The roll-up door is stuck, falling or will not latch. What is going on back there?

How a roll-up door is meant to work

A trailer roll-up door is a curtain of hinged panels running in two tracks, one on each side of the rear frame. Rollers at the panel edges ride inside the tracks, so the door can curve from vertical to horizontal and slide up under the roof when it is open.

The door is heavy, and what lets you lift it by hand is the counterbalance system. On most trailer doors that is a spring or a set of springs wound under tension on a shaft above the opening, connected to the bottom of the door by cables or straps. As the door comes down, the spring winds tighter and stores energy; as the door goes up, the spring gives that energy back and does most of the lifting. A properly balanced door stays roughly where you leave it and lifts with a steady pull.

At the bottom, a lock bar or latch engages keepers on the rear frame to hold the door shut, and seals along the edges keep water and dust out.

Read the symptom first

Before touching anything, work out exactly what the door is doing. Each symptom points to a different part of the system.

• Suddenly very heavy, dropping, or will not stay up. The counterbalance is not doing its job, usually because of a broken spring or a snapped or slipped cable. This is the most dangerous symptom, because a door with no counterbalance can fall under its own weight.
• Jams partway, binds or goes up crooked. Rollers out of a track, a bent track, a cable off its drum on one side, or a damaged panel catching.
• Will not come down all the way. Something is in the way: a bent track, a jammed roller, freight or a load bar in the doorway, or ice in the bottom of the tracks.
• Closes but will not latch. A bent lock bar or keeper, a door that is not reaching the bottom, or a rear frame knocked out of square.
• Will not open at all. A frozen or seized lock, ice sealing the bottom panel to the sill, a jammed track, or freight pressing against the inside of the door.

The usual causes

Once you know the symptom, the cause is usually one of these.

• A broken counterbalance spring. Springs fatigue with use and can snap without warning. TODCO, a major trailer door maker, warns in its owner's manual not to operate a door with a broken counterbalance spring, because the door is no longer counterbalanced and will fall if opened.
• A frayed, broken or slipped cable. Cables wear where they wrap and rub, and one that breaks on one side leaves the door lifting unevenly and jamming. TODCO advises having frayed, damaged or worn cables replaced.
• Rollers off the track. A door forced while it is binding, or pushed from inside by freight, can pop rollers out of the track and leave the door hanging crooked.
• A track bent by forklift contact. A forklift mast or load that clips the track or the header at the dock bends it inward just enough to stop the rollers. A door that jams at the same point every time often has one.
• Bent or damaged panels. A panel dented by freight, a forklift or a backing mishap can catch in the track and stop the door closing flat.
• Ice. Water collects at the bottom of the tracks and under the bottom panel and freezes, locking the door to the sill or blocking the rollers.
• A bent lock bar, keeper or rear frame. A rear frame that has been hit, even lightly, can be pushed out of line so the lock no longer meets its keeper.

The safety rules around trailer doors

Door faults look minor, but the risks around them are serious, and they are the reason to slow down before pulling on anything.

• Leave the springs alone. Counterbalance springs store a great deal of energy, and releasing it the wrong way can cause severe injury. TODCO's manual tells owners not to try to adjust or repair the spring or counterbalance assembly. Do not loosen set screws, remove brackets or cut cables on a door under spring tension.
• Stay out from under a moving door. A door with a failed spring or cable can drop without warning. Never prop up a door that will not stay open and then work beneath it.
• Assume a shifted load may be leaning on the door. The door may be the only thing holding the freight in, and opening it can bring cargo down on whoever is standing behind the trailer. Our post on a load that shifted on the highway explains the signs and what to do instead.
• Check whether the load is sealed. Do not cut a seal or force a sealed door open to diagnose a fault without authorization. Call your dispatcher or the carrier first; they know what the shipper and receiver require. This is not legal advice, and the carrier is the right source for the rules on your load.

What a driver can safely try

With the trailer parked and secured, look along both tracks from the ground for a bend, a roller sitting outside the track or something wedged in the channel. Check the lock bar and keeper for bending and make sure the lock handle moves freely. In freezing weather, look for ice at the bottom of the tracks and along the sill, and clear it without prying on the panels or striking the tracks, which bends them further.

If the door is simply stiff, TODCO recommends lubricating the rollers, hinges and bearings, and having a trained service person check it if it stays hard to move. Do not force a binding door; pulling harder is how rollers leave the track and panels bend. If the door is heavy or falls, stop cycling it to see whether it gets better.

Why a door fault can hold up a load

A trailer with a broken door drives fine and still cannot do its job. A door that will not close cannot secure the freight, one that will not latch can open in transit, and one that will not open means the load cannot be delivered. On a reefer, a door or seal that will not close lets cold air out and puts the load's temperature at risk even with nothing wrong with the refrigeration unit itself. Our post on a reefer that has gone down covers the temperature side of that problem.

What gets repaired on site, and what goes to a body shop

Roll-up and swing doors, hinges, latches, seals and damaged rear frames are all on our trailer repair list, whether the trailer is on a shoulder, at a dock or dropped in a yard. Rollers that have left the track are reset, bent track sections are straightened or replaced, cables and latching hardware are replaced, and seals are renewed so the door closes tight. Counterbalance work is done by someone trained for it with the proper tools, which is exactly why it should never be a driver's job. Tell us the door make if you can see it, so the right parts come on the truck.

There is an honest limit. A door torn out of its tracks with several panels crushed, a rear frame hit hard enough to need structural straightening or welding, or a damaged roof header is bodywork for a shop, and structural welding is not something we do. In that case we will make the trailer secure enough to move where that is possible and safe, tell you plainly that it needs a body shop, and tow it there if it cannot be driven.

Before you make the call

Describe exactly what the door does: heavy, falling, jammed partway, crooked, will not latch or will not open. Say whether you heard a bang when it failed, which often means a spring. Tell us whether the trailer is loaded, whether the load could have shifted, whether it is sealed and whether it is a reefer. Give us the location, the unit number and the gate procedure if it is in a yard, and send a photo of the door and tracks if you can take one from a safe spot.

Related reading

Leaking Wheel Seal: Oil on the Inside of a Truck Wheel — Oil or grease slung across the inside of a wheel, tire or brake usually means the wheel seal is leaking the lubricant that protects the bearings.

Leaking Glad Hands: Red or Blue Trailer Air Line Fixes — Most leaks at the glad hands come from a worn, torn or missing rubber seal, a bent or mismatched coupler, or a hose that has chafed or kinked where it hangs between tractor and trailer.

Trailer Landing Gear Won't Crank? Causes and Roadside Repair — When landing gear will not crank, the legs are usually seized from rust or dry grease, stripped inside the gearbox, or being forced to lift a load in high gear.