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 Post subject: Cut Brake Rebuild Tips
PostPosted: Sat Mar 28, 2015 10:34 am 
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WB Contributor

Joined: Sat Feb 04, 2012 11:14 pm
Posts: 1418
Location: Birmingham, Alabama
I just rebuilt my nasty cut brakes. One side was limp and affected the foot brake as well. You could pump the lt side up along with the pedal and they would be rock hard. But after they relax they go to zero. The piston assembly has a rubber washer at the back wall. In the middle is a port that goes to the wheel. Trash stuck to that wall won't let the washer, seal and hold residual back pressure and flows back to the reservoir after it relaxes. Therefore your next brake application goes to the floor. Here are some rebuild tips. 1) the tiny hex screws at 12 oclock will probably be gaulded so drill them out with a 11/64" drill bit while clamped in a vice. They are not that important anyway. 2) With the cylinders pointed at the sky, in a vice, cram a flat screw driver ALONG side the piston rod TIGHT. Put vice grips on the screw driver handle and turn as you hammer the top of the screw driver. It will screw out just be patient and realize creeks corrode everything. Now with the threaded rods gone you will have a piston and spring assembly down in there that you think there is no way to get out. I had 100 psi on my air compressor and put it against the brake line supply inlet fitting and it cannon balled out across the yard. Maybe 10 -20 psi will be enough maybe. Down at the back wall of the cylinder where the rubber washer holds residual pressure you will see lost deposits. NEVER stick a screwdriver in there to destroy smooth surfaces on the bore or back wall. Use wood or plastic. Fill the bores with carburetor spray and clean it all up. My cups were still in great shape. You can gamble on re-using them but look for missing chunks of rubber on sealing areas. Those rubber boots may keep out trash and water but they also hold it in. Just a drop of water can make a component stay sweaty an create rust. When you cross a creek , remember, you have 8 wheel bearings and 19 brake sealing surfaces. Any gone bad will mess up your next ride. Oh , and too much Teflon tape, if you have to use it, will break off and get between sealing surfaces and orifices and boom . There goes braking power and fluid leaking. And as always if your 3/4 cup blows out of your foot brake. World Parts brand at Auto Zone, they can order some $3 wheel cylinder kits for an old Ford Courier truck or any other with a 3/4 cup. The part no. reads the same upside down 66599. (3/4) will be stamped on the cup. Keep several kits in your truck and some retainer ring pliers. Maybe one of my problems is using a factory steel master cylinder that rusts a little and sends deposits down stream but then again steel brake lines rust from the inside too. I have got 1 question to y'all. Does synthetic brake fluid dissolve rubber parts in cnc brakes. Sometimes I have dark black fluid in my reservoir with micro silver dots flowing around. And the boot attached to the cap is limber. And the cups break down and chunks break off the sealing edges.


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