Used Bikes—What You Need To Know Before Buying


Front and rear suspension are fairly straightforward to test by simply pushing down on either the handlebars or saddle to cycle the shock and make sure it is functioning. However, troubleshooting either the fork or rear shock internally can be much more complicated. Each suspension setup is different, and I cannot list an exhaustive method to go through each brand’s idiosyncrasies and each of their products’ specifics.

All suspension brands have exhaustive technical documents that very accurately outline every step for any process on a suspension fork or shock, should there be specific questions that are beyond the scope of this article. These technical documents are readily available on each brand’s website.

That said, here are a few tests to try to see how things are stacking up:

First, visually inspect the fork and/or shock. Are there any signs of oil or grease on the fork stanchions or around the seals?

Clean Mountain Bike Fork Seals, Blister Gear Review
Clean fork seals with no issues.

Next feel the suspension by pressing up and down on either the handle bar (for the fork) or on the saddle (for the rear shock), in order to cycle each of them a few times. Does the stroke feel smooth, or sticky? Do they make any dry squeaking noises? Has any oil come up to the seals? If any of these symptoms are present, the part likely needs new seals and/or the lowers pulled, cleaned, and re-lubricated.

Then look at the stanchion(s) of the shock and fork. These are generally black or gold anodized. If you see anywhere that the finish is wearing, that means it might need new bushings. If there is actually any pitting (i.e. with your finger you can feel missing material in the stanchions), a fairly massive part replacement is due.

Most shocks on the market will have some level of adjustment, and there are three general settings to test: (1) the stiffness of the fork or shock (through either an air valve or a spring); (2) the compression damping (or the amount of suspension oil the shock pushes when compressing the fork), which serves to control the fork as it is pushed into its travel; and (3) the rebound damping, which controls the return of the shock to full length and prevents the shock from feeling too spring-like.

To evaluate the shock you need to identify the compression knob (typically blue), and the rebound knob (typically red). Set both the compression and rebound settings fully open, or backed out (all the way counter clockwise), and be sure to count the number of clicks on each knob so that you can return the settings once done (e.g., eight clicks from open, blue; four clicks from open, red). Compress and cycle the suspension. It should feel basically like a pogo stick: very easy to compress since there is no compression damping, and super fast return since there is no damping on the rebound side.

Now dial in the rebound all the way closed, and cycle the suspension again. It should still be easy to compress and then return very, very slowly—like, molasses-in-January slow. Then open the rebound back up and close the compression. The initial stroke should be very, very firm, basically locked out or nearly impossible to compress. Return the settings to their initial settings. If the rebound or compression adjuster do not function as described, the shock needs a potentially major overhaul and likely new parts.

Another common issue for used forks is that they do not get full travel. This typically means that fork oil has leaked out from the cartridge that creates the rebound and compression damping and into the lower leg of the fork. This is not particularly easy to test in a parking lot, so if something funny is noticed on trail, take the bike to your local shop and see what they can determine. It is a pretty easy repair, just a matter of a couple of bucks in seals and maybe 20 minutes of labor to fix ($20 in labor), more often than not.

One last item to check on a full-suspension bike is to lift up on the saddle slightly while resting both wheels on the ground. You are looking to feel for a slight tick. A light tick would indicate that there is a little play in the suspension somewhere. This can be in the bushing that is in the shock to adapt it to the frame, or one of the bearings or bolts that the suspension pivots around. By putting your hand on each pivot of the frame, you can get a sense for what might be loose. Of course, no tick = no problem!

Part and Labor Estimates:

Seals: $15-40 per seal
Install new seals and oil (labor): $20-$75
Fork Overhaul: $50-$200 and up. It really depends on what is wrong, and any parts.
New Bushings: $150-250. Typically you need to replace the lowers, and potentially the upper crown.
New Rebound or Compression circuit: $75 each to $300 for the set.



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