Manual Clutch Hydraulic Bleeding

Gary747

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I need to install a new Clutch Master Cylinder "only", without disturbing either the fluid pressure line below the Master Cylinder or the slave cylinder. My question concerns hydraulic bleeding.

Method 1.) The Maintenance Manual procedure is to crack the bleed screw under the Jeep with an attached tube going into a bottle of brake fluid while a helper pushes the clutch pedal down. I understand this.

Method 2.) I have read elsewhere that a pressure bleed can be accomplished by pumping brake fluid UP from under the Jeep into the Master Cylinder. Has any reader actually performed this? Can it be a "one person" job, or, does a helper need to hold the clutch pedal down while pumping fluid UP to the master reservoir?

Method 3.) Lastly, I was thinking that when replacing only the Master Cylinder, no air is introduced into the lower parts of the system, so one can install the new master, fill the reservoir, then slowly pump the clutch pedal, holding it down for 10 to 15 seconds. This would compress the air trapped near the top of the system, forcing it into the master. Holding the pedal down captures that air in the piston chamber. Releasing the pedal forces that air to move under the reservoir, allowing it to bubble up through the fluid. The piston chamber air gap is replaced with fresh fluid on the subsequent pedal push. Repeated "pumps" of the pedal clears the air. Top off the fluid level when you have good pedal feel.

Has anyone ever successfully accomplished Method 2 or 3?
 
I put the Clutch Master Cylinder replacement task off long enough. I'm replying to my own post because after 48 views, nobody has been able to say that they ever tried clutch bleeding Method 2 or 3. I broke into the clutch hydraulics today, deciding to go with Method 3 since I had no "helper" available. This was to be a "one-man job".

Removing the old master Cylinder was pretty straight forward with two "lessons learned". Use a paper towel or siphon to remove the fluid from the reservoir first. If you don't, that fluid will flow out from the pressure line fitting when you loosen it for removal. Quite a mess to clean up. Second, the hardest part of the removal turned out to be getting the Cotter Pin out of the clutch pedal assembly under the dash. I broke a Craftsmen Awl trying to grab it and wrestled with the thing for 20 minutes. For reassembly, I did not use a Cotter Pin, but installed an appropriate size Hairpin Clip which went in (and out) easily.

Before installing the new Master Cylinder, I filled it about half way with fluid and moved the piston by hand to get fluid to the pressure line fitting... a "bench bleed" if you will. However, in retrospect, I don't think that was necessary.

Installation was routine... no problems at all, including the under dash installation of that HairPin Clip. Popped right on.

I filled the reservoir, pushed the pedal down by hand and felt little resistance, mostly from the pedal return spring. Held the pedal down for about 15 seconds, let it up, and pressed a 2nd time. This time I felt some pushback. I climbed in the seat and pushed the clutch to the floor, waited a bit, then let the pedal up. It felt pretty good.

Got out to check the reservoir level and it was about 1/2 empty, refilled it and sat back down in the Jeep and began working the clutch pedal. It suddenly had what I consider a normal amount of force to push down. Checked the fluid level again, now about 1/4 low, topped it off, and started the engine.

The clutch worked perfectly. The engagement point was right where I expected it to be and I had plenty of "down pedal" available to hold the clutch open while idling in gear.

The test drive was completely normal with positive control of the clutch.

So, kind of a surprise to me, using bleed "Method 3" worked just fine and allowed this job to be performed by one man.

Some general info: The new Clutch Master Cylinder was purchased at a local NAPA store for $28.99 + tax. They had one in stock, p/n NCF 72208. I used standard DOT 3 Brake Fluid. A liquid called "Hydraulic Clutch Fluid" is sold at several stores, but on the bottle I looked at, there was no mention of DOT 3 brake fluid. I wasn't real sure what was in that can.
 
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Thanks for the update and pointing out the issues and how you resolved them. Can't say how many times people ask for advice and "poof" never seen again.
 
Reviving old thread to share that I replaced my master clutch cylinder and used “Method 3” . It worked perfectly, no additional bleeding of slave required. Thanks OP 👍👍
 
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Ive done #3 on dual caliper front motorcycle brakes. Worked great. Id also suggest a "mighty Vac" for bleeding and flushing. I did the slave and a clutch in my 91 and just let the slave bleeder drip and made sure the MC stayed full while dripping. This also worked and 2 years later is fine still.