Kent Sundling: Mr. Truck 2-27-12 |

Kent Sundling: Mr. Truck 2-27-12

I’m sure you’ve noticed semi trucks and trailers have air bag suspensions. The semi-tractors have had air bag axles, air ride cabs and air seat for decades. Our pickup trucks are rated for larger trailers and payloads each model year. Why aren’t we copying how semi trucks are made? Larger trailers and payloads also means more rear axle squat and more axle travel between empty and loaded. That difference between a loaded and empty truck, changes the pinion angle effecting the drive shaft alignment with the end of the transmission. When the angle from transmission to rear differential isn’t a straight line, your truck will buck, shake and pitch.

This is a growing problem in the last 10 years with truck manufactures trying to split the difference in pinion angle from loaded to empty by shimming the differential angle. This is not a good fix for the problem, but a band aid. The right way to solve the pinion angle problem is a total air bag suspension that self levels to keep pinion angle the same all the time automatically. Whether you are hauling one horse or four horses, the truck will be level.

We keep our trucks longer, Auto Flex air suspension can make it handle better than new. Fixing up your truck instead spending $60,000 on a new truck makes sense now more than ever. Gas engines can last 200,000 miles and diesels 300,000. We’ve been talked into trading trucks often but I say save money, keep your truck longer.

Auto Flex can dramatically improve your trucks ride and handling. Keeping your truck level automatically, with better braking, and handling curves flatter. Headlights won’t be star searching and oncoming traffic won’t be flashing you. Have you ever had your truck full of feed or a slide in camper and the truck squatted and wandered, making driving work? The suspension your truck came with is a compromise.

We installed two Auto Flex Systems and tested on different trucks, both diesels both 3/4 ton’s that tow trailers as part of their job description, both had aftermarket air assist. One was a 2006 Ford F250 diesel, with 129,000 miles new front brakes. Second was a 2006 GMC 2500 diesel, with 104,000 miles new front brakes.

It is easy to install as bow replaces the factory leaf springs, eye to eye replacement. No welding or drilling, just chain the axle, each side to the frame, put a jack stand under the pinion and take the leaf springs off. You’ll reuse the rear hanger on the new bow arm to fit where the spring was. Then you attach the lower swing arm to the axle and the front of the bow, add the air bags, compressor and tank. The tracking bar goes from the drivers side bow to the passenger side lower swing arm. All that’s left is the leveling valve from cross member to the differential, air lines and juice. AutoFlex comes with a dump valve to lower the truck to ease hooking to a trailer. Each air bag comes with a valve to lock air in or out. This allows you to level a slide in camper on uneven ground or hold air in the bags if you have a line leak.

It comes with all brass fittings, no 45 or 90 degree fittings in line from tank to air bags. This makes the air flow faster for the automatic leveling system. The steel braided line from the compressor to the tank makes for faster flow and pressure using a high performance air compressor with a check valve. The compressor has 20 amp fuse and fills a three gallon air tank. I went with the optional five gallon air tank. With the performance compressor putting out 120 psi, I can run an impact wrench to change tires. The system comes with a female coupler for attaching air hoses for airing up truck and trailer tires.

It also comes with new hydraulic shock absorbers. The air lines are 3/8-inch just like the semi-trucks. That keeps them from freezing as well as the compressor tank and brass drain petcock. My old system aftermarket air bag helper springs would freeze the 1/4 air line each winter. Then they stopped working until they thawed out, and you couldn’t do anything to speed that up. AutoFlex was developed in the cold part of Canada, if they don’t freeze there, I should be in good shape in Colorado.

Auto Flex and Trailer Flex are manufactured by LBC Trailers. They’ve been making logging trailers with lift-able axles since 1998. Fourteen years of building semi trailers with air suspension, I’d call that well tested.

Auto Flex single stage air bags self center. Double bellows used in after market air assist products, just support weight but aren’t a real suspension. Auto Flex is not an add on, but leaf spring replacement. No drilling, welding or cutting your truck means is doesn’t affect your warranty. The on-board air compressor adjust the pressure inside the air bags to match a truck’s load.

If you experience compressor or air line failure, each bag has a valve for filling or shutting off bags. Rubber stops inside air bags are there incase of air loss, you can still drive to get repaired. With an automatic leveling valve you don’t have to think about it. Just enjoy it.

Both trucks nosed dived braking from 60-0 mph with stock leaf springs. With Auto Flex there was less body roll, most trucks don’t have anti-sway bars anymore. The handling improved and the ride improved with more wheel travel. In our brake test stopping from 60 mph, factory leaf springs stopped in 133.9 feet verses 120.7 feet with Auto Flex, 13.2 feet shorter with the Ford F250. More controllable handling under braking.

During acceleration, the air bag pushes up on the truck body pushing down on the axle for more traction and better fuel mileage.

Wheel hop and pinion angle deflection are hard on U-joints. Imagine always being level in your truck, no sagging and being level with different trailers and heavy loads. You don’t always haul the same load with your trailer, so sometimes, the trailer is level and sometimes it goes down hill. Brakes on your trailer work best when an equal load is on both axles. The dump valve will lower your truck 5-inches to get under your gooseneck without as much cranking on the trailer jack.

The steering problems are not just from the front, with a loose rear suspension, the truck can wander. Auto Flex takes the slack out of the rear suspension. The two test trucks we used had over 100,000 miles on them and dramatically improved handling and steering after Auto Flex was installed.

If you race your truck or just accelerate when passing or the on ramp to the freeway, you’ve experienced axle rap from flexing both sides of the axle on leaf springs. This air suspension eliminates axle rap. When the rear of the truck squats, this changes the frame angle which changes the drive shaft angle to the pinion.

Adjustable tracking bar makes for tighter suspension. Your rear end won’t be doing the Elvis pelvis action. Auto Flex air bag is behind the axle for leveraging the trailing arm and is as wide side to side as leafs for stability and less teeter toter action than you get with after market air assist bags that are inside the leaf springs. Aftermarket air assist bags puts pressure on one spot on the axle and frame. With Auto Flex, the air bag pushes on the replacement bow not the frame.

For more information, please visit or call (807) 623-0590.


Kent Sundling (alias “Mr. Truck”) spent 20 years wearing out pickup trucks as only a farmer could. With over 1 million miles pulling trailers, Mr. Truck has a unique collection of truck and farm stories that will educate and entertain. Mr.Truck gave up his bib overalls and John Deeres in his quest to save the farm and moved to the big city to sell trucks. After selling trucks for 10 years, this farmer now writes for eight magazines and owns over two dozen Web sites, helping folks find the “Right Truck.” If you have a question for Mr. Truck, you may contact him at his Web site,

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