Clutch Slave Cylinder Measurements
 

If anyone has an original or dealer obtained clutch slave cylinder laying around not installed (or wants to pull theirs), I'm looking for some measurements and pics of it.

Primarily the the length from where the rod actually seats into the clutch fork to the bleed screw, though some other dimensions may be useful. I am becoming increasingly confident that my "OEM replacement" slave cylinder has a variance on that length, being slightly longer than OEM, a tenth of an inch or less, but still longer. Yes, it matters for correct clutch pedal adjustment.

yes the pedal needs the full sweep, so if something is off, its off!

if all goes well i should have one apart later this week, if nobody else has answered in a day of two, please shoot me a PM, i'd be happy to measure

Let me know if you need some more, these are hardly scientific.

The cylinder is completely dry so its natural rest point might be a bit off.

I can get the one on my car tomorrow if needed.

Looks like the rod from tip to where it seats in the fork is a touch over 1". The rest of the graduations should be visible on the tape measure. Pic 1 is at rest, 2 is compressed and 3 is fully extended to the limit of the boot.

Perfect, thanks!

I should be able to compare that to mine well.

Are you having an issue getting it to align on the bellhousing?

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No, the release bearing is in contact with the pressure plate with the hydraulic system at full relax, including if I completely pull the pedal assembly plunger back out of the master cylinder. I believe the pressure plate is loaded from it too, even if slightly, from what I can feel through the clutch pedal. I haven't had this on the factory clutch or on my last clutch. When the last clutch burst, I replaced the slave cylinder, master, clutch disc, pressure plate, and release bearing. I didn't mess with the pilot bearing since that is new as of the reman 14,000 miles ago.

Unbolting the slave cylinder from the bellhousing is a noticeable release of tension on the clutch fork. I don't recall that from the last clutch, or removing the original slave cylinder. I didn't notice it on installing either, but then there was plenty of air in the system from the replacements.

Did you try bleeding it? This would release the pressure if the slave piston is not fully bottomed out in the bore ( push-type slave). The system is designed to be self -adjusting as the clutch wears. Installing a new clutch changes the engagement point from where the worn clutch was.

Edit: not really clear to me what you're doing overall. You just replaced all those parts and now have this issue? If so that means it was likely already bled.


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wow that's odd. On DSMs we'd have to shim the clutch fork to make the clearance correct.

Sequence of events:
- Clutch pedal went to the floor on a shift and had to manually pull it up, clutch remained engaged clutch pedal would not disengage it. I limped it home.
- Inspected clutch pedal, no damage, worked correctly
- Bled the slave 3 times, no change
- Replaced master and slave (with many associated bleedings), no change
- Pulled the transmission, found the clutch disc had burst
- Replaced the clutch disc, pressure place, and release bearing
- reinstalled the transmission
- rebleed the slave as well as brake master cylinder.
- Have a devil of a time trying to get the clutch pedal adjusted properly. At first, engagement was right on the floor, though I could adjust that up. The bigger problem was that you can feel that it not fully disengaged with the clutch completely relaxed, as well as an audible scraping noise from the bellhousing. Noise continues unchanged with the pedal plunger backed completely out of the master cylinder. Yes, I greased the bearing.

Unfortunately I threw out the original slave cylinder weeks ago, but I remember thinking that the ball part of the slave that sits against the clutch fork looked slightly different than the original slave. Cylinder housing, bleed screw, boot, internals were all the same, just a slightly different shape to the thickening that the clutch fork rotates on.

I unmounted the slave yesterday and found that there was a definite relaxing of the clutch fork, and the slave was now out of alignment of it's bolt holes. It takes a fair amount of force to get the slave into position now as I am clearly have to lever against the pressure plate. Without the slave mounted in position, I can freely move the clutch fork around, and I can feel where it contacts the pressure plate. So I know that there is a possible position for it to be in where it isn't contacting it and this isn't an internal issue.

I'm thinking that I do actually have a difference in the slave cylinders between this one and the original, and this "oem replacement" actually isn't. With the problem point being that it is increasing the length from the mounting point to the minimum clutch fork relax point, adding load to the clutch fork forcing a partial loading to the release bearing on the pressure plate.

I'm ready to order a new slave from Mazmart to be sure to get an OEM one, though I figured before I do that I could measure out the lengths to see if I have a variance to an OEM one. If I don't, then this theory would be sunk and I'd have to keep searching for an answer.

Obviously I'm trying to avoid pulling the transmission again.

I'm thinking through how air in the line would affect it. I was assuming that it would be like the brake system, where air in the line means that you can't obtain full extension at the other end of the line, because the air is getting compressed rather than the fluid moving, to a degree in proportion to the amount of air the line.

If this is followed with the clutch line, then I'd have problems getting full extension with the clutch, not problems with full retraction?

Not trying to point you in the wrong direction, but what happens when the slave cyl is in place on the bellhousing with the clutch fork pressing back at it and without pressing on the pedal, you open the bleed screw?

I know you stated that you've messed with the rod on the backside of the pedal, but did you do it before or after bleeding? Is there any play at the top of the pedal stroke? According to the FSM there should be about a pedal-pad-thickness worth of play when the pedal is fully released.

The problem isn't at the pedal, since I can completely remove the interaction between the pedal and the clutch master cylinder and I still have engagement of the release bearing. What I do with the pedal is going to have to come after getting the rest of the hydraulics correct.

Your suggestion about opening the bleed screw with the clutch fork tension on it is an interesting one. In theory the clutch fork pressure should squeeze out some of the fluid. I'm not aware of any valving on the master cylinder that would hold too much fluid in the line, but the pressure still does exist there. That's certainly a good thing to try, to see what happens. It's free and just might solve my problem?

You can go buy a piece of aluminum or steel round stock at your local hardware store and make a shorter push rod too. That is if the rod is easily removed. (Another trick I did with the DSM to get correct clearance w/o pulling the trans to shim the fork.)

Easily done with a bench grinder.

that's what I suggested earlier as well in post#7, but I wasn't sure if you had already bled it since the parts install, the system is self correcting for wear so the takeup position changes between a new vs used clutch

Yep!
Back when I had my warranty engine done, I had the tech replace my clutch under the table. He never adjusted my clutch and it grabbed right by the floor when I got it back. I figured "Hey he's good at his job" but during the break in period I got massive amounts of chatter and from time-to-time an unpredictable engagement from a ACT street clutch and thought it was very odd. Did some free-revs in 6th gear one time after coming home from work and found the clutch dragging when disengaged.(Creeping forward when revving).
Climbed underneath and adjusted the master out to increase the plunger distance and the clutch felt literally 10x better. Rarely ever do I get chatter, engagement is perfect and very predictable. I highly recommend it after any clutch, master cylinder, slave cylinder replacement. (Well duh, but a ton of people forget after clutch replacement)

At your prior post I was thinking of bleeding: "having my wife apply clutch pressure to the system as I bleed out the air". I wasn't considering a bleed method that let the system depressurize itself. Now that I have corrected that misperception, I agree that I need to do it that way too.

1. When your slave cyl is on the car, if it's 100% bottomed out in it's housing and still exerting significant pressure on the clutch fork, something's wrong with the slave cylinder.

If the above isn't the case, try this:

2. Disengage the pedal rod from the CMC entirely, then crack the bleed screw on the CSC. This should force some fluid from the bleed screw with the pressure of the clutch fork (again, providing #1 isn't true).

3. Close the bleed screw, go back into the car and adjust the rod that goes into the CMC according to the FSM. You should have bout 1" of play.

If the problem returns then something's F'd in your clutch hydraulic system. Perhaps its the CMC if your CSC measures out correctly and properly retracts back into the body with the opening of the bleed screw, assuming pressure from the clutch fork.

Yes, that has entirely been the problem. I never considered the possibility of too much fluid in the line, because I was (and still am technically) unaware of a valve in the CMC that would prevent the fluid from returning to a proper balanced volume, like the brake system.

Apparently there is such a method in place, otherwise the pressure from the clutch fork at full relax would have forced the fluid back up into the fluid reservoir. Or something is jacked up with either the CMC or the CSC that is preventing this return flow of fluid.

It can't be a complete prevention, since the clutch hydraulics can still fully disengage the clutch disc, and releasing the pedal does return stuff back in the opposite direction, and it does so consistently and to a specific point.

I am still at work (long office days on the days I go into the office), and will be testing this theory out tomorrow morning.

kicking yourself in the butt yet? :)

Not yet :)

I've been slogging through this work stuff all day so far. Will be another hour or so before I can take a long enough break to do what I need to in order to justify and then start the self applied kicking.

It was an off-handed way of asking if you opened the bleed screw yet.

Yup, understood.

So you didn't do it yet?

Answered:

wasn't clear if you didn't do it or you didn't kick yourself in the butt yet, lol

I didn't do it yet, so I don't yet have the justification for kicking myself over this particular issue yet. It would be presumptuous and inefficient to start kicking now.

I do expect that your advice is in the correct direction and will solve the issue.

Well, no solid change. Slight improvement in that the release bearing is only faintly contacting the pressure plate forks, so the noise dropped away some, but not completely. I even bled the CSC by providing pressure on the CSC by hand from the clutch fork side, and I could apply enough pressure (with the bleed screw closed) to push the CSC piston almost completely back into the bore. It would still return back to a 'resting' state applying slight pressure to the clutch fork.

And somewhere in there the clutch interlock switch won't depress far enough with the clutch motion to allow the engine to start. I can manually push in the plunger and it will fire right up. Maybe another 1/8th of an inch of interlock switch plunger motion in order to close the needed circuit.



On top of all of that, I discovered that the access plate cover that sits on the rear iron behind the oil filter is missing, so there is a big hole in the top of the rear iron where stuff can fall in if luck swings that way. The dealer had to have removed it or forgotten to install it when they were doing the reman replacement.

If you can push the CSC rod back into the body with finger pressure with the bleeder screw closed, yet there isn't enough "push back" in clutch itself to prevent this light pressure applied by the CSC at "rest" from partially releasing the clutch... something's up.

Re: the interlock switch, whenever mine acts stupid I remove it, pull on the plunger to extend it fully, reinstall it, stomp the clutch once and it works for a few weeks. I know that's the wrong answer, but I can't be bothered to buy a replacement now.

It's a common FoMoCo / Motorcraft switch, available at O'Reilly's but I don't remember what the price or P/N is. I'd say between $20 - $25. Tasca Parts is down tonight, but Jim Ellis has it for $37. The Mazda P/N is D374-66-4D0A.

Did you go back and check the pedal position/master cylinder rod clearance after the bleed? You will need to make sure it's clear again

I pulled the transmission Sunday afternoon. The Exedy Stage 1 clutch disc was already starting to fray and stuffing the pressure plate with clutch material. Less than 100 miles on this clutch.

The last one failed in only 20,000 miles, I'm not sure why I went with that one again. Short story is that I'm not willing to put that clutch back in. Ordered an OEM clutch and will have it today.

Ray expressed concern about inconsistent or inaccurate dimensions for the Exedy, including mentioning that he is having trouble with them elsewhere as well.

Yeah, it doesn't make a ton of sense that the manufacturer of the OEM clutch would have trouble making an aftermarket variant. But going back to OEM either way.

Interesting. I opted out of the Exedy after hearing it was the same manufacturer of the OEM disc.
Went with an ACT HD clutch, of which I was somewhat skeptical of. (along with the ACT pro-lite + counter weight). After doing my clutch adjustments the clutch is awesome. It squeaks every now and then when it's cold, but the pedal feel is great with better engagement then OE (IMO).

Interesting you found an issue though, snap some pics!

After all our discussions, I wouldn't be surprised at all.

Thanks again for putting up with me through all of this Ray.

No brand affiliation, just have always used OE or OE replacement by Exedy without issue on my RX8

I've put so much abuse on the OE clutches it amazes me why anyone with an NA Renesis feels like they need to upgrade it. The one I just took out has at least several hundred high rpm drag launches on it and still has a lot of life left in it. It's probably at least my fourth or fifth one, haven't really kept count. My own advice is that unless you have added significant power mods then stick with either OE or OE replacement.

what did u do to ur clutch? seriously! ;)

that sucks, well mine has been holding up well and autox it couple of times. shit luck i guess?

OE clutch is in, everything installed last night, bled the clutch system just now. Lighter pedal pressure than the stage 1, but quick tests with the car in the garage seem to indicate that everything is back to normal with my clutch system.

Will be a few hours before I can take a break from work to give it a thorough test drive. Noises and weird pedal behavior are gone.

We have a similar problem but in the opposite direction. When my son and I installed a new clutch in his 2004 rx8 with a six speed transmission, we had to adjust out the clutch fork pivot bolt inside the bell housing 1/4" because there was too much distance between the slave cylinder push rod and the clutch fork. We thought maybe the clutch fork was bent, but we had two mechanics look at it and we ruled that out. We thought maybe we got the wrong clutch kit, but we ended up ruling that out. Are adjustments like this common?

I know it's a long time ago but have you still got the photos of the clutch slave. They will not display full size on the forum. The dimensions will be very helpful before I source a slave cylinder for me RX8 gearbox attached to an AJ30 3.0.