CJ7 Hydraulic clutch conversion questions - JeepForum.com
 
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post #1 of 6 Old 07-21-2009, 01:28 PM Thread Starter
mosshopper
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CJ7 Hydraulic clutch conversion questions

Ok I am a cheap SOB and I am trying to save some money. So here is what I am wanting to do. I want to use a clutch master cylinder out of a 93 wrangler which has a 17.75mm(.698") bore and then pair that with a CJ slave cylinder which has a .875" bore. So my question is will this work or will the bore sizes be too different? (.177") By doing this I am saving about $50 anyway If anyone has done this or has tried it or knows it wont work let me know if I'm out of my mind thanks for any help on this.

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post #2 of 6 Old 07-21-2009, 03:20 PM
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I would think you would want to compare the bore sizes of the throw out slave as well, but I think those year model clutch systems had internal slave type throw out bearings. So there is no way to make a direct comparisson.

Here is an excerpt from the experts at Novak on the matter:

"The hydraulic system, therefore, is simply a method of transferring that leverage - or better said, of transmitting force through the incompressable hydraulic fluid. This is very similar in principle as a good old mechanical linkage via pushrods, bellcranks or cables. Essentially no multiplication of force occurs within the hydraulic circuit itself as is common with other hydraulic systems like jacks, rams and presses."

"Nearly every clutch master cylinder is matched for size to its connected slave cylinder for a largely 1-to-1 relationship. So, a 3/4" bore master cylinder should connect to a 3/4" slave cylinder. A 1" master should have a 1" slave cylinder. A master cylinder that is larger might yield a rather spectacularly blown out slave cylinder and a master cylinder that is smaller will yield a rather disappointing lack of travel for your left foot's efforts. There are occasions where this ratio can vary slightly from this, but rarely more than 15%.
Once the installer understands this, the rest will come together more easily and in accordance with the principles outlined for conventional mechanical clutch systems. "


It would seem that you may be within the mentioned 15% range but there's no way to tell if it will work untill its done.

I am a cheep SOB as well, but my advise would be to be to spend the extra $$ and get it right the first time instead of taking a chance, and maybe having to re-do everything.


Last edited by jeepmaster03; 07-21-2009 at 06:36 PM.
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post #3 of 6 Old 07-21-2009, 04:06 PM Thread Starter
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Thanks for the info
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post #4 of 6 Old 07-21-2009, 05:30 PM
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You could try it and see.
If the master cylinder's bore is too small, you won't have enough travel and the clutch won't disengage all the way. You'll grind trying to shove the tranny into gear. As you go up in master cylinder bore size, you'll increase the travel at the slave cylinder while also increasing pedal pressure.

I run the stock 1980 4 cyl (GM Iron Duke) master/slave setup on my AMC 360. It works great.

'80 CJ5 w/AMC360, T176, D44 w/Detroit 4.56, RE 4" YJ lift and 35s..



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post #5 of 6 Old 07-21-2009, 07:58 PM
jeepmaster03
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That master cylinder and slave cylinder set up from 151 4 cyl is the ticket. Yo can't go wrong with it!
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post #6 of 6 Old 07-21-2009, 11:26 PM Thread Starter
mosshopper
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Right on thanks I will give the 4cyl setup a shot
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