Happijac lubrication
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Forum Discussion
More jack updates:
Well,I tried a few more things, but the problem 4500 jack is still binding on the way down. The bearing seems just fine. I thought maybe it had something to do with the clinch spring mechanism so I started looking closely at that.
I think I figured out the dynamics of the thing, but am puzzled why it was designed that way. Lifting, the spring applies no force to hold the 2 barrels on either side of the thrust bearing, and allows the bottom one to turn freely. The upper one is held tightly against the squarish plate shown in the following picture. Lowering, however, the spring tightens, locking the 2 barrels together. Now the upper barrel is forced to spin against that squarish plate. The friction is apparently meant to work like a drag brake.
http://www.jaysnest.com/JackPics/P1080474.jpg
In this picture, you see some round depressions in the squarish plate that are apparently meant to retain grease to keep the sliding surfaces from galling. Mine had a fair amount of galling on the squarish plate and Keller's picture looks like it might too. I thought this might be the source of the binding, so I used the same technique used for flattening the sole of hand plane to clean it up. I used various grits of sandpaper face up on my cast iron tablesaw top and ground the surface smooth, with the final step polishing it with #1200.
I lubed the outside of the barrels real good where the spring grabs them and I lubed the bottom of the squarish plate and put everything back together. (I can tear one of these things down in under 5 minutes now that I've done it so often.)
Anyway, no dice - the jack still binds on the way down. I've finally concluded that the problem is with the threaded fitting pressed into the top of the lower leg. There is a fair amount of slop between it and the acme threaded rod. Remember, my rod was dry and rusted (and frozen up), so there is probably a lot of wear on the fitting. I ordered a pair of 4600's to replace both front jacks. Since it's newer, maybe the 4600 design is better. I'll hack apart the lower leg of the offending 4500 jack and investigate further once I have the replacements in hand.
Curiously, the 4100 jacks do not have this drag brake mechanism. There is only a single barrel with the thrust bearing on top, and the weight is carried by the thrust bearing both lifting or lowering.
Here are the pictures I promised of the insides of a 4100. The first pic shows a 4500 (upper) with the clinch spring holding the 2 barrels together. The thrust bearing and races (thin washers) reside between the barrels. The 4100 (lower) has a single barrel, no clinch spring, and the thrust bearing and races are on top as shown in the second picture. When assembled, the upper race fits up against the gear plate in the upper leg. Also note, there is no squarish plate in the 4100. So, the 4100 does not appear to have a drag brake like the 4500 does.
http://www.jaysnest.com/JackPics/P1080471.jpg
http://www.jaysnest.net/JackPics/P1080470.jpg
Also note that I refer to the "squarish" plate in the 4500. That's because it isn't square. It is actually 1 1/2" x 1 11/16". I didn't note which way it was oriented when I took both my 4500s apart, so just some more advice on being very careful to note EVERYTHING when disassembling one of these jacks. I did notice there is a swaged area on 2 opposite sides of the jack right under the gear plate on the upper leg. When I reassembled the jack, I put the short sides adjacent to the swaged areas. Not sure if that's correct or if it really matters though.
-jj
Well,I tried a few more things, but the problem 4500 jack is still binding on the way down. The bearing seems just fine. I thought maybe it had something to do with the clinch spring mechanism so I started looking closely at that.
I think I figured out the dynamics of the thing, but am puzzled why it was designed that way. Lifting, the spring applies no force to hold the 2 barrels on either side of the thrust bearing, and allows the bottom one to turn freely. The upper one is held tightly against the squarish plate shown in the following picture. Lowering, however, the spring tightens, locking the 2 barrels together. Now the upper barrel is forced to spin against that squarish plate. The friction is apparently meant to work like a drag brake.
http://www.jaysnest.com/JackPics/P1080474.jpg
In this picture, you see some round depressions in the squarish plate that are apparently meant to retain grease to keep the sliding surfaces from galling. Mine had a fair amount of galling on the squarish plate and Keller's picture looks like it might too. I thought this might be the source of the binding, so I used the same technique used for flattening the sole of hand plane to clean it up. I used various grits of sandpaper face up on my cast iron tablesaw top and ground the surface smooth, with the final step polishing it with #1200.
I lubed the outside of the barrels real good where the spring grabs them and I lubed the bottom of the squarish plate and put everything back together. (I can tear one of these things down in under 5 minutes now that I've done it so often.)
Anyway, no dice - the jack still binds on the way down. I've finally concluded that the problem is with the threaded fitting pressed into the top of the lower leg. There is a fair amount of slop between it and the acme threaded rod. Remember, my rod was dry and rusted (and frozen up), so there is probably a lot of wear on the fitting. I ordered a pair of 4600's to replace both front jacks. Since it's newer, maybe the 4600 design is better. I'll hack apart the lower leg of the offending 4500 jack and investigate further once I have the replacements in hand.
Curiously, the 4100 jacks do not have this drag brake mechanism. There is only a single barrel with the thrust bearing on top, and the weight is carried by the thrust bearing both lifting or lowering.
Here are the pictures I promised of the insides of a 4100. The first pic shows a 4500 (upper) with the clinch spring holding the 2 barrels together. The thrust bearing and races (thin washers) reside between the barrels. The 4100 (lower) has a single barrel, no clinch spring, and the thrust bearing and races are on top as shown in the second picture. When assembled, the upper race fits up against the gear plate in the upper leg. Also note, there is no squarish plate in the 4100. So, the 4100 does not appear to have a drag brake like the 4500 does.
http://www.jaysnest.com/JackPics/P1080471.jpg
http://www.jaysnest.net/JackPics/P1080470.jpg
Also note that I refer to the "squarish" plate in the 4500. That's because it isn't square. It is actually 1 1/2" x 1 11/16". I didn't note which way it was oriented when I took both my 4500s apart, so just some more advice on being very careful to note EVERYTHING when disassembling one of these jacks. I did notice there is a swaged area on 2 opposite sides of the jack right under the gear plate on the upper leg. When I reassembled the jack, I put the short sides adjacent to the swaged areas. Not sure if that's correct or if it really matters though.
-jj
