The rear shocks on an MTB are one of the most abused and under-pressure components on the frame. The shock is always under pressure and constant loads from all directions act on it. This means that the shock needs to be structurally very strong and must resist torsional flex.
The tiny bushing that is often an overlooked component is what keeps the shock stable and functioning smoothly, it is called an Eyelet Bushing.
Eyelet bushings protect the shock eyelet from wear, also keeping the mount attachment snug. There are two common sizes of eyelet bushing (12mm and 12.7mm)
As well as size variations, eyelet bushings come in different materials as well. Polymer eyelet bushings are ideal for heavy-duty usage as they resist deterioration under regular cleaning and heavy usage they usually last longer too. The standard metal bushings are what usually come stock as OEM fitments on bikes. They tend to wear out faster and don’t provide a very consistent feel.
How to tell if it’s time to replace your bushings?
More likely than not, if there is any movement in the rear end it is usually caused by a worn shock bushing. A simple way you can check for wear is by lifting the rear end of your bike by the saddle a few inches and then pressing down on the rear wheel by hand, if you feel any play then the bushing is probably on its way out.
These eyelet bushings are often made from steel with a nylon/PTFE coating. Aftermarket bushings are also available in polymer materials for longevity. The bushings inside the eyelets of your rear shock are designed to wear out over time and usage, they are however an easily replaceable item with the right tools and a little technical know-how.
In the picture above we worked on a FOX float shock. It can be noticed that the inner walls of its eyelet bushing have worn out considerably with deep scratches and a worn-out PTFE coating.
This is what a new metal bushing should look like.
Continuing to use a worn-out bushing can destroy your shock as the increased play will structurally stress the shock body more. There is potential for mount damage.
After inserting a new bushing make sure there is no rotational movement of the bushing itself (by hand). If there is excessive play it can generate a lot of friction and heat out on a trail. This will ruin your frame and shock mounts beyond repair.
What are DU bushings?
The term DU itself is a carryover from the original OEM part number of the bushing, now used as a generic term.
It is actually an aftermarket bushing, commonly used by FOX that uses a steel backing, press-fit into the shock eyelet. The friction surface is comprised of a bronze layer covered in a polymer coating. This coating is what the connecting pin rotates within and acts as a self-lubricating bushing.
Needle bearings instead of bushings?
Some professional riders out there fit in aftermarket needle bearing kits to replace the eyelet bushings.
The bushings used in shock eyelets are really tight and draggy. The connecting pin has to move in your shock eyelet every time your suspension cycles. Replacing the draggy bushing with a nice smooth needle bearing gives you a more active and smoother suspension.
Companies like FOX have recently started offering needle bearing kits for their shocks aswell.
Eyelet bushings play a crucial role behind the scenes on your bike. A well-made bushing will keep the rear end feeling more plush and light. Wear and tear is also significantly reduced with a high-quality bushing.
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WHAT I LOVE ABOUT CYCLING
I’m an avid mountain biker and I like riding fast and flowy singletrack. As I keep riding, I continuously work on honing my riding skills. I like to ride whenever possible, especially with friends. I also like to influence folk into getting to ride more often.
Working on bicycles has also been a keen interest of mine for quite some time.
DISCIPLINE: Mountain biking and Road biking
CURRENT BIKE: Merida One Twenty 9.600 & Specialized Allez Elite DSW
DREAM BIKE: Santa Cruz 5010