How to Replace a Roller Blind Sidewinder Mechanism and Chain
Updated: Aug 28
If your roller blind chain has snapped, the mechanism is slipping or the blind has become stiff and difficult to operate, you may not need to replace the complete blind.
In many cases, the problem can be fixed by replacing either the operating chain (No.10, 4.5mm bead), the sidewinder mechanism, or both.
The important thing is identifying which part has actually failed and making sure any replacement mechanism is compatible with your existing roller tube.
In this guide, we'll explain how to identify the problem, replace a roller blind sidewinder and chain, and avoid some common mistakes when fitting the new parts.
What Is a Roller Blind Sidewinder Mechanism ?
The sidewinder is the control mechanism fitted into one end of a chain-operated roller blind tube.
The operating chain runs through the sidewinder. Pulling one side of the chain rotates the roller tube in one direction, while pulling the other side rotates it in the opposite direction.
At the other end of the roller tube is normally an idle end or pin end, which supports the opposite side of the blind.
Together, the sidewinder, idle end and brackets form the operating system that supports and controls the roller blind.
My Roller Blind Chain Has Snapped – Do I Need a New Mechanism?
Not necessarily.
The operating chain can normally be replaced independently of the sidewinder mechanism.
If the mechanism itself is still operating smoothly and isn't damaged or badly worn, replacing or repairing the chain may be all that's required.
However, the sidewinder will normally need to be removed from the roller tube so that the chain can be correctly fitted around the mechanism before it is reinserted into the blind.
This is also a good opportunity to inspect the mechanism for signs of wear.
When Should I Replace the Roller Blind Sidewinder Mechanism ?
Consider replacing the complete mechanism if:
The mechanism is slipping
The housing is cracked or broken
The blind has become unusually stiff to operate
The chain sprocket is damaged or badly worn
The mechanism doesn't consistently turn the roller tube
The chain repeatedly slips or jumps
The mechanism has become unreliable
If the sidewinder is damaged, simply fitting a new chain isn't likely to solve the underlying problem.
Step 1: Remove the Roller Blind From Its Brackets
Before working on the mechanism, remove the roller blind from its brackets.
Support the blind carefully, particularly if it is wide or heavy.
Once removed, place the blind somewhere clean and secure where you can access both ends of the roller tube without damaging the fabric.
Step 2: Remove the Existing Sidewinder
The sidewinder normally pushes into the end of the roller tube.
Carefully pull the mechanism out of the tube.
Avoid using excessive force or damaging the end of the roller tube.
Once removed, you can inspect the mechanism and accurately measure the roller tube.
Step 3: Measure the Outside Diameter of the Roller Tube
This is one of the most important steps.
Replacement roller blind mechanisms are designed to fit particular tube sizes and profiles.
Measure the external diameter of the tube, straight across from one outside edge to the other.
Don't measure the internal opening.
Removing the mechanism first normally makes it much easier to obtain an accurate measurement.
Common roller blind tube sizes include 25mm, 28mm, 32mm and 40mm, although other systems also exist.
If you're unsure what you have, see our guide to identifying your roller blind mechanism and tube size before ordering a replacement.
Step 4: Decide Whether You're Replacing the Chain, Mechanism or Complete Set
Once you've inspected the existing parts, there are three possibilities.
Chain Only
If the sidewinder is in good condition and operates correctly, you can normally replace the chain while retaining the existing mechanism.
The mechanism will still need to be removed from the blind to fit the replacement chain correctly.
Sidewinder Only
If you can obtain an identical or directly compatible replacement sidewinder, particularly on a relatively modern made-to-measure blind, you may be able to simply remove the old mechanism and insert the new one.
The existing idle end and brackets can then remain in place if they are fully compatible.
Complete Mechanism Set
If the replacement sidewinder is a different design, we'd normally recommend replacing the sidewinder, idle end and brackets together.
Replacement roller blind mechanism packs are commonly supplied with all of these components.
Trying to make an incompatible new mechanism work with old brackets is rarely worthwhile.
If the mechanism is different, use the correct new brackets rather than trying to modify or “fudge” the old fittings.
Step 5: Fit a Replacement Chain to the Sidewinder
With the sidewinder removed from the blind, the replacement chain can be fitted around the mechanism's sprocket.
Make sure the chain runs correctly and moves smoothly through the sidewinder before putting the mechanism back into the tube.
Roller blinds can use either a continuous/endless chain loop or chain that is joined using a suitable chain connector, depending on the system and installation.
If you're using chain with a connector, there is one particularly important point to remember.
Important: A Chain Connector Won't Pass Through the Sidewinder
A chain connector or joiner is larger than the individual chain beads and will not pass through the sidewinder mechanism.
Its position therefore matters.
If your blind fabric rolls off the back of the roller, position the chain so that the connector is on the section of chain closest to the wall when the blind is installed.
The aim is to position the connector so that normal operation of the blind doesn't require it to travel through the sidewinder.
Before refitting the blind, operate the mechanism by hand and check the complete range of chain movement.
Step 6: Fit the New Sidewinder Into the Roller Tube
Once the chain is correctly fitted, push the sidewinder into the roller tube.
Make sure:
It is the correct size for the tube
It matches the tube profile
It is fully inserted
The chain runs freely
Nothing is being forced into position
A mechanism that doesn't fit correctly shouldn't be hammered or forced into the tube.
If it doesn't fit, stop and recheck the tube diameter and profile.
Step 7: Replace the Idle End and Brackets If Required
If you're fitting a complete replacement mechanism set, remove the original idle end from the opposite side of the roller tube and fit the new one.
Replace the old brackets with those supplied for the new mechanism.
The new brackets can often be fitted in approximately the same location as the originals, although fixing positions can vary between systems.
Use suitable fixings for the surface you're mounting the blind to.
Step 8: Refit the Roller Blind and Test It
Once everything is assembled, refit the roller blind into its brackets.
Before repeatedly raising and lowering the blind, operate it gently and check:
The chain moves smoothly
The sidewinder isn't slipping
The tube rotates correctly
The blind raises and lowers evenly
The chain connector doesn't enter the mechanism
The blind is securely located in both brackets
If anything feels unusually stiff, don't simply pull harder. Remove the blind and check the installation.
How Long Should My Replacement Roller Blind Chain Be?
The operating chain needs to be appropriate for both the blind and its installation.
When replacing a chain, don't simply make the loop as long as possible for convenience.
The position of the chain loop and any child-safety device needs to comply with the relevant blind child-safety requirements.
As a general guide, where applicable, the bottom of an operating chain loop should be kept at least 1.5 metres above floor level, but the correct arrangement depends on the installation and safety system being used.
See our dedicated Blind Chain Child Safety Guide before choosing and installing your replacement chain.
Can I Change From Plastic to Metal Roller Blind Chain?
Often, yes, provided the replacement chain is compatible with the sidewinder.
Metal chain can offer greater strength and is available in decorative finishes, while plastic chain can be less visually noticeable, particularly against white window frames.
The important factor isn't simply whether the chain is plastic or metal – the bead size and spacing must be compatible with the mechanism.
See our guide to Plastic vs Metal Roller Blind Chains for a fuller comparison.
Common Mistakes to Avoid
Ordering by blind width instead of tube diameter
Blind width doesn't tell you which mechanism you need. Measure the outside diameter of the actual roller tube.
Measuring the inside of the tube
Mechanisms are normally identified according to the roller tube system. Measure the external diameter.
Keeping incompatible old brackets
If you're changing to a different mechanism system, use the brackets designed for it.
Forcing a mechanism into the tube
If it doesn't fit correctly, recheck the size and profile.
Forgetting about the chain connector
A connector won't pass through the mechanism. Position it correctly before reinstalling the blind.
Assuming a broken chain means a broken mechanism
Inspect the sidewinder first. You may only need a replacement chain.
Ignoring child safety
Whenever a chain is replaced, check that the installation and safety device meet the appropriate child-safety requirements.
Quick Troubleshooting Guide
Problem | Likely Action |
Chain snapped but mechanism works | Replace chain |
Chain connector broken | Replace connector or chain as appropriate |
Sidewinder slipping | Replace mechanism |
Mechanism housing cracked | Replace mechanism |
Chain jumps on sprocket | Inspect chain and sidewinder for wear |
Mechanism very stiff | Inspect and replace if damaged |
Different replacement mechanism | Replace mechanism, idle end and brackets |
New mechanism doesn't fit tube | Recheck tube diameter and profile |
Do I Need to Replace the Complete Roller Blind?
Usually not.
A broken sidewinder or operating chain is a relatively small fault.
If the roller tube, fabric and other components are still in good condition, replacing the mechanism or chain can give an otherwise perfectly serviceable roller blind many more years of use.
That's one of the reasons it's worth identifying the fault before deciding to replace the complete blind.
Need Help Identifying Your Roller Blind Parts?
If you're unsure which replacement mechanism you need, start by removing the existing sidewinder and accurately measuring the outside diameter of the roller tube.
Our How to Identify Your Roller Blind Mechanism & Tube Size guide explains what else to check.
You can also visit our Roller Blind Repairs & Guides section for help with other common roller blind problems.
Conclusion
Replacing a roller blind sidewinder or chain is often a straightforward and economical repair.
If only the chain has broken, you don't necessarily need a new mechanism. Remove the sidewinder, inspect it and replace the chain if the mechanism itself is still in good condition.
If the sidewinder is worn, slipping or damaged, identify the roller tube size before ordering a replacement.
Where an identical replacement isn't available, fitting a complete mechanism, idle end and bracket set is generally better than trying to adapt incompatible old components.
Most importantly: measure the tube, identify the fault and use the correct parts rather than forcing something to fit.
A relatively inexpensive mechanism or chain may be all that's required to get the blind working properly again.
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