When you said "I disconnected the MC and the brakes did not release." do you mean you removed the MC from the booster, or you removed the lines from the MC? If you removed the MC from the booster, it tells us the booster rod is not the issue. If you removed the lines from the MC and the brakes did not release, its not the master. You should be able to get your brake drag by pumping the brakes several times in a row. When the brakes are dragging, if you loosen the lines at the master, and get a high pressure squirt from either line and the brakes release, I'd suspect the master is at fault. If there is not a high pressure squirt when you loosen the lines or the brakes do not release, the master is probably not the issue. Could be: 1) E brake hanging up/not releasing fully/dragging. 2) Brake hoses collapsing inside. 3) Calipers not fulling returning when released. 4) Rear shoes not returning to the top stop. Unfortunately, in this day and age, "new" does not necessarily mean something is good. Put the car on jack stands & pull off the tires. spin each drum/rotor by hand and be sure they are free to rotate. Then, pump the brakes a few times, and determine which wheels are dragging. On the brakes that are dragging, if you open a bleeder screw, does that wheel release? Close the bleeder screw. Are all of the wheels released? Pump the brake pedal up several times again, determine which brake is dragging. Now loosen the brake line on the master side of the brake hose, does the brake release? Report back. Gene
Seems there's some confusion here between free play between the pedal and the booster and the clearance between the booster and the master. They're both necessary. Beyond that, I've had residual pressure valves locking up and failed flexible lines preventing (or restricting) fluid return. Or there might be residuals already in the master that aren't required? And let's not forget the pedal return spring which needs to be strong enough to hold the pedal off the booster (so that the free play can be just that!!). Chris
Happydaze just mentioned a highly likely culprit. I completely neglected to mention that in my responses earlier. Without that return spring allowing the play to fully allow the internal valves to open and return, the pressure still builds. Great call!!! I have my money on this!!! Sent from my iPhone using The H.A.M.B. mobile app
Couple of other things that come to mind; Is your brake pedal arm itself fully returning? And I can't really tell from your pix but is there a possibility that your exhaust header is heating up either the MC or lines and causing fluid expansion?
Booster input rods that I know of or have worked with have no adjustable free play, and attach solidly from the control valve to the brake pedal. (Free play is adjusted on the output rod) What is important is to make sure the pedal can move farther back when disconnected from the booster, ensuring complete booster return. A strong separate pedal return spring is also required, as you and others have stated, because the booster's internal spring is generally not designed to return pedals and linkage.
I had it on my lift. It is just the front calipes sticking. I changed one of the calipers already. I do have a return spring on my pedal. When l release the bleeder on a calipers the wheels free up. I have checked the booster and MC with my heat gun and they do not seem excessive. My emergency brake cable has lots of slack when released. Looking at the pic of my MC does anyone know what it woul
Are you 100% positive your return spring in the pedal is returning the MC plunger rod to the MOST extended position? A weak spring is equal to no spring. Sent from my iPhone using The H.A.M.B. mobile app
Mix/match of non original parts in a combination that is probably not allowing the master cyl/booster retract completely before the pedal assy (stop light sw included) hits the return stop.
I started it and let it run for 30 min in my shop. The brake line never got over 130 degrees. I do have a good return spring on the pedal and it fully returns as far as it can. I have a mechanical swith for the brakes that is independent of the rest of it.
When the caliper is hanging up, did you loosen the brake line above the hose to see if the brake released? If the hose is defective, loosening the line above the hose will not release the brakes. At this point, you have determined the issue is the front brakes, and releasing the pressure allows the wheel to turn, the issue is not the caliper or brake pads. By spacing the master away from the booster with washers, you have determined that the booster/brake pedal is not the issue. Now you need to eliminate the possibility of a hose problem. Beyond the brake hose, the only things above the hoses is the proportioning valve and the master itself, and a slim possibility the fluid is expanding. At 130 degrees temp of the brake line would make that a pretty slim chance, unless the brake fluid has a lot of moisture in it. Some brake fluid attracts moisture badly, and sometimes, fluid from a can that has had the seal broken for a while and attract moisture. What fluid are you using, and how long ago was the container first opened? You need to eliminate a bad hose before you can move on. Gene
When l let it run in my shop earlier l would pit it in gear just to see if the brakes would drag just from the engine running and heading something in the brake system up. I have not tryed to loosen the hose. I changed both hoses out a few months ago. I dont think l had mentioned it. I used new fluid in the system when l put it togeather maybe 24 months ago. I am in the Navy Seabees (reserve) and got home from deployment 70 or so days ago and been trying to get it on the road. It was kinda driving before l left home 14 months ago l just never drove it but, maybe 1/2 mile to my neighbors house
I wish I could draw you a diagram of a master cylinder's internal structure so you could see why so many have suggested it is likely pressure building from the rod not being pulled completely out to its outmost position. That little tiny last bit of slack in the rod plunger needs to be pulled out so there is no drag because pressure will slowly build and eventually you will be smoking your rotors. Mine would drive fine for about a mile or so but the pressure would build. Do this. Make sure the pressure on the calipers is released. Make sure your front wheels spin freely. Jack front end up a hair so they do. Now, Turn your engine on and just pump the brakes for a minute or two and then go check the wheels again. My guess is they are building pressure and my guess is again you need that fully retracted plunger. I know you're trying so please take my insistence to really take a closer look back at the MC. Best of luck. And THANK YOU FOR YOUR SERVICE! Sent from my iPhone using The H.A.M.B. mobile app
Yea l believe it is the MC as well. I think l just need to replace it. I did not have it off the gound yesterday but, l let it run and just bumped it in and out of gear and let it roll back and forth and no brake dragging. I totally agree it is the MC building pressure and not releasing. Even when they were dragging l disconnected the MC from the booster and they did not release. The only thing l did not do when l put the system togeather was add the residual valve for the rear brakes because l thought it was built into the proportioning valve
Have the plunger set correctly on the new master....i had replaced my master only because I broke a mounting stud installing the original one after a body off resto. I installed the new one and didn't have the plunger set right cause I didn't know...learning as I go. I ended up adjusting it on the car at least 3 times to get it right. I hope you get the fix soon so you can enjoy your time home! Sent from my SCH-I535 using The H.A.M.B. mobile app
Thanks for posting the diagram. As you can see, if that plunger/pushrods does not come completely out to the very end of its travel, the fluid cannot return and pressure builds Sent from my iPhone using The H.A.M.B. mobile app
A simple test. If you don't get small fountains of brake fluid coming out of the uncovered reservoir when you initially press the brake pedal, it's probably not fully retracting the seals past the intake & return ports when the pedal is released. Be careful to shield any painted surfaces if you try this test. The equalization ports may affect the test but you should still see from action on the fluid surface in the reservoir. Jack E/NJ
When l unbolted the MC from the booster would not my brakes freed up if it was my rod not fully retracted?
Not if the pistons inside the M/C are somehow stuck and not being pushed back far enough by the return springs. Jack E/NJ
When it builds pressure, start at the caliper and crack the hose fitting first and see if it releases the pressure. Then if it did, move to the next fitting working your way back to the master cylinder. When you finally crack a fitting and it does not release the pressure you have found the problem. It will be between the fitting that doesn't release the pressure and the last fitting that did release the pressure.
It just about has to be the MC l ran one line out amd split it for the front brakes. I have replaced rubber lines recently
Pull the top off the master cyl, have some one gently push the brakes. the release them and see if fluid returns through Both holes in the cylinder chamber. If it does not the small hole is plugged or missing. The piston has to return all the way to release, look and see that it comes all the way out to the snap ring. Gary
I researched what MC that came in my kit from Pirate Jack's. Their customer service sucks for the tech line by the way!!!!!! Anyway l got a brand spanking new MC from Autozone for 28.99 bench bleed it and installed it and used my a/c vacuum pump to bleed the lines after l reinstalled it on the truck. The MC was off a 76 corvette with power brakes and disc drum. The only thing that was different was there is a piece of steel that goes in the MC that the rod from the booster. It was a bigger diameter from the old MC. I chucked it up in my old drill pressed and turned it down with a file. After a little measuring and polishing with some 220 grit paper it worked. So long story l changed the MC and drove it for a hour and the breakes are fine now!!!! Thank you for all your replys and help on my issue!!!!
Awesome news!!! Glad to hear it. Such a Pain in the f'n ass to have to deal with this sort of bs. Just glad it's working!
Yes l totally agree total pain in the ass. I could of went to my favorite junkyard and got parts a lot cheaper with less issues
Just one problem....Corvettes went from drum/drum to disc/disc in '65....never had disc/drum. Anyway, glad your brakes are fine now.
Mustang II brakes. The mechanic at work told me they had to leave the wheel bearings loose enough or the calipers would not retract. I bought a company car (an 80 Pinto) at a time of no money and adjusted the tension on the tapered Timken bearings properly. The disc brake pads would not retract properly until I left the bearings looser. Problem solved.
The Jalopy Journal
