Black fluid in clutch master cylinder

[srisitt]

Well this can’t be good. Opened up the fluid reservoir in the clutch master cylinder and it is jet black and filthy. What would this indicate and is it possible to flush out myself? I’ve read it can be deteriorated rubber from the cap and lines, but this truck is new to me it could be something else. My manuals only cover topping off the fluid, what can I do for this?

 

[RonD]

Just indicates its old, it can happen as early as 5 years but usually closer to 10-15 years old

Yes, you can flush it yourself

Check brake fluid as well

Both systems use Dot 3 brake fluid


And just FYI the black rubber piece in your hand is there to prevent air contact to the fluid in the reservoir, brake fluid absorbs moisture from the air, which causes it to deteriorate faster
You can leave it out while flushing, and you can leave the cap off the reservoir, there is no pressure in the reservoir when you pump clutch pedal, if there is then Master is bad, lol.

 

[srisitt]

Just indicates its old, it can happen as early as 5 years but usually closer to 10-15 years old

Yes, you can flush it yourself

Check brake fluid as well

Both systems use Dot 3 brake fluid


And just FYI the black rubber piece in your hand is there to prevent air contact to the fluid in the reservoir, brake fluid absorbs moisture from the air, which causes it to deteriorate faster
You can leave it out while flushing, and you can leave the cap off the reservoir, there is no pressure in the reservoir when you pump clutch pedal, if there is then Master is bad, lol.

Thank you. That is good news. Would flushing the cylinder be as simple as disconnecting the hose and refilling? Surprised I can’t find more info on this in my manual.

 

[adsm08]

Thank you. That is good news. Would flushing the cylinder be as simple as disconnecting the hose and refilling? Surprised I can’t find more info on this in my manual.

Nope, you need to bleed it through the system as if you were installing a new part and bleeding it, or else you will introduce air to the system.

 

[RonD]

Use a turkey baster type device to suck out as much of the black fluid as you can from the reservoir, or unbolt it and dump it out
Refill with clean fluid, to the top
Open bleeder on slave
Some fluid will flow out from gravity
To speed things up you can use a helper to push down on clutch pedal while you open and close bleeder valve

Its good to put a smaller rubber or clear plastic hose on the bleeder so it drains into a container vs squirting out

Open bleeder
Have assistant press down clutch pedal to the floor, hold it down
Close bleeder
Release clutch pedal
Repeat until fluid is flowing clear

Maybe 5 or 6 pedal presses

KEEP RESERVOIR TOPPED UP!!!!!!!!!
Or you will get air into the system

 

[4x4junkie]

I dealt with this situation on my BII years ago shortly after I got it.
I recall it took a good bit of fluid before it started to come out decently clean from the slave (I think I used up about a third of one of those big quart-size bottles of DOT3). It was nasty.

×1000 on the reservoir! If air gets in, you'll soon learn just how much fun it is to deal with Ford's dumb air-trapping inverted master cyl design.