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Clutch fork travel
I installed and bled (several times) my slave and I *think* all of the air is out of the system. When I press the clutch pedal, I start to feel slight resistance at about an inch, and the slave rod barely starts to move out when I move the clutch pedal about 1.5". I adjusted the rod so in the slave so there is 1/8-1/4" play. Where the slave rod meets the clutch fork, I get a total of about 1/2" - 3/4" movement.
Do (1) the amount pedal travel before engagement, and (2) total fork travel seem right? Thanks! |
If the amount of pedal travel is about an inch before you feel resistance, then that's about right and can be fine tuned to suit your driving preferences.
The slave cylinder travel isn't anywhere near enough though, you will probably need closer to 1.5". You said that you bled the slave, but did you bench bleed the master? Sounds like you still have some air in there somewhere. If you're curious as to when you have enough engagement, have someone push the clutch pedal down, and if you can freely rotate the rear wheels with the trans in gear, you're on the right track. |
You will have to basically bottom out the slave cylinder in order to get the 3/4 inch movement needed at the clutch fork. However, bottoming out the slave cylinder will also put the throwout bearing in constant contact with the clutch. On mine I backed off the slave cylinder rod while working the clutch fork by hand and looking into the bellhousing opening with a flashlight. When I could see slight movement of the throwout bearing before movement of the clutch fingers I figured it was about right. I don't have a precise measurement but I would guess it more in the range of 1/16 inch free play in the slave cylinder/rod. 1/4 inch free play sounds like too much to get full stroke of the clutch fork. Seems I remember the slave cylinder has about 1 to 1.1 inches total throw - but a small amount of that gets lost in the linkage and free play.
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Doug at ERA mentioned the throw at the slave will be 11/16". I hope that's enough to disengage this clutch.
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My Wilwood on my Cobra moved about 1.5" and the hydraulic slaves that I send with SBF packages for FFR's, etc., move about that far as well. That gives you room for throw out bearing clearance, as well as room for dialing in the clutch pedal for how you want it to be while driving.
You can figure out how far the bearing would move based on an 11/16" movement at the end of the fork. How long is a fork....11-12"? The pivot point is about 3" in? If it's 12" long with a 3" fulcrum, that's a 4:1 ratio. You're not getting 11/16" at the bearing. Just pulled all that out of my hindend basically, but it's brainstorming. :) |
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Admittedly, most of my experience is on the opposite end of the engine bay, but aside from that clutch having two discs, there an't nothing else special about it.
You can give the McLeod guys a call and see how much movement they need at the bearing to engage the pressure plate. |
Hi Lippy,
I adjusted mine exactly as you described and it starts to engage about 1 1/2 to 2" off the floor, which feels good to me. If you do the test Brent suggested above to see when it is engaging, you're good to go at least until you get the car running and see how it feels. I was surprised at how easy the car is to drive regarding the clutch. Being very light and having a lot of torque I can almost let the clutch out without giving it any gas. Would be hard to stall it with the clutch. Point is - it sounds like you're fine for an initial setting. Keep posting on your progress - you're getting to the best part! |
Of course every pressure plate/driven plate combination is different, but with one that we use most of the time, I have measured complete disengagement with 0.65" travel at the slave end of the fork. My recollection is that the slave has more than 1.25" available travel.
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I spoke with McLeod. The tech guy there is excellent. For my combo (6911-07 dual disk clutch, 16031 bearing), I need 0.40" for full release at the clutch. It will even work at 0.35", but 0.40" includes safety for warpage and swelling. I can measure my fork/pivot ratio and movement at the slave end of the fork, and then figure out if I'm getting enough.
For the throw-out bearing, he said it can be in contact with the clutch, but it shouldn't exert pressure. The ideal "play" in the slave rod should be 0.10". |
The fork motion ratio is 1.75:1. i.e. 0.40" at the throwout bearing > 0.70" at the fork.
*Oops... Just noticed that the illustration in the manual needs a little resizing. Still readable though. |
That jives with my now corrected math. :)
I measured a fork I have here and it's approximately 12" OAL, with the pivot being around 4" from the end. So 2:1-ish depending on where the pushrod hits the fork. Sounds like Bob needs to be the speaker of the hour and I need to shut up and build engines. :) |
The problem with the TOB slightly touching the fingers is that it can be noisy. On my super street pro setup I had to keep it off the fingers. McLeod reccomended to have it off the fingers. Make sure you get the pivot ball height adjustment right so the fork contacts the fingers at the correct angle. Pedal stop position and the correct Master and slave cylinders should complete the correct movement and give you the correct gap .040
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Lippy - what size clutch master cylinder did they provide you with? I started out with a 3/4 inch but it made for a long throw to get full disengagement. I went to 7/8 to shorten it up some (feels about right for me now) but it increased the pedal pressure some which is a negative. But that is another element in the clutch system that you can play around with to get it to your satisfaction. Just noticed above that you said you have a dual disc clutch. That may be another whole ball game so my comments may have no bearing. |
Brent tells me the dual clutch disk is really easy to engage but holds a lot of power. I'm going to fool around with the setup I have now. I think it is close but I need to test it.
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So I we determined I need at least 0.35" at the clutch, which translates to 0.6125" at the slave, minimum. I bled the thing about 6-7x and adjusted the rod so it almost has no play. And after all of that I'm only getting 0.607" (measured with a caliper/depth gauge). I jacked the rear up and had my wife depress the clutch all the way, and I couldn't get the wheel to turn. So it's definitely not disengaging. Everything feels fairly tight and certainly not spongy. The clutch begins to engage pretty soon.
Update: I adjusted the clutch pedal because it occurred to me that may be a limiting factor. It was, but somehow it still didn't solve the problem. With more clutch pedal travel (and the footrest of the clutch pedal being out of position), I'm getting only 0.826" travel at the slave end of the fork. That *should* be enough, but it still doesn't disengage (jack the car up, put it in gear, depress the clutch, try to turn the wheel). I can turn the wheels when the trans is in neutral. What else could be the problem here? |
Lippy,
When you did the pre-install assembly and inspection, did you check that the input shaft wasn't bottoming out in the pilot bearing? |
About the only thing I know about dual disk clutches is that there is some set-up and shimming that needs to be done on the clutch assembly (or at least checked and verified) to provide proper air gap when the clutch is pushed in. I assume either Brent or you did this?
I guess as painful as Bob's question could be - a way to check to see if that is the problem would be to back off the transmission bellhousing bolts about an 1/8 to 3/16 inch and loosen the transmission mount bolts. Then pull the transmission to the rear for increased clearance and then try pushing in the clutch and see if the rear wheels will turn. |
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