I have a 1973 ford LN900 Grain Truck, it has a 18 ft dump bed with air breakes and tandem axles. the very back axle is lifted up and you can raise and lower it if you want to... my question is, in the cab there are TWO levers that raise and lower the very back axle, the FIRST BIG lever on the steering column says "not for parking" and when I hit the FIRST lever the back axle lowers without putting air in the airbags. but there is another SMALL lever on the dash with a PSI gauge right beside it and when I hit the SMALLER lever while having the FIRST lever turned OFF, the back axle not only lowers but raises the back end of the truck up just a little.... so my real question is what is the difference between the two levers and when should i use them and when not to use them?????????? the only thing I can think is that the first lever is for driving on the road with a load on with no down pressure on the rear axle and the second lever is for putting down pressure on the very back axle to raise the back end so that all the weight is resting on axle closest to the end of the bed when your dumping a load and not sittin on the front rear axle but that is only my guess. so someone who knows please help because we will be putting over 20,000 LBS of corn in this truck this fall. I cant afford to make a simple mistake to a simple solution... PLEASE HELP
some thing is not right the handle that says "not for parking" should be your trailer brakes
Boy, you really do have a problem. You appear to have a truck where someone who knew very little yet thought they knew more than they did, plumbed your drop axle. Tyler 1022 is correct, when he says something is not right. I would have a real wrench look at it and correct the problem. Better to do it now than on the side of the road under the direction of the DOT. DOT will also grace you with a pretty good ticket I would think if they discover it. Good Luck!
its a straight truck with a tandem axle so I wouldn't have trailer brakes, its and older truck and just about everything says not for parking except the actual parking break.... someone has to be familiar with this truck
Sounds like.it was a converted road tractor and they plumbed the trailer air into.the drop axle
Ok, I'm going to try to help by taking it in 2 parts. The first lever: does it put any pressure in the air bags? If not, then it is doing nothing for you. There would be no advantage having the axle down with no pressure on it. It sounds like a trailer service brake valve that someone has plumbed into the lift axle for whatever reason. This isn't a truck with a tandem axle, it is a single axle truck with a lift axle. The lift axle was probably added late, as they were rare as hen's teeth in 1973. If you are lucky this is a converted tractor, as they are usually heavy spec. The smaller valve with the guage sounds like a lift axle control. There should be an adjustable regulator somewhere thAt you can use to control how much weight that axle takes. 20,000 pounds of corn should actually be well within the capacity of a single axle truck.
All good advice so far, we call that setup a tag axle here.
im still having trouble thinking it was converted, it has a 18 ft grain bed on it and that would be a long frame to have a fifth wheel hitch for a road tractor. especially with a truck that only has a stationary single wheel and the tag axle option
^^^ I say that because I have found load tickets for grain under the seat that are dated back to 1978 LOL
It could have been a straight truck plumbed for a pup in it's former life. Perhaps it had tandem drive axles that were replaced with the single drive and the tag axle for whatever reason. The possibilities are many, if you haven't owned it since it was new there is no way of knowing. You could try searching the vin# for information at a ford dealer but since they no longer manf. heavy trucks, probably won't work. Anyway there is no telling what the original or subsequent purchasers did with it before you got it. You might try contacting the previous owner(s) if you can access this information. Still I would recommend you get an expert to check this out and make sure it is right.
The Freightliner dealer in our area ended up with the Ford / Sterling records. Check around with the heavy truck dealers in your area, one of them has the microfiche on your truck.
A drop axle will have 4 air bags, two to push it down, and two to lift it back up. Sounds like the first (not for parking) lever is plumbed into the air bags that keep the axle off the ground. When you pull on it, you likely dump the air out of the bags that hold the axle up thus it falls to the ground without any air in the bags that push it down on the road. What would this be used for? I don't know, perhaps to allow you to service the axle without lifting the rest of the truck up.
ok I think I figured it out... I started to play with the levers in different ways and I found that the second small lever will lower the rear tires and put 80 PSI on them, well if you apply the first lever after you apply the second lever, the pressure gauge on the second that reads 80 psi drops to 0... but if you work the first lever slowly back, the pressure on the second lever goes up... so my thinkin it that the second small lever puts the rear axle down with 80 psi and you have to use the first big lever to regulate how much down pressure (Air PSI)you have on the rear axle... its kinda weird to me how that works but that's how its setup... still don't understand why the first lever says "not for parking" thou.... does this sound right to anyone because there is no other way to regulate the air pressure than that
Just a guess, I've never seen or heard of this setup before, but it sounds like somebody took a normal lift axle setup and plumbed a trailer service valve for a dump valve. There is a regulator somewhere set to 80 psi. The only reason I can think of right off you'd want that is maybe to put the weight on the drive axle quick if you started spinning. I sure think this was backyard engineered somewhere.
I had a truck that had 2 levers to work the lift axle. One lever with to the air bag that lifted the axle, and the other lever went to the air ride bags. If you had both levers opened, the air bags would fight each other. Your setup sounds like it may have been a similar setup on the trailer spike.