External Clutch Slave Cylinder Repair
The Cheap way to repair your External Clutch Slave Cylinder
(Application – This applies to late model YJ’s, XJ’s and all TJ’s )
¾"(20mm)bore x 2"(50mm) stroke pneumatic cylinder Princess Auto-$31.95
Princess Auto part # 8003985
1/8"NPT x 5/16" compression fitting (straight or elbow) - $1.79 Home Hardware
5/16" x 5/16" compression fitting coupling - $2.79 Home Hardware
2 large washers with ¾" hole
mounting flange from stock slave cylinder
Motivation? – After my third hydraulic clutch system failed in four years, I decided enough was enough and there had to be a better way. I knew that the failure is most always at the bottom clutch slave cylinder. I have my theories on the how’s and why’s but pretty much the bottom line is that a plastic hydraulic cylinder isn’t up to the forces required to disengage a clutch time and time again.
( Fig 2 )
Installation – There is no need to remove the upper clutch master cylinder. Simply unbolt the lower clutch slave from the bell housing (two ½" socket nuts). (Fig 2) Next cut the plastic hydraulic line just back from the cylinder as there is a steel insert that’s about 2" back from the cylinder. Now for the hardest part of the whole operation is removing the snap ring that holds the mount flange to the cylinder. I used an angle grinder, but I had a real hate on for that cylinder! Two screwdrivers should do the trick. Once you get the metal flange off, you are done with the cylinder. Throw it away!
Now you are onto the new cylinder.
The 1/8”NPT fitting threads into the cylinder port farthest from the extending rod. NOTE: inspect the threads of your fitting before purchasing. You’ll find some have deeper cut threads than others. If the threads on the fitting are shallow, the fitting will screw all the way into the cylinder and bottom out before the fitting is tight and you’ll leak.
Depending on your wheeling style, you can also install in the other end of the cylinder a 1/8NPT barbed fitting and run a piece of tube up to a safe place in the engine compartment. This will keep debris (heavy mud) from getting into the cylinder and impeding a full stroke. Water is fine, as it will just shoot right back out. I left mine open and it’s my excuse to stay out of deep mud!
( Fig 3 )
On the rod end of the cylinder you’ll remove the nut that comes with the cylinder. Next place a washer over the ¾” (M20 actually), then the metal mount flange from the stock cylinder, your second washer, and lastly tighten the nut down and there’s your custom mount. (Fig. 3)
Next place one end of the 5/16” compression over the threaded end of the extending rod and as far down as it will go(Fig3).. The reason you are installing this fitting is to extend the rod out as it is too short to fully cycle your shift fork.( a metric thread long coupling nut Loctited on will also work fine. but I couldn’t find one anywhere!) . Tighten down the compression fitting onto the cylinder rod with a 9/16” wrench and a ½” wrench to hold the fitting still.
NOTE: If you have any doubt about the length, then error on the side of making it too short. If the cylinder doesn’t extend quite far enough you can shift gears no problem, but if you’ve got the rod too long the shift work won’t be allowed to come all the way back and you’re clutch won’t be fully engaged when you let the pedal out. Don’t be afraid of exactly where on the rod you tighten down the compression fitting, you can always put another one on. Took me a while to find that right at the bottom of the threads was about right.
Tighten down the compression fitting onto the cylinder rod with a 9/16" wrench and a ½" wrench to hold the fitting still. Next snug up the nut on the other end of the fitting, that will be your striker on the shift fork
You are now ready to test fit.
Working underneath your Jeep hold the cylinder up to the mount studs on the bell housing and insert as if to mount it. (Fig 4) You’ll find the cylinder is stopped by the clutch fork just about 1/2'” to 1” before it mounts flush with the bell housing. That is the amount you have to cut off the end of the coupler you just installed on the end of the cylinder rod using a hacksaw or angle grinder.
I have left this to your discretion as individual Jeeps and 4cyl/6cyl will have a slightly varying amount of play in the fork before engagement. NOTE; if you have any doubt about the length, then error on the side of making it too short. If the cylinder doesn’t extend quite far enough you can shift gears no problem, but if you’ve got the rod too long the shift work won’t be allowed to come all the way back and you’re clutch won’t be fully engaged when you let the pedal out resulting in a slipping clutch. (and that’s bad!)
Once you have cut the striker back a bit, and done a re-test fit, you are ready for final (hopefully forever!) install.
( Fig 4 )
Working underneath your Jeep, slip the end of the hydraulic line you’ve cut into the compression fitting that’s threaded directly into the cylinder. Make sure the line is well into the fitting and finger tighten the nut. Tighten the compression nut with the 9/16” wrench to seat the ring onto the hydraulic line. It will now be crimped on and you don’t have to worry about the line coming out. Next mount the cylinder onto the bell housing using the two ½” nuts you removed. (Fig 4) Your clutch fork will have about a little over an inch of play in it. The cylinder rod should push it in to take up that play. You won’t be able actuate your clutch by hand. It’s way too stiff. You want the fork to sit at just before clutch disengagement. Tighten down the 2 nuts and you are ready to bleed your new system that wasn’t bleed able before.
Loosen off the compression fitting holding the hydraulic line to just finger tight.. Next go up and fill your reservoir with brake fluid to gravity bleed the line. Give it a minute to fill the line and when it starts running out the fitting you loosened off, tighten it up to stop the leak. Then re-top up the reservoir. Have a friend work the clutch pedal the same as you bleed brakes, using the compression fitting as the bleed screw to force the air out of the new cylinder. Now haul your buddy out of there and check out your new $40 hydraulic clutch compared to a $250+ Dealership item!
Note! Do NOT vary from the ¾” bore of the cylinder. You CAN change the stroke depending on what’s available to you. The upper master cylinder is a ¾” bore and 1” stroke cylinder. What that means is so long as you stay to ¾” bore for the slave , your stroke can only be what the cylinder powering it is. 1”, no more no less. If you change the bore, you are into a world of MC squared over pie R squared.