Towing a large fifth-wheel trailer like ours requires careful and consistent adherence to various procedures to ensure that the rig and its contents arrive safely at the destination. Just like when I was piloting airplanes, Cheryl and I both use “checklist flows” for securing the interior and exterior of the RV, hitching and unhitching the trailer, and so on.

What is a trailer tug test?

One of our sacrosanct procedures when hitching up is called a “tug test” or “pull test”. After we visually confirm that the fifth-wheel hitch in the bed of our truck is closed and locked around the trailer’s kingpin, we raise the trailer’s front landing gear about an inch off the ground. Then I start the truck, depress the brake pedal, put the transmission in drive, hold the trailer brake controller to lock up the trailer brakes, and release the truck’s brakes. The trailer brakes should keep the entire rig from moving forward. (Our friends at Mortons on the Move have an excellent blog post that describes the procedure in detail.)

The tug test serves two important purposes. First, it proves that the trailer is securely hitched to the truck. If it isn’t–maybe because the hitch jaws aren’t properly closed, or the safety pin on the hitch isn’t engaged–the truck will roll forward and the trailer will drop an inch to the ground on its landing gear. When this happens (and we’ve had it happen once!), it is LOUD! But because the trailer lands on its landing gear rather than on the side rails of the truck bed–or even worse, comes detached while towing–nothing gets damaged other than our egos.

One reason for the tug test is to ensure that the trailer won’t detach from the truck, dropping on the bed and causing damage like this. (NOT OUR TRUCK!)

Second, and equally important, the tug test confirms that the trailer brakes are working properly. If they aren’t, the truck will pull the trailer forward during the test rather than the trailer remaining in place. This purpose of the tug test is just as important as verifying the security of the hitch–but for some reason, it’s rarely noted as a reason for the test. In fact, I’ve seen some instructions for performing a tug test that say to leave the landing gear on the ground and the trailer wheels chocked. Although this method will indeed verify the integrity of the hitch, it won’t tell you anything about the trailer brakes, because the landing gear and chocks will probably keep the trailer from moving even if the trailer brakes aren’t working.

A scary discovery

Last week, we discovered first-hand just how critical it is to test the trailer brakes. We were preparing to leave Loveland, Colorado for a one-hour drive to Estes Park, climbing into the Rocky Mountains where 6-8% grades are common. We did our tug test like usual…and the truck pulled the trailer forward a bit, even with the throttle at idle. We were both confused, as we’d never experienced this in the more than 300 times we’d done the test. We tried again and got the same result. We then double-checked the umbilical connection between the trailer and the truck, even though the truck indicated that the trailer was properly connected, and repeated the test…same result again.

Since our checkout time at the state park had passed, we slowly and carefully towed the trailer along the park’s level roads to a parking lot where we could troubleshoot the problem. The brakes had worked perfectly two days earlier, so why were they not working at all now? I started at the brake fluid reservoir, and the cause quickly became apparent: the reservoir was empty and there was a puddle of brake fluid on the floor of the compartment where the reservoir was mounted. After more investigation, I discovered that the flare nut on the outlet line from the reservoir was slightly loose, allowing the brake fluid to slowly drain from the reservoir over the last couple of weeks.


We unhitched the truck from the trailer and drove to a nearby Walmart to get some brake fluid and a roll of disposable shop towels. After mopping up as much of the puddle of brake fluid as I could, I tightened the flare nut, refilled the reservoir, and bled all six brake calipers (something I didn’t know how to do, but the service manager at New Horizons talked me through it). Then we hitched up again and repeated the tug test. This time, the trailer held the truck securely in place, just like it was supposed to.

David under the Majestic, bleeding the brake system. Another new skill learned.

As we finally got on the road–just four hours later than we had planned–we were both shaken. Had we not performed the tug test, the truck’s brakes would probably have been enough to stop the trailer on level ground. But on one of those steep Rocky Mountain downgrades, the brakes on our 9,000-pound truck would have been no match for the more than 24,000 pounds of trailer behind it, and the result would almost certainly have been catastrophic.

If your trailer brakes fail on a steep mountain downgrade, you might get to experience a runaway truck ramp like this one on I-70 near Silverthorne, CO. Not a fun ride, and guaranteed to cause expensive damage.

Never skip the tug test

What’s remarkable is that we rarely see other fifth-wheel owners perform a tug test before they drive off with their trailers. Maybe some feel it’s not needed–after all, most fifth-wheel hitches allow you to visually confirm that the hitch is closed and locked, so perhaps they think the tug test is redundant. Or maybe they just think, “this won’t happen to me”. We’ve even had some owners run over while we’re performing our tug test to warn us because they think we’re trying to leave with the landing gear still extended! Incredibly, they have no idea what we’re doing until we explain it to them.

If you tow a fifth-wheel trailer, never, ever skip the tug test every time you hitch up! Even if you tow with a gooseneck-type hitch, which supposedly can’t accidentally disconnect, you still need to test the trailer brakes. The tug test will almost always seem unnecessary…

…until that one time when it isn’t.

A trailer tug test saves the day
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2 thoughts on “A trailer tug test saves the day

  • May 31, 2023 at 10:14 am

    Excellent advise. Never thought to do this w our 34’ ultra lite to test the brakes beyond locking them up on purpose when going super slow to make sure they engaged. But I learned a new way to test the brakes from your post. Thanks and glad you caught this before your travels.

  • May 31, 2023 at 12:59 pm

    Bill does a tug test every time and while we’ve not had an issue, we know people who should have done one and didn’t – with disastrous results. Good for you for staying with your checklist and avoiding what could have been BAD!


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