QuestionFRONT BRAKE LEVER BUILT PRESSURE THAT LOCKED BRAKES--STRANDED SO I BLED FLUID AT CALIPERS--RELEASED OK , BUT LOCKED AGAIN SOON AFTER--BLED ALL FLUID--MADE IT HOME--I THINK MASTER MIGHT HAVE GOTTEN SOME SPECK OF OLD FLUID IN A RETURN PORT SO I DISASSEMBLED, CLEANED AND REASSEMBLED--NOW I HAVE NOT BEEN ABLE TO BUILD ANY BRAKE PRESSURE BY BLEEDING AT CALIPERS--IS THERE A SPECIAL PROCEDURE TO DO THIS OR IS THE CYLINDER BAD? I FOUND NO WEAR OR SCRATCHES OR IN HOUSING OR ANY WORN SEALS--HAVE BLED ALMOST A QUART OF FLUID--NO RESULTS--PLEASE HELP
AnswerHi Bob,
Bleeding hydraulic systems can be frustrating.
I have several tech information files that will assist you, but I don't have your eamil address as requested and explained in my instructions.
Reply with your email addy and we'll go from there.
Respectfully,
Mark Shively
(sample tech files)
Brake Caliper Sticking
By Mark Shively
This is very common and often causes brakes to over-heat, fade, and even fail.
What happens is with time brake fluid changes chemically into a solid gel or in severe cases a crystal powder. The gel or powder expands against seals and seals are pressed against caliper pistons and prevent pistons from returning completely after brake pressure is applied.
When an excessive build up of gummed or crystallized brake fluid is present behind the caliper seals, thorough cleaning may restore the calipers to service. The seal grooves and lands must be scraped clean, sterile like, so to speak.
When this gumming process begins, it may reoccur more easily. This may be a result of metal surfaces being etched. Etching causes surfaces to form mountains and valleys. A caliper in good condition will have smooth machined surfaces. Rough surfaces seem to promote this chemical change more easily.
Inspection, Disassembly, and Cleaning:
Remove the caliper, brake hoses, and brake pads per the Service Manual instructions. Drain brake fluid from caliper. Spray brake cleaner in and around caliper. Carefully remove caliper pistons with compressed air. This may be dangerous, take necessary safety precautions. Insert a material between the piston and caliper to absorb the energy as the pistons blow out. Wood, rubber, folded shop rag, etc... Pistons make a loud pop noise as they are blown out.
Use a Vice-grip or other pliers to remove the pistons. They may remain partially in, or sometimes only one piston blows out. If this happens, grip the piston with pliers near the exposed edge. Place one tool jaw in the piston opening and the other on the outside surface. Or, place both jaws on the piston exterior circumference. Use a minimal bite to avoid un-necessary damages to the piston surfaces. Some tool marks will be left. Tools marks near the edge are ok. The seals will not contact this area, so the seals will not be damaged by the tool marks. Tool marks may be sanded smooth in most cases.
Once pistons are removed, remove rubber seals. Use a dental pick or other suitable means for removal. Use a dental mirror to view seal lands and grooves. Work in a well lighted area for best results.
For cleaning grooves, use pipe cleaning brushes, gun cleaning brushes, picks, Wet/Dry fine sanding paper, tooth or wire brushes, an Allen wrench sized to fit groove and with formed or ground flat blade like tool tip. Other tools and items may be fabricated or modified to work.
Once grooves are thoroughly cleaned, reinstall new seals. Clean and mend piston surfaces accordingly, and press into place. Install new brake pads (recommended), connect brake hoses, flush and bleed system.
