Alex in SLC Posted September 26, 2020 Report Share Posted September 26, 2020 Hi Everyone! Got myself a problem with my new brakes. On my '48 D24 I have rebuilt the entire braking system: Master cylinder, steel lines, wheel cylinders and shoes. Put it all back together, got it bled and adjusted. Took it out for a spin and after just a couple times around the block the brakes were stuck and getting hot (all four wheels). After I parked it the pedal had no movement. I let the car sit for a day and when I return the shoes are retracted and I have movement in the pedal again. On the same note over the past couple weeks I have noticed that as the temperature rises throughout the day (here in SLC, UT) my brake light will randomly come on. I tap the brake pedal a couple times and it will go off. Could my problems be related to my proportioning valves? Thanks for the help! Alex Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted September 26, 2020 Report Share Posted September 26, 2020 Master cylinder to brake pedal free play to tight. Or issue with the master cylinder. 1 Quote Link to comment Share on other sites More sharing options...
plymouthcranbrook Posted September 26, 2020 Report Share Posted September 26, 2020 I would bet on the tiny vent inside the master cylinder being partially or fully blocked a search should bring up pics of it and you can clear it with a very small wire. If you take the cap off and GENTLY push the brake pedel you should if it is clear see a small spurt of fluid. If you don’t it is blocked 2 Quote Link to comment Share on other sites More sharing options...
greg g Posted September 26, 2020 Report Share Posted September 26, 2020 Brake pedal should have a couple inches of Freeplay before engaging master cylinder, there should be some air space above the fluid level in the mc, and check out the return port in the bottom of the reservoir. Shine a light in you should be able to see two holes big one is to feed the piston small one relieves pressure when pedal is released. Clear both with some mechanics wire. Also assure that the vent passages in the mc cap aren't plugged. 1 Quote Link to comment Share on other sites More sharing options...
milo9rat Posted September 26, 2020 Report Share Posted September 26, 2020 (edited) Rubber brake hoses could be partially plugged on the inside or the hose could be collapsing.. Master is strong enough to push fluid through but spring not strong enough to pull/push fluid back through towards master... Just a guess and only if you didn't replace the hoses..... Edited September 26, 2020 by milo9rat 2 Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted September 26, 2020 Report Share Posted September 26, 2020 I have seen the master cylinder piston sticking in the bore and not returning to the stop. Thus not letting fluid return to the reservoir...causing brake drag... This can also cause the brake pedal free play to be improperly adjusted. Piston cups being wrong and a course cylinder hone finish in the master cylinder can cause this situation. Quote Link to comment Share on other sites More sharing options...
BobT-47P15 Posted September 26, 2020 Report Share Posted September 26, 2020 Years ago my rear brakes would lock up on me. I eventually discovered that short rubber brake line hose at the rear was the culprit. The outside looked perfect, but the inside was worn out ...would collapse not allowing return of fluid to the MC. New hose was the cure. You said you have all new lines.....so if you replaced the short hoses that came on the car, that should not be the cause of your problem. 1 Quote Link to comment Share on other sites More sharing options...
Alex in SLC Posted September 27, 2020 Author Report Share Posted September 27, 2020 On 9/26/2020 at 11:38 AM, Dodgeb4ya said: I have seen the master cylinder piston sticking in the bore and not returning to the stop. Thus not letting fluid return to the reservoir...causing brake drag... This can also cause the brake pedal free play to be improperly adjusted. Piston cups being wrong and a course cylinder hone finish in the master cylinder can cause this situation. So I have inspected the master cylinder reservoir. The piston is clearing the relief port completely. BUT! there is no fluid flowing/spurting up through it? The pedal travel appears to be within spec of the manual. Also, after letting the car sit over night, the brakes are free and the pedal is traveling again. Thanks for all the help! 1 Quote Link to comment Share on other sites More sharing options...
plymouthcranbrook Posted September 27, 2020 Report Share Posted September 27, 2020 If you get a minute making sure the vents are clear can’t hurt could have been a small piece if rust or? Glad to hear is seems fixed Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted September 27, 2020 Report Share Posted September 27, 2020 odds are your rubber flex lines are suffering from internal collapse...pressure on applying the pedal will force fluid the to the brakes...on release the springs cannot overcome the collapsed inner lining and are thus very slowly bleeding back..... Quote Link to comment Share on other sites More sharing options...
Alex in SLC Posted September 27, 2020 Author Report Share Posted September 27, 2020 2 hours ago, Plymouthy Adams said: odds are your rubber flex lines are suffering from internal collapse...pressure on applying the pedal will force fluid the to the brakes...on release the springs cannot overcome the collapsed inner lining and are thus very slowly bleeding back..... The vents are clear and when I rebuilt everything I replaced all the rubber flex line. I forgot to mention that...☹️ Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted September 27, 2020 Report Share Posted September 27, 2020 is this all new recent made lines or NOS.....if NOS....I would suggest a quick test..... Quote Link to comment Share on other sites More sharing options...
Alex in SLC Posted September 27, 2020 Author Report Share Posted September 27, 2020 All new lines, steel and rubber, not NOS. Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted September 27, 2020 Report Share Posted September 27, 2020 still sound like it is not relieving pressure....ensure you brake pedal is adjusted to allow full return of the master plunger and said plunger if fully returning... Quote Link to comment Share on other sites More sharing options...
Alex in SLC Posted September 27, 2020 Author Report Share Posted September 27, 2020 I will double check. The manual says if not, disassemble the master cylinder and check the boots. What happens to the boots when they swell? Quote Link to comment Share on other sites More sharing options...
Sniper Posted September 27, 2020 Report Share Posted September 27, 2020 Simple crack open a rear bleeder when they are locked up, that will tell you if the issue is hydraulic pressure or not. 1 Quote Link to comment Share on other sites More sharing options...
Tooljunkie Posted September 28, 2020 Report Share Posted September 28, 2020 Exactly what sniper says. i would crack lines at m/c. That will tell all. Quote Link to comment Share on other sites More sharing options...
Alex in SLC Posted October 14, 2020 Author Report Share Posted October 14, 2020 On 9/27/2020 at 5:20 PM, Sniper said: Simple crack open a rear bleeder when they are locked up, that will tell you if the issue is hydraulic pressure or not. I know it's been a few weeks, but I finally figured out what was going on with my brakes locking up. It was a two-fold problem with the new master cylinder. Problem one: when I disassembled, cleaned and transferred the pedal assemble from the old m/c to the new m/c I was precise in measuring the length of the brake push rod. Turns out it needed to be drastically shorted from factory length for the "new" m/c. I am assuming the cup on the m/c piston where the push touches is much more shallow than the factory one. I shortened the rod and I get a nice little spurt of fluid between 1/8"-1/4" of pedal travel. So I feel good about that! Problem two: I found I had to adjust the pedal return stop screw slightly probably due to slight differences in the casting of the m/c. Because it would hit the floor board before fully returning. I took it for a test drive and it seems as if the brakes are working as they should (minus some slight adjustments in the drums). Thanks for all the help! 1 Quote Link to comment Share on other sites More sharing options...
Frank Elder Posted October 14, 2020 Report Share Posted October 14, 2020 22 minutes ago, Alex in SLC said: I know it's been a few weeks, but I finally figured out what was going on with my brakes locking up. It was a two-fold problem with the new master cylinder. Problem one: when I disassembled, cleaned and transferred the pedal assemble from the old m/c to the new m/c I was precise in measuring the length of the brake push rod. Turns out it needed to be drastically shorted from factory length for the "new" m/c. I am assuming the cup on the m/c piston where the push touches is much more shallow than the factory one. I shortened the rod and I get a nice little spurt of fluid between 1/8"-1/4" of pedal travel. So I feel good about that! Problem two: I found I had to adjust the pedal return stop screw slightly probably due to slight differences in the casting of the m/c. Because it would hit the floor board before fully returning. I took it for a test drive and it seems as if the brakes are working as they should (minus some slight adjustments in the drums). Thanks for all the help! Thank you for telling us how you fixed the problem, maybe the next person that has this problem will be able to fix their problem instead of scratching their head because there was never an answer to the question. bravo on your troubleshooting skills. Quote Link to comment Share on other sites More sharing options...
Frank Elder Posted October 14, 2020 Report Share Posted October 14, 2020 (edited) Please let us know how your brake drum adjustment turns out I'm really interested on how it turns out. Edited October 14, 2020 by Frank Elder Quote Link to comment Share on other sites More sharing options...
Sniper Posted October 14, 2020 Report Share Posted October 14, 2020 Thanks for following up. I was thinking about this thread the other day, seems my brakes are dragging now Turns out the pedal isn't coming up on it's own, if I pull it up with my foot the brakes stop dragging. I haven't gotten under the car to look at it. Saving it for a weekend project with my son. Probably a return spring. Quote Link to comment Share on other sites More sharing options...
Alex in SLC Posted October 14, 2020 Author Report Share Posted October 14, 2020 For the hell of it, I am going to replace my return spring also! 1 Quote Link to comment Share on other sites More sharing options...
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