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Clutch master cylinder size

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Old 06-17-2012, 10:05 PM   #1
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Default Clutch master cylinder size

Im nearing completion of my ls1/t56 wrx swap and had to get a new clutch master. I bought the wilwood compact cylinder with a .750" bore and 1.4" of travel and it disengages the clutch at the floor and the pedal is fairly soft, which I dont like at all. I have a remote bleeder with a speed bleeder on it so I know theres no air in it because I bled it alot. I have about .75" of travel for the master cylinder rod. So, Im thinking about going to their 1" bore with 1.12 stroke. http://www.wilwood.com/MasterCylinde...emno=260-10375
Is that what I need to fix my problem? I just dont know what kind of size increase is needed to fix it.

EDIT: I did the math and it tells me I need a 7/8 master, which will get me really close to original specs. I just wonder if my 3' long remote bleeder makes any difference vs the stock bleeder right at the trans.

Last edited by LsxWRX; 06-19-2012 at 05:02 PM.
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Old 06-18-2012, 07:28 AM   #2
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factory f-body 3/4" bore, 1.1" stroke...looks like you need more stroke
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Old 06-18-2012, 07:40 PM   #3
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I don't think that's possible with the way the clutch pedal stuff is laid out.
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Old 06-19-2012, 11:26 AM   #4
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Any ideas?
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Old 06-19-2012, 12:40 PM   #5
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if you cant move the pedal back can you space the master away from the pedal ?
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Old 06-19-2012, 04:58 PM   #6
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Unless I can adjust the pedal stop to let the pedal come up farther, moving the master won't do anything...the stroke is already determined by the pedal travel.
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Old 06-19-2012, 04:59 PM   #7
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If you only have .75 in of travel in a .75 in diameter master cylinder, you're only pushing .331 cubic inches of fluid, maximum. If Oange SS is correct with a stock .75 in master cyl diameter and 1.1 in of travel, then your pushing .486 cubic inches of fluid. It would make sense that your clutch engages at the floor if you only have .75 inches of travel.

So you are saying you have a total of 1.4 inches of travel with the wilwood installed, but you aren't able to use the total travel distance since the pedal hits the floor?

If you go with the 1" bore and you are still only able to travel .75 in, then you are pushing .589 cubic inches of fluid. That is more than the stock .486 cubic inches needed based on Oange SS's comment. Basically, if you go with the 1" diameter, you're not going to have to push the pedal in that far for the clutch to disengage.
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Old 06-19-2012, 08:42 PM   #8
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Quote:
Originally Posted by LsxWRX View Post
Unless I can adjust the pedal stop to let the pedal come up farther, moving the master won't do anything...the stroke is already determined by the pedal travel.
The further away the pickup point on the pedal is from the pivot point, the more travel you'll have. You're saying you can't move the pickup point lower? Or maybe you just don't want to...
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Old 06-21-2012, 11:21 AM   #9
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Yea the master has 1.4" stroke but the pedal hits the floor after .75" of travel. There's really no way for me to change the pedal travel the way everything is laid out. I went ahead and bought the 1" master because I had doubts about the 7/8 being enough since the 3/4 supposedly fully disengaged on the floor. Hopefully it won't be too much.
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Old 06-21-2012, 12:17 PM   #10
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As S10xGM stated, Could you move the masters rod attachement point lower on the pedal ?.. that would leave the pedal travel the same, but the lower point would cause the master's rod to travel a bit longer !

Its about leverage and ratio's.. Note - The bottom of the pedal travel is not the same as the master rod travel.

BC
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Old 06-21-2012, 10:54 PM   #11
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I think there would have been too much angle on the pushrod for it to work. I just installed the 1" master earlier and it's exactly what was needed. It disengages half way down and is stiffer like I wanted. I may fix the stop for the pedal a 1/4" up from the floor to make sure the slave doesn't get overextended or something.
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Old 06-21-2012, 11:33 PM   #12
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Good deal.. keep up the good work..
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Old 06-22-2012, 11:03 AM   #13
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good info here.
Thanks all
dave
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Old 06-22-2012, 06:10 PM   #14
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Originally Posted by LsxWRX View Post
I think there would have been too much angle on the pushrod for it to work. I just installed the 1" master earlier and it's exactly what was needed. It disengages half way down and is stiffer like I wanted. I may fix the stop for the pedal a 1/4" up from the floor to make sure the slave doesn't get overextended or something.
Glad it worked out for you. That's exactly what the 1" diameter was supposed to do. Good choice, the 7/8" diameter master cyl would have been slightly undersized based on your application of only .75" travel... would have been easier to push the clutch in though.

For any future readers, Bczee was correct in clarifying that... I have been referring to the master rod travel, definitely not the pedal travel.
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112, 71, a4, bore, chevelle, clutch, cyclinder, cylinder, disengage, length, ls1, master, rod, size, stock, stroke, t56, travel

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