I have a Joyce #154 25-ton capy mechanical jack. Appears to be in fine shape, the ratchet works in both directions. When you operate the ratchet, the entire body of the jack (the standard) rotates in circles about the foot, but does not go up or down.

I've removed the ratchet assembly and cover plate and looked inside, everything is shiny and oily and looks to be in fine order.

The general operating principle for these is the ratchet turns the inside bevel gear, which mates with a bevel gear in the head, and then turns the screw that moves the standard (body) up and down relative to the foot. This ones acts like a key is broken or something is stripped, but no evidence of that without taking the whole think apart.

We also have (2) Duff-Norton jacks with the same malady...everything seems fine but they just want to twist around in circles........looking for comments or suggestions from someone who may have had a similar problem?

Well, you could just use them as car stands....

Just kidding. Sounds like a key has fallen out, or a pin sheared off inside.

Only cure is to disassemble and investigate. Should be pretty clear what's fubar inside.

Many mechanical devices have parts that are intended to fail (gracefully) when the whole thing is overloaded. These might have shear pins (designed to be only as strong as necessary) that are intended to break and give their lives to save more expensive components.

Kind of like the mechanical equivalent of the electrical fuse, in case of an overload the fuse gives it's life to save the wiring and switch gear. And the fuse is inexpensive and easy to replace.

Many lawnmower engines have an aluminum key that locks the flywheel to the crankshaft. It is intentionally made of aluminum so when you hit a rock with the blade the key "shears" off and disconnects the momentum of the flywheel from the crankshaft. Otherwise you would have an expensive but useless bent crankshaft to replace instead of a 50 cent aluminum key.

Sometimes when people repair these they replace an intentional shear pin with something stronger and then the whole unit is damaged the next time it is overloaded.

The fact that your units seem to turn without major bad noises means the major components are probably intact but the rotary input from the ratchet is not making it to the lifting screw.

Good luck, cheers Kevin.

Joyce has a web site that has tech drawings, manuals for their products

http://joycedayton.com/products/machine ... crew-jacks

Perhaps a better page at Joyce is

http://joycedayton.com/technical-help/drawings-illustrations

I believe you have to sign up to get an account with them in order to download or print the actual drawing material - I don't think there's any restriction against using a 'free' or disposable e-mail account for the contact if you're (overly) concerned about privacy or having your contact information marketed.

Shear sounds like a sure pin issue to me!

That's normal for an unloaded jack. There is less resistance to rotating the top of the jack on the thrust bearing compared to turning the big screw in its nut, so that is what happens. If you (or a helper) hold the top from spinning while working the ratchet the jack should go up or down. Likewise, when under a piece of equipment, the weight will keep the jack from spinning so it should work OK.

Be sure that the big bronze nut isn't worn out before loading up the jack. It can be nearly stripped and still work fine until the weight applied exceeds the shear strength of the remaining bronze threads, and down she comes.

I think you have a problem with the jacking screw not being free in the column nut. It may only be a short portion of the screw that is damaged just enough to fetch up in the nut. I currently have an A. O. Norton apart for the same reason. These jacks normally use a buttress thread. You should be able to put the jacking screw in a lathe and rotate it slowly while you dress up the thread with a triangle file. I had to use an abrasive disc on a right angle die grinder. Once you get the jacking screw out of the jack you should be able to find the problem easily. You need to be able to run it up and down in the column nut easily by hand without the head attached.
If you send me an e-mail with your contact information I would be happy to call you to discuss it. rmne1887@optonline.net.

I would also have to wonder if gummed lubrication or debris between the threads and the bronze nut might be contributing to the effect. (As noted, the jack might still move correctly with substantial resistance to turning from an imposed load and contact friction).

My understanding is that fairly viscous lubricant is used in these things anyway, so it is not surprising that (especially in cold weather) you would see the jack rotate instead of extending when 'ratcheted'. But take care to keep both the screw and jack first clean and then smoothly lubricated. Part of the reason the nut is bronze is to allow grit to 'bed in' semi-harmlessly and not act as defective lapping compound; the problem is that the grit can embed in the bronze (as it does in brass clock bearings) and then act as a VERY effective lap, over time, against the mating steel. (There isn't the extended motion involved in a clock bearing, but much higher contact force.) So some care in cleaning the bronze nut beyond the usual solvent wash or ultrasonic bath might be a consideration.