, I imagine the same should apply to that part of the fluid that serves the clutch.
Now, when you replace the brake fluid, you use the bleeding nipples on all calipers, starting with the one that's farthest away from the reservoir, in order to ensure that the old, spent fluid is eliminated from the entire system and none of it remains in the pipes. Good. But what about the clutch? You can't do this with the clutch, since the slave cylinder has no bleeder.
How do you remove the old fluid from the clutch line and replace it with fresh one? Is this even possible in the S550? Or are we expected to just pray that it might eventually mix with the fresh one? Given the thinness of the clutch line and the consistency of brake fluid, I suspect this mixing won't happen too soon, if at all.

Thanks.

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[Nightmonkey]

The fluid in the clutch system is not relevant to safety.
Apart from that, the clutch system does not generate the same pressures and pressure shocks as a ABS braking system, that's what the boiling point is relevant for.
In other words, even if there were only water in the line, it would still work.
You can't bleed up to the clutch slave cylinder anyway.

 

[Vlad Soare]

When driven hard for enough time I imagine that the clutch fluid would get pretty hot. And while a disfunctional clutch may not be a safety issue, it would still be one hell of an annoyance to say the least.
Does Ford actually expect the clutch fluid to last indefinitely and not to require replacement until the slave cylinder fails?

 

[Rapid Red]

FWIW, have a 99 truck, brake fluid has never been serviced, system & anti-lock work as advertised.
BTW 160k.

As long as the reservoir is sealed, how does moisture contaminate it?

If one has that mental problem OCD, and monitors the fluid level. Topping it off as the pads wear, the chances of moisture contamination rise every time the cap is removed.

Having opened the sealed system, exposing the system to humidity.

Pads wear fluid level drops. An owner later replacing the pads, the fluid overflows the reservoir.

A co-worker, ask me " brake fluid low what did I think caused that" Wanting to have a clue before taking the car in for service.

Answer "worn pads"

 

[Skye]

https://www.bendix.com.au/bendix-news/bendix-provides-insight-importance-brake-fluid-issue-12

https://blog.amsoil.com/does-brake-fluid-go-bad/

Some insight into brake fluid and moisture absorption. IMO, it's akin to why tires eventually go flat: the atoms are small enough to ultimately escape the materials. Moisture in brake fluid is same, in the reverse.

Toyota recommends replacement at regular intervals. For the Tacoma, the clutch drain/bleed is included in the service. I intend to do same with Skye.

 

[Nightmonkey]

When driven hard for enough time I imagine that the clutch fluid would get pretty hot.

The heat transfer is totally different.
In the brake, the heat from the friction work goes directly from the brake pad via the brake piston into the fluid.
In the clutch, the release mechanism is located in the center, and the friction work takes place far away from it on the outer circumference of the clutch disc.
Before the fluid boils off, the clutch will fall out in pieces at the bottom.

As long as the reservoir is sealed, how does moisture contaminate it?

The moisture is diffusing into the system, especially through the hoses.
Even new brake fluid already has a water content of up to 0.05%, and above 3% (this depends on DOT-Rating) you can talk about having an impact on brake performance because the wet boiling point drops significantly.
This means that you will probably be able to run well until you really need the brake, and only then realize that you have neglected it.

 

[Vlad Soare]

The heat transfer is totally different.
In the brake, the heat from the friction work goes directly from the brake pad via the brake piston into the fluid.
In the clutch, the release mechanism is located in the center, and the friction work takes place far away from it on the outer circumference of the clutch disc.
Before the fluid boils off, the clutch will fall out in pieces at the bottom.

OK, so does that mean that the clutch fluid is supposed to last the life of the car (or at least the life of the clutch)? Does Ford officially consider it non-consummable and non-replaceable?

 

[Nightmonkey]

Now we're getting philisophical.
What is the expected service life for the clutch / car?

Assume that at some point between 100,000 ... 200,000 km (62,000 ... 124,000 mls), you will have to install a new clutch and release mechanism, and the fluid will be new by then.

From my experience, the clutch is more likely to have a mechanical problem than the fluid in the clutch line has a moisture depending boiling problem (no track use).

 

[jacknifetoaswan]

FWIW, have a 99 truck, brake fluid has never been serviced, system & anti-lock work as advertised.
BTW 160k.

As long as the reservoir is sealed, how does moisture contaminate it?

If one has that mental problem OCD, and monitors the fluid level. Topping it off as the pads wear, the chances of moisture contamination rise every time the cap is removed.

Having opened the sealed system, exposing the system to humidity.

Pads wear fluid level drops. An owner later replacing the pads, the fluid overflows the reservoir.

A co-worker, ask me " brake fluid low what did I think caused that" Wanting to have a clue before taking the car in for service.

Answer "worn pads"

Anecdotes about your experience with a truck should not be used as an indicator of ideal service.

Brake fluid is hygroscopic. The system is sealed, but it's still important to swap fluid at a regular interval. I live 100 yards from water in a high humidity area in South Carolina. My vehicles get a brake fluid swap with high temp fluid every two years. For $50 and an hour of time per vehicle, it's a cheap insurance policy.

JR

 

[BluePonyGT]

We should get back to answering the question of how to bleed it. The only way I know is to bench bleed the hydraulic throw-out bearing, which means the transmission has to come out. There's just that simple disconnection on the outside of the transmission to the hydraulic line. Can it be reached without unbolting the trans from the back of the engine?

 

[Rapid Red]

Anecdotes about your experience with a truck should not be used as an indicator of ideal service.

Brake fluid is hygroscopic. The system is sealed, but it's still important to swap fluid at a regular interval. I live 100 yards from water in a high humidity area in South Carolina. My vehicles get a brake fluid swap with high temp fluid every two years. For $50 and an hour of time per vehicle, it's a cheap insurance policy.

JR

Oh, I see truck brake fluid is different than Mustang brake fluid.

I lived in Miami for 37 years its a peninsula, you know what that means? So we don't need your Anecdotes about living 100 yards from the water.
For the record never had a problem with water and brake fluid.

What you say is important, may or may not be. The system is sealed. Try and explain how humidity enters the system.

Can you do that?

Cheap insurance, against what I'm betting you have no clue. If water were to contaminate the fluid. It could form some rust spots on the bore of the pistons. That would/could cause the O ring to chip and leak, or jam if extreme.

 

[sk47]

Hello; I do not have an exact answer as to how to bleed the clutch fluid on a Mustang. I have done so on other makes and on a ford pickup with a hydraulic clutch.
My Nissan Sentra is easy as the slave cylinder is external of the bell housing with a nipple. I have to remove the airfilter box to get good access. The process is simple enough. First I cut a short 1x2 board to a length which will hold the clutch pedal down to the floor with the stick braced against the front of the drivers seat. ( I also use a section of plywood between the seat and the stick to prevent damage to the seat.)
First i get access to the bleeder screw on the slave cylinder and also have a tube on the nipple to direct the fluid into a container. I then used the stick to push down the clutch pedal and wedge it against the plywood at the front of the lower seat.
Next; I open the bleeder screw and let some fluid out. Then close the bleeder screw.
Next; I remove the stick from the clutch pedal. ( note- on my car i have to mover the clutch pedal by hand thru it's stroke a time or two to get the pedal off the floor. ) Once the pedal is staying high on it's own I can repeat the process again.
Usually takes a few times to get clear clean fluid coming out. Once I get clean new fluid out, I stop and put things back together.
SPECIAL NOTES - Be sure to keep an eye on the reservoir near the clutch master cylinder to keep it topped off. Also keep in mind brake fluid will remove paint. I wrap rags around and around to catch spills.

The Sentra is easy but a 1989 Ford F-150 pickup with an hydraulic clutch is a pain. I had to replace the slave cylinder in such a pickup years ago. The slave cylinder is inside the bell housing so had to pull the 4x4 and trans to get at it. After putting a new slave cylinder, clutch, pressure plate, throw out bearing and for good measure a new clutch master cylinder I was left with getting fluid into the system and air out.
This was before I had decent internet so had to rig something. Tried several things. There was a nipple/valve sort of tube attached to the slave cylinder best as I can recall. Was not a simple straight forward nipple as sis on brakes best I can recall.
The thing i rigged up was to modify one of the small pumps used to add oil to an outboardd lower unit. Getting some thing to attach to the slave cylinder was the real chore. Finally just used a rubber bit i had to hold in place. Could have used three hands that day. Pushing new fluid up from the bottom was how i finally got it done.

I do not buy into a sealed clutch system will never need the fluid changed. After two or three years my old clutch fluid has a notable dark tint to it. I change brake and hydraulic clutch fluid evert few years. I will let the clutch go a bit longer than brakes. Longest maybe four years.
I do not know if the Mustang has an external slave cylinder or internal. If internal I would for sure try to change that fluid to get the moisture out and keep the seals pliable. Hell of a lot easier than pulling a bell housing.

Good luck and if you figure it out keep us posted. A good thing to learn.

 

[jacknifetoaswan]

Oh, I see truck brake fluid is different than Mustang brake fluid.

I lived in Miami for 37 years its a peninsula, you know what that means? So we don't need your Anecdotes about living 100 yards from the water.
For the record never had a problem with water and brake fluid.

What you say is important, may or may not be. The system is sealed. Try and explain how humidity enters the system.

Can you do that?

Cheap insurance, against what I'm betting you have no clue. If water were to contaminate the fluid. It could form some rust spots on the bore of the pistons. That would/could cause the O ring to chip and leak, or jam if extreme.

What an insanely overly aggressive response!

Water enters brake fluid through pores in the rubber hoses, in locations where the seals have cracked, receded, or split, where bad gaskets or caps on master cylinders do not properly seal the system, where fittings meet other fittings, etc. In many ways, this operates in the same manner that air loss from your tires does - through pores in the rubber, cracks in the valve stem, improper fitting of the valve. Tire installers sometimes try to get around this by upselling you with nitrogen filled tires, as nitrogen molecules are larger, and have more trouble passing through the pores in the tires. Of course, air in the ambient environment is about 78% nitrogen, but...

As for the braking system, itself, it is not a truly closed system, as there is air at the top of the master cylinder that is pushed out and pulled back in almost constantly. When the brake pedal is depressed, the fluid level in the master cylinder goes down. When the brake pedal is released, it goes back up. Why? Because the brake system operates like a fluid filled vacuum. Brake fluid being pushed into the system to engage the pistons causes air to be pulled into the master cylinder. Air circulates in and out of the master cylinder, bringing water vapor and moisture with it. The hygroscopic nature of brake fluid causes that water vapor to be absorbed, and since water is heavier than brake fluid, it settles at the bottom of the master cylinder. After a long enough time, when enough water builds up, it lowers the boiling point of the brake fluid. You can see that the system is not closed and that rust and dirt (and water) build up by looking at brake fluid that is a couple years old. It's not clear any longer, or even yellow tinged, it's dark brown. If you haven't changed the fluid in your truck since 1999, your brake fluid probably looks like smoker's lung.

I hope I answered all your condescending questions in an informative and non-condescending manner.

Cheers!

JR

 

[BluePonyGT]

Oh, I see truck brake fluid is different than Mustang brake fluid.

Well, if you wanna get techincal it actually IS different - especially if you track your car:

Motorcraft DOT4 LV High-Performance

Versus:

Motorcraft High-performance DOT 3

 

[Nightmonkey]

Can you do that?

Your world ends at the yard fence, right?
Click me hard!

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