Lift Axle Operation on Triaxle

[PeterG]

Help! Just got a 2007 Kenworth T800 triaxle and I can't operate the steerable lift axle. The truck is from the South Carolina area, but now is out West and needs to meet WA State DOT. There is a Handle to turn on the dash. I believe this regulates the pressure. There is a pressure gage on the dash. I do not see a pressure gage on the outside the cab which I believe is required in WA State. When I turn the handle, nothing happens. After the truck has been sitting for a few days, the axle slowly drops down to the ground. Starting the truck and filling the air tanks slowly raises the lift axle. Going in reverse raises the lift axle. There is nothing between the seats that I can see that is a switch as all there is only the controls for the PTO for dump, air gate, and pull tarp. What am I mission. Handle looks like a Sealco 5400. Brand of the axle is Watsun. Any help with all this would be fantastic.

 

[Truck Shop]

Have you hooked up to a trailer yet? Some lift axles are plumbed so that the axle will not drop until the air lines to trailer are connected and the emergency side {Red Knob} is pushed in.
On those set-ups you can use a dummy glad hand plugged off and connected to the red air line-push red dash valve in and axle will drop. But it all depends on how it was plumbed. You can install a dash switch
for raising and lowering. Parker makes the pressure regulator for the outside of cab installation.

 

[heymccall]

All of my later model lift axle equipped trucks require that the parking brake be released before the axle will lower.
This is done to prevent a rollaway condition should the primary suspension bags deflate while parked, since lift axles aren't equipped with parking brake chambers.

 

[PeterG]

Thanks for the reply. The truck does not have a red button on the dash, no air to the back, and currently no pintle hitch trailer set up. I will try releasing the parking brake and see if that does anything. Once you release the parking brake, do you turn the handle to the right to apply pressure to lower the axle to the right pressure? To raise the lift axle, do you turn the handle to the left, to release the pressure, the gage goes down to zero, and the lift axle come up? Does anyone know if a pressure gage is needed outside the truck by the cab in Eastern States. This one doesn't have one outside. CDL drivers out here in Washington State say that you do need one on the outside of the cab. What is the best way to know what pressure to apply?

 

[Truck Shop]

In Washington State the pressure regulator must be mounted outside of cab, with the pressure gauge mounted in dash and raise lower switch in dash. Wa DOT does not want the driver to have the ability
to raise and lower pressure on the drop axle when crossing scales. But in slick conditions a driver needs to be able to raise the drop axle to put more weight on the steer axle. There must be a switch
located somewhere in the cab. Most of the drop axle manufactures went to a single full function valve, it's the only way to fly. The old Parker/Norgren valving was a real problem, i don't remember the
part number for the full function valve but I keep one on the shelf at work, I will post the part number in the morning.

 

[Truck Shop]

Parker regulator #14R013FC, Full function drop axle valve #GTD 5040 411 01.

 

[PeterG]

Can you tell me where that part might be in the truck? I have found what looks like that part when I lift up the engine hood, and up on the firewall, near where the Pressure valve is. I'm going to see if I can track down the last owner of the truck and get info from him on the lift axle operation. Do you know of any good dealer in Seattle that would be good to work on this, and can install the exterior pressure regulator by the cab?

 

[Truck Shop]

I live in S.W. Wash so I have limited resources on who to take it to for repair other than the dealers, and those are all pretty much the same. Normally the regulator is installed right behind the cab on left side.
The air valve would or should be located left side/inside of frame just in front of drop axle, normally attached to a crossmember.

 

[PeterG]

Ok, think I got it. I found the right rocker switch on the dash. In order for it to work, you release the air brake. Then the steerable axle drops down. Then turn the handle to bring the pressure up. Does 50 psi sound about right for a 16.5 box and Watsun 13200? How do you test? To raise, put the allison Auto in Reverse. Put on the air brake. Or release the pressure and move the rocker switch. Anyone know the process on a 2007 Kenworth T800. Lift axle is OEM.

 

[Truck Shop]

Normally on our rigs it takes about 70 psi, with 9,000 on the tag 12,000 on the steer.

 

[PeterG]

Many thanks for all your help! Is the exterior gauge showing the PSI like the one inside the cab, or does is show the pounds of pressure? At what point do I need to use the lift axle. The truck is licensed for 70,000 GVW right now. If I have just 6 yds of gravel, do I need to put it down. With 10 yds of gravel, I would put it down with a bit less pressure? With 12yds, (36,000 lbs), then down with most pressure. Lighten it up with slick conditions to get more weight on the steers? What does WA State patrol want to see? When you back up the lift axle raises. Does this mean it's ok to dump with the axle raised?

 

[JPV]

My opinion is that truck would be good for 56,000 lbs in Washington. 34,000 on the drives, 12,500 to 13,200 on the steer and the rest on the drop axle. Anything below 48,000 leave it up, above that weight put it down. You need to load up to legal weight then put your steer axle on a scale and adjust the lift axle pressure until you get what you need, then check with the steer and lift axle on the scale and make sure it is at least 22,000. 70 psi should get you close. Then don't mess with it. Leave it up when you are dumping, backing up or off the pavement. Also in slick conditions.
I can't tell if the truck has airbag suspension but if so dump the air when dumping the load, to make it a little more stable and also to keep from yanking on the shocks when it tops out the airbags when the weight all comes off at once.
Looks like a nice truck!

 

[PeterG]

The truck has 23,000 lb rear axles, and 8 brand new 16ply retreads. The suspension is Haulmax. The front steers are 315/80R/22.5. This was never a tractor. Why would the truck be only good for 56,000 lbs? Empty weight is 28,000lb.
So I can only haul 10 yds of gravel? I only licensed it for 70,0000. My plan is to haul 15yds of dirt, and up to 12yds of gravel.
Where does one go or do the scale info?

 

[525isx]

tandem drives 34,000 max , 14,000 steer axle w/315, 8,000 on drop axle (drop and drives usually 42,500 legal bridge)

 

[PeterG]

Thanks for your help guys! But I'm still stupid on this. What does that mean 42,500 bridge legal? What is the max weight fully loaded I can carry legally then ON WA state roads? What is max weight I can tow? All I'm used to is my International 4900 with air brakes licensed at 38,000 GVW and eager beaver tag trailer for my 14,000 lb mini.

 

[525isx]

bridge formula= how much weight on set of axles depending on wheelbase. 3 axles = center of drop to center rear axle, 10 feet= 42,500. overall weight for 4 axles probably about 56,000 gross. how many trailer axles? wheelbase?

 

[mitch504]

In SC, that truck was legal for 70,000 with the axle down, and 50,000 with it up (if you stayed off the interstates). The pressure not very critical as long as you have no more than 20,000 on any one axle, and you wouldn't want to frequently overload your steer axle. If you got on the interstate, you had to comply with fed bridge law, so nobody would drive that loaded on the interstate.

 

[PeterG]

FYI, the length of the box is 16.5 feet. I haven't measured the axle distances yet. This truck is from South Carolina.

 

[mitch504]

Yep, that's why I mentioned what it was legal for here. It could gross 80,000 with any trailer here, as long as no more than 20,000 on any axle.

 

[JPV]

This might help, it is definitely confusing figuring all this out.
https://www.dropbox.com/s/9j30pj0t4ozt0y7/AxleWeightTable.pdf?dl=0