Center of balance

[Mach1 Driver 560]

I have a 69 Mach, 351w, FMX, PS, PB, and A/C. The concrete for my lift is long since dry and its time to install it. Since its a two post lift I wanted to be sure to have the center of balance for the Mach. Two post lifts creep me out, even if I do understand the math. 

I couldn't get reliable information on the web about the center of balance so I took it to a truck scale. Talk about feeling like Ant Man!! Anyway the scales are in three sections, one for the tractor, 1st trailer, and second trailer. I centered on the tractor scale and got a weight of 3426 with a full tank. I had marked a point on the door sill half way between the tires so next I positioned the car between the tractor and first trailer scales and got 2000 front and 1426 rear. This matches the gross weight.

Gas weighs about 6.3 lbs/gal so with half a tank (20 gal) the rear number drops to 1363. That gives it a weight distribution of 59.5% front to 40.5% rear. Pretty nose heavy.

 

For center of balance:

W1= FRONT WEIGHT

W2= REAR WEIGHT 

D1= DISTANCE FROM FRONT BUMPER TO CENTER FRONT WHEELS

D2= WHEELBASE + D1

 

(W1 X D1) + (W2 X D2) = TOTAL MOMENT

(2000 x 37.375) + (1363 x 145.375) = 272896.125

 

TM/GROSS WEIGHT= CENTER OF BALANCE BACK FROM FRONT BUMPER

272896.125/3363= 81.147

 

With half a tank the center of balance is 81-1/8" back from the front bumper. That's about 4" less than I originally guestimated. It gives me a little peace of mind knowing the car is at least balanced on the lift.

[RPM 1,190]

I'm by no means a numbers guy, but that is pretty cool! I too couldn't find much of anything showing front and rear weights. Ya saved me a trip to the scales when my car is running! Thanks!

[ray1970 88]

I was thinking the center of balance was the amount of money you had left in the bank

compered to what you still needed(wanted) to spend on the car...

 

Just more math...

[Mach1 Driver 560]

I was thinking the center of balance was the amount of money you had left in the bank

compered to what you still needed(wanted) to spend on the car...

 

Just more math...

 LoL, yep I always end up with negative numbers in the equation somehow

[1969_Mach1 333]

Are you applying first moment of inertia principles?  Sum (Wi*Ri) = Wtot *R where R is the mass center for the entire object (car) from the reference datum, and Ri is the mass center of each portion from the same reference datum.  Using the front bumper as the reference datum and assuming that Ri is located at the front and rear axle?  I may have missed something or be wrong.  I think D2 in your equation is the distance from the front bumper to the rear axle, not the wheelbase?  Which then makes sense.

 

Try using a single post (underground) hoist.  That's was the standard when I worked on cars for a living.  They only lock when all the way up.  They operated on air from the shop air compressor and some were air over oil which made them more difficult to operate.  The hoists wouldn't move until enough air pressure was built up to lift the vehicle.  Then is was hard to control, constantly opening and closing the valve to control the rate at which it lifted or lowered a vehicle.  The worst type I used was a dual post (underground) style where one hoist lifts the front and the other the rear.  Each with a separate control valve.  It lifted heavy vehicles but was actually frightening to operate.

[Mach1 Driver 560]

Are you applying first moment of inertia principles?  Sum (Wi*Ri) = Wtot *R where R is the mass center for the entire object (car) from the reference datum, and Ri is the mass center of each portion from the same reference datum.  Using the front bumper as the reference datum and assuming that Ri is located at the front and rear axle?  I may have missed something or be wrong.  I think D2 in your equation is the distance from the front bumper to the rear axle, not the wheelbase?  Which then makes sense.

 

Try using a single post (underground) hoist.  That's was the standard when I worked on cars for a living.  They only lock when all the way up.  They operated on air from the shop air compressor and some were air over oil which made them more difficult to operate.  The hoists wouldn't move until enough air pressure was built up to lift the vehicle.  Then is was hard to control, constantly opening and closing the valve to control the rate at which it lifted or lowered a vehicle.  The worst type I used was a dual post (underground) style where one hoist lifts the front and the other the rear.  Each with a separate control valve.  It lifted heavy vehicles but was actually frightening to operate.

 

I did the calculation correctly but in my haste I didn't write the complete formula for D2. I have edited D2 above to correctly state that it equals wheel base + D1.

I use the front bumper as the reference point. The distance from there to the front wheels is 37.375 and the wheel base is 108 for a total of 145.375. So I was using the same reference point, I just didn't add "+D1" to the formula for D2. Thank you so much for catching that. For reference go to: www.bendpak.com/support/balancing-safety/

[RPM 1,190]

Makes sense to me :)

[Tonyj 10]

Used to use these sorts of calculations to mark center of gravity points for military vehicles in preparation for transport by aircraft. These datum points were used to load the aircraft in such a way that trim could be maintained. Multi axled vehicles were the worst to calculate and tanks/dozers the easiest, just drive them on to a log until they balance.  

[Mach1 Driver 560]

Used to use these sorts of calculations to mark center of gravity points for military vehicles in preparation for transport by aircraft. These datum points were used to load the aircraft in such a way that trim could be maintained. Multi axled vehicles were the worst to calculate and tanks/dozers the easiest, just drive them on to a log until they balance.  

Huh, interesting! So all we need to do is get a log and two stout planks to drive up onto and then we can test the calculation...don't get me started on this, it only cost $12.50 to put it on a scale, but the lumber is gonna cost much more than that. Nope, nope not gonna do it...but it would be fun.

[RPM 1,190]

Oh come on...do the log thing! And take some pics :)

[Silver-Fox 3]

Questions: When you weigh the entire vehicle was your weight included in the number besides the full tank of gas ?

What size gas tank ?

 

Request: For us simple minded folks, how about the midpoint location specificly located on the vehicle, like how mnay inches forward or back from a door edge. We might not measure correctly from what point on bumper.

 

Mustang seems heavier then origal specs.

 

Thanks for the information.....good to know.

 

Tom

[Mach1 Driver 560]

Questions: When you weigh the entire vehicle was your weight included in the number besides the full tank of gas ?

What size gas tank ?

 

Request: For us simple minded folks, how about the midpoint location specificly located on the vehicle, like how mnay inches forward or back from a door edge. We might not measure correctly from what point on bumper.

 

Mustang seems heavier then origal specs.

 

Thanks for the information.....good to know.

 

Tom

 

No my weight was not included: as you know that would throw off all the calculations. The car had nothing in it except the spare tire that it came with and a full 20 gallon tank. Yes it is heavier than specs say it should be but it is completely stock, I am the original owner, the truck scales are certified, and the single weight matches the total of the axle weights.

Looking at the drivers side door sill, I took a measurement from the middle of the front attaching screw measuring toward the back of the car to the balance point for an empty tank, a half tank, and a full tank. The numbers are (rounded to the nearest 1/16"): from center of screw to empty= 1-1/2". from center of screw to half tank= 2-11/16, from center of screw to full tank = 3-7/8". The balance point moves back as the fuel tank gets fuller, to offset the weight.  

As usual I can't insert pictures so it is in the attached Word.doc

balance point.doc

[Silver-Fox 3]

Thanks again....it makes it a littler clearer......so will that change where your going to place the uprights for your lift ?

 

Interesting Ford  spec weight information:

 

2 dr coupe                     = 2690

2 dr sportroof march 1  = 3175 lb

 

Yours is the 2nd one I have seen at just over 3400 lbs 

 

They seem to gain weight just like people as they age :(

 

I was hoping with my mods (Aluminum top end and water pump over 60lbs lost) and long tube headers on my base 2 dr coupe to get the weight under 2900 lbs.......we'll see when I'm done.

[Mach1 Driver 560]

Thanks again....it makes it a littler clearer......so will that change where your going to place the uprights for your lift ?

 

 

 

Yes, it moves the lift points. I was going to pick it up in the rear from just in front of the forward "rear spring support", but the arms are too short to do that and still keep it in balance, so in the rear I'm lifting from the rear jacking point on the pinchweld. Actually weighing the car was very useful as it shifted my balance point that I had originally calculated from the published specs forward about 4 to 5". I did my first "lift" two days ago with no problems, but two post lifts creep me out so I'm going to use "Under Hoist Adjustable Safety Stands" from Harbor Freight. They will support 2 tons each and I'll have one on each corner. I've only seen the underside of the car when I had the tires changed and was actually surprised to see how clean it was. It has 77k miles and this third set of tires has been on there about 8-10 years, so its been a while since I've looked under her skirts ;)

[Silver-Fox 3]

My Mustang is currently on a 2 post lift in the body shop while we remove and replace a few rusted sections, The motor & tranny are out and when we removed the rear end this week it shifted the balance point a lot so we have safety stand under the fron section to keep it steady.

 

I'm curious about the lift because I'm think of putting one in my 3 garage but the ceiling is only 10' 4" at the middle.

I know you can some adjustment to set up. 

 

How high are the post ?

What is the width between the post ?

What is the width outside the post from one to the other ?

Is there a cross bar at the top or did you mount to the ceiling ?

Brand ?

Electric ?

 

PS: I hope you don't find the rust holes I found for what like a perfectly good car before I started removing stuff.

[Mach1 Driver 560]

How high are the post ?

What is the width between the post ?

What is the width outside the post from one to the other ?

Is there a cross bar at the top or did you mount to the ceiling ?

Brand ?

Electric ?

 

1. How high are the posts? In the down position the posts are 64-5/16" tall. However the hydraulic cylinder is mounted upside down with the body of the cylinder attached to the lift arm assembly. The Cylinder's shaft is attached to the base plate of the lift and as the lift rises the body of the cylinder rises with it, extending up to about 91". The roof of the car goes up to about 94.2". I have various obstacles in the way in my garage and had to put it in CAD to be certain everything fit- the lights and ducts are 96.5" from the floor and one beam is only 88" but since its at the front of back of the car (depending if it is driven onto or backed onto the lift) it still fits.

2. What is the width between the posts? 91.057" (see the Word.doc attachment)

3. What is the outside width? 100.557" (see the Word.doc attachment)

4. Is there a cross bar? No, and there is no need. The posts have wheels on them and are meant to moved to different locations and bolted down, or just moved out of the way. They are not attached to anything expect the floor.

5. MaxJax

6. It is hydraulic with an electric pump- 120vac 30A circuit.

 

PS: I don't expect to find any rust- I've had it since it was new, it was always garaged and we lived in SoCal (basically a desert) for all but the last two years.

not my thumbnails

MaxJax for 69 mustang.doc

[det0326 179]

Had the pony since it was new.   Wow that is cool. You and I must be around the same age. I wished a lot of times I had purchased one new and kelp it. I was more into Camaro's (what was I thinking) back then.  I see you live in Atlanta now, not to for down the road from me. You ever go to the swap meet near you. Maybe I will see you there sometime.

 

Dave

[Mach1 Driver 560]

Had the pony since it was new.   Wow that is cool. You and I must be around the same age. I wished a lot of times I had purchased one new and kelp it. I was more into Camaro's (what was I thinking) back then.  I see you live in Atlanta now, not to for down the road from me. You ever go to the swap meet near you. Maybe I will see you there sometime.

 

Dave

I'm 66 now Dave- bought her when I was 19. What swap meets do you go to around here? Let me know if you are in the area (and vise-versa) and we'll meet up some time :)

[skidmarky 50]

This is the lift I bought http://www.gregsmithequipment.com/Atlas-9KBP my garage has 10 ft ceilings and it lifts my mustangs to the perfect height (I'm only 5'9" though). Can only lift my truck 4 feet or so, but it beats laying on your back!

[det0326 179]

I'm 66 now Dave- bought her when I was 19. What swap meets do you go to around here? Let me know iorge f you are in the area (and vise-versa) and we'll meet up some time :)

I'm 69 just past March.  They have a car show and swap meet off I-85 I think the Commence exit. I think in the spring and fall may have already had the spring one I will have to check and see. I normally try to make a couple in Pigeon  Forge NC.  I've been to the one in Commence long time ago I need to get down there this year and see what all they have.  I sure will let you know if I make it.

 

 

Dave 

[Rsanter 152]

The center of mass is roughly where your shifter is.....

 

Bob

[Mach1 Driver 560]

The center of mass is roughly where your shifter is.....

 

Bob

yes, around the front of the base of automatic floor shifter, more or less

[skidmarky 50]

Ok, so this post has got me thinking now...once you have calculated the cars center of balance, do you then place that point in line with the posts of the lift? Or do you place that point halfway between the points where the arms contact the car? Might be overthinking this, but when I lift my car the front arms and rear arms are different lengths/angle to the posts. Wouldn't you have to have the arms positioned the same distance front and rear from the center of balance?

[Mach1 Driver 560]

Ok, so this post has got me thinking now...once you have calculated the cars center of balance, do you then place that point in line with the posts of the lift? Or do you place that point halfway between the points where the arms contact the car? Might be overthinking this, but when I lift my car the front arms and rear arms are different lengths/angle to the posts. Wouldn't you have to have the arms positioned the same distance front and rear from the center of balance?

All good questions. Maxjax says to put the center of balance on the center line of the posts. I know exactly what you are saying about the position of the arms. If you look at the attachment in post 16 above you can see how they are positioned when I lift. Scroll down to the second page of the attachment to see the car on the lift. I use the sub-frame in front because the front jacking point on the pinch weld is too close the the center of balance (I don't think two post lifts were around in 69). I had to use the pinch weld in the back because that's as far as Maxjax's stubby lift arms would reach. The car lifts level and only rocks enough to "damage your calm" ;) That's a quote from Jane in Serenity of which I'm a fan. I put safety stands under each corner once its up.

[skidmarky 50]

aah, didn't see your attachment. My lift has a plate across the bottom that bolts to the base of each post, no guessing on spacing between posts. When I first got mine I positioned the car where I thought it looked right, lifted it 6 inches and rocked it, seemed ok....there just happens to be an expansion joint in my concrete that lines up with the centerline of my rear tires, so I just push it to that point and lift away. Curious now, I am going to measure and see where my car is at that point.

 

But still, to me lining up the center of the balance of the car with the post is balancing the LIFT, not the car, it all depends on where the arms are located if the car is balanced.