Red Eye Garage Tip #5 - Repairing a Floor Jack June 12 2014, 3 Comments

Our Craftsman 2-ton floor jack started having lift issues after being used to lift a buddy's truck. It would lift only a little with each stroke. I thought that maybe the relief valve cracked, and it was just low on oil. I added some jack fluid, but that didn't solve anything. This jack was a gift to me, so I wasn't going to throw it away. Craftsman does not sell replacement parts related to the hydraulic power unit of the jack, but I was able to find HCRCnow.com that sells a rebuild kit for the jack for $50 shipped.

This is our Craftsman 2-ton jack, model number 9 50239.

The removal of the power unit is fairly simple. There are four bolts that hold the power unit to the body of the jack.

Once the power unit is free, remove the two springs on the underside and straighten the cotter pin with some pliers and push it through the hole.

Before you open things up, you'll want to remove the drain screw and then dump all the hydraulic fluid into a receptacle for proper disposal.

While grabbing the shiny cup with one hand, pry the retaining clip off the end of the master cylinder. The spring is under compression, so hold onto the cup while you take the retaining clip off. And for goodness sake, don't point the master cylinder near any cars or people (including yourself). Clamping the hydraulic unit to a table makes life easier.

I had to buy a 27mm wrench to get the master cylinder off. Forget trying to buy a socket. It would have to be very thin-walled and unreasonably deep.

Once removed, the piston comes apart from the cylinder.

There are two seals to be removed from this assembly. You can use a dental pick to remove the o-rings, but be careful because scratching the metal can cause leaks. Bamboo skewers are an alternative tool that is safer from scratching.

I then turned my attention to the slave cylinder. I had to buy a 50mm socket to put on the end of my 36" breaker bar. Clamping the hydraulic unit to something heavy helps a lot.

This is an exploded view of the innards. A retaining ring on the end of the piston keeps it all together. We took out all the seals and replaced them with new ones, with the exception of the seals for the relief valves. Since we didn't suspect anything to be wrong with the relief valves, and we didn't have the equipment to adjust the relief valves properly, we left it alone. 

This is an exploded view showing all the major components. See the old removed o-rings in the background. Put the new seals in where the old seals came out.

Since you took everything apart, you know how everything goes back together. The only tricky part is getting the retaining clip back onto the master cylinder. Pull the master cylinder out as far as possible before trying to put the retaining clip on. Once you're done, add jack fluid back into the jack (don't use brake or ATF fluid). Note that the oil level is supposed to be only slightly above the top of the slave cylinder. Pump the jack up and down a few times to bleed the air bubbles out, and top off if necessary. 

You just saved a few bucks from having to buy a new jack, and you rescued a jack from the landfill. It is not that hard of a job, but it does require some special tools that most people won't have in their garage. You've likely saved some money that can be used towards more parts or towards proudly declaring your love for motoring with some Red Eye Garage apparel.

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