Truck is F600 single axle dump truck.

Front axle is 7500#, Rear axle is 17,500#, which makes 25,000# of combined axle capacity rating.

Front axle has 2 springs rated at 3,750 each for total of 7,500#

Rear Springs available for this truck are: 7,500, 9,125, or 10,590 for a total of 15,000, 18,259 or 21,180 (assume the amounts are multiplied by 2) ??

According to sales literature I have for the truck..Auxiliary Springs of (2x) 2,250 are also available The truck does appear to have the auxiliary springs. I think...pics attached.. anybody know if these are the auxiliary 2,250# springs? Or what the primary "spring pack" is rated at?..or how to determine?

So..total spring capacity could be a minimum of 22,500# (7,500+15,000) or a maximum of 33,180# (7,500+21,180+4,500)

Tires are rated at approx 5,500# single and 5,000# dual...so (2x) 5,500=11,000 and 4x5,000=20,000 for a total of 31,000# total tire capacity.

So the question I have is: Why would this truck be rated at 21,700# ?? As the GVWR (weight of truck and load) would seem to be somewhere between 22,500 and 31,000. Are the amounts "de-rated a certain percentage.. like in electrical load calculations which is usually 20% leaving 80% usable) ?? Seems it ought to be rated at 25,000#..which is the combined capacity of the front and rear axles.

Vehicle was a former plow truck and seems to have been ordered with all available upgrades.. largest engine, best transmission, largest tires and wheels, largest axles, etc.. GVWR for the 1975 4x4 F600 were: 17,200...21,700...and 24,000... this truck is rated at 21,700

Just trying to understand how GVWR ratings are determined..and... seeking answers to life's persistent questions.


Thanks

 

First thing first is to go to a scale and get weight of truck at the front axle, then total weight, then rear axle, and compare those ACTUAL WEIGHTS to the tag limits, total weight would be different than the axle because where the weight is loaded can alter the weight rides on the axles. NEXT, visualize this, take a 5000 lb truck with a 7000lb GVWR, front of truck weighs 3000 lbs because of engine, back of truck weighs 2000 lbs because all open space. Add one ton of tungsten (heavy, dense metal) and load it onto the tailgate, nose of truck goes up, and weight of the truck transfers to back of truck along with weight of load on tailgate, VIOLA! back end of truck weighs 6000 lbs and front weighs 1000 lbs, rear is sitting on axle bumpers and front has -20 degree camber. truck still weighs 7000 lbs. Now, spread the weight to 1200 at front of bed and 800 across the rest of bed, that 1200 adds 400 to front with 1800 to rear, 3900 in front/3100 in rear, better weight balance, right?

 

the numbers above, well I just pulled them out of thin air, but to illustrate the point without getting into a chapter's worth of writing about weight percentages or weight and balance calculation.....

The GVWR is THE max amt of weight you can weigh, the truck, the load, the fuel, and of course, you. That does includes the aux springs in the total number

 

Agree, The GVWR is the maximum the truck and load can weigh. That IS the question..how to determine the GVWR amount with KNOWN weight ratings of components. Pretend there is no VIN tag showing total GVWR..the "puzzle" is to come up with a GVWR rating for the VIN tag. In other words..how do the folks making the vehicle determine what the actual GVWR is going to be?

GVW (weight of vehicle) is easy...go take it to the scale

Thanks for any input.

 

The known weight ratings of an individual axle are not just determined by the springs, but also by the bearings in the spindles, the bolts that hold the springs to the chassis, the thickness of the metal in the chassis, the length of the chassis, the size of the brake pads, the swept surface of the rotors/drums, even the ubolts that hold the axle to the spring. the chassis is more about the total weight, but the suspension mounting points are where the weight transfers to the chassis

 

The weight ratings of the axles, springs, tires, etc are already known so there is no need to examine the small individual parts that make up the larger piece.. that information was already used to determine the rating for the larger component. I doubt the mfr would put 12,000# of brakes on a 17,500 axle..if they did.. the axle would most likely be rated at 12,000. Weakest link of the chain theory. Would doubt that mfr would use a spring rated at 10,00 and a shackle rated at 6000 as springs and shackles should meet or exceed the capacity of the spring. As for mounting points.. would think that would only matter if the vehicle was something other than the usual configuration. In this case the bolt-up is nothing out of the ordinary. Same question remains.

 

When I would load up my 1 ton dump I would judge my load weight by how wet the 20 mil crush was. If it was dry I would take on 3 meters3 = almost 5 cubic yards, wet I would take on 3 cubic yards. The weight of these 2 loads was roughly the same. Because you would be taking on a lot of wet, high moisture content loads, it's likely the former owner got the heaviest suspension they could. This would make life easier on your motor to. You mentioned in a different post that the motor was replaced at 2 years old. A full load and ploughing into snow drifts is an easy way to snap a crank in the 361 version of your truck.
No more pennies in Canada so that's my nickels worth.

 

Turns out the motor was rebuilt or exchanged with same as original.. FT361....must admit.. Am unfamiliar with the term: "20 mil crush" ??

 

Sorry about that, too many years of the metric system. 20 mil crush is the same thing as 3/4" crushed stone with 40-60% sand. It's the base mix used under garage pads, driveways, sidewalks and flatwork concrete pads. Those trucks are used under unique conditions and as a result they wear a bit differently. The passenger side front suspension takes a beating from that angle plow. The kingpin and spring perch take a real beating and so will your steering box. Expect to replace the cloth steering joint as they rip up from fighting the steering wheel every time you hit a snow drift. Those snowdrifts cause trucks to do a weird twist and the drivers side rear axle seals, bearings and axle take a beating. Also check your pinion seal and bearing. It's not the crown gear that blows in that axle it's the pinion gear that starts to break up first. Don't know if you've been through the truck yet but those are some of our first places to check when we did our servicing.

 

I should have figured that out... Around here we call it 3/4 minus and 5/8 minus.. or "roadbase".
Thanks for the "heads up"..on the problem areas to check out.. The plow is a 12 footer ..curved.. larger at one end than the other, figure the whole thing weighs 2500#..with undercarriage ...alot of weight to be hanging out front..since it is 4x4.. the brake drums are "inside" of the hubs and the 4x4 hubs need to be pulled to get to the brakes for inspection ..so will be replacing all seals etc while in there.

 

5 cubic yards in a 1 ton? at 2800 lbs per yard that is about 14,000...more than my F600 with 21,700 GVW will carry. thats why I asked what 20 mil was.. cause I figured it couldn't be rock. as it would weigh too much .

 

Moved to correct forum.

 

My truck had a 8'x12' steel deck with 2"x6" TnG between the deck and rails, 15" sidewalls for 8' and then it stepped up to 42" high for the front 18". Under the deck I had twin 10 ton rams. Moisture is the biggest problem for weight, as a result I would over load the truck only when we had gone a week to 10 days without rain. It also helps to pick up at about 1pm once the dew is gone and the crush pile has been dug into a bit. 1 full scoop with a 3 yard bucket and a half bucket of side scrape from the pile. 7900 lb truck would weigh 19,200 - 19,900 on the scales, on the ground at 4" thick I would measure 4.5 cubic yards plus a bit. I don't do big time driving with my work trucks so my mileage to job site would be 25 miles or less. I don't do this on every load nor do I hotrod the truck when I drive and I avoid traffic. If your going to work a truck hard, only do it when the conditions are right and don't do it every day. Also make sure you slide under it to make sure everything is ok. When I retired the truck in October of 2012 it had 83,000 miles, it was born sept 1978 and was never winter driven. I was DOT'd 3 times in the first 2 years that I had the truck and passed with the inspectors complimenting the truck, after that I got waved by when 1 tons were being targeted. Always keep your truck clean, rust free, quiet and make sure your front tires match and the DOT will start to leave you alone if you treat them with respect. The DOT is just keeping the highway safe for us so their cool.

P.S. buy a tarp and install a draw bar, it will save you a lot of hassles in the long run. Do not use discount brake or suspension parts, it's just not worth it.

I see they relocated you to the big truck forum, you might have to retitle your truck to stay in the 73 - 79 forum.

 

Big truck forum is where i should have put this thread in the first place.. so all good with relocate.

That IS a lot of weight for a one ton even with duals. My 2014 ford brochure from dealer shows the beefiest f350 superduty max GVWR of 14,000 and payload of 7080 with duals.. max. Your numbers are 1.5x that. That is why I bought a F600.. figured a 1 ton could handle 2-2 1/2 yards of rock and f600 4 to 5 yards. at 2800# per yard. ..my use is private and local. 10-20 mile trips on farm roads. Do appreciate the input..good info Thanks

 

One thing to remember is the brakes. Many times the same weight capacity axle has different size brakes - the 15x5 and 15x6 used on the SAME axle rating, but the smaller brakes were used on the lighter GVWR trucks.

David