Quick answer
An extension spring system is a way of lifting a garage door with two long springs that stretch along the horizontal tracks when the door closes and pull back as it opens, through cables and pulleys.
DASMA defines an extension spring as one that provides power by stretching, usually mounted along the horizontal track. Each spring needs a containment cable through its center so broken parts cannot fly.
Quick facts
The key facts about Extension Spring System, with sources:
Key takeaways
- Extension springs stretch along the tracks; torsion springs twist above the door.
- They come in pairs, one per side, and both should match the door’s weight.
- Each spring must have a containment cable running through it.
- A broken extension spring without containment can whip through the garage.
- All work on extension springs, pulleys and cables is pro-only.
What an extension spring system is
Before torsion springs became common on homes, most sectional doors used extension springs. Many still do, especially older doors and doors with little room above the opening.
DASMA defines an extension spring as one that provides power or tension by stretching, usually mounted along the horizontal section of track from the front of the opening to the back hang 1.
The system includes more than springs: pulleys (DASMA calls them sheaves), sheave forks that attach the pulleys to the springs, lift cables, and adjustment clips at the cable ends 1. DDM Garage Doors, a parts supplier, groups extension springs into sectional-door and one-piece-door designs 8.
Like torsion springs, they are a counterbalance system: they offset the door’s weight so a person or opener can move it with little force 1.
How extension springs lift a door
With the door closed, each spring is stretched to its longest, storing energy.
A cable runs from the bottom corner of the door, up and over a pulley, to a pulley on the end of the spring and back to an anchor.
As the door opens, the springs contract, pulling the cables and lifting the door. When it closes, the door’s weight stretches the springs again.
The two sides work independently. If one spring is weaker than the other, the door can rise unevenly. That is one reason springs are sized as a pair for a door weight: DASMA’s color chart notes that two extension springs are required for the listed door weight 3.
Amarr notes extension springs connect to more parts than torsion springs and need a balance between springs and pulleys, which makes installation trickier 7.
Source: [1]
Extension spring end types and designs
| Type | What it is | Source |
|---|---|---|
| Open-loop end | Single open loop at the end | Amarr 7 |
| Double-loop end | Two loops for a stronger connection | Amarr 7 |
| Clipped end | Clip attaches the spring | Amarr 7 |
| Sectional door design | Pair along the horizontal tracks | DDM 8 |
| One-piece door design | Used with one-piece hardware | DDM 8 |
Example: DASMA extension spring color codes by door weight
DASMA’s official codes mark the door weight a pair of extension springs is made for 3. Excerpt below; DASMA says codes must be confirmed by measurements and door weights, and are not for homeowners replacing springs.
| Door weight (pair) | Color |
|---|---|
| 100 lb (45 kg) | Tan |
| 120 lb (54 kg) | Green |
| 140 lb (64 kg) | Blue |
| 150 lb (68 kg) | Red |
| 160 lb (73 kg) | Brown |
| 180 lb (82 kg) | Gold |
| 200 lb (91 kg) | Tan |
- 50 lbLightest door weight listedDASMA TDS-171
- 300 lbHeaviest door weight listedDASMA TDS-171
- 10 lbStep between listed weightsDASMA TDS-171
- 2Springs required per listed weightDASMA TDS-171
Source: [3]
Colors repeat across weights, so a color alone does not identify a spring. That is one reason replacements are matched by a technician using the door’s actual weight.
Where to find extension springs
Stand inside with the door closed and look above the horizontal tracks on each side. Long coiled springs running toward the back of the garage, with pulleys at their front ends, are extension springs. If the spring is wrapped around a bar above the door, you have torsion springs instead.
Look for a thin steel cable running through the middle of each spring, anchored at both ends. That is the containment cable. DASMA’s inspection checklist tells inspectors to verify it from inside with the door closed 2.
There may also be safety labels near the bottom brackets warning of extreme spring tension 4.
Why containment cables matter
A stretched extension spring holds a lot of energy along its whole length. When one breaks, the pieces can fly. Amarr warns that a broken extension spring can be extremely dangerous, sending parts around the garage, through windows or car windshields 7.
The fix is simple: a containment cable through each spring. DASMA defines it as a cable threaded through an extension spring to retain the spring if it breaks 1, and its checklist asks: are counterbalance springs and their attachment components restrained by a cable or shaft 2?
Torsion springs on a shaft are inherently contained; extension springs need the cable.
If your door has extension springs and no cables through them, ask a technician to add them. See safety containment cable.
When extension springs hold the most energy
Extension springs are stretched the most when the door is closed, because the door’s weight has pulled them out to their full length. As the door rises, they shorten and give up that energy. With the door fully open, they are at their least tension.
That is the opposite of what many people assume, and it matters for safety. A closed door with extension springs has its springs fully loaded along the tracks, right where people walk and park.
That is why the containment cable is so important: it is the only thing that keeps a breaking spring from whipping across the garage 1 2.
It also explains why technicians work on extension springs with the door raised and secured. Do not copy that at home. Securing a heavy open door safely takes the right clamps and training.
Pulleys, cables and clips
The lift cable on each side runs from the bottom bracket of the door, up past the front of the track, over a pulley at the spring’s end and to an anchor. The pulleys multiply the spring’s travel so a spring stretching a few feet can lift a door seven feet high.
DASMA’s terminology lists the 3-hole cable clip, a metal clip at the end of an extension spring cable that allows length adjustment 1.
Cable length on both sides sets whether the door hangs level. Pulleys wear at their bearings and can crack; a wobbling or squealing pulley is a sign to call a technician before it fails under load.
Pros and cons
Pros
- Need no wall space above the door.
- Common on older and low-headroom doors.
- Parts widely available 8.
Limits of extension springs
Extension springs are sized for one door weight. Adding glass, insulation, paint or trim can push the door past it, which DASMA lists as a cause of shorter spring life 5.
They also crowd the ceiling area beside the tracks, which can limit storage and makes the pulleys and cables easy to bump.
What drives the cost of extension spring work
No prices on this page. See the cost guide.
How a technician replaces extension springs
Professional work. Steps described so you can follow the job.
- Raises the door to the open position, where extension springs are at their least tension, and secures it.
- Confirms the door weight and the spring size needed 3.
- Replaces springs as a pair, with pulleys and cables as needed.
- Threads containment cables through both springs 2.
- Adjusts cable length so the door hangs level.
- Checks balance and, if an opener is fitted, tests reversal on a 2x4 6.
Owner care
- Look at the springs and cables from the floor every few months.
- Confirm containment cables are present and tight.
- Watch for frayed lift cables or wobbly pulleys.
- Keep storage away from the springs and pulleys.
- Book yearly door service; see preventive maintenance.
Warning signs
A door that rises crooked, a spring visibly stretched more on one side, a gap in a spring, a loud bang, frayed cables, or a door that suddenly feels heavy.
DASMA says not to operate a door with a broken spring and not to try to remove, repair or adjust springs, cables or brackets 2.
Never adjust extension springs yourself
Extension springs and their cables are under high tension and can snap with great force. DASMA says repairs and adjustments must be done by a trained door systems technician with proper tools 2.
Standards that apply
The voluntary counterbalance standard ANSI/DASMA 103 covers extension and torsion springs; DASMA’s account says it began as a 1970s standard for testing extension springs and requires tensioned parts to be non-removable, need special tools, or be red and labeled 9.
DASMA’s safety labels include one warning that bottom brackets are under extreme spring tension 4. If the door has an opener, the federal opener rule applies 10.
Extension vs torsion springs
Myths about extension springs
- Myth Extension springs are safer because they are smaller.
- Reality They hold large stretch energy and can fly if uncontained 7.
- Myth You can replace just the broken side.
- Reality They are sized as a pair; uneven springs tilt the door 3.
- Myth The color tells you the exact spring.
- Reality Colors repeat; measure and weigh 3.
Climate notes
Humidity and salt air rust springs, and DASMA says rust creates pits where fatigue cracks grow 5. In coastal areas, inspect extension springs and their cables more often.
Keep, upgrade or convert?
If your extension springs have containment cables and work well, keeping them is fine. If cables are missing, add them. If a spring breaks, ask about replacing the pair or converting to torsion springs; see spring repair.
Look for the cable
Check today: a thin cable should run through the center of each extension spring. If you cannot see one, call a technician.
Questions about Extension Spring System
What are extension springs on a garage door?
They are long springs along each horizontal track that stretch when the door closes and pull it up when it opens, working through cables and pulleys. DASMA defines them as springs that provide power by stretching.
Are extension springs dangerous?
Yes, if they break without containment. Amarr warns broken parts can fly through windows or windshields. A containment cable through each spring prevents that.
What is a safety cable on extension springs?
A containment cable threaded through the center of each spring and anchored at both ends. DASMA says it retains the spring if it breaks.
Should both extension springs be replaced?
Usually yes. DASMA’s color chart notes two springs are required for the listed door weight, and mismatched springs make the door rise unevenly.
How long do extension springs last?
Amarr says around 10,000 cycles. Years depend on how often the door runs, plus handling, installation and climate.
Can I convert extension springs to torsion springs?
Often, yes. A technician installs a shaft, drums, brackets and torsion springs sized for the door. It removes the need for containment cables.
What do the colors on extension springs mean?
DASMA’s codes mark the door weight the pair is rated for, in 10-pound steps from 50 to 300 pounds. Colors repeat, so measurements and the door’s weight must confirm them.
Can I adjust extension springs myself?
No. DASMA says spring and cable repairs and adjustments must be done by a trained door systems technician.
Sources
- DASMA Technical Data Sheet #160, Sectional Garage Door Terminology, retrieved .
- DASMA Technical Data Sheet #167, Residential Sectional Garage Door and Electric Operator Checklist for Home Inspectors and Consumers, retrieved .
- DASMA Technical Data Sheet #171, Official Color Codes for Torsion and Extension Springs, retrieved .
- DASMA Technical Data Sheet #172, Garage Door Labels, retrieved .
- DASMA Technical Data Sheet #190, Factors Affecting Spring Cycle Life, retrieved .
- DASMA Technical Data Sheet #369, Frequently Asked Questions Regarding Automated Residential Garage Door Systems, retrieved .
- Amarr, Your Complete Guide to Garage Door Springs (Feb 27, 2023), retrieved .
- DDM Garage Doors (parts supplier), Garage Door Springs: types, measuring and FAQs, retrieved .
- DASMA, The New DASMA 103 (interview on the counterbalance standard, Door & Access Systems, Winter 1999), retrieved .
- 16 CFR Part 1211, Safety Standard for Automatic Residential Garage Door Operators (eCFR, current), retrieved .
Expert review
Written by the HyreGarage Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Definitions from DASMA TDS-160; containment and safety from TDS-167 and 172; color codes from TDS-171; life factors from TDS-190; design and risk notes from Amarr and DDM Garage Doors; standard history from DASMA’s DASMA 103 article.
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