jjinatx
Austin, TX, USA
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Super_Dave wrote:Quote:Also note that to FULLY extend them you're going to need to pull them off the camper (or park on a railroad trestle.)
Why?
Sorry, I was thinking of my camper barn. AC would hit the roof before the jacks reached the red line.
-jj
Current Rig: 2017 F350 Crew Cab Short Bed 4X4 Powerstroke, 2018 Grand Design Reflection 29RS. Dearly Departed: 2003 GMC Sierra 3500 Dually, 2002 Bigfoot 25C10.6.
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Super_Dave
Harrisville, UT
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Quote:Also note that to FULLY extend them you're going to need to pull them off the camper (or park on a railroad trestle.)
Why?
Truck: 2006 Dodge 3500 Dually
Rig: 2018 Big Country 3155 RLK
Boat: 21' North River Seahawk
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jjinatx
Austin, TX, USA
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Super_Dave wrote:Did you guys see where the Happijac suggested maintenance suggests a once a year full extension and retraction of the jack to redistribute the grease on the screw?
Saw that, and from the condition of my front jacks when I took them apart, I'd say it's good advice. Also, I would add that it is probably a good idea when the camper is stored to raise the jacks completely and snug them up so the O-ring at the top of the screw seals tightly. This will keep the entire acme screw sealed inside the lower leg and away from moisture that caused the rust on mine.
-jj
* This post was
edited 08/31/10 01:15pm by jjinatx *
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Super_Dave
Harrisville, UT
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Did you guys see where the Happijac suggested maintenance suggests a once a year full extension and retraction of the jack to redistribute the grease on the screw?
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stevenal
Newport, OR, USA
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Thanks wnjj and jjinatx. Tried again with a long bent nail, while taping on the shaft, and the gear came loose this time.
'18 Bigfoot 1500
Torklifts and Fastguns
'17 F350 Powerstroke Supercab SRW LB 4X4
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jjinatx
Austin, TX, USA
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I just did a quick look at a recirculating ball screw on Wikipedia and I guess what I was assuming to be just a threaded fitting pressed into the lower leg may actually be a recirculating ball screw mechanism. If so, then I guess the one in my jack is shot. That might explain the slight gravelly feel when I threaded the acme screw in and out with my fingers after re-lubing it.
-jj
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jjinatx
Austin, TX, USA
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wnjj wrote:
jjinatx wrote:Curiously, the 4100 jacks do not have this drag brake mechanism.
This is probably because the camper weight cannot backspin an acme thread but can backspin the recirclating ball setup. Notice how much steeper the threads are? Steeper = easier to backspin. The drag brake adds enough extra resistance that the camper will not fall while the motors can still power it down.
WNJJ,
Pardon my ignorance, but I'm not sure exactly what a recirculating ball mechanism is. The 4500 and the 4100 appear to have the same acme screw, thrust bearing and gears and are pretty much the same except for the clinch spring drag brake mechanism. Is the bottom end of these jacks, the part inside the lower leg, different somehow? Is that where the recirculating ball mechanism resides? I haven't wanted to cut mine apart until the new 4600s arrive on my doorstep.
-jj
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wnjj
Cornelius, Oregon
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jjinatx wrote:I think I figured out the dynamics of the thing, but am puzzled why it was designed that way.
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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.
You answered your own question there. It's meant to act as a one-way drag brake to keep the camper from falling. There no reason for your camper to suddenly lift and very little force making the jack fall down when on the truck.
jjinatx wrote:Curiously, the 4100 jacks do not have this drag brake mechanism.
This is probably because the camper weight cannot backspin an acme thread but can backspin the recirclating ball setup. Notice how much steeper the threads are? Steeper = easier to backspin. The drag brake adds enough extra resistance that the camper will not fall while the motors can still power it down.
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jjinatx
Austin, TX, USA
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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
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MTBob
Montana
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wnjj wrote:MTBob wrote:My 4600's have a small plastic handle just under the gear box that moves a nylon gizmo (technical term) and disengages the gear box drive from the ball screw. I don't know if that is a "quick" release, but it does disengage the gear drive from the jack leg. Are you talking about a second release lever that is called a "quick release"?
I haven't tried pushing the leg down with the lever in the released position. If the leg does go down easily, I'll be fairly concerned about an inadvertent release. I'll give that a try tomorrow and see what happens.
If you have 4600's then yes, you can push down on them and they will go down. There is no second lever. The one-way brake and ball-screw design allows for free wheeling down but not the other way. The brake plus re-engaging the lever once you are nearly down makes sure the camper cannot fall. Always run the jacks down a bit more so the square drive re-engages after you drop them. I find this feature VERY nice for putting the jacks down quickly and fairly quietly.
Depending on the lube condition you either can just barely push down or you may have to stand/jump on them. They aren't going to fall down if you leave the lever up, especially if the last thing you did is power them up with the motors. It no more likely than leaving your truck in neutral and having it roll away.
This morning I went out to test my front jacks to see if they would do a "quick release". After moving the lever I pushed and whacked on the foot trying to get the leg to go down and, dang, I noticed I've got 4500's not 4600's up front! The 4500's apparently don't have the quick release feature noted in the above post.
Perhaps in cases like this the Webmaster should re-title my status label to "Senior Moment", rather than Senior Member. Or, as my Air Force friends would say: "I had a bit of fog in the cockpit" when submitting my previous post.
Bob
2002 10-2000RR Northern Lite
2008 Chevy 3500 DMAX, SRW,
2001 Lund 1700 Fisherman
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