eddie27 Posted June 29, 2014 Report Share Posted June 29, 2014 Working on a 37 Plymouth coupe. The brakes worked fine but when driving it the pedal would get higher and higher until the brakes would just lock up. After some research and reading I found the brake pedal needed adjustment to let the piston in the master cylinder come back past the relief port. I did that and got the 1/4 inch free play before the rod contacts the piston. My problem is that now the pedal goes to the floor. I have bled to brakes and am positive there is no air in the system. There are no leaks in the system. I have also adjusted the brakes with the cam bolts until the wheel locks up and then backed them off just until the wheel frees up. Now, short of replacing the master cylinder I am at a loss. Any ideas? ThanksEDIT>>>>> Just verified... If I adjust the pedal (tightening it up) I get good pedal, but not until after the piston blocks the relief port. Then I am back to the same problem of the brakes locking up after driving a while. Quote Link to comment Share on other sites More sharing options...
BenFrog Posted June 29, 2014 Report Share Posted June 29, 2014 Did you rebuild the master cylinder? Quote Link to comment Share on other sites More sharing options...
st63 Posted June 29, 2014 Report Share Posted June 29, 2014 I had a similar issue when rebuilding the brakes on my 41 Coupe...When I disassembled the master cylinder I found it was pitted pretty badly, so wound up replacing it with a rebuilt unit. You can have the original re-sleeved too, but it was about the same price for a rebuilt one, and I was able to get it more quickly since I was pressed for time. Not a bad idea to pull apart the wheel cylinders and check and possibly rebuild them too since the system will be apart. Quote Link to comment Share on other sites More sharing options...
eddie27 Posted June 29, 2014 Author Report Share Posted June 29, 2014 I had a similar issue when rebuilding the brakes on my 41 Coupe...When I disassembled the master cylinder I found it was pitted pretty badly, so wound up replacing it with a rebuilt unit. You can have the original re-sleeved too, but it was about the same price for a rebuilt one, and I was able to get it more quickly since I was pressed for time. Not a bad idea to pull apart the wheel cylinders and check and possibly rebuild them too since the system will be apart. I had the master cylinder out yesterday and apart to make sure everything was there and put together right. It looked good. No pitting or scoring at all. Cups all looked good. I am going to take all the wheel cylinders apart today to see what condition they are in. Quote Link to comment Share on other sites More sharing options...
eddie27 Posted July 1, 2014 Author Report Share Posted July 1, 2014 Wheel cylinders are looking good.... not sure what the next step would be. I mean... this system is not that complicated. So why am I losing my hair. Quote Link to comment Share on other sites More sharing options...
nonstop Posted July 1, 2014 Report Share Posted July 1, 2014 Is the travel too much but there are still brakes, or do you have absolutely no pedal? Where did you measure the free play from, the pedal or the rod itself? Might be worth experimenting with the rod and try adjusting it out in small increments. See if any pedal comes back. Quote Link to comment Share on other sites More sharing options...
Young Ed Posted July 1, 2014 Report Share Posted July 1, 2014 Check your minor adjustments. I had a low pedal in my 46 where I had to pump it once to get brakes and all it needed was the brakes adjusted up. Quote Link to comment Share on other sites More sharing options...
eddie27 Posted July 1, 2014 Author Report Share Posted July 1, 2014 (edited) Is the travel too much but there are still brakes, or do you have absolutely no pedal? Where did you measure the free play from, the pedal or the rod itself? Might be worth experimenting with the rod and try adjusting it out in small increments. See if any pedal comes back. Yes... I can just see the LF wheel cyclinder start to move as the pedal is nearly to the floor. (With the drum off) The only way I get good pedal is if I adjust the rod past the relief port. Then the brakes are great. But with that port blocked they lock up after a few miles. The fact they lock up tells me things (master cylinder and wheel cylinders) are sealed and working properly or at least no fluid is passing the seals. Edited July 1, 2014 by eddie27 Quote Link to comment Share on other sites More sharing options...
Solution desoto1939 Posted July 1, 2014 Solution Report Share Posted July 1, 2014 Hvae you used either the Ammco brake tool or the miller brake tools to set the arch of the shoes to the drum. It sounds as if you have not done the major brake adjustment or if you did it is not correct. I have the Ammco Brake tool. Rich HArtung Desoto1939@aol.com Quote Link to comment Share on other sites More sharing options...
greg g Posted July 1, 2014 Report Share Posted July 1, 2014 you need to assure that you have sufficient free play at the top of the pedal travel, 1 1/2 to 2 inches, and you have to assure the return port in the bottom of the master cylinder is free of debris and allows for fluid to return when brakes are released. Also assure you master cylinder cap vents are free, and that the MC is not overfilled with fluid. Quote Link to comment Share on other sites More sharing options...
eddie27 Posted July 1, 2014 Author Report Share Posted July 1, 2014 Hvae you used either the Ammco brake tool or the miller brake tools to set the arch of the shoes to the drum. It sounds as if you have not done the major brake adjustment or if you did it is not correct. I have the Ammco Brake tool. Rich HArtung Desoto1939@aol.com Can you bring it with you???? Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted July 2, 2014 Report Share Posted July 2, 2014 Can you bring it with you???? This is a tool that can be mailed. I am not traveling and hand delivering it to your home. Contact me directly about the use of the tool. rich Hartung Desoto1939@aol.com Quote Link to comment Share on other sites More sharing options...
deathbound Posted July 2, 2014 Report Share Posted July 2, 2014 (edited) Not sure where you're measuring the free play, but in my 1936-1942 Plymouth service manual, page 77, says: (1) "Free play in the brake pedal should be from 1/4"-3/8". This free play may be readily felt by hand and is the movement of the pedal before the push rod touches the master cylinder piston. If necessary, this free play may be altered by changing the length of the piston push rod." "CAUTION:piston cup must clear port when pedal is in released position." (2) "After the free play is taken up, and the pedal is pushed slowly for an additional 5/8"-3/4", fluid should be forced up through the relief port in the master cylinder. If it does not, and the free play is correct, the master cylinder should be disassembled and checked for swollen cups or improper assembly of parts. The additional pedal travel of approximately 1" is required to move the brake shoes outward against the brake drums." This is verbatim, except where it references a couple of figures. All measurements are taken at the foot pedal pad. Edited July 2, 2014 by deathbound Quote Link to comment Share on other sites More sharing options...
greg g Posted July 2, 2014 Report Share Posted July 2, 2014 OK, but my 46 has had around 1.5 give or take and has been working just fine for 10 years. perhaps the earlier cars have a different measurement due to MC design and application. The measurement is what it is, the important aspect of the discussion is that free play must be present, and sufficient to relieve the pressure upon brake release. Without that relief of pressure the brakes will behave as described above. I would think that a free play discussion, would spur looking into the situation which would include checking of references for to ascertain proper specs their particular vehicle, and not take off hand dimensions which may be part of the dialog at face value. Quote Link to comment Share on other sites More sharing options...
deathbound Posted July 2, 2014 Report Share Posted July 2, 2014 Every car will have different requirements. I included the directions from my 36-42 Plymouth service manual, because it pertains to the OP's car.....a 1937 Plymouth. Some may take 1/4" free play, another may take 17/64", another may take 35/128" & on & on & on..... Quote Link to comment Share on other sites More sharing options...
eddie27 Posted July 2, 2014 Author Report Share Posted July 2, 2014 This is a tool that can be mailed. I am not traveling and hand delivering it to your home. Contact me directly about the use of the tool. rich Hartung Desoto1939@aol.com I was kidding.... 1 Quote Link to comment Share on other sites More sharing options...
eddie27 Posted July 2, 2014 Author Report Share Posted July 2, 2014 (edited) As I said in my original post... I have 1/4 inch freeplay in the pedal. When I bought the car I was told that the brakes had just been redone. Whoever did them had the pedal way out of adjustment. I have that taken care of. Thank you for all of your replies so far. I really do appreciate the help. I am going to try to do a major adjustment this weekend and see where that leaves me. The thing I think that puzzles me is that if I adjust the pedal to where the piston blocks the relief port the volume of brake fluid in the master cylinder is plenty to give me good pedal. But if i adjust it back to where it does not block the port, it goes to the floor. that is why I don't think adjusting the linings will make much of a difference. But I have tried everything else I can think of. Edited July 2, 2014 by eddie27 Quote Link to comment Share on other sites More sharing options...
Robert Horne Posted July 3, 2014 Report Share Posted July 3, 2014 It took me very much time to finally get my 38 brakes good. I installed a small 86 Dodge master cylinder on to the original brake pedal assembly. It worked good for 10 years, and then I installed a larger Ford Bronco MC, that worked about the same. Where my problems were, was the new brakes lines had a small leak, replace one fitting 3 times, and the driver side wheel cylinder, rear, always had a small leak. One of my brake drums was out of round, even after it was shaved, so I replaced that. First,I adjusted the brake adjustments just to where the wheel would only move a little, made sure the MC push rod had a little free play, and then I bleed the system. The past couple of years, full pedal, after 20 years of always having to checking the system.... I installed 70s Granada linings on my Plymouth shoes, good fit... Quote Link to comment Share on other sites More sharing options...
eddie27 Posted August 21, 2014 Author Report Share Posted August 21, 2014 Just wanted to give a quick THANK YOU to Rich Hartung (Desoto1939) He loaned me his Ammco 1750 (for nothing more than the price to ship it to me) and that did the trick. Happy to report that the brakes are high and tight. 1 Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted August 21, 2014 Report Share Posted August 21, 2014 Just wanted to give a quick THANK YOU to Rich Hartung (Desoto1939) He loaned me his Ammco 1750 (for nothing more than the price to ship it to me) and that did the trick. Happy to report that the brakes are high and tight. Glad the tool worked to solve your issue with the adjustments on the brakes. Quote Link to comment Share on other sites More sharing options...
eddie27 Posted February 22, 2015 Author Report Share Posted February 22, 2015 (edited) edit Edited February 22, 2015 by eddie27 Quote Link to comment Share on other sites More sharing options...
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