What is this stuff in my clutch master?

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Last Flight Out

Last Flight Out

Joined
Feb 15, 2022
Threads
94
Messages
547
Location
Atlanta, GA
Long story, short, I had a clutch fluid flush done about a week and a half ago from my go to spot here in Atlanta. Yesterday, coming home from a lunch, the clutch was almost impossible to push down and engage while I was on the road and then became very inconsistent and loose and then would tighten up again. I double-pumped it all the way home and had no issues pulling into the garage. This fluid was absolutely clear when I picked it up - but What could’ve happened in this situation?

The slave in the master look fairly new (no leaks anywhere under rig or inside cabin. But I’ve never touched them since owning this vehicle and I’m not sure if after a flush, it may have dislodged a bunch of stuff from the master of the slave. Does this commonly happen?

Pictures below… The darker thing you see is the rubber stopper floats on top as normal I assume. The gray stuff below it is what I’m talking about.

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Stick a paper towel in the res and soak it up, my guess, water. I would open the bleeder at slave and let gravity flow an entire res worth of fluid thru, don't let it go empty. whatever they flushed with could have destroyed a seal and that grey stuff could be the remainder. If it's not water you may need a new MC.
 
I'm guessing they used some incompatible brake fluid or cleaner that got into the system. Perhaps some water from clean up operations.

This is why I do my own service - no surprises that way.

Get a new bottle of brake fluid Dot3 usually. Get a 10mm wrench. Open reservoir, open bleed nipple on slave. Have buddy slowly work the clutch as you pour in fluid. A mighty-vac could replace your buddy.

You could need a kit for master and slave.

Do something soon before it rust/pits and seizes.
 
Followup?
 
Last Flight Out said:
Long story, short, I had a clutch fluid flush done about a week and a half ago from my go to spot here in Atlanta. Yesterday, coming home from a lunch, the clutch was almost impossible to push down and engage while I was on the road and then became very inconsistent and loose and then would tighten up again. I double-pumped it all the way home and had no issues pulling into the garage. This fluid was absolutely clear when I picked it up - but What could’ve happened in this situation?

The slave in the master look fairly new (no leaks anywhere under rig or inside cabin. But I’ve never touched them since owning this vehicle and I’m not sure if after a flush, it may have dislodged a bunch of stuff from the master of the slave. Does this commonly happen?

Pictures below… The darker thing you see is the rubber stopper floats on top as normal I assume. The gray stuff below it is what I’m talking about.

View attachment 4013896

View attachment 4013897
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sea monkeys
 
Apologies I didn’t close this one out - it ended up being contaminated and had to flush out the entire system… and decided to replace the slave and the master all the same time. Even replaced the clutch line from the engine bay down to the slave and was all fairy straightforward. Until I ran into some differences in the newer Aisin slave units that did not come with the internal conical spring and had a plunger that did not have the center gasket (so had to Frankenstein a few of the parts together). How was the plunger to work correctly without the internal spring!? After bench bleeding and getting it set up, it was fairly straightforward although I feel now my clutch pedal has a little bit too much top and play, meaning that play you’re supposed to have at the very top before the master engages. Still trying to figure out how to adjust that. Also adjusted the slave arm to the clutch fork and really made sure there was slightly a little play in that so it wouldn’t burn out the clutch overtime. That was a bit of a mystery and a ton of topics covered here on mud to figure out how to do that properly.

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… one last thing I’ll say is when I found out it was contaminated, on the way home I lost considerable pressure in the clutch and then it got very hard to engage the clutch and that’s when I decided to get it in the garage quickly to investigate. And that’s when I saw the sea monkeys living in my master cylinder, swimming around like happy creatures.🐙

Really upset with the shop that flushed my lines…paid some good money for a bigger headache. Will not go back.
 
Last Flight Out said:
Until I ran into some differences in the newer Aisin slave units that did not come with the internal conical spring and had a plunger that did not have the center gasket (so had to Frankenstein a few of the parts together).
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Hmmm.... I literally put a new clutch slave in 2 hours ago. Mine is an aisin i got from city racer but I didn't pull it apart and thus didn't see anything unusual. What were the symptoms with your slave without the spring and gasket? Mine went on...bled ok..and seems to do the right thing...although haven't driven it yet as i wait on an alternator.

Oh...And Merry Christmas to all!
 
Not sure what is going on, I will say brake fluid and diesel are hydrscopic. Make sure you have fresh brake fluid. Water goes to the bottom, you can catch it and drain in a diesel set up. However, I'm not so sure you can in a brake system. I would drain it and replace the fluid. And then you still have to figure if it is safe to use. Safety comes first, ask the brake place that did the flush and let them know. And maybe they will reimburse you. Im not sure if replacing the fluid is enough.
 
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fjwagon said:
Not sure what is going on, I will say brake fluid and diesel are hydrscopic. Make sure you have fresh brake fluid. Water goes to the bottom, you can catch it and drain in a diesel set up. However, I'm not so sure you can in a brake system. I would drain it and replace the fluid. And then you still have to figure if it is safe to use. Safety comes first, ask the brake place that did the flush and let them know. And maybe they will reimburse you. Im not sure if replacing the fluid is enough.
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This was all done weeks ago. As I mentioned, completely replaced my entire clutch hydraulics from slave up (including fluid)
 
wimberosa said:
Hmmm.... I literally put a new clutch slave in 2 hours ago. Mine is an aisin i got from city racer but I didn't pull it apart and thus didn't see anything unusual. What were the symptoms with your slave without the spring and gasket? Mine went on...bled ok..and seems to do the right thing...although haven't driven it yet as i wait on an alternator.

Oh...And Merry Christmas to all!
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Not sure man, but as I was beach testing the new Aisin, without that internal spring, plunger would not return to its proper position. Also, I didn’t like not having two gaskets around the plunger versus the one as that is where most slaves fail overtime. And for reference, these were brand new units from the manufacturer direct so I don’t know if they changed the design with less parts or expect you to reuse some things.
 
I've run across slaves with and without the internal springs. Maybe it helps the piston run true in the bore. I don't think it's that big a deal. The key is to have an adequate return spring to seat the piston in the back of the slaves bore when at rest. Recently I ran across a relatively new Aisin slave that started leaking after a short amount of use. Upon disassembly I found the piston was missing a seal. I purchased a rebuild kit from Cruiser outfitters and their rebuild kit had 2 seals on the replacement piston. I'm guessing using 1 seal is an economical decision driven by pencil pushers.

To get consistent pedal feel, adjust the clutch per the fsm. Adjust pedal height, which ensures maximum stroke, pedal free play(when the piston starts to move), then adjust the rod at the slave. The last adjustment sets where the clutch engages during pedal operation.
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I don't recall any springs in clutch slave cylinder in the last 43 years I have had my 72. 1 clutch disk and pressure plate, several masters and slaves plus a few kits in both over those years.
 
charliemeyer007 said:
I don't recall any springs in clutch slave cylinder in the last 43 years I have had my 72. 1 clutch disk and pressure plate, several masters and slaves plus a few kits in both over those years.
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My oem slave from Toyota had one inside.
 
I have a number of new Aisin slave laying around along with one in each 40. You never know when one will go out. If I go on a long or extended trip, I'll throw in a master too. My spare slaves all have springs in them. I wonder if they added the spring and removed the 2nd seal at the same time.
 
Last time I went to rebuild the clutch master, the retaining clip had rusted away. I bought the master, slave and a braided stainless hose from like JOETLC on ebay for like $130 in June 2025. The hose is long but it was like $40 more for the shorter correct length.

Much easier to install hose in slave, mount the slave, route the hose, connect to master.

Hasn't missed a trick yet. Removed old oem hard line and rubber line that was looking every bit of its 50 years.
 
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