Ramp Door Spring Systems FAQ
Specify a Ramp Door Spring System
To properly size a ramp door spring system, please complete the following form. We will crunch the numbers for you and provide quick feedback on the right system for you. Alternatively, you can complete the following sheet and send it back to us.
How to Measure for a Ramp Door Spring Assist System?
Door Height – It is also helpful to know the distance from the top of the door to the end of the open door. This is an easy check to be sure the cable will be long enough. Standard cable lengths are 150”. Lengths of 110”, 125”, and 174” are also available and can be substituted in any standard system. Standard M-3 drums require 13” of cable to remain on the drum when the door is open. This is a safety precaution that insures that the cable does not disconnect from the drum.
Header Width – Width of available headroom inside of the trailer. This determines the length of tube in the spring assist.
Frame material of trailer – Spring assist systems are built with either steel or aluminum weld brackets that attach to the header above the door frame.
Ramp door hinge style – M-3 spring assist systems are designed to be used on doors with pipe-style hinges attaching the ramp door to the trailer frame. Spring-type hinges should not be used with M-3 spring assists as they alter the physics of the door and you will not achieve satisfactory lift.
Please use the following M-3 Spring System Spec Template to help us size your system. Fill in the relevant information and send it to us. We will respond with a system that will meet your needs.
Altering the Length of the Tube On Spring Systems
The tube on spring systems can be shortened by cutting the tube with a hacksaw and re-positioning the component parts on the resulting narrower tube.
Here’s how to determine the minimum possible tube length:
The springs will grow in length as they are wound so it is possible to cut a tube too short. Here is the method to determine how much can be removed and still have enough tube to wind the system properly.
160# dual spring 96” system:
10 inches for drums and end bearings + (27.5” + 1.5” (spring and cones)) x 2 since it has two springs + (0.218 wire x 10 turns (length spring grows)) x 2 since it is a dual = 72.36”
This tubecan be cut to 75” and still function properly.
50# 66” single-single system:
10 inches for drums and end bearings + 22” + 1.5” (spring and cone – do not double as this is a single-spring system) + (0.187 wire x 10 turns) (length spring grows – again do not double since this is a single) = 35.37”
This tube can be cut to 37” and still work correctly.
250# 96” dual spring system:
10 inches for drums and end bearings + (28.5” + 2” (spring and oversize cone)) x 2 since it is a dual system + (0.250 wire x 10 turns (length spring grows)) x 2 since it is a dual system = 76”
This tube can be cut to 78” and still function properly.
Cable Jumps Off Drum
Customer has installed spring assist system on a “used” trailer. After winding the spring the door opens and closes but the cable on one side “jumps” off of the cable spool, pulley, or drum.
Things to check – cable anchor brackets are the same distance down on both sides of the door.
Suggested fix – Close the door and secure it. Go inside the trailer and loosen the set screw on the cable drum that the cable is coming off of. IMPORTANT – BE SURE THE DOOR IS CLOSED BEFORE YOU MESS WITH THE CABLE DRUM. LOOSEN THE SET SCREWS ON THE CABLE DRUM NOT THE WOUND SPRING OR YOU MAY BE HURT. After loosening the set screws wind the cable up on the drum until it is finger tight. Tighten the set screws. Open and close the door a couple of times to set the cable into the grooves of the drum. This should correct the problem.
If it does not – either the door is racked or the rear hoop frame of the trailer is racked. Both drums are the same diameter and they move on a common shaft at the same speed. Since both cables are the same length, the “take up” is the same on both sides. The only variable is the squareness of the door and trailer frames. Racking of frame components is not a situation M-3 can correct with the spring system.
Positioning the Cable Drums
Questions regarding the placement of cable drums (spools) usually fall into one of two categories.
First – “I bought an 81” wide system but my trailer is only 75” wide. Can I cut it down? Where do I re-position the spools?”
Answer – The drums (spools) are never placed exactly where they will be on the tube after installation. We position them at the factory for ease of shipment. The installer always has to position the drums. They should be positioned as far apart as possible, just inside of the door opening so that the cable cannot rub the door frame when the door opens and closes. Placing them as far apart as possible gives the user maximum clearance to load gear without catching the cables.
Second – “My system is too long. Can I cut the tube without effecting the performance of the system.
Answer – As the springs are wound to create the tension that lifts the door, they grow longer in length. Space must be available for this growth or the springs will “hump up” as the door opens and closes when they run out of space. This will take lift force from the system and it will so cause premature failure of the system and the door will be too heavy. What is the minimum space needed for the springs to function properly? Here is the formula to calculate minimum tube length:
Unusual Trailer Size – Custom Options
Spring weights – Springs are stocked at M-3 to handle doors with springing weights of 45 lbs through 300 lbs. 205 lbs through 300 lbs systems have a center bearing plate and weld bracket assembly for added support.
Drum sizes – Standard M-3 drums are 4” diameter. Both 3” diameter and 6” diameter drums are available. The 3” drum is often used in trailers with less than 6” of headroom clearance above the door opening. The 3” drum will carry only 150 inches of cable and requires 10 inches to remain on the drum as the safety wrap. The 6” drum is often used in extra tall trailers. The 6” drum will carry 240 inches of cable and requires 29 inches to remain on the drum as the safety wrap.
Trailers with extra heavy doors – If the springing weight of the door exceeds 315 lbs, M-3 does not recommend using a spring assist. We recommend that doors exceeding 315 lbs be raised and lowered using an electric winch of the type used in loading boat trailers. The cost of a winch is generally similar to the cost of a spring assist for these extra heavy doors, and the safety factor is greater with a winch system.
For more information on any of our ramp door spring systems, or for assistance with custom needs, contact M-3 & Associates at 574-294-3988 or send us an email at firstname.lastname@example.org.