hydraulic clutch - clutch won't disengage - JeepForum.com

 
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post #1 of 14 Old 10-19-2009, 07:14 AM Thread Starter
kercher
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hydraulic clutch - clutch won't disengage

This is killing me. 4 threads and 12 weeks and I still cannot drive the jeep because I cannot get the clutch to disengage. I am totally at a loss as to where I am going wrong.

3.7L 225 v6 oddfire and ford t18a transmission. New pilot bushing w/ oil wick, TO bearing, pressure plate, clutch disk, clutch fork, pivot ball, slave and master cyls.

The slave is from Novak with 3/4" bore and 2.5" stroke.
The master is wilwood and I have tried 2 versions, one with 3/4" bore and 1.4" stroke and one with 7/8" bore and 1.4" stroke.

No matter what I do, I only get 3/4" movement at the slave-clutch fork pushrod.

With the 3/4" bore MC, the pedal pressure is fairly even throughout and I get 3/4" travel at the slave pushrod for about 1" of travel at the MC pushrod. (Air?). To get more travel at the slave pushrod, I bumped up to a 7/8" bore MC because I really need 1.5-1.75" of travel at the slave cyl.

With the 7/8" bore MC, the clutch pedal is very soft for the first inch and there is NO movement at the slave-fork pushrod. Then, it gets noticeably harder to push and through the remaining pedal travel I get the 3/4" slave-fork pushrod travel.

Does this sound like air in the system? I have bled and bled and bled and there are no air bubbles in the fluid. I don't have any high points in the lines that might trap air either...the MC is the highest part of the system.

I am really at a loss. Air and more travel at the MC pushrod are the only things I can think of at this point. The clutch pedal is about 14" long with the pushrod being ~2.5" below the pivot.

Thanks for any help.

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post #2 of 14 Old 10-19-2009, 08:06 AM
CJuncky
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With the = size bores on slave and master, and 1.4" stroke on the master you will only get 1.4" of movement of the slave. You are moving a fixed amount of fluid with the stroke of the master so with a slave of the same size it will move the same fixed amount. For example if you had a 1" bore master with a 1.4" stroke and a 1/2" bore slave. The slave should stroke 2.8". Is your slave pushing or pulling the fork?

81 CJ5 258/T18/dana20/ARB locked diffs/33's
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post #3 of 14 Old 10-19-2009, 08:56 AM Thread Starter
kercher
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slave pushes the fork. Your explanation of bore size is why i bumped up to a 7/8". I actually had a 1" bore MC because the slave could handle the fluid volume, but it was a PITA to push the pedal. With 7/8" bore MC and 1.4" of throw I should get 1.75" of travel at the fork.

Neither is giving me anything close.
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post #4 of 14 Old 10-19-2009, 09:08 AM
CJuncky
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Have you manualy checked the fork travel ?

81 CJ5 258/T18/dana20/ARB locked diffs/33's
80 CJ7 258/auto/d 44 diffs/ 4" lift/rebuild started 80 CJ7 #2 stock(sold)
82 CJ7 stock DD
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post #5 of 14 Old 10-19-2009, 09:52 AM
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Have you checked to make sure your bleeder isnt upside down? Ive done this on calipers(put the on the wroung side) and they failed to bleed properly.. Thats about all i got hehe
Goodluck!
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post #6 of 14 Old 10-19-2009, 10:20 AM Thread Starter
kercher
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fork travel has been measured and it shouldn't be limited by anything (moved freely on the bellhousing before installing the bellhousing on the engine. It does not hit the pressure plate.

slave bleeder is at the top. It is Novak so it's orientation is fixed.

Does it sound like air in the system? I bench bled the master and then bled the entire system.
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post #7 of 14 Old 10-19-2009, 11:12 AM
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Did you bleed the master using the pedal first, then compress the slave (with your hand) and bleed it as well?
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post #8 of 14 Old 10-19-2009, 11:48 AM Thread Starter
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Quote:
Originally Posted by jayhawkclint View Post
Did you bleed the master using the pedal first, then compress the slave (with your hand) and bleed it as well?
Just bench bleed the MC

Connected the hardlines to the slave

Bled the slave and line through full compression cycles (of the slave) before connecting the pedal.

Bled the system with the pedal.


Please tell me something is wrong here!!!!!!!!
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post #9 of 14 Old 10-19-2009, 11:55 AM
BESRK
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Definately sounds like air in the system.

As a last resort, you might even unbolt the slave, clamp the pushrod in place somehow, raise the slave above the master and see if you can get it to bleed like that (without spraying brake fluid all over your paint). It shouldn't come to that though. Usually, the clutch slave is pretty easy to bleed out since it's such a short line. I assume you have a helper stepping on the clutch pedal while you crack open the bleeder screw?

A trick I've used to get stubborn air out of lines... I crack the bleeder screw and place my finger over it to act as a "one-way check valve". I then have my helper pump the pedal quickly so as not to give any small air bubbles a chance to "float" back up the line. Have to check the master cylinder reservoir frequently to make sure it doesn't go empty.

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post #10 of 14 Old 10-19-2009, 12:22 PM Thread Starter
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Quote:
Originally Posted by BESRK View Post
Definately sounds like air in the system.

A trick I've used to get stubborn air out of lines... I crack the bleeder screw and place my finger over it to act as a "one-way check valve". I then have my helper pump the pedal quickly so as not to give any small air bubbles a chance to "float" back up the line. Have to check the master cylinder reservoir frequently to make sure it doesn't go empty.
i just can't figure out where the air could be. The MC is the highest point. There are no bends that could trap air...

hmmm. I guess I will try some new bleeding techniques.
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post #11 of 14 Old 10-22-2009, 04:20 PM
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Any progress? Have you tried messing with the thread-in post on the back of the Wilwood slave. Mine has loosened up on me a couple times before letting air bubbles in. Not enough for fluid to leak out, so no signs of leak, just enough for air to get in so difficulty in getting fork throw.
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post #12 of 14 Old 10-22-2009, 05:34 PM
Unbalanced
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How about back-bleeding?

Get a pressure bleeder and push the fluid into the slave, pumping any air up and out through the master cylinder.

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"Temporarily Detained" maybe, but ~never~ stuck...
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post #13 of 14 Old 10-22-2009, 05:42 PM Thread Starter
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haven't messed with it in a couple days, but should have some time tomorrow and the weekend. All the fittings are good and snug. My wilwood didn't come with an adapter so I put that in.

Back bleeding might be a good idea. is there a reasonablly priced, good, kit for the do-it-yourselfer? I tried it bleeding brakes once. What a waste of time.

any other ideas are welcomed as i am out (other than the air in the system)
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post #14 of 14 Old 10-24-2009, 11:27 AM Thread Starter
kercher
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well, i made a new clutch pedal with a slightly smaller ratio and little large throw and that did it.

went for a drive and no issues other than a little smoke from the brake fluid burning off the exhaust.

thanks again for all the advice.
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