QuestionI purchased a 78 Honda CX500, with 3500 miles on it, that had been sitting for few years. It's ready to license except for one problem. When I purchased the bike the front brake was locked up. I had a friend completely rebuild the master cylinder and that's working. I tore apart the caliper and cleaned it. I did not lubricate the ring the piston rides on. The ring and piston were in fairly good shape. I got it put back together and back on the bike. I've tried bleeding it several times and tried various other methods of getting the brake to work, adding fluid through the bleeder valve, adding fluid through the brake hose, and nothing works. I've used the Clymer manual and have followed the steps in bleeding the brake. Nothing works. The caliper isn't leaking, the master cylinder has fluid in it (new clean fluid). I can stand there all day and squeeze the brake lever and never any pressure build up. Do I need to overhaul the caliper? When I took the piston out I had to have it blown out. Please help.
Ed
AnswerHi Ed,
Review the tech files about brake bleeding listed below. (I return tech files by email. Please include your email address with all questions as requested.)
Over time, brake fluids changes chemically into a gel-like solid and obstructs brake system components. If the problems persist, consider checking the brake hose for obstructions.
To do this, try bleeding the system again. Verify that brake fluid is present at the caliper. Open the Banjo bolt (brake hose bolt) at the caliper instead of loosening the bleeder valve.
If no fluid is present, one of the following may be happening: the brake hose is obstructed; and/or the master cylinder needs bench bled; and/or master cylinder rebuild kit was not properly assembled (or defective).
To continue checking this, move backwards along the hose to the next point that the system can be opened. Attempt bleeding from each point and observe. Repeat this until you get fluid from one of the opening points.
If no fluid is present at any point, try bench bleeding the master cylinder and then the entire system.
I suspect you did a thorough job of cleaning the caliper. Lubing the seals on the caliper piston is not mandatory, but helpful. Use a light finger swabbing of brake fluid.
Keep in mind that the manufacturer recommends replacing brake hoses with time. See the periodic maintenance table in the Owner's or Service Manuals for details.
Respectfully,
Mark Shively
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Brake/Clutch Bleeding 101
By Mark Shively
Use high quality DOT 4 brake fluid (or preferred type) from a sealed container. Remove the old fluid from the master cylinder reservoir. Use a cooking type squeeze bulb baster to remove the bulk of the fluid. Use a paper towel to remove any remaining fluid. Top off the empty reservoir. Top them off periodically during this procedure. Do not spill any fluid on your bike because it may damage the paint. The front brake reservoir tends to spit fluid out the top during this process so make sure you place a bunch of rags, old blankets, or towels over the fuel tank.
You can make a bleeder drain container fairly easily by taking a plastic container with a screw on lid. Put a hole in the container lid just large enough to get the hose through. Put a short section of hose on the bleed valve on the brake caliper. Put the drain container on the other end to catch the runoff. You'll need to move the hose and container around to each caliper as you work, or use more than one container.
Use a wrench to open the bleed valve while simultaneously squeezing the lever (or pedal). About 2/3 of a turn on the wrench will do it. Fluid should run out of the hose at this time. When you squeeze to within 3/4 of your full lever pull, use the wrench to close the bleeder valve. It is important that you close the valve before hitting full travel on the lever. Release the lever and repeat the process (squeeze lever, open valve, close valve, release lever) until the fluid runs with no bubbles and the lever is firm. You'll be amazed how firm you can get your system.
While this way will work and there is absolutely nothing wrong with it, it's a misconception that you have to shut the bleeder valve between every pump/squeeze of the lever. People do this on their cars, too. Pump, Open/Close; Pump, Open/Close…. You really don't need to do this. As long as you've got fluid flowing through the bleeder tube, you can just keep pumping/squeezing the lever until fresh brake fluids runs through the system. The end result is a flushed and bled system. Just make sure the reservoir stays topped off. If you bleed it dry, you'll have to start all over again.
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Brake/Clutch Bleeding 102
By Mark Shively
Vacuum bleeders are sometimes more troublesome than efficient. Other times they work well. The old school way to bleed is to allow the master cylinder to purge the system of air. This may be slow at times, but effective.
To begin, flush the existing brake/clutch fluid from the reservoir. Pump it through the lines to the bleeder valves. Flush thoroughly until you see new fluid exit each valve. Start with the closest bleeder valve and work away from the master cylinder, to the next furthest valve.
To flush, pump the lever a few times and hold the lever in as if bleeding the line. Open the bleeder valve wide open and leave it open. Begin pumping until you see fresh fluid at the bleeder. When you see fresh fluid, hold the lever in on the last pump and tighten the valve. Pump the lever and crack the valve for a quick bleed. Repeat for all bleeders. You may not need to bleed the system after the last valve is flushed.
If bleeding is necessary, bleed the system by starting with the furthest bleeder valve and work towards the master cylinder (just the opposite of flushing).
If master cylinder needs purged of air (rare) do the following: adjust the master cylinder so it is as level as possible on the handlebar. Remove the reservoir cap and top off fluid to proper level. Very, very, slowly pull the brake lever in while monitoring the inlet/outlet ports in the bottom of the reservoir (machined holes). Release the lever slowly, alternating lever pulls of about 1-2mm, and full pulls. The shorter pulls seem to purge air best. Look for air bubbles to rise from the ports. Repeat until no air is seen and/or lever feels firm.
If no air is seen, pull the lever in and let it return quickly by releasing it from your fingertips. It should snap back under the tension of the plunger spring. Repeat this several times while watching for air bubbles. Switch between the two methods described above: slow short pull method and long quick release method.
When no air is observed, the master cylinder is purged of air. Be patient, this may take several minutes. If no air is observed and “brake” lever feels soft, bleed lines until lever feels firm. Clutch levers should feel soft. Synthetic brake fluids may result with a softer than normal lever feel. Old rubber brake hose may result with a softer feeling lever due to expansion of the hose from age. For best results, use braided steel brake lines and DOT 3 or 4 brake fluids.
Tip: Shake or gently tap brake hoses with a tool to send residual air up the lines to the master cylinder.
Note: Clutch levers are not intended not pump-up to a firm feel.
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Brake Bleeding Tips
Bleeding the brakes on a GL1000 is straightforward and well-covered in any manual. However, this can be a most aggravating task. Below are some tips to reduce your frustration.
Precautions:
1. If you have any problems with less than perfectly bled brakes, take immediate and comprehensive steps to rectify this ASAP. Do not ride your bike with anything less than brakes which are operating absolutely perfectly.
2. Keep in mind that brake fluid is a VERY effective paint remover, so take adequate steps to protect your paint whenever you do any brake work. When I'm bleeding brakes, I take time to cover the bike carefully with plastic. I use large plastic leaf bags. I also keep a spray bottle of soapy water and another spray bottle of plain water handy just in case a spill occurs. Rapid application of soapy water following by lots of rinsing will prevent paint damage should a spill occur.
There are 3 major problems you might encounter:
• "Mushy" lever
• "Leaky" lever
• "Hard lever with too much travel"
Note: In this tech tip, "lever" generally means both lever (front) and pedal (rear).
"Mushy" lever indicates the need to bleed more thoroughly or replace brake lines which have lost their structural resistance to expansion. You may also have a "trapped" air bubble at a banjo fitting or other high point in the system.
"Leaky" lever provides a firm initial brake feel that deteriorates quickly; i.e., the lever slowly pulls all the way the the handlebar grip. This indicates an external leak in the hydraulic system which is easy to diagnose (there will be a puddle or drip somewhere) or an internal leak past the seals on the master piston inside the master cylinder. IMMEDIATE REPAIR IS NECESSARY!
"Hard lever with too much travel" is a fairly common issue with early GLs but rarely mentioned in Troubleshooting Charts. The soft alloy of the front brake lever itself can wear on the engagement "face" which contacts the actuating rod of the master cylinder to the point that the geometry is compromised. The solution is easy...replace the brake lever. See also: http://www.randakks.com/TechTips.htm#18
Bleeding Methods:
"Old Reliable" - I usually bleed brakes the old fashioned way ... with a simple catch container and a suitable length of clear tubing. This is all you need really. My catch container is "dedicated" to brake bleeding, so there's not much set-up or cleaning required for each use. It actually started life as a toddler's "sippy" bottle (really!). I've modified it a bit to meet my needs...mainly by adding weight to the bottom to make it tip-resistant.
Vacuum Bleeding - I also have a Mity-Vac system which works great. I find that vacuum bleeding provides no real advantage and takes me longer to setup and clean when I'm done. Thorough cleaning is an absolute must with a Mity-Vac or similar since vacuum pumps are used for many other purposes besides brake bleeding. Mity-Vacs usually come with a "motorcycle brake bleeding" supplement in the manual plus adapters specifically designed and sized for motorcycle brake bleed nipples.
Reverse Bleeding - Some people reverse bleed by adding fluid through the bleed nipple at the caliper with a large syringe or pump-type oil can. I have a simple set-up for this that works very well .. a jumbo syringe from a medical supply house. You can also purchase these from vet-supply dealers that cater to large animals. I don't usually find reverse bleeding necessary unless every component in the system is "dry." Reverse bleeding can be very effective for stubborn cases of trapped air bubbles. Since air bubbles naturally want to rise, reverse bleeding easily moves the air upward to the master cylinder reservoir. Also, when attempting to fill and bleed a completely "dry" braking system, reverse bleeding can save time and aggravation. However, reverse bleeding is a bit riskier in terms of creating an opportunity for spills and ruined paint since you're pushing fluid up to the master cylinder reservoir. If you're not paying attention to the level in the reservoir, fluid can easily overflow with dire consequences.
Bleeding Tips:
When bleeding, keep these points in mind:
• It helps to "pre-fill" the calipers, master, and lines as you re-assemble the components after an overhaul.
• Move the lever (or pedal) deliberately…don't thrash!. You're trying to move fresh fluid in a manner that displaces the fluid and air froth already in the system. If your action on the lever (or pedal) is too aggressive, you risk creating more froth in the system.
• When moving the lever (or pedal), stop about ½" short of max travel on each stroke.
• Put some grease on the bleed nipples to prevent air entry when the bleed nipples are cracked open (especially important when vacuum bleeding)
• Open the bleed nipple on each stroke just as you begin moving the lever (or pedal).
• Very important: open the bleed nipple just enough to let a very small amount of fluid pass through. If you open the bleed nipple too much, you will lose "feel" at the lever (or pedal) and you'll have a harder time stopping at the right moment on each stroke.
• Close the bleed nipple at the end of each stroke before you release the lever (or pedal).
• It's sometimes necessary to "burp" the banjo fittings to release trapped air.
• Judicious tapping with a suitable rubber mallet at suspected locations of trapped air is sometimes helpful in getting them to move.
• If you have a highly aerated (frothy) mixture in your system, sometimes it helps to put pressure on the fluid by squeezing the lever (or pedal) overnight. For the lever, I use a zip-tie and for the pedal, I use a 5 pound dumbbell hanging from the end of the pedal. This will firm up your lever by putting the air back into suspension with the brake fluid. Then, you will need rebleed again the next day to replace the air-contaminated fluid in the system. Otherwise, the lever firmess you gained overnight will soon be lost as the air falls back out of suspension again...trust me it will!
• DON'T MIX DIFFERENT TYPES OF BRAKE FLUID. GL1000s require DOT 3 brake fluid. I use Castrol brand brake DOT 3 fluid with great results. Brake fluid specs are confusing. For example, DOT 5.1 is marketed as "univeral" brake fluid and is supposed to be compatible with DOT 3 and DOT 4. However, DOT 5 brake fluid is silicon-based and not compatible with any other type of brake fluid. Be safe and don't confuse the next owner of you bike or your mechanic. Always use DOT 3 brake fluid.
• Brake fluid is hydroscopic (attracts water). This has two implications. Over time, the water absorbed by brake fluid will effectively lower the boiling point of your fluid rendering it less effective under hard use. Secondly, the absorbed water wreaks havoc on calipers and brake pistons causing rust and pitting. If you don't change your brake fluid regularly, eventually your brakes will fail ...it's a cetainty! I recommend that you change brake fluid ever 2 years religiously.
• Make sure the by-pass port in your master cylinder is open and clear. This port is the smaller of the 2 ports which allow fluid to travel from the reservoir into the cylinder. This small orifice is easily blocked by small amounts of crud. If this small port is blocked, you'll have all sorts of brake problems including difficulty bleeding the system. You must remove the reservoir to inspect and clean these very important ports.
