The difference in feel and...
The difference in feel and control of a rebuilt fork is amazing. After fixing our worn fork we could feel much better damping and a crispness to the action that had been missing. Replacing all the bushings gets all the tolerances much closer to like-new. Sure, there's wear on some parts that aren't economical to change, but you're shooting for no side play in the tubes, with the pistons and shims working like they should. If you plan to undertake an overhaul like this, make sure you get the tools needed to get the job done right.
Tech How-To
Dirt Rider has shown the ins and outs of disassembly and reassembly of the common cartridge fork designs and how to handle seal replacement and routine service. Here we focus on what to look for when inspecting the fork internals and how to know which parts are worn and need to be replaced. We used a Kayaba fork from an early '90s Kawasaki for many of the photos, since that type of open-cartridge fork is extremely common and is found on models that are probably long overdue for service by now. Specific problem areas of later-model sealed-cartridge Kayaba and Showa forks are included as well. Many suspension parts aren't available from the bike's manufacturer. For example, if you ask for new valve shims, the dealer parts book will most likely say you must buy the entire cartridge. Fortunately, the aftermarket has responded and these parts are available. All of the parts and tools used to refresh this old fork are from Race Tech. Since we aren't dealing with any specific brands here and this isn't a step-by-step rebuild, you'll certainly need a manual to address the bike you intend to service.
Your first step is to check and record the suspension settings (so they can be reset later), then turn the adjusters all the way out before disassembly. In addition you see if the adjuster is still working. Normally adjusters should have click detents and a positive stop going in and out. If not, the fork cap or base valve must be replaced. Disassemble the fork as shown in the manual and drain the oil. There may be a different number of spring preload washers in each fork, so keep them with the proper spring. Inspect the parts for damage or wear. At this point the best indicator of problems is the used oil. If it is dark and black or it holds metal chips, there is trouble inside.
01 On late-model Hondas with...
01 On late-model Hondas with Showa Twin Chambers the bolts for the fork guards and disc cover look the same, but if the longer bolts are used in the fork guard, it will dimple the tube and prevent the spring from coming out of the lower tube. The axle clamp must be removed to fix it. Race Tech sells a tool for it, but this is a job for suspension pros.
02 If applicable, remove...
02 If applicable, remove the parts from the cartridge rod. Inspect the spring guide for wear or cracking. This one has been sanded smaller to clear an aftermarket spring, but is fine to use. Honda CR80/85R forks commonly break these guides. They have no hydraulic bottoming system, and the kids riding them jump them hard.
03 On this Kayaba fork the...
03 On this Kayaba fork the bottoming piston has two parts that are unscrewed from each other. Two wire clips under the piston are located in a groove. The clips hold the piston in place, and they can't come out when the two halves of the piston are screwed back together.
04 The top of most cartridge...
04 The top of most cartridge systems has a bushing that acts as a seal or a bushing and a seal. If they're worn, the damping will suffer. To remove the seal head, heat it with a torch or heat gun to loosen the Loc-tite. It's almost impossible to remove the seal head without a cartridge-holding tool and a vise-mounted block to safely hold the cartridge tube.
05 This is the little seal...
05 This is the little seal bushing that needs to be replaced. Ronnie Williams easily popped it out with a small blade screwdriver. This seal bushing should be changed every year for serious riders for both early inverted forks and Showa Twin Chambers. Weigh the cost of the tools involved here to what a shop charges; it might be cheaper to have it done.
06 This is a late-model Twin...
06 This is a late-model Twin Chamber seal. Under the seal is a regular steel/Teflon bushing. The seal should be changed roughly once a season for KYB or Showa forks. If the seal wears, the cartridge doesn't offer the damping that it should.
07 This chamber is part of...
07 This chamber is part of the compression side of a late-model Kayaba fork. At the front, you can see a similar seal to the one used to seal the cartridge tube. When this leaks, the pressure builds inside the chamber and breaks it. Race Tech drilled the one in the rear to solve the problem. Change this seal every time you service the fork.
08 Once the cartridge is...
08 Once the cartridge is out, the inner and outer fork tubes should be empty. All that's left is to slide-hammer the fork apart. First remove this spring clip under the dust wiper. Then, holding the upper tube in one hand and the lower tube in the other, slide the fork together, and jerk it lightly to full extension. Repeat this until the two tubes come apart.
09 The old seal, bushings...
09 The old seal, bushings and a washer will all come out with the steel tube. On some models that washer can cup and should be replaced. On modern forks it may be a machined part that must go in a certain direction, so make note of its orientation.
10 Remove the old bushings....
10 Remove the old bushings. One slides off, the other must be spread by inserting fingernails into this vertical slot. You can see that the Teflon coating is peeled back from the removal process. This bushing must be replaced with a new one.
11 The bushings are steel...
11 The bushings are steel but are plated with brass and the wear surface is coated with Teflon. We straightened this bushing to make the wear easier to see. If you can see the steel on the side opposite the Teflon, like on this one, get new ones.
12 Race Tech recommends changing...
12 Race Tech recommends changing the bushing often, anyway. This close-up photo of the bushing surface reveals metal chips imbedded in the surface of the Teflon. Metal chips aren't as nice to slide on as Teflon, so this bushing is toast.