[tdriver1959]

I know that most of the lift axles on tractors are steerable. if they were not they sure are hard on the tires

[Mackman]

I allways put up the lift axle on a turn its hard on the truck and you don't have no turn radius with it down. I would need 40 acers to make a turn if i didn't lift it up. That's on a tri axle straight truck am talking about not a trailer.

[Jumbo]

Here in Wisconsin and Michigan I believe the rule is that the switch can be inside but the regulator must be outside to keep us outlaws from cheating the scales. On the other hand, I haven't heard of anyone getting ticketed for the regulator being inside. It is normal that the new trucks have the regulator on the outside.

[yoopr]

All our Tag axle switches are on the Inside and this Outside Tag axle switch is beyond my Comprehension.

[Myth_Buster]

?393.207 Suspension systems.

(a) Axles. No axle positioning part shall be cracked, broken, loose or missing. All axles must be in proper alignment.

(b) Adjustable axles. Adjustable axle assemblies shall not have locking pins missing or disengaged.

(c) Leaf springs. No leaf spring shall be cracked, broken, or missing nor shifted out of position.

(d) Coil springs. No coil spring shall be cracked or broken.

(e) Torsion bar. No torsion bar or torsion bar suspension shall be cracked or broken.

(f) Air Suspensions. The air pressure regulator valve shall not allow air into the suspension system until at least 55 psi is in the braking system. The vehicle shall be level (not tilting to the left or right). Air leakage shall not be greater than 3 psi in a 5 minute time period when the vehicle's air pressure gauge shows normal operating pressure.

(g) Air suspension exhaust controls. The air suspension exhaust controls must not have the capability to exhaust air from the suspension system of one axle of a two-axle air suspension trailer unless the controls are either located on the trailer, or the power unit and trailer combination are not capable of traveling at a speed greater than 10 miles per hour while the air is exhausted from the suspension system. This paragraph shall not be construed to prohibit-

(g)(1) Devices that could exhaust air from both axle systems simultaneously; or

(g)(2) Lift axles on multi-axle units.

The rule applies to air system exhaust not lift axles.

Be safe.

[Fredog]

the air exhaust IS a ift axle, it exhausts the air which makes the axle lift up

[Myth_Buster]

(g) Air suspension exhaust controls. The air suspension exhaust controls must not have the capability to exhaust air from the suspension system of one axle of a two-axle air suspension trailer unless the controls are either located on the trailer, or the power unit and trailer combination are not capable of traveling at a speed greater than 10 miles per hour while the air is exhausted from the suspension system. This paragraph shall not be construed to prohibit-

(g)(1) Devices that could exhaust air from both axle systems simultaneously; or

(g)(2) Lift axles on multi-axle units.

Depending on the design of the axle. If there is a device that lifts an axle, i.e. spring then the rule prohibiting the air from being exhausted doesn't apply. If the system only deflates the air bags on one axle (without lifing it) the system cannot be activated from inside the cab.


Be safe.

[Fredog]

Here is the answer I got from askthelaw.org.. it is all clear as mud now.


This used to be one of the things I looked for when working the road. I would look for vehicles that had lift axles and would love to stop them when they had the lift axles up in the air. By the time I got them stopped, the lift axle was usually down. I would tell them that I saw them operating the vehicle with the lift axle up, so I would make them raise the lift axle up and then proceed to weight them. Inferably, I would get a weight case because they would need the lift axle to be down so they would not be overweight.

If you are operating the vehicle, when loaded, with the lift axle down, then that axle will be used to calculate you allowable weight.

Now there is a regulation in Part 393.207(g) (attached below) on where the exhaust valve for a lift axle can be located. He maybe getting the 2 confused.
(g) Air suspension exhaust controls. The air suspension exhaust controls must not have the capability to exhaust air from the suspension system of one axle of a two-axle air suspension trailer unless the controls are either located on the trailer, or the power unit and trailer combination are not capable of traveling at a speed greater than 10 miles per hour while the air is exhausted from the suspension system. This paragraph shall not be construed to prohibit-

(g)(1) Devices that could exhaust air from both axle systems simultaneously; or

(g)(2) Lift axles on multi-axle units.


Note: The State of Georgia could have a law that supercedes Federal law on "lift axles".





Thanks for the question. Hope this helps.



Sr. Trooper Monty Dial
Texas Highway Patrol
Commercial Vehicle Enforcement Division
Garland, TX 75043

[Myth_Buster]

Section 393.207—Suspension Systems

In response to a petition from the Truck Trailer Manufacturers Association (TTMA), FMCSA is amending § 393.207 to prohibit any device which is capable of dumping air individually from either of the two axle suspension systems on a semitrailer equipped with air-suspended ‘‘spread’’ or ‘‘split’’ tandem axles. TTMA indicated that the petition was not intended to prohibit:

(1) Devices that could exhaust air from both axle systems simultaneously, or

(2) lift axles on multi-axle units. The petition is available for review in the docket.

According to the TTMA, about 30,000 semitrailers are manufactured each year with split tandem axles and air suspensions. These axles are not
genuine tandems, but rather two single axles spaced at least 3,048 mm (10 feet) apart, the minimum separation required by the bridge formula [23 U.S.C. 127(a)] before each of them can carry the full 9,072 kg (20,000 pounds) allowed by Federal law. The TTMA estimates that 5,000 of these trailers are also equipped with valves to depressurize the
suspension system of one of the trailer axles, and sometimes of either axle. These valves are installed to compensate for problems created by the split tandem configuration. Normal tandems experience moderate tire
scrubbing in turns because the trailer pivots around a point that lies between the two axles. Tire scrubbing is more severe in split tandems because the pivot point is much farther from either axle. Dumping air pressure from the suspension system of the rear (or less often the leading) trailer axle reduces its load and allows the trailer to pivot
around the other axle with less resistance and tire scrubbing. The
TTMA’s own tests showed that if each axle in a split tandem is loaded to 8,845 kg (19,500 pounds) and pressure in the rear axle is dumped, the resulting weight shift will make the front axle 3,175 to 5,443 kg (7,000 to 12,000 pounds) heavier than the rear.

Dump valves were originally designed to aid maneuvering at 8 km/hour (5 mph) or less, mainly at terminals or other loading points. According to the TTMA, however, many drivers now activate them at higher speeds on streets and highways to turn corners more easily and to reduce tire wear. The TTMA also believes that suspension pressure is sometimes vented
accidentally because of wiring problems the moment the tractor hooks up to the trailer. In both cases, the inevitable weight shift often produces a load on the pressurized axle that exceeds the manufacturers’ ratings for that axle and its wheels, tires and brakes. In addition, the loaded axle frequently exceeds the single-axle weight limit.

FMCSA continues to believe the petition has merit, and the agency is
amending § 393.207 to prohibit controls of this type. Although § 393.3, which allows the use of equipment and accessories that do not decrease
operational safety, could be interpreted as prohibiting the use of equipment to disable the air suspension of one axle on a two-axle trailer, addressing this issue through rulemaking is the most appropriate course of action.

FMCSA has modified the language included in the 1997 NPRM in response
to comments from the ATA. ATA agreed with the proposal, but expressed
concern that motor carriers need the flexibility to exhaust air from the
suspension during low-speed turns. ATA believes this is necessary because there is significant resistance or tire scrubbing when drivers make low-speed turning maneuvers with a spread tandem trailer. FMCSA agrees and has revised the language to allow the exhausting of air if the controls are either located on the trailer, or the power unit and trailer combination are not capable of traveling at a speed greater than 10 miles per hour while the air is exhausted from the suspension system.

The above information is from the Federal Register from when Part 393.207 was changed. The Federal Register is the explanation of why a rule was interduced.

Be safe.

[Fredog]

problem solved, the mechanics installed a switch outside and also left the switch inside, now I have an outside switch to use if the dot asks, and an inside switch to use as I need to.