Clutch slave cylinder

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 In this page you will learn how a clutch slave cylinder works, how to diagnose problems related to its operation, and a step by step guide on how to replace it and bleed the air out of the system.

 What is a clutch slave cylinder?

 A clutch slave cylinder is a device used in the hydraulic clutch system, this item is mounted in the transmission, either on the outside, or in the inside.
If it is mounted on the outside, it is usually attached to the manual transmission by two bolts, the clutch slave cylinder has a rod that extends out every time hydraulic pressure is applied to it by the clutch master cylinder ( you operate this part every time you push on the clutch pedal).  The rod that extends out makes contact with the clutch fork, in this design the clutch fork is the one who activates the clutch pressure plate.

 In an internal clutch slave cylinder design, the clutch slave cylinder and clutch release bearing are one unit, this unit slides in the input shaft of the manual transmission and is held by two or three bolts that attach the unit to the front of the transmission ( inside the bellhousing).  By being a single unit, the need of a clutch fork is eliminated.

What are the symptoms of a bad clutch slave cylinder?
Usually when you have a bad clutch slave cylinder you know it right away, because since it is a hydraulic part, once a seal  inside the slave cylinder gets bad, it will start leaking fluid, at the same time, because the seal is not sealing properly, it will allow air inside the system, causing your clutch pedal to  feel soft and  spongy.
When a clutch pedal feels that way, it is an indication of air in the system, and when this happens, it makes it hard to operate the clutch properly because it engages even with your foot almost all the way to the floor, at times you may not even be able to place your car or truck in gear due to this problem.

NOTE: A bad clutch master cylinder will have similar symptoms, make sure that you look closely at each one of these items to determine which one is the problem ( the one malfunctioning is the one leaking fluid ).

Related video:

We will move on to how to replace and bleed a clutch slave cylinder, to make it even more interesting, we will show you how to bleed a clutch slave cylinder without a bleeder!!.
- To bleed a clutch slave cylinder with a bleeder is easy, you have an assistant depress the clutch pedal as you open the bleeder to allow air out, once the pedal is all the way to the floor, you close the bleeder, and you ask your assistant to slowly let the clutch pedal up. You repeat the same step several times making sure that you have plenty of fluid in the reservoir till there is no more air in the system.
 To make it even easier, you open the bleeder  and you allow fluid to escape, keeping an eye on the level in the reservoir, you allow enough fluid to run out of the slave cylinder till you feel that all the fluid in the line has been bled and new fluid has entered it. 9 out of ten times , that's all is needed to bleed a clutch that has a bleeder, , if  after you do this you still have a soft spongy pedal, have an assistant help you and bleed it as we described earlier.

Now, bleeding a clutch slave cylinder that doesn't have a bleeder, that is more challenging, and that is the reason why we are going to illustrate step by step how to do it.
- Why doesn't it have a bleeder? We don't have any idea, but what we do know is that if you call the dealer and ask to buy a clutch slave cylinder, they will tell you that is not available, that you can only buy the entire system!!! ( Master cylinder and slave cylinder together ) We didn't ask them if the system they sell is pre-bled, but it better be because we don't see a point to buy both items if only one is bad.
Anyway, the vehicle we are working is a 2003 Dodge Dakota pick-up 2wd with a 5 speed manual transmission.
The reason why we needed to install a new clutch slave cylinder in this truck is because the old one had a crack in the housing ( they are made out of plastic ), we glued the old part while we waited for the new one to arrive, that way the owner could use his truck in the mean time.
We noticed that the old clutch slave cylinder didn't have a bleeder, and we were hoping that the new one would come with a bleeder, well..........nope, it was the same exact thing, and after scratching our head a few times, we came out with a way to bleed this clutch slave cylinder that doesn't have a bleeder, this is how we did it.....










1- Push on the plastic built in tool in the hydraulic line with a flat screw driver, do it all around it till you feel that it has seated completely against the outer housing, this built in tool pushes the clips that hold the line  in place out, allowing you to disconnect the line, to do so, just pull it out, it should slide out without too much effort if you did this correctly.

  2- Once the hydraulic line has been disconnected, remove the two nuts that hold the clutch slave cylinder in place and remove it from the transmission.

  3- Because it is much easier to disconnect the line directly from the slave cylinder unit rather than the adapter built in the line when bleeding the air out,and because we needed to fill the slave cylinder with fluid, we opted to remove the pin that holds the line adapter in the new clutch slave cylinder in place, when you do this be very careful not to damage the plastic housing, we used a small socket under the unit and a small punch and a hammer to drive the pin out.




  4- With the line adapter off, secure the new clutch slave cylinder by the metal part in a vise, with one hand, compress the rod all the way in, as you slowly let it out, fill the slave cylinder with new fluid.

  5- Install a temporary pin instead of its original locking pin for now, because in the event that you didn't let all the air out  of the clutch slave cylinder when you were filling it up with new fluid, you will need an assistant to help you push on the pedal as you slide the pin out to allow air ( and fluid to scape )



  6- Connect the hydraulic line to the clutch slave cylinder, and then proceed to install it in the transmission, if you don't do it this way, it will be very hard for you to do it because with the line unplugged, you will have to push on the slave cylinder very hard as it is trying to depress the clutch mechanism, ( there is no room for the fluid to go to, that's why ), so, connect the line first, then bolt it to the transmission

  7- make sure that the reservoir is full before you activate the clutch, if you did everything right and there is no air trap in the system, you are done, just remember to remove the temporary pin and install its original to hold the line adapter in place.

 In the event that the pedal feels spongy because there is air still trapped in the system, this is what you can do............

First, make sure that you have safety goggles protecting your eyes, and you are wearing clothes that you don't care much for because this is a very messy job......

 Have an assistant depress the pedal only till he feels that it is starting to get hard, next hold the line with one hand as you pull the pin out, crack the line open slightly to let fluid and air out, don't pull the line all the way or you will lose all your fluid!!.
- You need to be very fast , it may take you a couple times to get the hang of it, every time you crack the line slightly, have your assistant push the pedal all the way to the floor once the line is partially open, that way you will get more air out.
Keep doing this till all the air is out of the system, once you are done, remove the temporary pin and install the original back on.

 NOTE: The reason to depress the pedal  only to the part of its travel that starts feeling hard is because that makes it easier when sliding the pin out and cracking the line partially open, if your assistant depresses the pedal all the way to the floor before you have the pin out, it will be very hard to pull the pin out then  because of all the pressure in the line.

This method works, and it works very well, we only had to do this about 5 times and we had full clutch pedal, so if it worked for us, we know 100 % that it will work for you.