Slave cylinder piston

[kieranod1]

Hi guys, I just replaced the clutch master cylinder, after bleeding the system I was backing out and the pedal went right to the floor and fluid draining out of the
clutch cover. My question, is it possible for the slave piston to be forced out of the cylinder? Thanks.

[RSLyrick]

Hey, just to be sure, you didn't forget to place back the spacer between the master cylinder housing and the firewall ?

I'm talking about the following part : https://www.zip-corvette.com/84-96-c...er-spacer.html

[kieranod1]

Thanks for the reply, I did put the spacer back in after much debate over the difference between the OEM and the aftermarket master cylinder. At first it looked like I didn't need it but after installing the master cylinder the pedal was really high. So out it came and reinstalled the spacer, if I don't do something twice I just won't do it!

[RSLyrick]

Ok, so you did install it first without the spacer. Did you start the bleeding process (pushing the clutch pedal at least) without the spacer before noticing the "mistake" ?

I recently replaced the slave cylinder with a LuK LSC116. I got it from Amazon (https://www.amazon.com/LuK-LSC116-Cl...ustomerReviews)

One customer posted a review and he mentionned that he forgot to use the spacer. Too much pressure built up within the hydraulic circuit and it blew up the slave cylinder seals. That's why I'm asking

Another possible issue would be that you didn't properly seat the cylinder?s actuation rod in the clutch fork divot. Did you remove the slave cylinder from the transmission housing when performing bleeding and placed it back ?

The rod could get trapped somewhere in between and cannot extend properly. Then, same situation, too much pressure in the hydraulic line and the seals are gone.

If you do not fully lift the car during the procedure it can be difficult to really see where and how you're engaging the slave cylinder rod.

Final reason that I could think of would be a bad part (bad luck)...If you replaced your master cylinder because it was leaking, the slave cylinder is probably about the same age and about to fail as well. I usually replace both at the same time (depends on the vehicule history as well...)

I still have my old slave cylinder, I just tried to pull rod out without success. I don't know if that's also the case with my new LuK (i didn't want to try as it's not meant to be pulled )

If these scenarios are not valid for you, i'm curious about what the other owners would say .

[kieranod1]

Thanks, My transmission guy is going to handle it on tuesday, I'll let you know how it turns out.

[ScottZ95ZR1]

As stated above, I think it is highly recommended to replace both master and slave when one unit fails.

I had an issue getting my clutch properly bled until finally "reverse bleeding" as Bill Boudreaux outlines on his ZFDOC website.

http://www.zfdoc.com/clutch_hydraulic.htm

https://www.youtube.com/watch?v=P9SiMPuFa00&t=263s

[Neat]

It sounds to me like the pushrod for the slave missed the pocket in the clutch fork. Without anything to push against, the slave over extended and pushed out the piston.

There's 2 options on the replacement slave; a cast piece and a tube style that is usually referred to as DOM style. I've never found a functional difference between them. However, one time I had a DOM style twist off the small cup where the line attaches. Because of that, I prefer the cast ones - but I really don't think there is much difference.

When your guy replaces the slave, you might ask him to pop the new slave open and check for debris in the bore. I've done maybe 100-150 of them over the years, and most of them have junk of some sort in the bore.

Another easy reliability thing he can do is to harvest your old boot retainer (the star washer looking thing) from the defunct slave and install it on top the boot retainer that will come in the new slave. 2 boot retainers is something I picked up from ZF-Doc years ago. Sometimes, the slot the retainer clips into is wider than the retainer, so the retainer kind of bobs around as you push and release the clutch. Installing a second retainer on top the first takes up the gap in the groove, firms up the mounting of the retainer, which helps keep the boot from coming loose. Even if the retainer slot is nice and snug, you can still install the second retainer by clocking it so that it's not exactly lined up with the other retainer. With the retainers clocked differently, the teeth will miss each other, and you'll still be able to install both.

A LONG time ago a lot of the slave cylinders (from GM or an auto parts store) had the cup seal on the piston installed backwards. Delco (or whomever the OE manufacturer was) had been putting them in backwards. The auto parts store copies of the OEM slave followed suit. The issue has been resolved for 10 years or more, but every once in awhile I still find one that has the seal in backwards.

An extremely small percentage had a piston installed that was for a smaller bore. The cup seal was / is fat enough that it'll take up the space and sort of seal up. The slave will work-ish for a few hundred clutch pedal cycles, then the cup seal will fail and strand the car. This was almost exclusive to the McLeod adjustable slaves from the early 2000's, but I've seen one auto part store slave that was this way.

If your guy doesn't take the slave apart, he can leave the plastic strap on the push rod when he installs it. The first press of the pedal will break the strap and let the system work. The piece of plastic will remain pinched between the pushrod and clutch fork, which (IMO) is a good thing. I think it's less wear on the pocket of the clutch fork, and there is less potential for the fork to make noise. I almost never do it this way though, because I almost always take the slave apart to check for debris in the bore.

Bleeding is a pain, even for an experienced transmission shop. The bleeder is on the bottom of all the new slaves. The air naturally wants to rise, so the bottom side bleeder makes it really hard to get all the air out of the system. The "self bleeding" description of the system is pretty optimistic; I can't ever recall one sorting itself out on it's own.

The way I do it (not saying this is the best, or even the right way) is:

-Fill the slave while it's on the bench. ZF-Doc recommends using a syringe for this; I agree that is the best way to do it.
-Attach the line in the orientation it will be when the slave is installed in the car (do not use thread sealant or tape) but don't put the slave in place. Let it dangle beneath the car. The position of the line when the slave is installed is with the metal tube parallel to the slave, with the line pointing towards the front of the car. Getting the line in the right spot before you bolt the slave in lets you install the slave without having to loosen the nut, potentially allowing air to get in. Again, no thread sealant.
-With your hand, hold the slave in an orientation that makes the line to the master the highest point. The idea is that air naturally wants to rise, so making the line the highest point helps to shuttle the air up towards the reservoir.
-Slowly push the rod in and out with your other hand. It's helpful to have someone up top watching the reservoir. Slowly cycle the pushrod until bubbles stop coming out of the reservoir. You'll need a glove or something, the pushrod isn't crazy difficult to push in, but it'll wear a hole in your palm before you've cycled it enough times to get the air out.
-Install the slave and bolt it down. The pushrod is a smidge too long, it will have to collapse a little to get the nuts started. That's normal, and gives you a slight bleeding action on the system. Depending on how brave you are, you can use a prybar or screwdriver against a solenoid on the side of the transmission to collapse the slave and start the nuts. I've never broken or damaged a solenoid doing this, but it's something that I'm always afraid will happen. If you can manage it without the assist from the prybar, I think that's the prudent move.
-With your hand, slowly cycle the clutch pedal through roughly the top 2 inches of movement. You'll notice the pedal moves a small amount before it firms up and starts to actuate the hydraulics. You'll want to cycle the pedal through that area, and very slightly into the area where the pedal stiffens. It's not much, maybe 2 inches of movement. Watch the reservoir while you do this (or have someone watch for you). You might get some bubbles out of the reservoir, but you probably won't. You might notice a slight change in the fluid level, which is normal. Once you've achieved no bubbles, cycle the pedal through the top 2 inches another 10-15 times. At that point, the system should be air free. I always cycle the pedal slowly to the floor and back a few times while watching the reservoir before I declare the job done. That shouldn't be necessary, but for whatever reason I always do it.
-Cap back on, computer back in, and test drive.

When you are cycling the pedal with the cap off the reservoir, moderately quick pedal movement can make fluid spurt out of the reservoir. It's not harmful in terms of the bleed procedure, but I hate getting brake fluid on stuff / paint in the engine bay.

The blue and white bottle of DOT 3-4 is what I always use. To my knowledge, I've never had a failure because of this fluid. I've heard to not use DOT 5, but I've no actual data as to why. "It'll kill the seals" is usually what I hear, or sometimes, "The silicone in the synthetic fluid will damage the seals." That might be true, I'm not sure. I've never seen a chemical compatibility chart for the material the seals are made from. A typical Viton o-ring / seal shouldn't have an issue with synthetic fluid or silicone, so I'm inclined to think that DOT 5 wouldn't create a problem, but... As I've never had an issue with the DOT 4 stuff, I haven't tried anything else. If it ain't broke and all...

Good luck man!