The front forks are damping-rod forks. In the simplest term, oil is forced through fixed orifices. Fixed-orifice forks have very little "low-speed" damping and a lot of "high-speed" damping (vertical wheel speed). With very little low-speed damping, the fork dives excessively, and with a lot of high-speed damping you'll get a harsh spike.
T.R.A.C (Torque Reactive Anti-Dive Control)
To reduce the affect of fork dive, Honda developed the "TRAC" system. One of the two front brake calipers is hinged behind the fork leg on a pivoting link. When you apply the brakes, the pads grip the disc and this tries to drag the brake caliper around with it. The caliper pivots, pressing against the anti-dive mechanism's activating valve and closing off the fork's compression-damping oil passage.
This valve, in the shape of a piston, is normally held open by a spring. Forward weight transfer during braking compresses the fork, raising fork oil pressure against the underside of the TRAC activating valve and, through the valve, pushing against the caliper's braking torque. These two opposing forces - fork-oil pressure and braking torque - interact through the valve to provide progressive anti-dive. Hitting a bump causes a sharp pressure rise in the fork. This rise can cause the valve to push hard enough against the opposing force of the caliper to open, partially or fully, the normal compression-damping passageway. This opening allows the fork to respond to a bump. Moreover, TRAC's design provides a constant modulation between fork anti-dive and bump response.
The TRAC system has a four position adjustment on one of the fork legs. The adjuster controls a small secondary oilway parallel to the main compression damping passageway. This secondary passage provides a way to bleed-off fork-oil pressure from under the anti-dive valve. The rates at which this bleed-off occurs are controlled by orifices, the size of which can be controlled by an external adjuster.
Position one corresponds to the largest orifice, which offers the least resistance to the passage of fork compression-damping oil; positions two and three expose progressively smaller, more restrictive orifices, increasing fork damping pressure. The fourth position exposes no hole; all fork-oil pressure comes to bear on the valve's underside and against the braking torque.
Normally, a fork has much lighter compression damping (one-fourth) than rebound damping. In the TRAC system, when the anti-dive seals off the main compression-damping passageway, compression damping becomes two or three times stiffer than normal when the adjuster is set on position one. On successive settings the compression-to-rebound damping ratios become increasingly biased toward compression.
The part of the fork that is clamped to the triple clamps is called the "tube" or "upper". The part of the fork that the axle goes through is called the "slider" or "lower". Inside the fork from top down:
- Fork Cap
- Pre-load Spacer
- Fork Spring
- Damping Rod (or piston)
- Damper Valve
- Rebound spring
- Bolt to attach the Piston
(To prevent the fork oil from leaking out at the junction between the lower and upper, an oil seal is used. The oil seal is held in place by a circlip. Above the oil seal is a dust cover)
The manual recommends using ATF fluid as fork oil. As ATF fluid viscosity is not rated and may vary from mfr. to mfr. and bottle to bottle, Fork Fluid is recommended. Fork fluid comes in 10w, 15W and 20w viscosity. Normal recommendation is to use 10w unless you are toward the heavy end of the scale or ride 2-up quite often.
Replacing oil seals
To replace the oil seals all the oil must be drained out of the forks. Some models have a specific drain screw while others may drain from the damper bolt.
- Place a pan under the fork to catch the fluid.
- I find it's helpful to tape a piece of aluminum foil to each side of the leg. This will deflect all the oil down into the drain pain instead of your rotors or whatever is beside your bike
- Put the bike on the center stand and bleed the air out of the forks - THEN remove the drain/damper bolt on one fork.
- Sit/stand on the bike, and push up and down on the handlebars while holding the front brake lever. Do this until all the oil is drained from the fork.
- Repeat for other fork
- If the damper bolt is not already removed, remove it.
- The spring should keep the damper rod from spinning while you attempt to remove the damper bolt. If the damper rod still spins, an impact wrench will remove the bolt.
- Mark on the forks or measure where the top triple tree clamp meets the top edge of the fork (for reassembly)
- Use the frame to support the front end so the front tire does not touch the ground (forks or triple clamp should not be used)
- Loosen the top triple clamps and remove the fork cap.
- Caution: the fork cap is soft aluminum and prone to rounding. Some bikes have a very shallow nut on the fork cap. The best method is to find a six-side socket to fit and grind off the chamfer so the gripping part inside the socket is flush with the top of the socket.
Grind off chamfer seen here on top edge of socket
- The fork cap is under pressure from the spring so be careful as the fork cap releases itself from the tube.
- Remove the front wheel, detach the calipers and speedometer (if applicable), remove fork brace and fender.
- Remove the pre-load spacer and the spring.
- If a foam and plastic washer is present, discard it as it is no longer used (per Honda manual).
- Raise the dust cover (no special tools needed as its just a rubber plug that fits on top of the lower).
- Use a pair of circlip pliers with angled nose to remove the circlips from the groove inside the lower.
- Some have found difficulty using the inexpensive "universal" circlip pliers.
- The circlip may have corroded and fused itself to the lower and be difficult to remove. Spray PB-Blaster onto the circlip every day and allow it to soak.
- If the end of the circlip breaks off, it may still be removed by using a small screwdriver and a dentists pick.
- If all else fails, a hole can be drilled into the fork lower - inline with the circlip - where it can then be pushed out.
- Drill the hole on the backside of the lower where it will not be seen.
- Once drilled, fill the hole in with epoxy.
- Loosen the lower triple clamps and slide the tube out of the triple clamps
- Grasp the lower in one hand and the upper in the other hand and forcefully pull apart. This is using the fork lower and upper as a slide-hammer to unseat the seal.
- Once the lower and upper are separated, remove the components from the upper and lower and clean out the old fluid.
- Examine the bushing(s)s. Replace if there is excessive scoring or scratching, or if the teflon is worn over 3/4 of the entire surface
- Older busings were split, newer ones are not split
- The TRAC system can be taken apart and cleaned.
- Examine the portion of the fork tube for nicks or burrs that may have compromised the oil seal and caused it to leak. They can be removed with a whetstone or other grinding device. The fork tube should be as smooth as possible.
- Lube the bottom of the fork upper with fork oil and slide the oil seal up from the bottom
- Sliding the oil seal down from the top may cut it due to the many imperfections normally present at the top.
- On OEM fork seals, the writing on the seal is facing UP
- Replace the components in the fork upper and lower (minus the top spring and preload spacer)
- Put the upper inside the spacer and hand tighten the lower bolt.
- Place the fork in an vertical position with the lower resting on a padded surface.
- Slide the old seal down over the new seal and slide both down to the top of the upper. The old seal will act as a buffer.
- A seal driver should be used to install the new seal.
- Go to your local hardware superstore and get a piece of 1 1/2" PVC pipe. They'll sell you about 4 feet more than you need, but it's cheap and you can cut off the right amount with a hacksaw. This only works with the 39mm forks of the V45s. V65s have 41mm forks. For these, get a piece of 2" PVC and a 1 1/2" coupler. Grind or rasp the coupler down so it will fit inside the fork body and cut a piece of the 2" pipe to use on top of that.
- Use a slamming motion to get the new seal to seat. Only moderate pressure is needed
- Remove the old seal and install the circlip.
- For V65's a Kawasaki Concours circlip can be used. It is "Z" shaped and less likely to corrode and fuse to the lower.
- Slide down the dust cover and reinstall the fork onto the bike. Lightly tighten the triple clamp bolts to keep the fork from sliding out.
- Add oil and install top spring, preload spacer and fork cap
- The fork cap should extend past the fork upper by about 1/2" to 1". This makes it difficult to compress the spring and screw in the fork cap without cross-threading the threads on the cap. The socket on top of the cap can help keep the cap straight when pushing down and screwing it in. Be careful!
- Repeat for other fork.
- When both forks have been remounted to the triple clamp, reinstall the rest of the front end of the bike.
- Torque the bolts starting from the axle and move up the bike
- Before torquing the triple clamp bolts, be sure the forks are positioned correctly and match your measurements or where you previously made a mark.
- Test drive the bike in a safe area until you are convinced that everything is correct. This is where wearing all of your gear is important.
- You can try to refresh the seals by using Pete Springers method. It doesn't take much time or money and is well worth the effort. '
Another method that works to remove gunk from the seal
- Clean the fork upper just above seal.
- Wrap a couple layers of QUALITY packing tape (like 3M) -sticky side in - around the fork just above the seals. Try not to have any wrinkles. And cut the tape cleanly, you don't want any pieces of tape ripping off and getting stuck in the seal.
- Then lock the front brakes and forcefully rock the bike back and forth pushing the tape into and out of the seals.
- Remove the tape (you can CAREFULLY cut with a razor blade if you have to - don't mar the fork surface) and clean the fork upper and lower of any oil.
- Go for a ride and see if any oil/dark ring shows up on the fork upper. A slight film you can only see on your finger when you wipe it on the fork upper should be OK. Any more and you will need to replace the seals.