I take no credit for this article, I found it.
Scroll down for pics.
In the past I have had a problems with the anti dive system on my GL1800’s, until I fixed them.
I have two medium mileage GL1800’s (2003) one for me and one for my wife, both bikes have suffered with an anti dive problem. The brakes operate a slave cylinder that activates an anti dive actuating valve on the left hand side of the front forks, this slave cylinder only functions when the bike is moving. The slave cylinder has been changed twice on one bike and once on the other leaving me to believe that GL1800’s suffer with this problem. I have ridden many other 1800 wings and least two of them had the same problem but the owners were unaware anything was wrong until they rode my bike! My bikes are regularly serviced and the brakes have had the brake fluid replaced twice to date.
The symptoms :
While riding along normally the bike rides wonderfully smooth until I had to slow down or stop. The anti dive valve stays on until it decides to relax; during this time the front end of the bike becomes skittish at very low speeds or while cornering. The problem is also evident while negotiating speed humps in the road, I always slow as I approach them and then release the brakes before I make contact with them, but the suspension remains firm and seems to bounce over the speed hump. The result is that the suspension can finish up almost fully extended after crossing a series of speed humps. I once stopped after crossing one of these speed humps and put the bike on its side stand and waited almost 10 minutes for the front forks to relax back to the normal position.
On the third time this started to happen I (being an engineer) decided to take a look for myself.
The brake slave cylinder is the problem, it forces a 5mm pin into the anti dive actuator to lock up the left fork during braking. This slave cylinder is supposed to return upon releasing the brake lever but it doesn’t always behave as it should, it can take some time to return to its resting position. I took it upon myself to effect a fix that works better than ever and has been working well for the past year. My fix was to fit a small rubber 'O' ring over the pin and remount the slave cylinder to its rightful place, that’s it!
The rubber ‘O’ ring is 2.5mm(0.098”) in section x 5mm(0.196”) bore and 10mm (0.393”)O/D made of black silicone rubber, it sits in a void between the slave cylinder and the anti dive actuator. It doesn’t impede anything or prevent anything working it just helps the plunger to return to its rightful position.
To get at both the slave cylinder and the anti dive actuator is simple… first, remove the top front portion of the mudguard (top front fender) by unscrewing the four recessed (5mm) socket screws. This brings the two units into view on the front of the lower left fork leg, There are two (4mm) socket screws, one each side of the slave cylinder. Undo these… (don’t worry the two items can be separated and there should be no leaks, springs or nasty surprises) and insert the ‘O’ ring, checking first that your ‘O’ ring fits comfortably, without friction, over the 5mm pin on the slave cylinder and in the 10mm recess in the top of the anti dive actuator.
You can use two ‘O’ rings instead of the one.(above) The first ‘O’ ring dimension - 1.8mm (0.070”)in section x 5mm (0.196”) bore x 8.5mm(0.334”) O/D and theSecond ’O’ ring dimension - 1.8mm(0.070”) in section x 6mm(0.236”) bore x 10mm(0.393”) O/D, both black silicone rubber. The smallest ‘O’ ring sits on the 5mm pin without friction and the larger ‘O’ ring sits in the recess on top of the anti dive actuator, one on top of the other when assembled. Note: when putting the two units back together be sure the ‘O’ rings are still in place. This gives a slightly slower anti dive reaction under very light braking. I favor this fix.
You can, if you’re daft enough, (yep that’s me) ride the bike with the two units separated!!! but the bike will dive every time you use the brakes.
. If you try to fill the void between the two units with rubber the anti dive becomes next to useless. If your bike is still under warranty let Honda sort it. If you have found a leak of any kind from either unit STOP what you’re doing and inform your service centre.
Photos and their descriptions
Here are the pictures I hope they are useful Below is a description of each picture
The front mudguard (fender) removed 4x5mm socket screws
Using a 4mm Allen key to detach slave cylinder
The slave cylinder detached and not leaking
The top of the anti dive actuator showing the recess
The two rings I use are still in good working order and the only two tool required for the job
The largest silicone ring in the recess
The smallest ring over the 5mm pin - indicated by a screwdriver
Care taken to place the two items together
Securing the slave cylinder into place using the 4mm Allen key
Replacing the front mudguard (fender) using the 5mm Allen key