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Have you ever wanted to weigh your vehicle (each corner, etc) and didn't want to go to a gravel pit or scrap dealer to get it weighed?

Here is a little trick I learned from professor95 over on the RV forum.

"My homemade jack scale.
You will need to locate a hydraulic bottle jack that has a service port. This will be a screw out plug on the bottom of the jack. Unfortunately, jacks at Wal-Mart and Pep Boys (made in China) no longer seem to have the service port. So, you may need to search out yard sales or an older friends garage to find a bottle jack with the port. Remove the plug from this port and install a pressure gauge - I selected a liquid filled gauge that will measure up to 3,000#. To convert this to weight, measure the diameter of the jack cylinder (mine was 1.125 inches) and apply a little math to get the area of the cylinder (3.14 x radius squared). In my case 1.125 diameter /2=0.5625 radius x 0.5625 radius = 0.3164 x 3.14159 (pie) = 0.994 (my jack factor). Multiply the area by the pressure and you get weight.

The above information was originally found on an RV Camper forum and written by “Professor95”.
I changed the numbers to match my jack dimensions.
If you use a jack with a 1-1/8” cylinder you can use the direct read from the gauge and be accurate within 6 pounds per thousand. Gauge reading =1000# = 994# actual.


Gauge at Northern Tool was 12 bucks and the adapter fitting was about $6.59.
If you have a rubber plug and spring behind the service port metal screw remove the rubber and leave the spring. If the spring is so small in diameter that it slides into the new fitting you should cut a small hole in the rubber disk and use it as a spring stop. I think the spring holds pressure on a metal ball valve.

The front of my Baja weighs 706#


Dia Factor

1.125 0.994018711
1.5 1.767144375
2 3.14159
2.5 4.908734375
Here are the pictures 1-4.




Marvin

Great post! Great pics and explanation! Thanks.

doc

Wonderful trick!

I do professional corner balancing at work where you drive the whole car on a scale bed, but this is a pretty neat trick for home use.

Some thoughts: The weight distribution depends a LOT on how level the car sits. Small changes in ride height of less than 1/2" in one corner, can make a 100lbs change. In other words, when you lift the car up on a jack like this, your weight will shift away from the jack point and you get a lower number, than you would if the car was level.
If you wanted to start getting your corner weights more even, you need to position the car and jack in such a way that when you have the jacked corner in the air, the car is level.
You could possibly make it easier if you removed a wheel... just need to factor in the weight of the wheel.

Jan

Bugfuel, I forgot to mention that. What I do if I want real accuracy is drive up on 2 x 8 boards with all tires and then jack one corner. Once you clear the board remove it and lower jack slightly. You need to be on a level area though.

If you haul your Bug, Baja, or Rail on a trailer this jack placed under the trailer tongue will let you determine the proper tongue weight by moving the loaded vehicle forward or back. As a general rule you want 10% of total trailer weight on tongue.
Marvin

GA_Boy wrote:Bugfuel, I forgot to mention that. What I do if I want real accuracy is drive up on 2 x 8 boards with all tires and then jack one corner. Once you clear the board remove it and lower jack slightly. You need to be on a level area though.

If you haul your Bug, Baja, or Rail on a trailer this jack placed under the trailer tongue will let you determine the proper tongue weight by moving the loaded vehicle forward or back. As a general rule you want 10% of total trailer weight on tongue.
Marvin

Good stuff.

In European countries, they don't specify tongue weight by a percentage of the trailer weight, but instead they give an actual tongue weight to follow. I am not 100% sure if it is the same for all cars, but it has been around 80kg ( 176lbs) for all vehicles I have bothered to check. The vehicle's registration papers list tongue weight.

Was that a threaded port already or was their a fitting there with spring cylinder and ball in there like I have on one jack?? Thanks ED

Unless I missed it, that gauge measures fluid pressure.

Pressure = force/area.
Force = pressure * area

You need to multiply your gauge reading * the piston area of the jack. If your jack has a piston area of 1 square inch then you are golden Otherwise, note.

Probably would would work reasonably well on hydraulic press too..... Need a spread sheet with formula or build a chart to have scale for pressure to weight conversion...

For corner weights you could use a couple of 300 lb bathroom scales and a couple of ratio boards...



With this setup, scales reading is 1/3 of actual weight at wheel...

I know, its gets a way from hydraulic scales but with two scales and ratio boards you can do a pretty accurate balance side to side or front to rear....

Dale

Ed ke6bnl wrote:Was that a threaded port already or was their a fitting there with spring cylinder and ball in there like I have on one jack?? Thanks ED

It was threaded with spring and plunger.
Marvin

Steve Arndt wrote:Unless I missed it, that gauge measures fluid pressure.

Pressure = force/area.
Force = pressure * area

You need to multiply your gauge reading * the piston area of the jack. If your jack has a piston area of 1 square inch then you are golden Otherwise, note.

Steve, In my post I gave the Diameter factor equation for various size jacks.
If you have a 1-1/8 " jack you will be accurate within 6 pounds per thousand.
Marvin

I can't read....

Keep up the good work.

Dale, correct my math, but I think the setup you are showing will read 1/4 the corner weight, not 1/3. Key thing with corner wight is the car must remain level, so if the board doohickey is 3 inches tall, stack 3 inches of junk under the other three wheels.

fusername wrote:Dale, correct my math, but I think the setup you are showing will read 1/4 the corner weight, not 1/3. Key thing with corner wight is the car must remain level, so if the board doohickey is 3 inches tall, stack 3 inches of junk under the other three wheels.

You know, you may be right.... For some reason I was thinking the "3X" value in graphic was "2X"....

Must have mistyped value when doing graphic...

And yes other three wheels need to be at same "ride" height as one on "scales"...

Dale