Engineered spring systems for cargo & enclosed trailer ramp doors

A ramp door should lift with one hand.

If your door takes two people, hurts your back or has you saying a prayer, the springs are wrong or worn. We engineer and build M-3™ spring systems matched to your door's weight and geometry, so it lifts easily and lowers under control.

Size my door How sizing works

M-3™ has designed dual-spring assist systems for trailer ramp doors since 1995. Engineered in Elkhart, Indiana by Wait Industries.

Sound familiar?

Worn springs don't fail politely.

Ramp door springs work every time the door moves, and they wear out long before the trailer does. A door that fights you is telling you something.

  • The door gets heavier every season. Now it's a two-person job.
  • It slams down instead of lowering under control.
  • Cracking or popping sounds from the spring tube.
  • The door sits crooked in the opening, or one side lifts first.

Size & quote

Tell us about the door. We'll do the math.

These are the same measurements our engineers put into the M-3 spring calculator. Send them once and a person who sizes ramp doors every day will reply with the right system, usually within one business day. Prefer the phone? 574-264-9504, Monday to Friday, Eastern.

1. Your door Measure in inches with the door closed unless noted. The diagram shows each one. Not sure of one? Tick "not sure" and we'll follow up.
Hinged weight: lower the door flat and rest its free end on a bathroom scale.
From the hinge to the top edge of the door.
Width of the door opening. The torque tube can be cut down to fit your door; we’ll confirm the minimum width for your system.
From the ground to the door hinge.
From the hinge up to the centre of the spring tube.
From the top edge of the door (its free end) down to where the cable attaches. This one matters most. Please measure it.
choose steel, aluminum or not sure.
choose the cable setup or not sure.
Custom or unusual brackets? Choose "Custom" and an engineer will check the fit with you.
Nothing is sent until you press "Request my quote".
2. Where to send your quote
enter your first name.
enter your last name.
enter a valid email address.
choose one.
please add the trailer make.
please add the trailer model or size.

We use these details to size and quote your door and to follow up on this request. They are stored in our customer system (HubSpot) and seen only by Wait Industries staff. We don't sell them or share them for anyone else's marketing, and we won't add you to a mailing list. To see or delete what you sent, email sales@waitindustries.com. We usually reply within one business day.

Three ways to buy

M-3 spring systems for every door, and every buyer.

M-3 spring systems, by Wait Industries

For trailer manufacturers

OEM programs

Production-volume spring systems engineered to your door design and delivered on your schedule from our Elkhart plant. Send us the door drawing and we'll specify the assembly.

Start an OEM conversation

For dealers & repair shops

Replacement kits

Complete kits sized to the door, with everything the job needs in one box and step-by-step instructions.

Dealer & distributor inquiries

For trailer owners

Retrofit & repair

Your trailer, fixed right. Send the door measurements and we'll match the system, with install instructions in the box.

Fix my door

Sizing is everything

Real measurements pick the right system.

  1. Weigh & measure

    Door weight sets how much lift the springs must give. Door height, hinge height, spring-tube position and cable attachment set how that lift is delivered. The form asks for each one.

  2. We size the system

    Our engineers run your door through the M-3 spring calculator and pick a system that balances the door without over-springing it. A door that flies up is as wrong as one that slams.

  3. Confirmed, then shipped

    You get the system and the price to approve before anything ships. Kits ship with instructions and safety guidance.

Who makes them

Designing ramp door spring systems since 1995.

M-3 & Associates began designing dual-spring assist systems for enclosed trailer ramp doors in 1995. Wait Industries acquired the M-3 business in 2017, and today M-3 is a division of Wait Industries, a full-service metal fabricator in Elkhart, Indiana. The same M-3 systems we supply to trailer manufacturers ship to your shop or driveway.

Need fabrication beyond springs: laser cutting, welding, powder coating or complete assemblies? That's the parent company, waitindustries.com.

1995designing spring systems since
Elkhart, INengineered & shipped
Welded steel brackets hanging on the finishing line conveyor at the Wait Industries plant in Elkhart
On the finishing line at our Elkhart plant.