All forks respond better to persistent nurturing than intermittent guilt-ridden frenzies.
Sadly there isn’t room to include all the popular fork configurations here but this should give you an idea of the kinds of thing that go on inside. We have used the RockShox Reba as an example, since they’re widespread and respond well to attention.
The fork has an air spring in the left leg and a damping assembly in the right leg. The rebound adjusting knob is on the bottom of the right leg, with the compression damping adjuster and lockout at the top of the right leg, and both lower legs have an oil bath for lubrication. This arrangement keeps the entire damping mechanism as far away as possible from the heat of the disc brake, mounted on the left leg.
Damping performance depends on the viscosity of the damping oil, which is affected by temperature. If you ride in extreme temperatures, get to your local bike shop for a recommendation on oil weight. The damping oil level and condition is critical, so check it twice a year and replace once or twice a year depending on your mileage. There are three levels of servicing:
- Level 1: Every 50 hours, take the fork apart, cleaning the lower legs and stanchions, and reassemble with fresh oil. Follow steps 1–5 to disassemble, then steps 13–14 to reassemble.
- Level 2: Every 100 hours of riding, the air and damping chambers will need to be cleaned and filled with fresh oil. Follow the procedure all the way through steps 1–14. If you’re not confident about this level, take the fork to your bike shop and ask them to do it.
- Level 3: A specialist suspension tuner can customize your damping internals to suit your weight and riding style. Either take your forks into your bike shop or send them away to one of the service centres listed.
Before you start servicing your forks, make sure all external surfaces are clean. All lefts and rights are given as if you were sitting on the bike looking at the forks.
“The damping oil level and condition is critical, so check it twice a year”
Step 1: Before you start, make a note of the air pressures and rebound setting you’re currently using. Remove the valve cap from the bottom of the left fork leg. Release all negative air pressure by depressing the central stalk in the Schraeder valve, as show. Repeat with the positive air pressure, at the top of the left fork leg.
Step 2: Pull off rebound damping knob from bottom of right fork leg. Look at the forks from below. Undo the 5mm Allen key bolt on the bottom of the right fork leg five complete turns. On the left leg, use a 10mm socket wrench to undo the nut on its shaft until the top of the nut is flush with the end of the shaft.
Step 3: Have a container handy to catch the oil as it drains out of the bottom of the fork legs. Place a 5mm Allen key into the bolt in the bottom of the right leg. Tap the Allen key gently with your plastic hammer to free the damping shaft from the lower legs, releasing oil. Repeat on the left leg, with your 10mm socket placed over the nut
to protect it.
Step 4: Pull the stanchions out of the lower legs gently, keeping the lower legs over the container to catch the old oil. Leave the lower legs draining while you clean and inspect the upper legs.
Step 5: Clean and check for scours on the stanchions. Badly scratched stanchions need replacing – get a second opinion from your bikeshop if you’re unsure. Clean the insides of the lower legs by wrapping a clean rag around a stick and winding it down in there – repeat until it comes out clean. If you’re only doing a lower legservice (every 50 hours) go directly to step 13. Otherwise continue with step 6.
Step 6: Double check that you’ve released all the positive air pressure via the valve at the top of the left fork leg. Remove the air cap carefully with a 24mm socket and drain any oil on top of the air piston.
Step 7: Remove the circlip with your circlip pliers from the underside of the left leg. Pull out the air shaft, catching any oil that comes out. At this point, you can change the travel if desired by adding or removing the black plastic spacers below the piston. Clean the air tube and air shaft, then reassemble, pouring 5ml of 15wt oil onto the air piston through the crown. Then refit the top cap.
Step 8: Remove Floodgate adjuster with a 1.5mm Allen key then remove either the lockout lever or lockout remote spool (depending on your fork model) with circlip pliers. Undo the top cap with a 24mm socket.
Step 9: Remove the Motion Control damper and clean.
Tips for servicing forks
Circlips always need to be fitted back into their groove with the sharp edge facing outwards. Run your finger over either side – you’ll feel the sharp edge. This catches on the groove that it sits in, keeping the assembly securely attached.
- You may have been supplied with a random 20mm black C-shaped spacer along with your fork. These can be inserted under the air piston to change the overall travel of your fork. Reduce the travel for a steeper geometry and crisp raceday steering, increase travel for more control on fast downhills. The spacers are also available in 15 or 25mm lengths from your local dealer. For full suspension bikes, as a general rule it’s not worth having more than 20mm more travel on your fork than you’ve got on your rear shock.
- Always reassemble lower leg bolts with blue Loctite 243, to ensure they don’t shake loose. It’s also worth while fitting new crush washers onto these bolts at every service – your bike shop may have to order them for you, but they’re very cheap. Fit these in step 13.
- If you’re planning on servicing your own forks regularly, invest in a torque wrench to tighten bolts accurately. All the correct torque setting will be available on the manufacturer’s website – check those that apply to your particular model.
“If you’re planning on servicing your own forks regularly, invest in a torque wrench”
Step 10: Upend the fork and pour the damping oil into your pan, cycling the damper shaft to help it out. Remove the circlip on the underside of the stanchion, catching remaining oil. Remove and clean the damper shaft. Clean the interior of the fork legs carefully with a twist of clean cloth – it may need a couple of goes. Reinsert the damper shaft. Reinstall the circlip in its groove, sharp edge outwards.
Step 11: Inspect the O-ring seal at the top of the Motion Control damper and replace if there are any cuts or tears. Refill the damping chamber, from the crown, with 110ml of 5wt oil.
Step 12: Refit the Motion Control damper. In order to overcome the resistance of the oil, gently twist as you push the damper towards the threads. Then do up the top cap firmly and refit the lockout lever or lockout spool and circlip. Refit the Floodgate adjuster, with a 1.5mm Allen key.
Step 13: Slide the stanchions carefully onto the lower legs, past the seals. They’ll slide on a little way, then you’ll have to wiggle them to get them through the upper bushings inside the fork leg. Get the stanchions through the bushes (gentle wiggling!) but don’t push them fully home yet. Up-end the fork and inject 15ml of 15wt oil carefully through the holes at the bottom of each leg with your syringe.
Step 14: Wait five minutes while the oil runs into the fork, so that it settles between upper and lower bushes. Keeping the forks upended, push the lowers carefully home, wiggling past the lower bushings. The air shaft will appear through the hole in the bottom of the lower legs. Install crush washers, then firmly refit the 5mm Allen key onto the damper shaft and the 10mm nut onto the air shaft.
Step 15: You noted your air pressures before you started – reinflate the positive air spring, then the negative air spring. Recheck all nuts, bolts and controls, with a torque wrench if possible. Refit the rebound damper knob and valve caps.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “Cleaning and lubricating the stanchions”