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Old 06-01-2011, 06:35 PM
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LT1 T56 slave cylinder -- extend push rod?

I am not getting enough distance from my slave cylinder -- my master is .75" and my slave is 1.25". I think this translates to less than 1cm of travel at the slave.

I'm trying to figure out a way to solve this issue without buying a new slave with a smaller bore -- one of my ideas is cutting my spare push rod from my old busted slave in half, threading both sides and putting a coupling nut between the pieces to get the extra 1.5cm's that I need. Will this work? My friend seems to think it will just push on my throwout bearing and wear it out prematurely -- i feel like this will only happen if the stock pushrod sits at its extreme point in the slave.

What do you think?

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Old 06-02-2011, 09:47 AM
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You say "distance", are you meaning travel? If so, I'm afraid you'll be needing a new cylinder. Travel is strictly a matter of master bore size and stroke vs. slave bore size and stroke.

Russ
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Old 06-02-2011, 11:02 AM
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Sorry, let me clarify --

The distance the slave cylinder is stroking is less than 1cm when I push on the clutch pedal. My master stroke is about .8" and the master bore is .75". The slave is a 1.25" bore --

so lengthening the pushrod wouldn't compensate for the loss of stroke? I was hoping that since the pushrod would be closer to the TB at rest, my small amount of stroke would be compensated for.

Do you have any suggestions on a smaller slave to use? Or a larger master? I'm using a Wilwood compact master (which is the only style of master that fits my application...) and using the largest available size they offer. If i could get a master that is larger, I should be okay too...

This is the slave that I have:

http://www.summitracing.com/parts/DHB-CS360052/

This is the master (.75")
http://www.wilwood.com/MasterCylinde...ter%20Cylinder

Last edited by tylerwerrin; 06-02-2011 at 11:06 AM. Reason: aditional info
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Old 06-03-2011, 08:40 AM
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M/c

Hey Tyler, Check out the Wilwood 260-3380, 1.125" x 1.00". The remote reservoir cap makes it compact. Look at the PDF to see what it looks like assembled. Will displace .994 cu. in. at full stroke. Sounds like you need 2.5 cm travel at the slave(.975 inches). If the slave is 1.25", an inch of travel will require .767 cu. in. If you're getting .8" of travel at the clutch pedal you'll displace .795 cu.in. It should work. Nolan

http://www.wilwood.com/MasterCylinde...me=Combination Remote Master Cylinder
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Old 06-03-2011, 11:47 AM
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Hey nolan,

that master looks good, but I think the math is incorrect:

master bore - 1.125"
master stroke - 0.8"

fluid pushed
(0.5*1.125)^2*3.14*0.8 = 0.7948 in^3

travel with current slave
(0.5*1.25)^2*3.14*x = 0.7948
x = 0.648 in

no matter what, because the master is smaller than the slave, i won't be able to move the slave more than .8" (my stroke). I'll always be getting less. Argh! My next idea is somehow increase stroke, but i just dont know how. Either that, i'll go with a smaller slave, which will kinda suck.
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Old 06-04-2011, 07:01 AM
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Yep

Yep, There is an error. I don't know how I came up with .767 cu. in. on the slave, must have not cleared the calculator or something. Duh.
There is still a solution to this problem. I'm not convinced that the stock slave is actually 1.25 bore. I'm going to open one up and check the bore. I'll let you know what I find. Nolan
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Old 06-04-2011, 09:17 AM
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Good News

Okay Tyler, I took a stock slave cylinder apart. Even though the housing looks big, there is a stainless cylinder sleeve within that is just .997 in diameter. See attachment. So one inch of throw at the slave will only require
.781 cu. in. of displacement. With the 1 1/8" master cylinder @ .8" of stroke you get .795 cu. in. Real close. If you don't get enough slave cylinder stroke to get the clutch disengaged you can adjust the master cylinder push rod attachment point down on the clutch arm a tad to achieve a full inch of stroke which should be plenty. The 260-3380 specs show 1.1" as full stroke so make sure you don't go overstroke with the clutch pedal.

I don't know where you got the 2.5cm figure from(.975")needed to disengage the clutch but I just rounded to an inch. If you figure it at .975 to disengage the clutch you only need .761 cu. in.

Did you ever pull the transmission to make sure the junkyard clutch and throwout bearing were freely moving? Lots of times, when sitting up, the clutch disc will glue itself to the flywheel and pressure plate. Also the throwout bearing will rust itself to the transmission input shaft sometimes.

Hope this works, I'm waiting on a video of you doing a smoky burnout in that Jag. Nolan
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Old 06-04-2011, 12:49 PM
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Hi Nolan!

Thanks for taking that slave apart -- i always wondered what one looked like in there!

The 1.25" figure came from rock auto & summit:

http://www.summitracing.com/parts/DHB-CS360052/

I bought the slave from summit. It was weird, because I had read that the ones that were stock were only 1". If you measured the slave and got the 1" figure, then I'm just going to go with that -- maybe the summit cylinder is taking something else into the measurement?

The 2.5cm to disengage the clutch was just a rough guess -- this is where I got most of my info regarding the clutch setup:

http://www.jaguarspecialties.com/project2.asp

He lists the slave as being 1", and has a master cylinder that is the same bore as me. The one catch is that he has more stroke than I do -- a full 1", where I am locked into the .8 figure. I tried to adjust the master like you said last time I was working on the car, but I noticed that how the pedal interfaces with the plunger rod is by screwing into an attachment. You can sort of make out how the mechanism works in this pic:

http://cgi.ebay.com/ebaymotors/Jagua...#ht_500wt_1182

I thought that I could possibly raise the master up (it's already spaced off the pedal box with an aluminum spacer) but I'm still locked into how the pedal "swings".

I think we are getting close though!!! Thanks again for your continued help!

T
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Old 08-14-2011, 11:28 AM
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What master cylinder did you end up using? I would like to use the stock lt1 t56 slave with a compact aftermarket master cylinder like the little ones wilwood offers.

Thanks for any help!
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Old 08-14-2011, 12:42 PM
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Hi Mason,

I ended up using a 7/8 wilwood master cylinder and a 1.25" slave (although i'm still not sure if it is 1.25" or just 1"... it looks exactly the same as the stock slave, which was 1", summit listed my piece as 1.25" though.)

However, I think the 7/8" master is moving the slave too far -- when i push the clutch pedal completely to the floor I get a "clunk clunk clunk" feel on my pedal (i can actually feel it vibrating" and it makes a tapping noise. If I'm careful, and I only depress the pedal 3/4 of the way down to the floor, i can still shift through my gears fine, and the clunking doesnt happen.

So, long story short it's not completely done -- i'm going to go back to the 3/4" master I think and experiment with a smaller slave this time, or just bleed the hell out of it with my Mityvac -- who knows, maybe when I tried it last time i still had some air in the system. I say this because in a stock application, the master is 3/4" and the slave is 1", so it should translate over.

Let me know how your project comes along.
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Old 08-14-2011, 01:24 PM
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Thanks for getting back with me. I have the stock slave and plan to use it. I am like you and not sure what the factory slave moves 1" or 1.25".

Just looking for the right MC from wilwood to use...

Good luck, on your project
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Old 08-15-2011, 05:45 AM
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I am using a slave for an 86 Chev pickup and a master from an 88 Chev pickup on my 59 Elky.

I forget the bore sizes of each right now----I think 13/16 slave and 3/4 master.

I get right at 1" of movement at the slave with this
I also get right at 1" of movement with the mechanical clutch in my 66

I would venture to guess, that getting an inch of movement where the rod contacts the fork---would be a good starting point.
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Old 08-15-2011, 11:22 AM
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1" of movement, aye --

It's all very perplexing, I'm getting so many different measurements. Obviously what I have now isn't working -- apparently a 7/8" master with 1" of stroke is moving the 1" slave too far -- I'm not getting 1" with this arrangement -- I'm getting .76" (according to this place)

http://forum.mcleodracing.com/showth...tem-experience

He says that we need .655" of movement at the slave -- so apparently that .1" of excess travel is causing my throwout bearing to disengage too far.

Which model of pickup did you get the slave from? does it mate up to the t56 the same as a stock one? Are there larger slaves available, so I don't have to swap out my Master again?

The only other option is to get another master, a 13/16" and try that -- I know a fellow who went with a 3/4" master and a 13/16" slave -- maybe a 3/4" master and 15/16" slave would do it...
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