Scale Ticket, Slack Chain, and a Coil That Moved
At a weigh station your 5-axle combination scales: steer axle 11,600 lb; drive tandems 33,900 lb; trailer tandems 32,700 lb; gross 78,200 lb. Your company enforces the legal limits of 12,000 / 34,000 / 34,000 / 80,000. The load is three 21,000-lb steel coils on a flatbed. At the shipper you watched the middle coil get chained down. At this stop you notice the front chain on that middle coil is slack enough to lift off the deck by hand, and there is a fresh scrape mark in the deck 4 inches behind where the coil now sits. The tandem slide is free to move and there is 6 feet of rearward travel available.
1. Which axle is the real problem, and which direction would you slide the trailer tandems - and what happens if you slide them the wrong way?
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The drive tandems are the problem: 33,900 against a 34,000 limit leaves 100 lb of margin, while the trailer tandems have 1,300 lb and gross has 1,800 lb.
Sliding the trailer tandem rearward increases the distance from the kingpin to the trailer axles, which puts a larger share of the trailer's weight on the trailer tandems and a smaller share on the fifth wheel - so weight comes off the drives and onto the trailer axles. That is the direction you want.
Sliding forward does the opposite: it loads the drives further and you would be over 34,000 before you left the scale. Sliding rearward also must be checked against the trailer tandem limit and against any state bridge/axle-spacing rule; on a short trailer a big rearward slide can create a spacing problem even while fixing the axle weights.
One caveat: with 100 lb of margin, you are one fuel stop away from being overweight. The 4-inch scrape suggests the coil has moved, which may be the actual cause of the heavy drives - so correct the load before you correct the axles.
2. What do the slack chain and the fresh 4-inch scrape tell you, and what must happen before the truck moves?
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They tell you the coil has moved forward about 4 inches and the securement has either failed or was never adequate. A slack chain on a coil that has shifted is not a cosmetic issue - the chain is slack precisely because the load traveled and took the tension out of it.
The truck does not move. A 21,000-lb steel coil that has shifted is not secured, and a coil that is free to roll forward under braking will go through the bulkhead, the cab, or the traffic ahead.
Before moving: reposition the coil to its blocked position, re-block and chock it so it cannot roll (coils are secured against rolling with chocks, racks, or a cradle, not just chains over the top), re-tension and re-check the entire tiedown system including the other two coils and their dunnage, and verify the aggregate working load limit of the tiedowns suits the load. Then reweigh. The forward shift is also the likely explanation for the heavy drives, so fixing the load first may make the tandem slide unnecessary or much smaller.
3. You reposition and secure the load, then reweigh: drives 34,150, tandems 32,450, gross unchanged. What is your next step, and what would be a mistake here?
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You are now 150 lb over on the drives with 1,550 lb of capacity on the trailer tandems, so the correction is a small rearward slide of the trailer tandem and then a reweigh.
- Move the slide a modest amount rather than all 6 available feet - a full rearward slide could fix the drives and overburden the tandems or create a spacing violation.
- Weigh again. Weight transfer per inch depends on where the load sits over the trailer, so you cannot calculate it reliably from the ticket; guessing and rolling is how drivers get put out of service at the next scale.
Mistakes to avoid: topping off fuel before the reweigh (fuel is weight carried largely by the drives on most tractors, so you would silently eat your margin back); sliding the tandems forward because it looks like the trailer axles are the light ones; and accepting 'close enough' on the drives. Also confirm that after the slide the landing gear, mud flaps, and trailer tires clear the tractor - a slide that puts the trailer tires into the tractor frame is not a fix.