New clutch setup won't disengage

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I don't have a hydraulic TO bearing... if there were one, then I wouldn't need a fork! ;) I've read too many horror stories about leaks requiring removal of the transmission, temperature changes affecting adjustment, not to mention the expense.

My setup is a pull slave cylinder actuating a stock fork and TO bearing.
 
just had that same short hole thing on this 340 4spd package i'm working with , cut some of the input shaft off , and i'm using the jeep bearing in the auto bung of the crank . no more dealing with the bushing holes to small to big , not deep enough stuff .
 
DrCharles said:
I don't have a hydraulic TO bearing... if there were one, then I wouldn't need a fork! ;) I've read too many horror stories about leaks requiring removal of the transmission, temperature changes affecting adjustment, not to mention the expense.

My setup is a pull slave cylinder actuating a stock fork and TO bearing.
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O crap, ok, I'm slow to the party, but when I get there, I'm on like a rock star.

I will have a chance on Sunday to get some help and measure what you want. I just can't do it alone. Then I'll post it for you.

The only thing is I have Long fingers in my cover, but I run about .125 air gap. My numbers should be close enough to get you where you need to be.
 
Finally got a chance to look at my setup.

Good news - the disc is definitely not stuck to the flywheel :) With the clutch pedal depressed and the car in 4th, brakes set, it cranks just as rapidly as if in neutral. Trial with the clutch engaged - big bump against the brakes, as expected. So that's good news. Whatever I have to fix isn't inside the Lakewood!

Now "feeling" the clutch pedal carefully. It seems that about two inches of pedal movement occurs before I can really feel the diaphragm spring taking up the load (like air in the system is compressing). There's so little throwout bearing clearance to the fingers that I would not expect that much pedal free play.

Next step is to measure the actual fork movement, as I noted. But I'm sure that the clutch is (partially) disengaging since the starter cranks normally with the pedal depressed in gear. Just not getting enough travel.

For the rest of this afternoon, though, I'm installing my inner valve springs, and a new set of Accel ceramic-boot plug wires since #4 and #6 keep pushing themselves off the plugs due to the heat between the header pipes.
 
Valve springs in, plug wires made. Back to the clutch! This afternoon I had a helper slowly depress the pedal while I watched the fork. It starts to move immediately with the pedal, but only travels 3/4" (at the hole/rod) with the pedal on the floor. I bled the system again, but no air bubbles came out. The slave I'm using (a Howe #829) is capable of 1-1/8" stroke. Master is a Wilwood 260-1304 with a 3/4" bore (the larger one, they also make a 5/8").

So at this point it looks like I don't have enough fork travel. I think it should be about 1". My overall pedal to fork ratio must be too (numerically) high... it doesn't feel as "stiff" as a clutch for 500 hp should be, either, although I don't have a scale to measure it with.

Possible ways to fix it:
1) even bigger bore master, but might run out of stroke in the slave,
2) remove the clutch pedal and cut/reweld the linkage to the master,
3) drill a 1/4" hole in the fork closer to the pivot, for the pull cylinder rod.

I think I'm going with #3. A moderate PITA to drill it lying under the car with the fork installed but I don't dare yank it out because I can't get a hand in there to get the TO spring clips back on the fork... at least I have a decent Milwaukee right-angle drill!
 
I don't think that's right. A larger bore master will take MORE pedal effort, because it has more square inches of piston. The pounds per square inch also increases, as the clutch springs deflect more. So, (pounds/sq in) * (sq in) = (pounds at pedal). PSI larger, piston larger = pounds at pedal larger. You may be looking at this from the slave end, not the pedal end.

I can't add any more pedal stroke because it's already on the floor at 3/4" slave travel. The overall leverage is fixed in the clutch, fork, slave piston, master piston, and pedal ratio. The only way to move more fluid to the slave is a bigger master piston. Or move the same fluid but decrease the reduction ratio at the fork (hole closer to pivot) so the fork will move further with the same 3/4" slave travel. Both will increase pedal effort, doing more work.

Think about brakes, same principle... the reason to go to a smaller master is to decrease pedal effort at the cost of increased pedal stroke. Bigger master, more pedal effort, shorter stroke.
 
Look at it another way. The clutch spring is "pushing back" against the slave cylinder which has a certain area, generating so many psi. Now that psi is applied against the (bigger) master piston, so more piston area, more pounds required on your leg to hold it the same distance...

My brain hurts ;)
 
DrCharles said:
I don't think that's right. A larger bore master will take MORE pedal effort, because it has more square inches of piston. The pounds per square inch also increases, as the clutch springs deflect more. So, (pounds/sq in) * (sq in) = (pounds at pedal). PSI larger, piston larger = pounds at pedal larger. You may be looking at this from the slave end, not the pedal end.

I can't add any more pedal stroke because it's already on the floor at 3/4" slave travel. The overall leverage is fixed in the clutch, fork, slave piston, master piston, and pedal ratio. The only way to move more fluid to the slave is a bigger master piston. Or move the same fluid but decrease the reduction ratio at the fork (hole closer to pivot) so the fork will move further with the same 3/4" slave travel. Both will increase pedal effort, doing more work.

Think about brakes, same principle... the reason to go to a smaller master is to decrease pedal effort at the cost of increased pedal stroke. Bigger master, more pedal effort, shorter stroke.
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Yup, I had it backwards. The bigger piston will make the pedal easier, and IIRC make the throw shorter, as in brake pedal travel, or in your case, clutch pedal travel. So that would make the slave push, or pull the fork more, if I'm not blowing smoke up my own hind parts. I keep forgetting your using a slave to push or pull the fork rather than a hydraulic throw out bearing.

#3 will still work. How does the slave hook to the fork?
 
Your hind parts are still smoking a little bit, YR :D
You can't make the pedal easier and the throw shorter at the same time, if the clutch is moving the same amount or more!

Bigger master piston makes the pedal harder (and a shorter stroke for the same amount of TO movement). Since my pedal stroke stays the same, and the slave will move farther (which is what I need), the pedal is harder at full deflection.

Conversely, smaller master piston makes the pedal easier (and requires a longer stroke to move the same amount of fluid at the same pressure). Again, my pedal stroke stays the same so the pedal is easier - but the slave won't move as far. That's why it's easier.

Anyhow, the pull cylinder currently attaches to the same fork hole where the original Z-bar rod did. The only difference is that it's pulling from behind the fork instead of pushing from in front of it. I do have the round-nosed spacer for the rod, but that won't help with a new hole since it won't be countersunk and I may not be able to get to it with a big drill from the front.
 
DrCharles said:
Your hind parts are still smoking a little bit, YR :D
You can't make the pedal easier and the throw shorter at the same time, if the clutch is moving the same amount or more!

Bigger master piston makes the pedal harder (and a shorter stroke for the same amount of TO movement). Since my pedal stroke stays the same, and the slave will move farther (which is what I need), the pedal is harder at full deflection.

Conversely, smaller master piston makes the pedal easier (and requires a longer stroke to move the same amount of fluid at the same pressure). Again, my pedal stroke stays the same so the pedal is easier - but the slave won't move as far. That's why it's easier.

Anyhow, the pull cylinder currently attaches to the same fork hole where the original Z-bar rod did. The only difference is that it's pulling from behind the fork instead of pushing from in front of it. I do have the round-nosed spacer for the rod, but that won't help with a new hole since it won't be countersunk and I may not be able to get to it with a big drill from the front.
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Unreal.
Yup. A smaller bore makes it easier to push with longer travel. That's why when I convert from power to manual brakes you use a smaller diameter piston.

Damn the crack pipe.

BTW. If you move the hole in on the fork, it can't be the same sized hole as what's there. It will have to be smaller. How small can you make it? A 1/2 inch move will make a big difference.
 
Since I have only 3/4" fork travel currently, and the clutch is just barely dragging enough so that I can't get the trans into gear with the engine running, I estimate I need 7/8 to 1" of travel. The available stroke is limited to 3/4" unless I make other mods as we discussed above, which I'm trying to avoid. So I need to decrease the fork ratio at the new hole by a factor of 3/4 (so that 3/4" of slave movement causes the original hole to move 1".

Pics of similar forks:
(A-body) Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists
This one is 12.5" overall length, or about 12" hole-pivot-TO. From the pic I'm estimating it's 2:1 ratio (4" pivot to TO, 8" hole to pivot).

(B-body) Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists
10.87" overall, again looks like 2:1 in the picture. I think this is the one I actually have, not an A-body fork. Will try and get a more accurate measurement next time I have a chance to work on the car.

Anyway, the new hole would then have to be closer to the pivot by 25% (1/4) of the original hole-to-pivot distance to get 1" travel from a 3/4" stroke. If that distance is 7 or 8 inches, the hole has to be relocated 1-3/4" to 2 inches toward the pivot! Half an inch won't be nearly enough. The fork is stamped into a C-channel shape and it looks big enough to drill a 5/16" hole anywhere I need it. (Nut will go on the flat side towards the front of the car, since it's a pull cylinder).

I may try 1" closer(12-15%) and see if that's enough. Unless there's an error in my math...
There are similar 7/8" master cyls that look like direct replacements. Going from a 3/4" to 7/8" piston makes it (.875/.750)**2 or 36% more piston area. That's about right to go from 3/4" stroke to 1" stroke, since 1/4" is 33% of 3/4... hmm... still more work than relocating the hole though.
 
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Turns out this issue has been covered in depth right here on FABO...
Anyone running a hydraulic clutch with their 833?

It does seem that 1" of travel at the original fork hole is required. So I will be locating the new hole where I get 1" with my current setup, rather than mess with different master cyls and the associated mounting, connection and bleeding issues.
 
Sure, but that requires removing the pedal and re-welding the spacer (that lines up with the original hole). The spacer is about 1.5" tall, thick-wall tubing which gives the proper offset from the pedal to the clutch master. I figured drilling one hole in the fork would be simpler...

Wrong! That damned fork is hardened, or at least made from some extremely hard steel alloy. It looks just as shiny as the day I bought it, and laughs at my drillbits (even titanium nitride coated ones). So I sloooowly ground my way through with a small die grinder and a round carbide burr, then enlarged the hole to slightly over 5/16" so the pull cylinder rod doesn't bind. It's about 1/2" closer to the bellhousing than the notch where the fork return spring sits, or about 1-3/4" from the center of the original fork hole.

The pedal is now noticeably stiffer, which means it has more fork travel as I calculated. I need to adjust out a bit more free play tomorrow but I feel confident it will work properly now. (My Isky rocker arms are at the machine shop being narrowed, so I can't try a live test for a while).
 
DrCharles said:
Sure, but that requires removing the pedal and re-welding the spacer (that lines up with the original hole). The spacer is about 1.5" tall, thick-wall tubing which gives the proper offset from the pedal to the clutch master. I figured drilling one hole in the fork would be simpler...

Wrong! That damned fork is hardened, or at least made from some extremely hard steel alloy. It looks just as shiny as the day I bought it, and laughs at my drillbits (even titanium nitride coated ones). So I sloooowly ground my way through with a small die grinder and a round carbide burr, then enlarged the hole to slightly over 5/16" so the pull cylinder rod doesn't bind. It's about 1/2" closer to the bellhousing than the notch where the fork return spring sits, or about 1-3/4" from the center of the original fork hole.

The pedal is now noticeably stiffer, which means it has more fork travel as I calculated. I need to adjust out a bit more free play tomorrow but I feel confident it will work properly now. (My Isky rocker arms are at the machine shop being narrowed, so I can't try a live test for a while).
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I always struggle with the ratios, but I know a small move can make a noticeable pedal effort change.

On my last race car, I decided to make everything hair triggered. The throttle would go from idle to WFO in about 3/4 inch of pedal travel and the clutch was about the same. Could barely drive it's through the pits. Like driving toggle switches.

Luckily, I made everything with adjustability built into it so I could change it.

A small move makes a big difference.
 
Well, I'll be driving my Dart mostly on the street, so I definitely don't want a clutch (or a throttle) that's either all the way in or all the way out!

I think that I may have simply bought too small a master for my pull cylinder to achieve that magic 1" travel at the fork, since the pedal is connected at the stock location. Anyhow the proper clutch plate departure is the most important factor, not pedal effort - the left leg requirement is what it is.

How far from the fingers should the throwout be? Is there any particular spacing other than "not touching"? On a hydraulic clutch I hate to feel "slop" in the pedal.
 
I run my mechanical set up pretty tight, with the TO "all but touching". Yeah adjustments are more frequent in terms of mileage driven, but it still lasts pretty much all summer.
That 1inch freeplay slows me down too much,lol.
 
AJ/FormS said:
I run my mechanical set up pretty tight, with the TO "all but touching". Yeah adjustments are more frequent in terms of mileage driven, but it still lasts pretty much all summer.
That 1inch freeplay slows me down too much,lol.
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That's ok as long as you don't have some kind of lever that has counterweight. Well, all fingers or levers are subject to centrifugal force, but I know my fingers have about .060-080 movement. So I give myself about .100 and don't ride the clutch like a sissy!

If you ride the clutch pedal, you have to have more free play.
 
hmm... I have a Centerforce DF disc & pressure plate, which does have a ring of weights on the fingers. How far do those fingers deflect?

On the other hand, I don't ride the pedal and the car will only see high rpm in short bursts...
 
I have a CF also, And I must admit, I had not thought of that. I guess I'm ok then, at my setting.....Or I just don't rev it high enough, or drive it hard enough, to notice any slippage, lol.Or they don't work anymore,heehee; I mean it's been in there since about 2004
 
DrCharles said:
hmm... I have a Centerforce DF disc & pressure plate, which does have a ring of weights on the fingers. How far do those fingers deflect?

On the other hand, I don't ride the pedal and the car will only see high rpm in short bursts...
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It depends on the lever and I don't use either diaphram or center force stuff. The lever won't always move due to CF but it's something to think about.
 
I may regret opening this can of worms... but why don't you use diaphragm clutches? Or Centerforce?
 
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