Brake Bleeding Help

Kurt Halverson

Kurt Halverson

PCS Northland Chapter President
Hello Everyone!
Please go easy on me, this is the first time I have had the pleasure of bleeding brake lines. I am working on the '77 Miller Meteor Cadillac which has front disc and rear drums. I replaced the master cylinder (which I bench bled according to the instructions that cam with it), the front hoses, the rear hose, and the steel line that goes to each rear wheel and the line that goes from the portioning valve to the rear hose. I was able to bleed the rear wheel cylinders without issue, but now I am working on the passenger caliper and I am not having luck. When I first started at that corner, I would have my wife pump and hold the brake pedal down; once I cracked the bleeder screw I could see air bubbles coming out of the hose into the glass jar of brake fluid. After doing this 3 times, no more air bubbles were coming out, but no fluid was coming out either. I noticed that when my wife let off of the brake pedal, the caliper did not loosen up. I can use a small pry bar to spread the caliper so the pads are not clamped down to the rotor. I consulted the Chilton's manual, and that had a special note about bleeding cars with front disc brakes that said something about a pin on the master cylinder that has to be held down while bleeding, but I could not find any such pins. Does anyone on the board have any tips or tricks that I could try? Thank you in advance for any suggestions.
Kurt
 
Brakes

With the parking brake off and key on is he brake light on? The pin they are talking about is in the proportioning valve. It will have a small rubber boot around it. The valve is off center do to the loss of brake pressure. Some times you can re center the valve by cracking the front and rear lines at the valve while applying pressure with the brake pedal.If not the pin needs to held up to let the valve re center and allow fluid to flow front to back. The valve proportions the pressure front to rear and in case of brake failure in one side of the dual system will close off still allowing half the system to work.
 
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Disk brake calipers don't release, since there is no release mechanism built into them. They are designed to have a close tolerance to the disk itself, and the pads slide on the surface of the disk with barely any contact, until you depress the brake pedal. Doing brake bleeding is quite easy, and you should be bleeding all four brake wheel cylinders if you have replaced the master cylinder. You start with the rear right, then the rear left, front right, front left. It will take about 10 pumps to do the first one, since you need to push all the old fluid out, and displace all the air that is trapped in the line. The second one doesn't take as many, since you have already moved all the old fluid out of the line from the master to the rear distribution block that is located over the top of the center of the differential. The same applies to the front right, but it shouldn't take as many pumps, since there is less distance for the fluid to travel. After each 3 pump cycle, you should refill the master cylinder, before starting the next 3 pump cycle. When blading, have the helper pump the pedal to bring up the pressure between each bleeding procedure.
When your assistant pushes the pedal and you open the bleeder, they should hold their foot on the pedal until you have tightened the bleeder, so you don't draw any air back into the system. The short hose that goes from the bleeder to the bottle isn't a positive seal.
Your car does have is a centering piston for the brake failure light on the dash. If that comes on, make another post and I will help you resolve that.. One issue at a time is the best way to learn...
Paul
 
why did you change the master cylinder? it is most likely the proportion valve but it may also be the rubber hose. if it has broken down inside the liner can plug off the brake. but of course you remembered to add fluid to the master reservoir as you bleed. I usually can get the proportion valve to center it self buy opening the rear. and jabbing the brake hard. then close it up. there are as many way to bleed brakes as there are mechanics. but I find if you open every bleeder first and let them drip till its a steady drip . then close them off and do the pump, hold and open. you work less at getting the air out.
 
As Ed stated there are many methods and mechanics but not all know all. My 70 MM Caddy combo had one front wheel grabbing before the other for years and several mechanics had no idea why. I figured maybe caliper sticking so replaced them with no results and one day we had a mobile mechanic come by the dealership to do some work and I ask him about checking it and told him the symptoms. He said he would and after only a few minutes he said he had fixed it. WOW, that was quick and he actually fixed it. Turned out to be as Ed mentioned one of the front brake hoses had collapsed internally. I guess it had a right to after 40 years and 140,000 miles. Works great now and cost a lot less than the calipers I put on for nothing. I did save the old ones instead of turning in for cores as they told me they were getting hard to get.
 
Usually when a rubber brake hose collapses internally, it will allow the fluid to move through it to the caliper or wheel cylinder, since the fluid is under pressure, however, it will not allow the cylinder or caliper to release, since the fluid return is not under pressure. I would recommend that the rubber brake lines be replaced at least every 10 years, and that the brake fluid is changed every two years, unless you are using silicone brake fluid. When you use silicone brake fluid, it has no deteriorating effect on the rubber parts, doesn't absorb water, and your brakes will work as well in 10 years as they did the day that the system was rebuilt and the silicone fluid installed. Installing silicone brake fluid requires a complete rebuild of all braking components prior to it being installed in the system. It also isn't recommended by the manufacturer for use with disk brakes, because of its lower boiling point. Heat from the braking action transfers to the brake fluid will cause certain brake fluids to boil. Each type of brake fluid has a DOT (Department of Transportation) number assigned to it. The fluids have chemical or formulation differences that are what determine this number. There is no correlation of this number, so don't assume the higher the number or the lower the number, has anything to do with the quality of the product.

If you want to learn more about brake fluids, read this article on Super Chevy magazine.
 
Thanks for the advice everyone! Bill, I would say your advice sounds like the most fun AND the most expensive! At first I thought my problem was the pin in the Bendix valve. The other night I was in the process of bleeding, I started with the right rear, then the left rear, then the right front. When I had gotten to the right front I did not get any fluid out of the bleeder. So tonight, I tried the left front bleeder, and I got fluid out. Then, I loosened the hose to caliper banjo bolt for the right front, and fluid the leaked out of the hose. I tightened the bolt back up, and tried bleeding again, and still no fluid out of that bleeder. So, my thought is that instead of having a problem with that Bendix portioning valve, instead I have a bad caliper on this corner. What are your thoughts?
Thank you!
Kurt
 
Assuming that you had someone depress the pedal while the banjo fitting was loose, my thoughts are that the hose on the right hand side has collapsed internally, and is completely blocked. If that isn't the case, then you still don't know if it is the hose or the caliper. I would just unscrew the caliper bleeder screw and take it out completely, and then see if the screw is blocked. It is is blocked, then you can usually clean it with a straightened paper clip. If the bleeder screw is clear, then that leaves either the hose or the caliper, or both. Check both, and report back, but don't just start changing parts assuming that the part is bad without first verifying the part is defective.
 
Thanks Paul! I have already put new hoses on the car as part of this project. I will check the banjo bolt for obstructions. If that is clear, I will replace the caliper. And yes, my very patient wife has been my brake pedal pusher for this project.
Kurt
 
What I was referring to as being clogged is the bleeder screw. Totally remove the screw, and check to see if it has an obstruction. If it doesn't, then depress the brake and see if fluid comes out. If it does, then the caliper is good, and it has to be the bleeder screw. Only time that I have ever seen a caliper go bad is when it leaks or is stuck. Never had one go bad internally when bleeding them. There is a clear hole between the caliper and the bleeder screw. If the screw is clear, then try putting the paper clip end into the bleeder screw hole, and see if that is blocked. If so, a little wiggling of the paper clip should clear it and then bleed the brakes again.. Paul
 
that's were the drip method I do comes in handy you take the bleeder out and leave it out till your get a steady drip out of the hole. then you know the lines are clear. you also get to look at the bleeders to see if they are plugged. usually if it's a hose the brake will lock up and not realise. all the caliper is is a void with one wall a bellows diagram. nothing in there to plug up except the bleeder hole. the only other place would be the bolt holding the hose on. I have never heard of a caliper pluggin up. not saying it could not fill full of rust and sludge enough to do it but if it was that brake would not have been working for a long time.
 
Collapsed brake hose

Kurt Halverson said:
Thanks Paul! I have already put new hoses on the car as part of this project. I will check the banjo bolt for obstructions. If that is clear, I will replace the caliper. And yes, my very patient wife has been my brake pedal pusher for this project.
Kurt
Click to expand...

MY 2 CENTS IS BETTING ON A COLLAPSED BRAKE LINE HOSE. THE HOSE IS LIKE A CLOGGED HEART ARTERY AND THAT IS WHY NO BRAKE FLUID COMES OUT NOR DOES THE CALIPER RETRACT.
BEEN THERE AND DONE THAT!
CHUCK:biker::4_11_9:
 
Kurt Halverson said:
Thanks Paul! I have already put new hoses on the car as part of this project. I will check the banjo bolt for obstructions. If that is clear, I will replace the caliper. And yes, my very patient wife has been my brake pedal pusher for this project.
Kurt
Click to expand...

Charles Commerford said:
MY 2 CENTS IS BETTING ON A COLLAPSED BRAKE LINE HOSE. THE HOSE IS LIKE A CLOGGED HEART ARTERY AND THAT IS WHY NO BRAKE FLUID COMES OUT NOR DOES THE CALIPER RETRACT.
BEEN THERE AND DONE THAT!
CHUCK:biker::4_11_9:
Click to expand...

He already replaced the rubber brake lines...
 
After a busy few weeks I have finally had time to get back to my project tonight. Thank you Paul for providing me with the right answer, the bleeder was indeed plugged. I have the problem fixed; hopefully my wife can help me bleed the brakes this weekend and just MAYBE I can finally take my car for a drive! Thank you again everyone for your advice and help!
Kurt
 
Thank you to everyone for your advice, and thank you to Paul for taking the time to visit with me on the phone about this issue. We did get the problem resolved, we ended up bleeding at the master cylinder, then the proportioning valve, then at all four corners. She stops great now!
Thank you again,
Kurt
 
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