Submitted by: Lloyd Oliver (TwoTired)I wrote this many tears ago and it used to be available on the SOHC4 site. But, it vanished. I've been requested to offer it for the FAQ.
Here it is again slightly revised.
Front Brake Caliper Overhaul Walk-through
Preparing to overhaul your front brake caliper?
Sooner or later, the front brake on the Honda SOHC4s will need to be rebuilt. The bike's way of communicating this can be subtle or blatant. A spongy lever, high hand pressure to effect a stop, or leaks, are sure signs that attention is needed. So, here’s what I do.
Is the master cylinder leaking? If so, you'll have to rebuild that, too. Get a rebuild kit at the Honda dealer. Examine the hydraulic lines. Bend them around a little. See any surface cracks? If so, its time to replace those, too. You’ll really appreciate the improved brake performance offered by braided steel brake lines. But, new rubber ones will work ok. The rest of this article will assume you don't need these other parts. Only the brake caliper overhaul is discussed here. Trot down to the Honda dealer and get a new brake caliper seal. Shouldn't be more than $5. Get some brake fluid, too. Find some Dow Corning High Vacuum Grease (available here:
www.ellsworth.com/display/productdetail.html?productid=403; thanks "MrHellPop") This is pure silicone. Not a petroleum grease with silicone added, which just won’t do. If you can’t find the right stuff, don't clean off ALL the grease behind the pucks as directed later. AND DON'T USE REGULAR GREASE THERE INSTEAD OF SILICONE GREASE!! At higher temperatures, petroleum grease will ooze out onto the rotor, lubricating and soaking into the porous friction pads. If you can find some hydraulic brake assembly lube get that, also. Also get some brake parts cleaning solvent!
Got all the parts? Tools? Time? Then, let's get busy!
Remove the two bolts that hold on the caliper/piston/pad assembly together. Maneuver the assembly so the hose clears the fender hook/grommet and let the caliper assembly dangle over a catch pan. Take out the brake pad from over the caliper piston. If the pads are worn to the red lines or they are contaminated with brake fluid or petroleum products you'll have to replace them, too. Stock Honda brake pads last a long time. But, they need a strong hand to get lots of stopping power. After-market pads can make stopping easier on the hand, but they wear faster. Choose what's best for you. I always use the bike’s master cylinder to remove the Caliper puck/piston. You might want to put some plastic sheeting over the gas tank. Brake fluid squirting from the master reservoir will remove paint. We're going to flush the system while we get the brake puck/ piston out. Look in the master cylinder reservoir. Is it clear and clean? Here it’s a judgment call. If it’s really mucky, you don't want to push that stuff through the master and brake lines. A Mity-Vac will suck it out so you can put fresh in there. If it's just a bit dark, pump the lever slowly. (A fast pump will shoot some fluid straight up in the air.) WEAR EYE PROTECTION! As you slowly pump the brake lever the piston will start to move out of the caliper.
Watch the fluid level in the reservoir. Don't let it all pump out! When it gets very low stop pumping and use paper towels to wipe out and clean the reservoir. Refill with fresh fluid and resume the slow pumping (and refilling) until the piston pops out of the caliper. Yuck, what a mess! Now clean up all the brake fluid and crap that's now splashed all over the place. Done? Okay, back to work on the caliper. Wipe off and examine the piston and the caliper. Now you know why the brake was dragging...YECH! The piston can have some pits in it and still seal okay. But, if it’s too bad, you'll need another one. Judgment call, as they are expensive from Honda. I thought mine was bad cause it had about twenty small pits in it. When I showed it to Bruce, our local Honda mechanic, He said; "Oh, it looks brand new! Use it". I put it back together and it’s been fine. However, lots of deep pits can impede piston retraction by the square section caliper seal, causing drag and squeal. There was a seller on eBay that was offering a phenolic replacement. Looks interesting but I haven’t tried it, yet. I like to clean the caliper body on the bench; my knees and back start sticking if I bend down for too long. But, you can probably clean up the caliper while its dangling off the bike. You're call. If you want to remove it, disconnect the metal tubing at the caliper body. (You might have to reinstall it with the two bolts temporarily to do this.) I know some mechanics just clean out the gunk, put in a new seal, and put it back together. But, I'm just not comfortable unless I can get the internal surfaces as close to new looking as possible. Here's what I do. I used an "L" scribe to hook out the old seal, being careful not to score the soft aluminum insides of the caliper. Wash out the caliper with the brake solvent. I found that Allen wrench "L"s were useful for cleaning the seal groove which often builds up a layer of corrosion or hardened brake fluid deposits. I also used 320 grit aluminum oxide paper over the end of the Allen to clean the groove and piston wall. Wash out the caliper and piston with the brake solvent again. Without the seal, check for clearances by putting the piston in the caliper. It should drop in and fall out with gravity only. If not, investigate and correct that problem.
If you are using new brake pads, check for fit into the caliper. If there is any binding that prevent s free movement of the puck, file or sand the puck as appropriate to ensure free operation.
All set for re-assembly?
Coat the inside of the caliper groove, wall, seal, and piston with the Brake Parts Assembly Lube. (If you couldn't find assembly lube, you can use brake fluid. But, I much prefer the assembly lube since some of the fluid will be exposed to the atmosphere. The hygroscopic qualities of brake fluid will draw moisture from the atmosphere and begin corroding the caliper body.) Put the seal in the groove and push the piston in the caliper cylinder. Clean all the exposed surfaces of the piston and caliper with the cleaning solvent. Using the High Temperature silicone grease, coat the back of the brake pad puck, the piston face, and the caliper socket for the puck. Don't get silicone grease on the fiction surfaces of the brake pads! The purpose of the grease is strictly a water barrier to prevent metal behind the friction pad from subsequent corrosion. I don't want to have to do this again for another 15 years! Reassemble the caliper onto the bike. Adjust the stationary pad on the wheel side of the disk for .006 inch clearance from the disc. Reconnect the metal brake line at the caliper.
Brake Bleeding
I've heard people complain about how hard it is to bleed the brakes. Some people fill the system from the bottom (caliper bleed nipple). This really only works without a big mess if the system is completely empty. I use a method that's not particularly quick but fairly simple to do. Just be patient. I use a two-part principal for brake bleeding. It's a combination of pushing the air out of the caliper and letting the bubbles rise to the master and escape the system at the reservoir. Run a hose (see-through is nice) from the brake caliper bleed nipple to a catch jar and crack open the bleed nipple one quarter to a half turn.
Refill the master reservoir and, from now on, never let it pump or bleed dry. Gently pump the lever (short strokes, a quarter to half inch) and observe the bubbles in the reservoir and or fluid/bubbles at the caliper bleed. Sometimes you have to jiggle the brake lever to get the master to prime. Turn the bars to the left slightly so that the hole in the master reservoir is the highest part of the system and air bubbles will rise naturally to this point. Now, the hole is too dang small for the large bubbles to push out through the tiny hole against the weight of the fluid so very short strokes with 10 -15 second pauses between them should push large bubbles out the tiny hole in the reservoir. At some point you'll notice fluid running out the tube at the caliper. Close this off to the point of a trickle or very slow drip. You want to avoid putting high pressures in the brake hydraulic system until most, and ideally, all of the air is out of it. If you do it too soon the large bubbles in the system turn into a whole bunch of tiny ones that don't move around to the exit points very fast. When you stop getting any air out of either of the exit points. Stop. Close off the caliper bleed and wait a full minute. Go get a fresh cold one. Visit the rest room. Clean and put some tools away.
Vacuum the living room. Have a snack. Stare off into space thoughtfully.
Now go back and gently stroke the hand lever. Did you get more bubbles? Stroke gently until no more bubbles. Turn the bars to the right. Leave it alone for awhile again. Go cut you fingernails. Throw out some old junk mail. Have another cold one. Turn the handlebars back to the left. Wait a minute for bubble in the system to rise to that exit hole... Now gently stroke the hand lever again. Did you get more bubbles? Repeat the above processesuntil you can't get anymore bubbles out after sitting for awhile. Then put pressure on the brake lever slowly (or you'll get brake fluid on the ceiling) when the piston and brake pad move out to contact the disk you should get a hard brake lever. This is good. If it still feels spongy, you didn't get all the air out and tiny bubbles should pop out of the reservoir hole as you short stroke the lever. Keep it up until you get a hard lever. Or, wait until morning for the air to collect at the master reservoir hole. But, remember to keep the hole at the high point of the system. The above has ALWAYS worked for me. But, the bubbles will finally find their way to the master reservoir supply hole, given enough time and patience. I've heard others have had good results (and possibly quicker) using a Mity-Vac. Use it if you got it. But, I don't think it's necessary to do the job.
