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Old 04-18-2011, 04:11 PM
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1993 T56 clutch operation questions

Hi guys,

I posted a while ago about this -- i thought i had it figured out, but apparently i am very wrong, or there is something very messed up with my clutch.

I have a Wilwood Master cylinder, which is a .75 bore, 1.4 inch stroke. The slave cylinder I used was a 1" bore, with a ? stroke. It came from a 1990 Camaro, rather than the 93 camaro which my T56 is from. I had read on various forums that this slave (the 90) could be swapped because it was essentially the same as the stock (93) slave, but it had a bleeder.

I was beginning to bleed the system, and I was noticing that the pedal effort was quite high. Suddenly, KABLAM. The slave cylinder burst. It looked as if the cylinder had extended past its end, and blew all of its seals.

I am not sure what size the original stock master cylinder/slave is. On rock auto, there is a slave cylinder which is 11/16" and a master that is 7/8". On summit, the Master is listed as a 3/4" and the slave is 1 1/4". I'm not sure which source to believe -- and what is more troubling is that since I don't know the stroke length on the stock master, I am unsure exactly how much fluid is being displaced.

Cdboy warned me about Pedal effort/pedal ratio -- I am limited on Master cylinders (my application can only fit the Wilwood compact master -- the .75 is the largest of the type that i see on their site.) What should I do? I am also unsure exactly how much throw I need from the slave to fully disengage the clutch -- 1/2 an inch? .75 inches?

Any help would be much appreciated! Thanks guys...

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Last edited by tylerwerrin; 04-18-2011 at 04:17 PM.
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Old 04-18-2011, 06:37 PM
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Alright, so here's some new info -- apparently I only get 3/4" of useable throw from the master cylinder -- so whatever I'm displacing is roughly half of what should be possible -- should I just get a larger bore master, or what?
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Old 04-18-2011, 09:33 PM
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Maybe Ok

Hey Tyler, I could possibly be your bleeding procedure. Are you sure the slave blew it guts? Did you take it out and look at it? They have a plastic retainer to keep it retracted while you bleed, this speeds the bleeding process.(if the slave is cylinder is retracted and empty, there is no big pocket to bleed air from) The bleeding is accomplished by lightly stroking the pedal(not pushing it all the way down). When all air is bled out, then you push the pedal all the way in. The new found hydraulic force pops the plastic retainer straps and leaves the plastic seat for smooth clutch operation. Could be what you experienced is just the plastic strap popping. If the clutch ain't working yet, you still have air, bleed it some more. Light stroke till you start getting pedal feel. Could be that '90 slave is the wrong stroke too. I don't know about the '90 bellhousing arrangement, but I do know the later T56 uses a pull clutch versus a push clutch.(Traditional push clutch pushes the clutch fork towards the rear of the car which in turn pushes the throwout bearing into the clutch fingers towards the front of the car to release the clutch.) (the newer pull clutches utilize a throwout bearing with a collar that is behind the reversed clutch fingers. The clutch action pushes the clutch fork towards the front of the car and pulls the clutch fingers toward the rear of the car to release the clutch) Here is a pic of the slave with the retainer strap still intact.http://www.rockauto.com/catalog/moreinfo.php?pk=967940 Hope you get it going. Nolan
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Old 04-18-2011, 10:39 PM
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hey nolan,

yeah, it blew its guts -- it cracked along the base on the sides. I actually took the plastic shipping strap off before i installed it. Bad idea?

I called the guy who sold me the pedal box conversion kit -- he told me that while the master has the potential for a 1.4" stroke, I really can only get around .75" (or slightly more he said) from depressing my pedal. So i'm working with a small amount of stroke :-/

I'm just not sure what could be the problem -- i'm starting to think my pushrod might be too short -- if i lengthened it, maybe i could still take advantage of what i have installed. It's very frustrating -- i can't find any information on what the stroke of the master is on a stock camaro -- i just know that the stock is 3/4 like my master -- i'm guessing either the stroke is much longer, or that the slave that i bought (for the 1990 camaro) is different in some way (longer push rod?).

any ideas?
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Old 04-19-2011, 08:00 AM
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??????????

Well,
1)If you blew up the slave cylinder, sounds like you were making hydraulic pressure.
2)Removing the plastic strap may have allowed the slave cylinder pushrod to go in crooked missing the seat in the clutch arm. In this case, when you achieved hydraulic pressure, you simply shot the piston out of the cylinder.
3)Possible that one or more components in the clutch is froze up and you blew the cylinder trying to move an un-movable part. Or, it was froze up and when it broke loose, the extremely high hydraulic pressure just blew everything. (Had a chain break while lifting a big block, the resulting energy release shot the piston/rod out of the hydraulic jack, blowing the end of the jack cylinder completely off, sounded like a gun,never under estimate hydraulic force.)
4)Possible restriction in the line which will allow high pressure hydraulic force into the slave, but won't allow low pressure return back to the master cylinder. (I had a brake hose do this one time.) Also make sure you used a high pressure (3000-5000psi) braided line with the proper composition for brake fluid Vs. a braided line rated for say 300psi for use on a oil pressure gauge or something.
5)Might just be a defective slave cylinder, they are, after all, just plastic POS nowadays.

Food for thought. olnolan
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Old 04-21-2011, 05:16 PM
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hey nolan,

thanks for the ideas -- let me go through what i've read, and see if you, or anyone else on the board thinks it makes sense...

i asked a buddy of mine who was a physics major in college. he told me the distance i was getting out of my slave with my current setup:

pi = pi
Rm = radius of the master
Hm = height of master
Rs = radius of slave
Hs = height of slave (what you're trying to find):
pi * Rm^2 * Hm = pi * Rs ^2 * Hs

Dm = diameter of master
Ds = diameter of slave
Radius = Diameter / 2:
so
Rm = Dm / 2
Rs = Ds / 2

substitute radii:
pi * (Dm / 2) ^2 * Hm = pi * (Ds / 2) ^2 * Hs

isolate Hs:
Hs = pi * (Dm / 2)^2 * Hm / (pi * (Ds / 2) ^2

cancel pi & combine exponents:
Hs = Hm * ( (Dm / 2) / (Ds / 2) )^2
cancel the /2's:
Hs = Hm * (Dm / Ds) ^ 2

now you can double check by thought experiments:
if Hm is very small (or big) then does it make sense that Hs is very small (or big)?
if Dm >> (or <<) Ds, then does it make sense that Hs >> (or <<) Hm?
if Ds = 2 * Dm , does it make sense that Hs = 1/4 * Hm?

It all looks like gobbledy gook until the variables are plugged in:

Master diameter: 1.9cm
Master stroke: 1.9cm
Slave diameter: 2.4cm
Fluid displaced by master: 5.38cm^3

the total distance the slave travels is 1.06cm -- I don't know how far the slave needs to travel to disengage the clutch -- so that is my next problem. I have read differing reports, from 1.6cm or more. I guess that means a new pushrod needs to be made. Have you done this before? Or is there a place to get em?
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Old 04-22-2011, 08:56 AM
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Clutch

Hey Man, Thats slightly less than 7/16" of travel at the clutch arm. While I don't know what the minimum travel is to disengage the clutch, I don't think thats gonna do it. I think you're gonna need more displacement from the master. This can be achieved by changing the pivot point to get more stroke or going with a bigger bore. Without doing the volume calculation, a master with a 1" bore stroked 1" will move a 1" bore slave 1", agreed? Since the masters are not generally more than 1" diameter, then you HAVE to get more stroke from the master, agreed? You need to move the pushrod attachment point down. Disconnect the pushrod, then push the clutch pedal in and out and measure the achievable stroke with a ruler at different points on the clutch pedal arm. An adjustable length pushrod will allow for fine tuning the adjustment. You'll want a bit of slack to allow the master to fully release as well choosing a attachment point that does not allow the pushrod to bottom out the piston causing damage to the seals.

This still does not explain why your slave blew up. You need to look into cause of the failure before you can make it work. I've got a feeling that one or more clutch components are frozen up. I know this is not what you want to hear, but pulling the transmission and inspecting the components should be next on your list. You could try another slave, if you blow it up, you'll know for sure something is stuck.

Let us know what you find. olnolan
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