Motorcycle Repair/Front brakes
I have a 1974 honda cb350 four. Front brake handle lever is dead , there is no resistance at all. Break light doesn't even go on when pressing on lever. I tried to bleed the fluid but nothing came out of the bleed nozzle. Any suggestions where to start. Also how do I properly drain the brake fluid from the system? Thanks
Jim, 40 year old brake systems need some TLC and rebuilding every so often. The solid feel on the master cylinder can be due to:
Frozen caliper piston/seal
Blocked release port in the floor of the master cylinder reservoir.
Collapsed brake hoses.
Contamination of the brake fluid inside the master cylinder, causing rust and decay of the internal parts, including a frozen master cylinder piston in the bore.
First thing to do is flush the master cylinder of any old fluid and check to see if the bleed hole is open at the bottom floor of the reservoir. You need to see air bubbles come up when you move the brake lever. If not, then get a tiny drill bit or piece of stainless steel safety wire and poke the hole open again. If the master cylinder looks too far gone, then plan on either replacing it or rebuilding it using a repair kit. You will need a set of special 90 degree snap ring pliers to get the snap ring out of the master cylinder piston clip groove.
If the blocked port isn't the problem, remove the brake caliper from the bracket with the pressure line still attached. Use the pressure of the master cylinder to push the caliper piston out of the caliper bore. Once it is out, check the piston for pitting which can lock the piston in place where it contacts the caliper seal. Remove the seal and thoroughly clean the seal groove in the caliper body. I use a 90 degree scribe tipped tool and brake cleaner to scrub out the groove. You can either leave the caliper body dangling off the brake line or disconnect it. Use a 6 pt socket to loosen the caliper bleed valve and clean it carefully.
Replace the caliper seal and install the piston if it isn't pockmarked with pits. Replace a pitted piston. Push the piston back all the way into the caliper body after you have lubed up the seal and piston with brake fluid. Check with 4into1.com for OEM and aftermarket repair parts. If the master cylinder bore is pitted/scored inside, then putting a kit in it will be a waste of time and money. Replace it with a good used one or a complete replacement part.
Leave the bleed valve open and allow brake fluid to trickle down the lines until it begins to exit the bleeder valve. Install the brake pads into the caliper and install it back on the bracket. Make sure that the caliper bracket is free to swing back and forth without forcing it. Clean/lube as necessary. Use brake cleaner or clean, clear water in a spray bottle to neutralize any spilled brake fluid, especially on painted surfaces.
Use the now operating master cylinder to pump fluid down the brake lines and out the bleeder valve. If the lever pressure isn't firm after a few minutes, wrap some rags around the handlebars, just below the master cylinder hose fitting and then bleed the master cylinder at that fitting, then move down to the junction on the steering stem. Bleed fluid until it comes out with no air bubbles and lever pressure feels firm again.
Scuff up the faces of the brake disc to minimizes brake pad squeal.