At long last, after multiple requests for this maintenance task, it's here! It's a very easy, inexpensive, and quick task to keep another part of your Harley in top form.
The hydraulic clutch uses the same DOT4 fluid as the brakes. It needs to be bled out of the line and replaced at minimum once every 2 years. Preferably earlier. You can make it part of your brake line bleeding routine while bleeding the brake lines.
The process is very much the same as bleeding brake lines. You can either push from the bottom at the transmission or pull through the master cylinder down to the bleed valve at the transmission. You don’t have to be concerned with air getting stuck in an ABS module and taking the bike in to have the line electronically purged.
Clean Old Fluid From Master Cylinder
I choose to push bleed the hydraulic clutch using a syringe. The reasoning for this is that air bubbles will rise. If by chance air was somehow introduced into the line, it would work its way up the line and out into the master cylinder. Start by removing the transmission outer cover to access the bleed valve. Then begin sucking out the brake fluid from the master cylinder. This will make room for the old and new brake fluid you will be pushing through the line.
Clean Syringe For New Fluid
Clean your syringe, or use a second one for the clean fluid, and fill it up with new brake fluid. If there are any air bubbles in the syringe, hold it upright and flick it until they rise to the top at the nozzle end. Put the nozzle into the brake fluid canister and easily depress the syringe plunger until the air bubble comes out. Then hold the syringe upright with the tubing upright so no fluid comes out. Doing this prevents getting an air bubble into the tubing.
Begin Pushing Fluid Into The Line
Work the tubing onto the bleed valve, and you should not have any air bubbles at the connecting point. Turn the bleed valve about ½ and turn counterclockwise to loosen it so that fluid can be pushed through. You might want to get someone to stay by the master cylinder while pushing the fluid through to prevent overflow. Begin pushing the fluid out of the syringe with steady even pressure. You don’t want to mash down hard on the plunger; this could cause the tubing to pop off the bleeder valve.
The new fluid will push the old fluid up into the master cylinder. When the master cylinder fills up. While maintaining pressure from the syringe, tighten the bleed valve. Empty the syringe if you only have one. Or use your second syringe to empty out the master cylinder of the old fluid that came out of the line. You may have to perform this process a couple of times before getting all of the old fluid out.
Complete By Filling Master Cylinder
Once you see clean fluid coming into the master cylinder, you can stop pushing Fluid into the line. Tighten the bleed valve, and fill the master cylinder with DOT4 brake fluid from the bottle. Next, gently pull the clutch lever in and release it a few times to check for air bubbles coming out of the line. If you see any air come out, continue to pull and release slowly on the clutch lever. This will work any air you may have gotten into the line out. Put your master cylinder cover and transmission outer cover back on, and you are done.
It's Quick And Inexpensive
This process only takes about 15 minutes and is not difficult. Depending on how much you purchase, a brake fluid canister and the brand will cost under $10. If you go with some high-end synthetics, it can run upwards of $20. I only used 6 ounces in the video below, which was only half of the canister. Properly dispose of unused brake fluid because it is hygroscopic and will begin accumulating moisture once the seal is broken. This is another good reason to bleed both brake and hydraulic clutch lines simultaneously.
This video covers the process of bleeding the hydraulic clutch line on a Harley Davidson Touring bike. The line uses DOT4 brake fluid and should be bled every 2 years at a minimum.