T18 throw out bearing or clutch fork is the problem

Be doubly sure your through-out arm return spring is strong enough to return the slave piston all the way back into the cylinder.

 

Okay...so this begs the question...how far back into the slave cylinder should the piston go?

I believe that I'm getting all I can get out of the hydraulic system. When the fluid in the master is exhausted, or the pedal hits the floor, there simply aint no more push. If this happens, should the piston in the slave be at the brink of blowing out the end?

 

Talked to someone at Novak today. He suggested that the setup should work, but admitted that most of his expertise was with GM conversions and not AMC stuff. He asked me to measure the amount if throw at the slave which I just did.

I made the adjustable push rod as long as physically possible which bottomed the piston... When i pressed the pedal all the way to the floor I get 1 inch of throw at the end of the fork by the push rod. With a fork ratio of 2:1 I think that means I'm only getting 1/2 inch at the TO bearing. I think I need at least a 1/2 inch or more at the push rod on top of what I already have.

FWIW...Since the MC and SC are 1:1 ratio I measured the push on the MC as well and also got an inch. The push rod at the master is extended all the way when the pedal is at rest.

But at this point I'm not exactly sure if all this is correct. I think I'll be removing the trans yet again this weekend and trying some mockup and measurements to find out what it is that I can do to fix this.

 

more leverage on the clutch fork ie longer from ball to slave end,move the slave farther from the bell(towards the frame) extend the clutch arm and gain mechanical advantage

 

Mechanical advantage isn't the problem. It's length of throw. If you go longer on the fork from the ball out, you get less throw, not more.

 

Well...it does seem to go back to hydraulics and the amount of throw from each cylinder. I've ruled out replacing the throwout bearing because there simply aren't any out there with the right internal diameter, I've got the "longest" one there is for this setup.

I think I have limited options if I keep the 11" B&B clutch. Since I'm only getting 1" of throw at the master before hitting the floor, try to figure out a different attachment point for the master cylinder push rod at the pedal for more throw into the master, I should be getting almost 2" max if necessary...can also be enhanced by getting an adjustable master push rod (assuming the original can be replaced to begin with). Or, I can try to use a 3/4" slave cylinder, raising the MC to SC ratio from 1:1 to 1:1.25, giving me an extra quarter inch of throw at the slave cylinder.

I'm pretty confident the clutch hardware itself is installed correctly, and short of replacing the B&B clutch with a smaller Rockford clutch I'm backing off my idea of removing the trans again...I just don't think it will reveal any solutions.

 

If you are getting a full inch of travel at the outer end of the fork, that would be enough to release a diaphragm clutch cover. I'm pretty sure I don't get more than that. I'll have to take a measurement on my trravel today and confirm that. Also, the pedal set I'm using is from Advance Adapters and they are quite a bit shorter than the Jeep pedals. That may be giving me more travel at the MC than you are getting. When I set mine up I could not get the Centerforce disc to release. Even though it looked almost identical to the NAPA disc I took out, it was different enough to be a problem. I'm using a Centerforce II cover (pressure plate) with a NAPA disc. While Novacks article didn't come right out and say not to use a three finger clutch with a hydraulic setup, they did mention that the diaphragm cover took less throw to get it to release. I'll post up my measurements today for you to compare.

 

I would appreciate that measurement. I'm not sure what a normal throw should be at the fork. I re-measured tonight and its definitely an inch at the fork where the push rod sits.

 

geometry never was my strong suit...

 

I just went out and measured the throw on my fork. At the slave end I have 1" of movement. Mine releases just fine with a diaphragm pressure plate. Also I have no freeplay at the pedal, only at the fork.

 

Thanks, that helps a lot. One more thing, do you know about how far it has to move before it engages?

 

Can you be more specific?

 

Yes...when you say you have a full inch of throw is that for clutch engagement or the total? What I was getting at is how much throw do you actually need for your clutch to engage?

 

I have a full inch of movement at the slave end of the fork and my clutch begins to engage about halfway up on the pedal stroke.

 

Since I'm getting some clutch release at 1" before the pedal hits the floor and there aint no more I'm pretty sure that changing out the current 7/8" slave for a 3/4" slave will get me an additional 5/16" of throw...and I think that will be enough to get a full release of the clutch.

After checking the master again I see that it's stamped 13/16" on the side, if that's true then the MC to SC ratio is not 1:1 as I thought but is slightly less. If you bear with me I'll explain where my calculations took me.

The cylinder volume formula is V=PI x r sq * h where, PI=3.14; r sq=radius squared; h=height...which I equate to max stroke that I get on the MC of 1"). So when I plug in the MC numbers I get a volume of .518223.

Using the same formula, if I plug in the MC volume and solve for h (height or in my case the stroke) using the 3/4" cylinder radius I get a height(stroke) of 1.174". I did the same for the current 7/8" slave and got a stroke of 0.862" which is a difference of 0.312", or about 5/16" of added stroke if I swap the SC to a 3/4".

So my decisions are to either buy a 3/4" slave, $20 + hose, and fab a mount and see if it works. Or, change out the clutch to a diaphragm style that supposedly requires less throw to release, and probably will cost a $100 give or take.

I think this all sounds logical based upon my reading of the Novak clutch information...but it is a Jeep after all and sometimes logic doesn't apply.

 

It's worth a try, for sure. It's hard to argue with math anyway. But like you said, it's a Jeep and they sometimes operate outside the basic rules of the Universe. For reference, I'm using a Wilwood 7/8" MC with 1 7/16" stroke and a Wilwood slave that's 3/4" bore with a 1.38" stroke. It's a pull back slave not a pusher. Slave pn 260-1333, MC pn 260-6765

 

Thank you for this thread everyone. Having the same issues and this helped a lot. I went with longer fulcrum point and stronger spring to ensure slave cyl. returns fully. My TO bearing was riding on my clutch fingers and boy...that'll wipe out a bearing in a hurry.