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Why do I keep exploding clutch slave cylinders?


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I'll be dropping my AX-15 for the third time in about a year to replace yet ANOTHER internal slave cylinder.  The issue is the slave cylinder works for about 2-3K miles and then starts to leak very slowly as it gets progressively worse to the point where I can't even get enough pressure to disengage the clutch.  The simple answer is to simply go with the external clutch slave bell housing, but I'm not really in the mood to go junkyard diving in hopes to find all of the parts I need.  Of the people who are selling these parts, they know the pains I'm going through in order to replace such a simple component so they price their parts as such.

 

A couple of thoughts I have had as so why this is happening:

 

  • The master cylinder is somehow defective and is producing TOO much pressure that is causing premature wear on the slave cylinder
  • The stainless steel braided line that I installed from the master to slave cylinder has a smaller ID than the stock tube, which is causing my pressures to be higher
  • I am installing the slave cylinder incorrectly
  • I somehow managed to purchase two defective clutch slave cylinders

 

I am thinking that bullet points 1 and 2 are related and may be the root cause of my issue.  Anyone have any other thoughts?

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If the bore of the master cyl is bigger than the bore on the slave, you are pushing too much fluid in to the slave.  A prescription for blow out.

 

Can you check the bore on both to make sure they're equal.  

 

It could be more expen$ive, but replace both while you're replacing the $lave.

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That's a good point - I didn't think to check on that.  The master cylinder was said to be brand new when I bought the truck so I never really messed around with it and always assumed it was good and built for the truck.

 

I'll definitely be replacing all components this go around so I hopefully never have to drop the transmission for this reason again...

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I have read about some slaves being a touch short which leads to a slight over extension and premature wear. I have heard that a fix is to place a small spacer behind the slave to get it closer to the clutch. I don't have personal experience with this but I do know your pain as I recently went thru 3 slaves in two weeks before paying for a Luk which seems to be working.

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I'll be dropping my AX-15 for the third time in about a year to replace yet ANOTHER internal slave cylinder.  The issue is the slave cylinder works for about 2-3K miles and then starts to leak very slowly as it gets progressively worse to the point where I can't even get enough pressure to disengage the clutch.  The simple answer is to simply go with the external clutch slave bell housing, but I'm not really in the mood to go junkyard diving in hopes to find all of the parts I need.  Of the people who are selling these parts, they know the pains I'm going through in order to replace such a simple component so they price their parts as such.

 

A couple of thoughts I have had as so why this is happening:

  • The master cylinder is somehow defective and is producing TOO much pressure that is causing premature wear on the slave cylinder
  • The stainless steel braided line that I installed from the master to slave cylinder has a smaller ID than the stock tube, which is causing my pressures to be higher
  • I am installing the slave cylinder incorrectly
  • I somehow managed to purchase two defective clutch slave cylinders
I am thinking that bullet points 1 and 2 are related and may be the root cause of my issue.  Anyone have any other thoughts?

 

1. Pressure in any hydraulic system is uniform throughout. The pressure you apply with your foot builds only until the clutch springs start to compress, after which the pressure remains constant. What are you running for a clutch pressure plate?

 

2. See #1

 

3. Probably impossible

 

4. Very possible. Also, what are you using for clutch fluid? Maybe try D.O.T. 5 silicone.

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One thing to add here. If you use DOT 5 on a system that was designed for DOT 4 or 3, the seals will swell. 

You should never use a silicone based fluid on systems that are not designed for DOT5.

Ive seen many guys destroy brand new AP Racing calipers because their mentality was "Because Racecar", when in reality the seals are not designed to withstand the silicone. They swell up and then will never work again.

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One thing to add here. If you use DOT 5 on a system that was designed for DOT 4 or 3, the seals will swell. 

You should never use a silicone based fluid on systems that are not designed for DOT5.

Ive seen many guys destroy brand new AP Racing calipers because their mentality was "Because Racecar", when in reality the seals are not designed to withstand the silicone. They swell up and then will never work again.

This is completely incorrect. I've been running D.O.T. 5 silicone brake fluid in both the brakes and the clutch of my '88 Cherokee for more than ten years -- closer to twenty years for the brakes. No swelling of the seals, and no problems. I ran it in my AMXs for years before I got the Cherokee.

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Just a thought but have you tested one of the slaves that you changed while it was out of the truck to see were it is "leaking" from?

 

The reason I ask is having changed a few i have had a couple of instances were the leak was from the "o" ring at the connection point were the metal line goes into the slave. I determined that it was caused by the slight movement the line took when it twisted when it moved as the torque was applied to the drive train.

 

On one i just adjusted the line to allow it to move more freely with the bell....the other i just put in a fatter o-ring.....just a thought  . :MJ 2: .

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