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I have two different opinions on whether a clutch should be replaced when a slave cylinder fails:

  1. It WILL coat the clutch plate and will wear the clutch plate. The clutch plate MUST be replaced. $1500

  2. Even if it fails catastrophically, at worst, it will be 50ml of brake fluid, which can just be rinsed off with water (or hose pipe), and slave cylinder replaced. At worse, gear box taken off and bell housing also rinsed out.

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  • Everything I'm seeing to do with the Jeep JK (2007-newer Wrangler) shows the slave as an external unit, meaning if it fails (actually leaks), all of the fluid would be external of the clutch. Replacing the slave cylinder should usually be done with a new master cylinder in the process (doesn't have to be, but should make it easier). The only place you'd experiencing leakage is from a rear main (usual place) or tranny input shaft seal. Other than that, this should not affect the clutch at all.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jul 22, 2015 at 16:03
  • @Paulster2 Thanks for the input. I was somewhat trying to see if I was fleeced or not. Really no replacement to first hand knowledge.
    – Anthony Horne
    Jul 22, 2015 at 18:50
  • You can check the location of the slave yourself by crawling under the Jeep and seeing. The slave should be on the driver's side of the vehicle (left) and at the bell housing. Not hard to find. I'm pretty sure from what I've seen, there should be a fork (lever) which the slave pushes upon to disengage the clutch.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jul 22, 2015 at 20:15
  • I will look tomorrow. Currently 11 pm local time and 9°C - too cold for crawling under cars outside (unnecessarily) :)
    – Anthony Horne
    Jul 22, 2015 at 20:45
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    Exactly! Is cold for around a week a year, even then it's blue, blue skies. Then it rains, is warm and is muddy - best for the Jeep :)
    – Anthony Horne
    Jul 22, 2015 at 22:06

2 Answers 2

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The slave cylinder is mounted on the bell housing with the fluid valve outside, and the piston within the housing. If there is a catastrophic failure, it is likely to be from the piston gasket: then all the fluid goes straight into the bell housing, wetting the clutch.

Some points to consider:

  • They may be rather more fluid than the slave piston volume; the circuit is pressurized (by pedal action) and some fluid will be coming in from the pipes.
  • The clutch disk will have received fluid projections. Since it was spinning at the time (engine turning), projections will have affected a large part of the disk surface.
  • Once on, clutch fluid gets into the disk material and cannot be removed.

The end result will be a slipping clutch, even if you clean the interior of the bell (and the disk).

Taking the transmission line apart requires some labor since you need to move the T-box out of the way. Even if you do manage to save the clutch disk (which I do not think you will), you would still need to spend quite a lot of time to take it apart - or pay to have it done. I don't see much saving to be made here.

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  • Not sure if this another question, but would one, if one was to inspect the slave cylinder, see any likely wear that would be expected to fail "anytime soon"?
    – Anthony Horne
    Jul 22, 2015 at 12:38
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    @AnthonyHorne Imminent gasket failure can be difficult to spot. In any case, you would need to dismantle the slave cylinder off the bell housing to see if there is any play around the axis and inspect the state of the rubber in the gasket itself. On a JK, I have the impression the slave cylinder just presses onto the clutch lever, so it should be possible to take it out without moving anything else. I may be wrong though - will update when/if it needs to be changed on my JKU.
    – ALAN WARD
    Jul 22, 2015 at 12:57
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You won't be able to rinse brake fluid off the friction material, if it has become contaminated it will remain so for ever.

Whether it needs changing depends on whether it has been contaminated to such an extent as to have a detrimental effect on the clutch performance - which it may not have done - you'd only be able to tell by driving the car (n.b. on the other hand, if brake pads get contaminated at all, they MUST be replaced for safety reasons).

However, if you have to take the gearbox and bell housing off to change the cylinder and/or check the clutch plate, then you may as well change the whole clutch at the same time - the vast majority of the cost of a clutch change is the labour to remove and replace the gearbox, so it's worth doing while it's off...

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  • Have you ever heard of anyone suggesting to just rinse it off with water? Also, Just so I have reference the mechanics involved, do you do this type of maintenance regularly? I am in IT, so I know only the basics and will troubleshoot engine codes or electrical issues.
    – Anthony Horne
    Jul 22, 2015 at 12:35
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    I've heard people suggesting it, but I know it doesn't work! I'm in IT as well, so it's not something I've done much at all, and not on anything that modern...
    – Nick C ♦
    Jul 22, 2015 at 13:07
  • both answers equally good, but since Alan's is a little more detailed and he has less points, I have awarded to him. Thanks again - maybe I can help you one day. Maybe in IT, though.
    – Anthony Horne
    Jul 22, 2015 at 13:30
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    That's fair enough!
    – Nick C ♦
    Jul 22, 2015 at 13:32
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    @NickC To be honest, I think you beat me to it by about a minute. ;-) We are definitely in agreement that this type of leak would be a Bad Thing (TM) to happen to you, which is as a JK owner is rather worrying given the amount of people talking about changing clutch slave cylinders on this model.
    – ALAN WARD
    Jul 22, 2015 at 14:03

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