Pusher Springs: Preventing Cables Off Drums With Jackshaft Sidemount Openers

Pusher springs create a downward acting force against the top section of your garage door to prevent cables from slipping off the drums. They are most often required when jackshaft side mount openers are installed on standard lift doors which lack a natural downward acting force.

1. What are pusher springs used for?

The main purpose of spring pusher installation is to assist in maintaining constant cable tension when the door is starting the down cycle. This is especially the case on standard lift doors that lack a downward acting force achieved with high lift or full vertical lift doors. When an opener starts running with the door in the open position there is a tendency for the door to initially jump – causing cables to be thrown of the drums.

Jack shaft operators installed on standard lift doors are especially prone to cables being thrown off the drums because they lack a natural downward acting force.

Another secondary benefit of pusher springs is the prevention of the door flying off the back end of the horizontal tracks in the event of user or operator error.  This is especially the case on manually opened and closed doors where the user might fling the door open with excessive force.

This problem is quite common in loading dock bays and storage facilities where people fling the door upward as fast as they can. Although track bolts are fastened to the ends of the horizontal track to stop door travel, pusher springs do a much better job stopping door travel.

2. Do I Need Pusher Springs or Track Bumpers?

Pusher springs are often called plungers or bumpers, but shouldn’t be confused with a different part called a leaf bumper.

As the name implies, pusher springs are spring loaded and leaf bumpers are not.  As the garage door travels towards the end of horizontal track the top section compresses against the pusher spring.

Then when the door starts downward travel the pusher springs unloads the compression force against the top panel, avoiding the sudden jump at the start of door travel. This push force is usually enough to keep the cables from slipping over the grooves of the drum.

If you are looking for an aid to keep your garage door cables from jumping off the cable spools pusher springs are needed. If you are looking to keep your garage door from slamming into the track bolts at the end of the horizontal tracks “leaf style” bumpers are needed.

• Pusher springs are installed at the back of the horizontal tracks compressing against the top section as the door opens. When the door starts closing that tension is slowly released to prevent the sudden jump start that causes cables to slip off the drums. Pusher springs are often referred to by other names such as plungers, bumpers, stoppers and pushers.

• Leaf bumpers also mount at the end of the horizontal or vertical garage door track. Unlike pusher springs that compress as the door opens, bumpers don’t move or compress. The primary purpose of the bumpers are to keep the door from opening too far and calling off the back of the tracks. This is common in settings where users fling the door open quickly during manual operation. Some examples would be storage units and loading docks where doors need to be opened quickly by hand.

3. Parts of Pusher Springs

Spring – 30lb, 60lb,150lb Compression Options

Rod – 1″ Diameter Galvanized 27″ , 15″,  9″ Options

Rubber Bumper – 2″ Diameter Rubber Stop

Mounting Bracket – 12 Gauge Galvanized With Adjustable Groove Placement

Mounting Hardware – (2) 3/8″-16 Hex Bolts (2) 3/8″-16 Hex Nuts (Flat Washers Optional)

4. Pusher Spring Size & Compression

Selecting the correct size pusher is important to get your door running smoothly. Installing a push down bumper that is too strong could damage your garage door opener.

For example, using the 27″ spring pushers on a residential door with an 8500W would cause excessive wear as the 27″ pushers have 150lbs of force per pair.

The pushers should match the door and opener size and should be adjusted further or closer from the top panel when the door is in the open position.

Side mount jackshaft openers like the Liftmaster MJ5011 & J5011 operators are not designed to be installed on doors that lack a downward acting force.

In plain terms, if you don’t have high lift or full vertical lift track your warranty will likely be voided if you install the operator on a standard lift door.

With that being said most people still install them anyways and quickly discover that their garage door cables frequently get thrown off the drums rendering the door unusable. Any side mount opener installed on a standard lift door should have pusher springs installed as well.

5. Pusher Spring Chart

Pusher Spring Length, Compression & Rating

6. Pusher Springs for Side Mount Openers

Pushers For Liftmaster 3800, 8500W Cable Tension Monitors (41A6104)?

Yes, pusher springs are frequently used with the Chamberlain Liftmaster side mount jack shaft opener models 3800 & 8500W. These models come with a built in device called a Cable Tension Monitor (41A6104) , although medium duty and full duty commercial grade openers don’t come with this part.

As the name says this device monitors cable tension with a small lever that maintains contact throughout the opening and closing cycle. The part connects directly into the liftmaster residential openers allowing for real time adjustment.

Even with this device installed and configured it is still often necessary to install the 9″ residential pusher springs for standard lift doors. Chamberlain Liftmaster acknowledges that pushers are often needed if the opener forces can’t be adjusted to fix certain issues.

7. Installing Pusher Springs

Pusher springs are sold in pairs with a right and left side mount. The brackets attached to the springs are mounted at the outside ends of the horizontal tracks using track bolts & nuts.

In the rare case of the horizontal track being too short a piece of angle iron can be added to the end of each track with the pushers being mounted to the punch angle. The pushers should always be mounted at equal distances to ensure that balanced for is applied to the top section of the garage door.

Here are a few key points to keep in mind when starting installation:

• Size your pushers according to the door size & opener strength.
• Pushers should be installed on the outsides of the horizontal track.
• The full travel and compression rating doesn’t have to be used even though it is best practice.
• Using too strong of pushers will wear out your opener over time.
• If preventing cable slipping during the down cycle is needed pushers should be used.
• If the goal is only to stop the door from coming out of the tracks bumpers should be used.

8. DIY Pusher Installation Instructions

1. Pushers are sold in pairs with a right and left side mount. The brackets mount to the outside of the horizontal tracks and angle inward. Identify your right and left side pushers
2. Using a pair of vise grips or C-clamps temporarily mount the pushers as far back on the tracks as possible with the rubber stop end facing the door.
3. Raise the door to the open position aligning the rubber stop end of your pusher with the top corner of your door.
4. Repeat the the same process on the opposite side using the exact length spacing for balance.
5. Chances are the end of track positioning won’t be correct so your will need to move the pushers further up the track for the right amount of pusher compression.
6. Measure the amount of compression with a tape and adjust accordingly keeping in mind the compression rating for the pushers you purchased.
7. Once you have the right distance and alignment you can mark the hole locations. You will need to drill 2 or more holes for your fasteners to mount to.
8. Fasten the pusher to the horizontal tracks with 3/8″ track bolts & nuts.
9. You can expect the spring pushers to be noisy during operation so be sure to lubricate each of them.

9. Troubleshooting Pusher Springs

The culprit of most cable slip issues comes from improper spring installation. If you face re-occuring issues with cables coming off the drums start with the springs before anything else. Pusher spring are not a substitute for poor spring installation.

Make sure your torsion springs calibrated correctly for the door weight, size and lift type. This is achieved through a spring engineering report using special computer software.

After you have confirmed that your springs are correct through an engineering report, make sure they are installed correctly.

• Do the springs have the correct amount of turns (tension)?
• Is the door moving smoothly around the track radius?
• Are the opener forces and limits set correctly?

Spring Adjustment Balance Test

With your opener disconnected and the door in the closed position you can perform a  balance test. Raise the door manually about half way open. At this level the door should sit in the opening without moving up or down.

If it begins drifting too far up or down you can be sure that your door isn’t balanced. Drifting up implies the springs are running “hot” while drifting down implies “cold” or “heavy”.

If your torsion springs have too much tension (set too hot) the door will raise too far. The bottom section of your door should be slightly handing down in the opening for proper cable tension.

Initially most people install torsion springs “hot” meaning they add slightly too much tension in order to make the door easier to open by hand. However, running your springs hot isn’t necessarily the best option with jackshaft openers.

This is the one circumstance where you would want to door to run on the heavier side – allowing the door to drift slightly lower to take advantage of gravity.

Horizontal Track Slope Adjustment

If after installing and adjusting the pusher springs you still have the reoccurring problem of cables slipping off the drums a few extra options exist. If your horizontal tracks have been installed level you may consider adding a slight down slope of 1″-4″ on each side.

Creating a slight down-sloping track angle could help the force of gravity push down on your door section around the track radius.

The radius of the track itself can affect cables slipping. The most common track radius are 10″ Radius, 12″ Radius and 15″ Radius .

The higher the radius the more gradual the curve of the track. Using a 15″ Radius track results in much smoother door operation and a door that hands down slightly in the opening to create a downward acting force.

Cable Loose Slack

Torsion cables should be taut on each side of the door like a violin string. If one or both cables have slack with the door in the closed position that is a sign of a door installed out of alignment, slipped drums or improperly configured torsion springs.

If at any point during door operation the cables get loose something is wrong. You can examine the cable slack when the door is in the fully open position by looking at the upper right and left hand gap at the top.

Never use pusher springs as a band aid to cover up the poor installation of other door components like springs and openers. Pusher springs create a necessary downward acting force on standard lift doors.

For further information on why cables get thrown off drums please read our guide: Troubleshooting Broken Cables: 20 Reasons Cables Come Loose Off The Drums