Hey.next thing ya know forum posts become admissive evidence and I'm paying his over gross tickets ...and about the nuclear detonator assembler, let's just hope we never have to launch a nuke, so many wires all the same color
Dog chimp is correct. You cannot weigh more than the max weight of the truck with a load in the box, so you need to find the tare weight first like everyone is recommending.
Well you all are close but the vehicle with a box on it is more likely than not considered an incomplete vehicle when it was made and the box manufacturer or the company that put the box on the chassis will have to have another sticker that states the GVW of the axles. There are a few times that there are modifications to increase the GVW and many times the company will lower the GVW. However if this truck is sold without a sticker like that, then the gvrw is 25,950 lbs.
Is it a 3500 dully? If its a factory bed they say the truck is good for hauling up to 23K lbs total weight including the trailer (goose neck). If I'm not mistaken the bumper pull is good for 7-8K lbs tongue weight. Being a box it will go down some because of the weight of the box alone. This will give you a little bit of an idea. My guess would be not to exceed the tongue weight of the goose neck load rating by more than a couple hundred pounds. A goose neck has a concentrated weight over the rear axle but spreading the weight inside of a box and more towards the front you might get a little more. I would look at the GM website and also look at DOT's website for guidelines on that class of truck as far as weight goes. Figure the biggest U-Haul truck available for rent can't exceed over 26K lbs total GVW so that might help as well. In fact look at the U-Haul website and find a truck similar to yours and find out what they have the total weight it is capable of hauling. That should get you pretty close to a general idea.
from the PENSKE truck rental site. typical 6 wheelers. 1 a CDL truck vs a non- CDL shows 10,000LBS freight wt for non-CDL http://www.pensketruckrental.com/business-truck-rental/commercial-trucks/medium-duty-trucks.html
Truck and load weight combined can't exceed 26Klbs. 26,001 lbs requires a CDL. Penske trucks are a bit bigger than the standard U-Haul which most are internationals with air brakes and such and U-Haul uses the Chevy Kodiak 4500cab and chassis which are VERY rarely fitted with air brakes but neither can exceed the 26K limit but those trucks are to big as to what the OP is referring to. It is on the light duty side which would be a 1ton dually with a box. From what I see of the 16' light duty trucks on the Penske site and what the GM website says, I probably wouldn't push it more than about 5,500lbs no more than 6K max. Some years ago I worked for a portable car wash company and we had a Ford 350 box truck that carried 2-500 gallon water tanks, 2 pressure washers with 2- 50' pressure hoses and 6 guys and that truck was overloaded. Need to say I quit do to the safety concern of riding in that truck to job sites and ultimately the truck gave out. Twisted driveshaft, broke leaf springs and the differential was FUBAR. But that was direct load on the truck rather than halfing the weight out with a trailer and pulling it rather than hauling it.
3500s gross out at 36k all day long with loaded trailers, make sure you have good brakes on the truck and trailer, don't exceed axle/tires ratings and you will be legal.(provided correctly registered and licensed)