Two post lift and center of gravity

[WCPoe]

I want to raise my 2004. 5 325/600 48RE Quad Cab 2WD short bed on a two post lift and need to know the center of gravity. I found the jack points in the service manual but it doesn't specify where the CG is. The lift manufacturer instructions are specific about the CG being centered between the posts, neither too far forward nor too far back. Any help from you experienced in lifting these beasts would be appreciated. Thanks in advance. Bill

 

[klenger]

2500 or 3500?



ST, SLT, or Laramie?

 

[rbattelle]

If you place the lift arms at the points indicated in the service manual, the CG should lie in a safe zone. Just be careful (obviously), and remember to use safety stands.



I tried to lift my truck on a 2-post once and only once. I put the arms at the locations specified by the service manual, and as I began to lift the vehicle one of the arms slipped and flew out from beneath the truck. Never again will I even attempt to put this truck on a 2-poster. If I ever purchase a lift it will be a 4-post drive on.

 

[klenger]

Assuming that you have a stock 2004 2500 SLT or Laramie, the Dodge website provides the following stats:



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The important numbers are the front and rear curb weights, which are 3766 and 2636 lbs, and the total curb weight of 6402 lbs.



Dividing the rear axle weight by the total vehicle weight (2636/6402) yeilds a weight ratio of 0. 412. Multiply the wheelbase by this ratio (140. 5" X 0. 412) and you get a CG of 57. 85" aft of the front axle or 82. 65" forward of the rear axle.



To get a more precise answer, actual weights from a CAT scale would help.



If my math or logic is in error here, someone please correct me.

 

[WCPoe]

Two post lift vs center of gravity

Thanks Klenger. I knew I could count on someone to come up with a solution to my CG question. The truck is a 2500 like the figures represent. The lift is a Mohawk 10,000 pound System 1A-10 for Rbatelle's info and has steel gripper teeth to prevent slippage. The lift is built from 3/4" channel similar to a fork lift and not the formed thin wall channels some units are constructed of. I'll report back later with the results when I get a chance to put the truck on the lift. Thanks again.

 

[ThomasLawrence]

I had my '03 up on my two-post lift when I swapped the transmission. You can see some pictures here:



http://home.earthlink.net/~tlawrence5/trans/trans1.html



In several of those shots, you can see where I placed the lift arms. You can also see the four 2-ton safety stands I also used. You can see my four-poster in the background on the first picture, which I generally prefer to use for the big dually, but since I needed the driveshafts free to turn, I opted for the two-poster.



This truck is a long-bed dually, so I had some more weight in the back to counter-balance the heavy front end. Even with that, the front end was noticably heavier (the front arms flexed a good 2-3 inches when the truck was first lifted).



Once you position the pads under the frame rails, raise the truck a couple of inches off the ground, and try bouncing the front (or rear) end up and down - to make sure you have the truck balanced well. It's OK for the truck to rock, but the lift pads should never lose contact with the frame. Once this checks out, raise it up all the way, but never do any kind of work under the truck without safety stands at the front and rear of the truck. The safety mechanisms in most two-post lifts are plenty strong to prevent the truck from falling straight down, but you need the aux. safety stands to make sure one end of the truck doesn't fall, especially if you're pounding and wrenching underneath it. 8K of truck landing on you hurts



-Tom

 

[WCPoe]

ThomasLawrence thanks for the post. The pictures are great and the advice is well heeded. WCPoe

 

[Matt400]

The lift is a Mohawk 10,000 pound System 1A-10

With your short bed it would be a good idea to have the lift posts where the drivers door handle is in the middle of the beam. Place the lift pads contacting a flat portion of the frame and spread them as far apart as possible for stability. The 10k Mohawk is a great lift but with no overhead support beam the concrete should be 8" thick minimum with re-bar to be safe.



If you decide to use added support like Tom did be sure you lower the lift onto its mechanical locks first and then set the supports as a safety measure should the lift bleed down any.

 

[tpuig]

I go to a local shop (buddy's hot rod shop) and use his 2 post on all the vehicles. Typically, the post is about even at the front cowl or windshield. My truck is a 2500 QC short bed 4x4, so it's a bit nose heavy. I've readjusted the lift a number of times until I felt comfortable enough to get under it for the oil changes, etc. It's a Rotory lift and very heavy duty, but I still raise it up a couple inches and shake the truck on it's lift points before lifting it any higher. Hope this helps.

TP

 

[ThomasLawrence]

Typically, the post is about even at the front cowl or windshield.

This is probably an asymmetrical lift (the columns are installed on a 45° angle, pointing towards the rear of the vehicle). On a symmetrical lift (with the openings of the columns facing each other - which is what I use), the posts will be around the area of the driver's door. I roll my truck into the bay just enough to be able to open the door, then I roll it back 10-12".



What's important to remember about any two-post lift is that the total capacity of the lift is based on equal loading of the lift arms. On a 10K lift, each arm is only rated for 2,500lbs. If the vehicle is positioned improperly, it's easy (especially with our trucks) to overload the front lift arms.



When first figuring out the positioning, raise the truck a couple of inches, and measure the amount of deflection between the front and rear lift arms. They should be within 1/2" of each other (distance from the bottom of the arm to the floor) at their mid-point (where the smaller bar slides into the box portion of the arm). If the front is lower, you need to move the vehicle back. If the front arms are as far forward on the frame rails (which is where you should position them to begin with - just behind the control arms), then you need to shorten up the rear arms and move the contact points farther forward on the frame rails.



Of course, if you have a newer Rotary lift with the computer on it, you don't have to do any of this stuff - just select the vehicle from it's built-in list, and it tells you exactly where to position everything

be sure you lower the lift onto its mechanical locks first and then set the supports

Good point, Matt... I forgot to mention this. I place each stand under the truck and run it up until it just makes contact. Once all four are in place, I spin up the fronts equally until I see some tension come off the lift arms. I then tension the rears as well. It's important that both sets of stands be in place before you start cranking up on one of them - as you may go too far and dump the thing right off the lift (extreme, but it could happen - a friend that owns a garage had an employee dump a brand new Caddy off his lift, to the tune of about $8,000 in damage)



-Tom

 

[WCPoe]

Tom, Matt and Tony -- I appreciate all the info. The collection of experience and knowledge found on this forum is invaluable. I'll probably have time to get to truck on the lift this weekend and see how it works out. Bill

 

[Matt400]

What ya gonna do when its on the lift? Fun stuff or regular maintenance?