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user removed · 11-10-2014, 08:28 PM

To isolate brake circuits and properly diagnose spongy pedal.

Clamp off each brake hose (the flexible ones). Either use one or more vise grips, carefully adjusted so they do not damage the hose. I prefer to do all 4 at the same time, but it just takes more time if you can only do one at a time.

This eliminates that (or those) calipers-wheel cylinders from the system.

If you do all 4 simultaneously and you know the system is properly bled. The brake pedal should be as hard as a rock with virtually no travel, since the fluid can not move through the lines.

1. Pedal still spongy, bad master cylinder.

2. Pedal hard as a rock, master is good.

Once you have determined the master is good, then unclamp each wheel individually and when you get the spongy pedal you can be fairly certain that caliper or wheel cylinder is your problem.

Rear drum brakes on old cars tend to loose their "self adjusting" capability. Sometimes you can get it to work by just using the emergency brake, especially if it does not stop the car with 6-8 clicks of the emergency brake.

Sometimes you have to pull the drums and manually free up the adjusters. Not a bad idea to pull them anyway to check for shoe condition and hydraulic leaks.

Front calipers are notorious for frozen sliding pins on the single piston type calipers. Get them loose and clean lube the pins and the orfices they slide in.

Not a bad idea to check the pads, which in in severe cases can have much more wear on one pad if the pins were sticking-frozen. Also look for uneven wear on the pads friction material due to sticking pins.

If you really want to get adventurous, extend the pistons in the caliper and then clean the exposed surface of the piston,with scotch brite and some brake fluid, wipe them down and compress them back.

If you find that after all that work the brakes don't want to release completely, suspect the rubber hoses are collapsed internally and acting as a "check valve", stopping the fluid from returning from the caliper-cylinder to the master. Seen them come in the shop smoking because of collapsed hoses.

I have found the best way to bleed brakes is to use a glass jar and a piece of hose that you connect to the bleeder, with the other end in the jar. Top off the master reservoir and pump it with the bleeder open. This provides much greater movement of the fluid and will even get air bubbles out that will not be removed by conventional bleeding. The hose must stay under the fluid level in the jar at all times for this to work, good use for old crappy fluid.

Make sure the emergency brake cables are not deteriorated to the point where water can get inside and freeze, locking up the rear brakes if it gets cold enough.

regards
mech

11-10-2014, 08:28 PM	#35 (permalink)
user removed Master EcoModder Join Date: Sep 2009 Posts: 5,927 Thanks: 877 Thanked 2,024 Times in 1,304 Posts	Brake testing To isolate brake circuits and properly diagnose spongy pedal. Clamp off each brake hose (the flexible ones). Either use one or more vise grips, carefully adjusted so they do not damage the hose. I prefer to do all 4 at the same time, but it just takes more time if you can only do one at a time. This eliminates that (or those) calipers-wheel cylinders from the system. If you do all 4 simultaneously and you know the system is properly bled. The brake pedal should be as hard as a rock with virtually no travel, since the fluid can not move through the lines. 1. Pedal still spongy, bad master cylinder. 2. Pedal hard as a rock, master is good. Once you have determined the master is good, then unclamp each wheel individually and when you get the spongy pedal you can be fairly certain that caliper or wheel cylinder is your problem. Rear drum brakes on old cars tend to loose their "self adjusting" capability. Sometimes you can get it to work by just using the emergency brake, especially if it does not stop the car with 6-8 clicks of the emergency brake. Sometimes you have to pull the drums and manually free up the adjusters. Not a bad idea to pull them anyway to check for shoe condition and hydraulic leaks. Front calipers are notorious for frozen sliding pins on the single piston type calipers. Get them loose and clean lube the pins and the orfices they slide in. Not a bad idea to check the pads, which in in severe cases can have much more wear on one pad if the pins were sticking-frozen. Also look for uneven wear on the pads friction material due to sticking pins. If you really want to get adventurous, extend the pistons in the caliper and then clean the exposed surface of the piston,with scotch brite and some brake fluid, wipe them down and compress them back. If you find that after all that work the brakes don't want to release completely, suspect the rubber hoses are collapsed internally and acting as a "check valve", stopping the fluid from returning from the caliper-cylinder to the master. Seen them come in the shop smoking because of collapsed hoses. I have found the best way to bleed brakes is to use a glass jar and a piece of hose that you connect to the bleeder, with the other end in the jar. Top off the master reservoir and pump it with the bleeder open. This provides much greater movement of the fluid and will even get air bubbles out that will not be removed by conventional bleeding. The hose must stay under the fluid level in the jar at all times for this to work, good use for old crappy fluid. Make sure the emergency brake cables are not deteriorated to the point where water can get inside and freeze, locking up the rear brakes if it gets cold enough. regards mech