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Lift Axle Operation on Triaxle

jonno634

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Dec 19, 2018
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141
Location
Garfield, WA
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Farmer
https://secure3.wsdot.wa.gov/commercialvehicle/permits/public/AxleSpacingReport.aspx

You can measure your truck axles, fill out this report and should tell you legal weight, and permit able weight.

my regulator for my drop is inside the compartment of my sleeper, with gauge. So it can’t be messed with by the driver while driving, or POS people in a lot. I haven’t had any issues with it with dot. I am not a dump Trk however.
 

PeterG

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Apr 14, 2015
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Seattle WA, United States
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Landscape Construction, General Contractor
Thanks for all the info and help. I had Pape Kenworth install the outer guage and handle. I will see if I can get a real number on my load capacity. Seems like 10yds of gravel, 14 yds of dirt, shooting for just under 15tons load. I see trucks with 56,000lb solo stickers, but higher GVW. As I have paid for a GVW of 70,000 for now, does this mean I can tow my mini excavator with load? Can I tow say, six yards of gravel (Lift axle up 18,000lb), and tow mini excavator Takeuchi TB153FR (13,000lb) and Eager Beaver equipment trailer, 7,500? Truck weight is 28,0000lbs.
Questions:
Do I load truck with Lift axle down or up? Must be up I think, as when air brake is on, lift is up.
Once lift axle is down, leave it down all the time (steerable axle) until I get to the dump location?
At the dump site, Lift axle and back up (backing up raises it) and dump. It's Haulmax suspension
Once lift axle PSI is set, just leave it alone? Don't adjust per load or weather?
Does WA State patrol at a weight station just check to see if you have the lift axle down and "reasonable amount of pressure". or do they weigh your load and say, sorry your at 70PSi, now you have too little on your steers, you should have it set at 67 psi?
Better to have too much weight on your lift axle, or too little? Some people say leave it at 50 psi. I've never been in a weigh station, and I'm scared!
 

lumberjack

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Dec 24, 2011
Messages
1,044
Location
Columbus, MS
Get a load and go play on a scale, see what does what, and take notes.


When I’m helping my excavator on the truck I have my tag at 40psi. If I have a heavier load or rear heavy load I’ll bump the pressure as required. Fully loaded I can crank the pressure up all the way and not overload my steer, although my tandem (single drive plus tag) could be overweight.
 

Hallback

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Jun 1, 2011
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Location
Aberdeen Wa.
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Gyppo tower logger
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?
If you are still looking for a good shop in the Puget sound area look up Scott Latherow Repair.
 

Hallback

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Aberdeen Wa.
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Gyppo tower logger
Dodge the scales at all costs!
In Washington you are required to have your drop axle(s) down when loaded, regardless of weight.
Screenshot_20200621-062718.png Screenshot_20200621-062727.png
 

hwrdbd

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May 6, 2013
Messages
21
Location
CT
Just want to add, once you get your weights figured out and set the pressure on your lift axle you don't want to be messing with the regulator all the time. You just use the dash switch to raise and lower it. It goes up in reverse to prevent damage if you forget to raise it on your own. Get in the habit of raising it when you pull into the jobsite.
 

PeterG

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Apr 14, 2015
Messages
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Location
Seattle WA, United States
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Landscape Construction, General Contractor
So I took the truck to Pape Kenworth and they have moved the pressure gauge to the outside. Did a good job, but a big hassle. They did not want to use the original handle which was working fine, but they finally did. They charged $243.81 for a $35 gauge! A metal bracket cost $156.84 and I had them install a new panel cover to cover the interior dash hole to complete the new oem look for $$189.58. Don't ask about labor! The exterior gauge is set to 60psi. I haven't done the scale thing yet. The interior gauge reads 51psi though! Regarding the lift axle down when loading, is that best for the truck or just needed for the State? Seems like you can do whatever you want until you touch a Public roads. I hauled a couple of loads of 12yds of dirt this week.
 

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hwrdbd

Member
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May 6, 2013
Messages
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Location
CT
So I took the truck to Pape Kenworth and they have moved the pressure gauge to the outside. Did a good job, but a big hassle. They did not want to use the original handle which was working fine, but they finally did. They charged $243.81 for a $35 gauge! A metal bracket cost $156.84 and I had them install a new panel cover to cover the interior dash hole to complete the new oem look for $$189.58. Don't ask about labor! The exterior gauge is set to 60psi. I haven't done the scale thing yet. The interior gauge reads 51psi though! Regarding the lift axle down when loading, is that best for the truck or just needed for the State? Seems like you can do whatever you want until you touch a Public roads. I hauled a couple of loads of 12yds of dirt this week.

You'll save yourself a ton of money if you can take care of simple mechanical work yourself versus going to the dealer.

In regards to using the lift axle, I'm not familiar with your state laws concerning axle weights and when you're required to use the axle, but I can give you some general guidelines. First thing you need to know is your empty weight. Next you need to find out your max legal weight with all axles on the ground. Comparing these two numbers you'll know how much payload you can legally haul. You'll also want to determine the max legal weight of a tandem axle/ten wheeler dump truck, for those times when you're only hauling a partial load. If you only have a few ton on, then you likely won't need to use the lift axle to maintain legal axle weights.
If you're running at your max weight or near it, then you'll absolutely want to have that axle on the ground while on public roads. When you pull out of the jobsite or quarry, put it down. When you pull into the jobsite or wherever you're dumping, lift it up. Out on the road you want it down both for your own benefit and to make the state happy. While running your max weight, having the axle down will prevent components from being overloaded, it will provide you all of the available braking your truck has to offer, and will be more stable than having it up in the air. Hope this helps.
 

PeterG

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The truck has axle temperature gauges in it. The front one runs hotter than the rear which I think is a bit normal. With the lift axle down, will I see a lower temperature on the front axle? Also, does anyone have a temperature gauge on the lift axle?
 

hwrdbd

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Messages
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Location
CT
The truck has axle temperature gauges in it. The front one runs hotter than the rear which I think is a bit normal. With the lift axle down, will I see a lower temperature on the front axle? Also, does anyone have a temperature gauge on the lift axle?
No the lift axle isn't going to affect your drive temps. Those are measurements of the gear oil in the differentials, which is dictated basically by how hard you're working the truck. Light loads no hill=low temps. Heavy loads pulling long hills=higher temps. You should realistically never reach problematic numbers in a dump truck, the weight just isn't there to put enough strain on the truck. If you do see temps climbing into the red then that might be an indicator of a problem within the axle.
As an example, guys that will see those temps rise to dangerous levels are generally heavy haul dragging 150k+ uphill for miles.
 

mitch504

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The other thing that will cause you to see high axle temps is low oil level.

Like hwrdbd said, you won't see a temperature gauge on a lift axle because it doesn't have gears.
 

PeterG

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Seattle WA, United States
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Many thanks for this information. Is there any issue with a steerable lift axle to make as tight a turn as you can loaded with the lift axle down? Is the tire sliding a bit or still rolling on a super tight turn when you have the steering wheel all the way turned? This would be making a tight U- turn in a parking lot, or at the end of a street, or onto a narrow side street etc. My lift axle tires have a lot of tread, but the tread does have some uneven tread wear.
 

hwrdbd

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CT
Many thanks for this information. Is there any issue with a steerable lift axle to make as tight a turn as you can loaded with the lift axle down? Is the tire sliding a bit or still rolling on a super tight turn when you have the steering wheel all the way turned? This would be making a tight U- turn in a parking lot, or at the end of a street, or onto a narrow side street etc. My lift axle tires have a lot of tread, but the tread does have some uneven tread wear.
Personally if I'm in a truck like yours I will still lift the axle on a super hard turn. Normal intersections aren't a problem, but if I was doing any sort of U turn I would definitely lift it. Just use your judgement, if you think its a really sharp turn then lift it.
One caveat to this- before you go lifting the axle on a public roadway make sure there aren't any cops around. I'm sure some won't bother you if they see you lift it momentarily for a hard corner, but I know for a fact that some will stop you for it.
Depending on what sort of uneven wear you are seeing, it could be a few different things. One of the most common I see is flat spots, usually caused by locking up the brakes. When you first lower the axle it takes a few seconds for the bags to build enough air pressure to actually put some weight on the axle. You want to avoid using your brakes right away if at all possible. Imagine you pull out of the job, drop the axle, and two seconds after you flip the switch a car cuts you off forcing you to slam the brakes. 99% chance that you're going to lock up the brakes on the lift axle and possibly flat spot the tires.
I'm not sure what your tire setup is, but many guys will run the steer tires down a ways, then swap them onto the lift axle and buy brand new steers. I would say this is most common with 385s and 425s. I say this because it is possible that the tires on your lift axle were used when put on, and may have been worn oddly from before.
 

PeterG

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Very good info. I was reading up about when to lock the rear axles together for more traction. There was no info on locking the rears with the lift axles. Just don't go over 25mph etc. I suppose if you backed into an area to dump and the rear wheels were slipping upon leaving you could lock the rears and move out in low, low gear. Putting the lift axle down might lift the truck a bit out of the rut, but then would you loose traction? Any thoughts on that? My suspension is Haulmax. Also, yesterday when I was leaving the place where I was loaded where the dirt and gravel road was rough it seemed like I could hear rapid air escaping. Does the lift axle suspension work by quickly releasing air from the air bags as the lift axle go up and down over speed bumps and rough terrain. I don't think the pressure gauge in the truck moved.
 

hwrdbd

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Very good info. I was reading up about when to lock the rear axles together for more traction. There was no info on locking the rears with the lift axles. Just don't go over 25mph etc. I suppose if you backed into an area to dump and the rear wheels were slipping upon leaving you could lock the rears and move out in low, low gear. Putting the lift axle down might lift the truck a bit out of the rut, but then would you loose traction? Any thoughts on that? My suspension is Haulmax. Also, yesterday when I was leaving the place where I was loaded where the dirt and gravel road was rough it seemed like I could hear rapid air escaping. Does the lift axle suspension work by quickly releasing air from the air bags as the lift axle go up and down over speed bumps and rough terrain. I don't think the pressure gauge in the truck moved.
Ya when you're offroad you want your axle up and as much weight as you can get on the drives for traction. I'm not sure what locking setup you have in the truck, if just an interaxle or full lockers. I wouldn't worry about running lockers at whatever speed, just make sure that you aren't already spinning if you're going to engage any locker. If you do have full lockers you aren't going to have quite the same turning capability if you have them all locked up. It will want to push you straight. Just be careful with the full lockers though, only using when you're on slippery stuff. You never ever want to lock everything in on pavement and try to turn, especially loaded. Make sure you get them disengaged once you get out of the mud/snow/whatever and before you get yourself back on the road.
In your scenario of slipping as you pull back out after dumping, you would stop the truck and lock up, get yourself out to solid ground, then just flip them back to the unlock position-no need to stop to unlock. It can work just like 4x4 in a pickup, and maybe take a little bit of distance for them to actually disengage.
In regards to the air you're hearing, yes that is just the bags on the axle dumping air to keep from over pressuring themselves. Your knob adjusts the psi they are supposed to max out at (in order to set desired weight on that axle) and as you drive over uneven ground sometimes the axle will be pushed upward so far that it compresses the bags, effectively increasing the pressure in them. This activates the pressure relief and some air is let out to keep the axle from taking too much weight. Totally normal.
 

PeterG

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Regarding the drives, which axle is always driving? Is it the front rear axle or the rear, rear axle? I have an Allison RD4500 I'm still learning how to utilize it fully. Seems as though you can put it in drive low, and then even lower the low by pushing the down button. I will have to see which locking rear axle I have. I believe it's just a far switch on the right side of the panel. What do most 2007 Kenworths T800's have? This was always a dump truck. What is the difference between full lockers, and interaxle?
 

mitch504

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Both axles are always driving, it's just like the differential in a car.

Actually, many people are confused about that. An open diff ALWAYS APPLIES EQUAL TORQUE (twisting force) to both sides, or both differentials in the case of an interaxle diff on a tandem truck. When one slips, it can't apply any more torque to one side than the other.

All tandem trucks can lock the differential between drive axles, some can lock the side-to-side diff in one or both axles, That's a full locker.
 

hwrdbd

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May 6, 2013
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Location
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Regarding the drives, which axle is always driving? Is it the front rear axle or the rear, rear axle? I have an Allison RD4500 I'm still learning how to utilize it fully. Seems as though you can put it in drive low, and then even lower the low by pushing the down button. I will have to see which locking rear axle I have. I believe it's just a far switch on the right side of the panel. What do most 2007 Kenworths T800's have? This was always a dump truck. What is the difference between full lockers, and interaxle?
Trucks can be spec'd very different from one to the next, depending on who ordered it, where it was intended to run, what kind of job it was meant to do. Post a pic of the switches if you can. If the label isn't worn off the rocker switch it will probably give you a clue as to the locker setup you have. If it is only one switch, then I would guess a simple interaxle lock, but I suppose thats no guarantee.
Just to elaborate on an earlier reply, an interaxle locker just guarantees that you are sending power to both drive axles. Each axle would still operate with an open differential, ultimately meaning you will see one wheel spin on each axle if you get stuck. Full lockers would be when you have the interaxle, plus a locking differential in both drive axles. This would guarantee that both sides of both axles would always be turning together.
 
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