4 Post 9000 Pound LIft owners, I have a question.

[TraderGuy]

I have a sliding bridge jack I took when we moved from my previous home, thinking I could use this on my next 4 Post lift. I had an 8000 pound Direct Lift that had rails with no support for a rolling jack. I see the current crop of 9000 pound lifts do have a different type of rail to support rolling jacks. My question is, what is the clearance from the top of the runway to the top of the rolling jack rail? I need 2.5" or more of clearance to use the sliding jack. I've reached out to Bendpak, Advantage, and Tuxedo asking this question, but no one has given me a solid answer. A picture of my type of jack is below, I'm wondering if the rolling rail will interfere with movement.

 

[Poolshark314]

It sounds like you want to use your existing rolling jack on the top of the runways instead of the j-channel. If your proposed future lift will have the j-channel in the middle, what is the reason to not use it?

 

[Poolshark314]

Here is the measurement on an Atlas 9000 anyway:

 

[pbon]

I have the Bendpak rolling jack, but a special version that is lower profile, and I think it sits about 2.5 inches above the runners in the center where the body is located. Can’t help with others but the sliding jacks I have seen sit on the runners rather than on the channels mounted halfway up the inner side of the runners that are part of most lifts.

The problem is that the jack body has a certain thickness for the scissor mechanism and hydraulic pump. This thickness is more than the thickness of the runners. If you tried to mount the jack lower, it would lift up off whatever runner part is was resting on when you lowered the runners to the floor.

A lighter duty jack may have a lower profile. Research whether there are any 3500 lb jacks that would fit your lift. Many a manual pump jack is more compact?

What about a jack tray and low profile floor Jack sitting on it?

 

[ronr80]

I also have a Bend-Pak rolling jack RJ-45 , I work on alot of corvettes and other low slung cars including mine , I had to put 1 inch rubber mats to make the ramp higher so the cars would not hit the rolling jack. this worked real good but I use the J mounts on the side of the ramps . I can send you pics if you want Ron

 

[TraderGuy]

It sounds like you want to use your existing rolling jack on the top of the runways instead of the j-channel. If your proposed future lift will have the j-channel in the middle, what is the reason to not use it?

The existing jack is sliding, I want to know if it can be used on a lift with a j-channel. Based on your measurement, it looks like it would work on an Atlas. Here is a pic of the jack I own.

What about a jack tray and low profile floor Jack sitting on it?

I'm kind of spoiled at this point. I want a sliding or rolling bridge jack if I go 4-post again.

 

[TraderGuy]

I have the Bendpak rolling jack,

I also have a Bend-Pak rolling jack RJ-45

Can one of you post up the measurement of your Bendpack lift as done by @Poolshark314?

 

[Poolshark314]

The existing jack is sliding, I want to know if it can be used on a lift with a j-channel. Based on your measurement, it looks like it would work on an Atlas. Here is a pic of the jack I own.



I'm kind of spoiled at this point. I want a sliding or rolling bridge jack if I go 4-post again.

Is it bad practice to put the sliding jack onto the the j-channel instead of the tops of the runways? Seems like from a weight capacity standpoint it would be fine. Maybe ask a lift rep if that's a possibility? I would gather that the nylon sliders on the bottoms of the arms wouldn't last as long

 

[stingry]

Bendpak HD9 is 3 1/2 inches from top of rail to top of runway

 

[TraderGuy]

Is it bad practice to put the sliding jack onto the the j-channel instead of the tops of the runways? Seems like from a weight capacity standpoint it would be fine. Maybe ask a lift rep if that's a possibility? I would gather that the nylon sliders on the bottoms of the arms wouldn't last as long

It might work, but as you say, with all the weight on the minimal surface area, the pads would wear quickly. And there would not be much room for slop when sliding the jack.

Bendpak HD9 is 3 1/2 inches from top of rail to top of runway

Thanks, that would be plenty of clearance.

 

[pbon]

But you can’t put your sliding Jack on those channels if you want to lower the lift all the way to the ground. The bottom of the sliding Jack will hit the ground before the lift and move the jack assembly upwards by several inches.

Measure minimum clearance height off the ground of collapsed jack. Compare to height of runner surface from the ground.

 

[TraderGuy]

But you can’t put your sliding Jack on those channels if you want to lower the lift all the way to the ground. The bottom of the sliding Jack will hit the ground before the lift and move the jack assembly upwards by several inches.

Measure minimum clearance height off the ground of collapsed jack. Compare to height of runner surface from the ground.

Fair point. I don't see why I couldn't use the sliding jack as intended, on the main rails. Am I missing something?

 

[pbon]

Yes, assuming it fits. It probably will fit

 

[racecougar]

Your sliding jack should be just fine. I have two of them on my Forward EFP9 / Direct Lift Pro Park 9 Plus.

 

[TraderGuy]

Your sliding jack should be just fine. I have two of them on my Forward EFP9 / Direct Lift Pro Park 9 Plus.

Thanks for the confirmation. Looks exactly like my jack and shows the clearance.

 

[tfalk]

I have that exact jack on my Forward EFP8 as well. You should be fine. My only problem with it is that
it stick up enough above the runners that I tip the jack with the bottom of my mustangs, particularly
the track car that is lowered quite a bit. I usually keep the jack at the far end of the lift from the ramps
otherwise I hit the jack pretty much every time. Cars are in storage otherwise I would post a pic.

 

[racecougar]

Yep. With the pads removed, the platform itself sits 2" above the runways. As long as I don't leave one near the ramp end of the runways, I'm good.

If you don't use the jacks that often, one or both can be stored under a workbench on a furniture dolly. They are easily reinstalled by rolling the jack into place with the lift up, lower the lift, turn the jack 90 degrees, and raise the lift.

 

[Yankeefarmer]

Here are measurements on my Advantage DX9000XLT:

 

[05snopro440]

Is it bad practice to put the sliding jack onto the the j-channel instead of the tops of the runways? Seems like from a weight capacity standpoint it would be fine. Maybe ask a lift rep if that's a possibility? I would gather that the nylon sliders on the bottoms of the arms wouldn't last as long

It's a completely different loading scenario on the angle iron looking part of the support. The load that would be distributed across the flat horizontal area is now concentrated as edge contact between the angle and the top of the J-channel. Not to mention, there will almost certainly be a large bending moment induced between the contact point on the angle bracket and the vertical part of it. "Seems like from a weight capacity standpoint it would be fine." No. When the loading scenario changes that significantly, we don't have enough information to conclude that. This is how materials can become overloaded, when the loading varies significantly from how the assembly was designed. There's a chance it could be fine, but it's a complex problem with a lot of variables.

 

[Yankeefarmer]

It's a completely different loading scenario on the angle iron looking part of the support. The load that would be distributed across the flat horizontal area is now concentrated as edge contact between the angle and the top of the J-channel. Not to mention, there will almost certainly be a large bending moment induced between the contact point on the angle bracket and the vertical part of it. "Seems like from a weight capacity standpoint it would be fine." No. When the loading scenario changes that significantly, we don't have enough information to conclude that. This is how materials can become overloaded, when the loading varies significantly from how the assembly was designed. There's a chance it could be fine, but it's a complex problem with a lot of variables.

While you are correct in everything you wrote, the manufacturer of my lift sells a rolling bridge jack that transfers it’s load to the lift through the “J-channel,” so they have indicated that the J-channel is capable of the load. As far as the angle bracket is concerned, any bending moment imposed upon it would be lessened, due to the shortened arm as compared to setting on the runways.

 

[pbon]

Obviously the J channel can support rolling jacks designed to use it. I am not sure I agree with the analysis above that the sliding jack on the J channel is OK because the flanges designed to support the load when extending several inches onto the runners will be fine when extending half that much over the lip of the J channel because the flanges will not be extending as far outwards since the J channels are inboard of the runner surfaces.

Probably be fine, but the actual determination is probably a fancy engineering calculation.

But none of this matters because you can’t put the sliding jack flanges on the J channel. The jack body extends down too far. The sliding jack is designed to not quite touch the floor when the flanges are in the runners. It can’t be lowered 3-4” further. The rolling Jack is designed to not quite touch the floor when the rollers are on the lip of the J channel.

 

[Poolshark314]

I understand the point about the nylon rollers being ruined and the jack body sitting too low and hitting the ground first, but most of these lifts ship with steel jack trays for use with bottle jacks. Those jack trays sit on the jack channels, and there are no special rollers on them. Wouldn't that mean it should support the weight without fear of bending the channel?

 

[pbon]

Yes, a jack tray designed for a J channel obviously works fine. That jack tray is not relying on distributing its load through a 5 inch piece of angle iron with only the outer 2 inches making contact. The jack tray has an upside down C or J channel to fit over the runners’ J channels. The C or J shape is much stronger than a one angle piece (angle iron). This matters even more when you want to put all the load at the outside edge of the angle iron. The C or J is also safer since it locks in on the J channel on the runners.

If you are not maxing out the weight limits of the jack you will probably get away with what you propose. But I would not claim it is just as strong. I am not an engineer but it seems pretty obvious to me that the sliding jack mounted on the J channels rather than the runner deck would calculate bout as carrying less load. If I was going to do this, I would at least cut the angle iron back so the testing point on the J was as close to the angle as possible. I might also weld a lip on to catch the J for safety purposes. The Delrin liner to facilitate sliding should wear out faster since there would be less of it and the load would be more concentrated but it can be replaced.

This is probably a moot discussion since the sliding Jack will be bouncing off the floor if it is resting on the J channel when you lower the lift.

 

[05snopro440]

While you are correct in everything you wrote, the manufacturer of my lift sells a rolling bridge jack that transfers it’s load to the lift through the “J-channel,” so they have indicated that the J-channel is capable of the load. As far as the angle bracket is concerned, any bending moment imposed upon it would be lessened, due to the shortened arm as compared to setting on the runways.

The rolling bridge jacks usually roll on the bottom of the channel, it doesn't line load along the top. Your design may vary. Rollers Also allow some alleviation of angled stresses. Also, you're incorrect on the bending moment comment. The sliding jack is designed for uniform contact along an area, so less pressure evenly distributed throughout the surface. Putting it on a J-channel with loading in one line increases the forces applied to the angle by many times, which creates a large bending moment because instead of a uniform load all across the surface, you have a much higher load along one line a certain distance from your load location.

 

[Yankeefarmer]

Bending moment is force x distance. Analysis of a cantilevered beam must consider shear stress and outer fiber(bending stress.) Putting the load (which is the 1/4 the weight of the jack plus 1/4 the weight of the load it is supporting) on the J channel moves it closer to the bridge, thus shortening the moment arm.

You seem to be confusing loads with surface pressure at the point of support.

 

[Poolshark314]

Yes, a jack tray designed for a J channel obviously works fine. That jack tray is not relying on distributing its load through a 5 inch piece of angle iron with only the outer 2 inches making contact. The jack tray has an upside down C or J channel to fit over the runners’ J channels. The C or J shape is much stronger than a one angle piece (angle iron). This matters even more when you want to put all the load at the outside edge of the angle iron. The C or J is also safer since it locks in on the J channel on the runners.

If you are not maxing out the weight limits of the jack you will probably get away with what you propose. But I would not claim it is just as strong. I am not an engineer but it seems pretty obvious to me that the sliding jack mounted on the J channels rather than the runner deck would calculate bout as carrying less load. If I was going to do this, I would at least cut the angle iron back so the testing point on the J was as close to the angle as possible. I might also weld a lip on to catch the J for safety purposes. The Delrin liner to facilitate sliding should wear out faster since there would be less of it and the load would be more concentrated but it can be replaced.

This is probably a moot discussion since the sliding Jack will be bouncing off the floor if it is resting on the J channel when you lower the lift.

My jack tray is just a welded box. It doesn't have any channels on it.

 

[pbon]

What does it sit on? How is the load distributed and across how much surface area? I am sure it is designed for its intended application, but not sure it is designed for an unintended application. The Bendpak jack tray uses the J channels since the Bendpak 4 post has J channels, and is as I described.

 

[Poolshark314]

What does it sit on? How is the load distributed and across how much surface area? I am sure it is designed for its intended application, but not sure it is designed for an unintended application. The Bendpak jack tray uses the J channels since the Bendpak 4 post has J channels, and is as I described.

It sits on top of the channel. It is the jack tray that came with the lift

 

[pbon]

Ok. The box makes a good strong design too rest on the lip. That tray looks like it was designed for the lift in the photo you posted -/ intended purpose. This is very different than the original question of putting a sliding bridge with angle iron flanges designed to have what looks like 5 inches hanging over the runners to instead sit on a little lip on the side of the runners.

 

[05snopro440]

Bending moment is force x distance. Analysis of a cantilevered beam must consider shear stress and outer fiber(bending stress.) Putting the load (which is the 1/4 the weight of the jack plus 1/4 the weight of the load it is supporting) on the J channel moves it closer to the bridge, thus shortening the moment arm.

You seem to be confusing loads with surface pressure at the point of support.

I'm talking about the change in loading and therefore moment on the angle iron itself. You don't understand. Don't worry about it.

 

[Mark128]

Bendpak experimented with nylon sliders on their bridge jacks for a while, I have one like that. Works the same as rollers except it will wear down over time if you don't keep the channel clean.