Technical Brakes lock after first push of pedal

I have a 48 Dodge sedan with 4 drums. I put new rubber in the whole brake system last summer; hoses, 6 cylinders, and master. Since then, I have had one wheel lock up after pressing the pedal once on a cold start. It started with the left rear wheel. I replaced the cylinder with a new one, but the problem moved to the right front wheel (2 cylinders in each front). Those bleeders are a pain to get a socket to grip them; I'll likely drill a larger hole in the backing plate whenever I fully disassemble them.

So that's the problem... but to throw a wrench into it, I can reverse just fine. The wheel only locks when going forward. It will still drive forward, but scrubbing the one tire that locked up. This happened when the rear wheel locked up, too.

I'm not out to throw more money at it out of hope, but this has parked the car for months as I worked on other projects (I'm ready to return to it). I've tried adjusting the shoes, but no difference. I have a hunch that the master might be the source of the problem because it was a pain to bench bleed and I kept getting super tiny bubbles; though not every time. Money is tight at the moment, so I'd just like to hear opinions and take it from there. Thanks!


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There is a bypass port in the master cylinder, a tiny one, that lets fluid return when you let the pedal up. If it's plugged, or the pedal does not have any freeplay so the piston does not return fully, it could lock the brakes.

also rubber hoses get degraded inside and will cause brakes to lock.

And those old Mopar brakes with two pistons don't work like single piston brakes...they work good forwards, but don't do much in reverse.

 

There are primary and secondary shoes, you have them reversed or you put both short on one side and long on the other. The short shoe should be toward the front of the vehicle (I think) but if you reverse them it will fix your problem.

 

All rubber is brand new... hoses and all cylinder kits. Also new springs.
I never removed the shoes, just moved them out of the way.

I think I'll look to disassemble/clean/reassemble the master. I'm pretty sure I checked that all ports were clear, but that was almost a year ago. Is there any concern with the push rod? Because I'm using all original parts there and didn't change anything except rubber. The old system worked fine, but was rotted.

Thanks guys!


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oil on the linings?

 

if the pushrod is too long, it can cause the cup to block the bypass port.

To help diagnose whether it's a hydraulic or mechanical problem, after you push the pedal and a brake locks, open a bleeder and see if the system is under pressure.

 

Bench bleed again,off the car in a vice using a tool of some sort to push in the cup all the way to the bottom of the stroke. be sure whatever your using to return the fluid to the reservoir is not leaking and is returning the fluid into the fluid not just shooting it back into the Master. when bubbles stop fill master and then remove tubing or whatever and plug the master fitting till your ready to connect lines permanently..If it's not plugged air will migrate into the master and F up what your trying to do. Some say it's OK to bleed the master on the car but if you use the brake pedal you will not get the full stroke to the bottom of the master and can never get the air out. Ralphie

 

The pedal really should always be able to fully stroke the master with an open system(s). The first thing to check for in a custom setup. You're correct that not being able to fully stroke will make a good bleed difficult, if not possible.

 

My stroke has gotten shorter in my old age.

 

I have had this happen with cracked linings. Locks up with very little effort.

Just sayin'


Cosmo

 

What type of fluid? some of the synthetics will close the rubber hosing up if it isn't designed for that fluid. When they close up the MC can push fluid thru and some but not all will return keeping pressure to the Wheel cylinders. Safest to use DOT 3 on our old stuff.
I doubt they'd 'lock up' where the wheel wouldn't turn but they'll pull to one side for sure.

 

Using regular DOT 3 fluid.

Put the car up on stands to better evaluate. The whole thing is kinda screwy, but as of now, after pumping the pedal, the front wheels will spin in both directions with very slight drag. Rear wheels will spin and then stop; as in hitting something. Car is not in gear, parking brake off. Immediately after pumping the pedal, the left will spin but not the right. Opened the bleeder, remembered that I installed one-man bleeder screws (the only kind the parts store had of that size), then pumped once and fluid came out. I suppose that leads to a cylinder problem... but why would the front wheel lock when going forward when it's on the ground?


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Came across this many times when I had a REAL job repairing trucks. Sometimes you can get away with cleaning contaminated brake shoes with brake-kleen but usually the linings will need to be replaced. The old brake fluid and oil will come to the top of the lining with brake heat and it's a sticky mess...will grab and lock up that wheel.
I'd replace the linings.
BTW, I've been in the same boat with a 55 dodge 1/2 ton pickup I owned. I chased wheel cylinder leaks from one wheel to another. Wisest and ultimately cheapest fix is to replace all wheel cylinders and linings at once.

 

I agree that if the linings have been contaminated, you need to replace them first...

 

Replace the linings or at the very least clean them up with emery cloth and then turn the drums. You would be surprised how much smoother everything will work with fresh cut drums and clean shoes.

 

I understand the heat part, but I can't even make it out of the driveway like this. It happens when I push the pedal to put it in gear.

A drum turning and new linings would be amazing, but out of the current budget. I'll look into cleaning them up.

It's funny that the rear wheels will spin in one direction, then stop suddenly and sound like they're hitting the pumpkin gear or something. I'll make a video.


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these are all good suggestions but do not explain why one wheel locks. then the opposite side when get the one side too work.

 

Car is on stands. Went out and tried spinning each wheel cold; without touching the pedal. Transmission in neutral, parking brake off.
- Front left sticks, but does free up with effort.
- Front right is okay (the one locking up after hitting the pedal).
- Rear left sticks, but not as bad as front left. Moves one way better than the other.
- Rear right takes a lot of effort to budge, but goes eventually.

I'm assuming at this point that the master is likely the culprit.

Can't get the lower bleeders to move on the fronts. Too chewed up. The front uppers have shot fluid with a freshly pressed pedal. Rears shoot when open and pressed (one-man bleeder screws installed).

 

Check that there is a very slight amount of clearance from push rod to master cylinder when pedal is up. You may have to pull out the pin to pedal to check this.

 

I have the same brakes on my 53 Dodge.
I got alot of strange brakeproblems after i had restored them.
In the end it was the brakeshoes that not was centered in the drum.
They do not selfcentering like in newer systems.
Each shoe have a adjustible mountingpoint.
Center them in the up and down direction until they centered.
Then put on the drum and adjust the shoes with the adjustscrews.
I made a tool to put on the spindle to do this but i guess you could do it by measuring.
And you must be sure that its no brakefluid in the linings and the master release all the way.

 

Nice. I'm going to pull the master anyway to go through it again to better rule it out, but I'll check that centering, too.

If I had a smooth driveway, I'd probably procrastinate less on this project!


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I've seen pictures of this tool, but haven't actually seen one in front of me. What did you use to make it? It might be handy to have it around.


Went back to the Dodge for a little bit tonight before dinner. Front wheels were locked up, with no pedal, and the right rear. Left rear (with new cylinder) was good. Possibly just from sitting and it's been raining a bit over the past few days. They freed up with a little effort. I guess the biggest find today was that without hitting the brake pedal in a few days, opening the top bleeders on both fronts hissed out pressure. On modern cars, I usually gravity-bleed the brakes. I was able to open all 4 front bleeders, but aside from the pressure hissing and a tiny spritz from the top ones, nothing dripped... even with them -really- open. I played with the adjusters some, but didn't take drums off(no time). They're better now than they were, but I'll have to put this off for another few days because this week is hectic.



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The tool was/is a skeletal brake drum, which can be replicated by cutting a hole in a spare drum to intersect the wear surface. The object is to be able to insert a feeler gage to determine the gap between shoe and drum.

Dependent on how much pressure (residual valve will hold some, not much, 5 lbs or so), you may have a master that is holding pressure. Did you remove the master from the car (it's a bitch, I know)?? Or try to rebuild in place?? Time to pull that master and figure it out.

That works a whole lot better if your master was actually above the wheel cylinders. It's not, so they won't.

Cosmo

 

Just made it from some scrape pices laying around.

 

http://p15-d24.com/topic/35370-factory-brake-job/

 

Thought I was getting somewhere. Did one of the rears last night by touch/sound and I'm satisfied with it. Went to the front today and just when I think I'm getting close, I can't get the darn drum on anymore! I moved the adjusters back to square one and opened the bleeders. Thing has been kicking my ass with the sun beating down on my neck for the last hour. I can't move the adjusters down any more and it's still too much.


Edit: Finally got it on, but it's barely moving. Guess I need to make a tool after all. I don't know why it would be so tight though! Never touched the pedal!

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If you open any bleeder and the problem goes away its the master cylinder if not it's at the wheel.

 

"If you open any bleeder and the problem goes away its the master cylinder if not it's at the wheel."
Sage words, here. Inside the master cylinder there's a small hole that allows the pressurized brake fluid to run back into the master cylinder's reservoir when the pedal is released. If that hole is plugged, the brakes will not release or they'll release very slowly, depending on how plugged the hole is. Also, if the pedal push rod into the master cylinder is ajusted too long, the piston won't come back enough to uncover that hole, leaving pressure in the master cyliner, applying the brakes. I've had luck unplugging this hole with a piece of wire or an o-ring pick.
I had a 47 caddy I rebuilt the master cylinder on one day...the master cylinder push rod seemed a little short,,there was about 1/8th inch slop in it. I figured if I got rid of that slop, the brakes would be better so I adjusted that 1/8th inch to zero. The brakes were fantastic! I took an 85 mile trip and at the end of that 85 miles, the brakes were dragging and getting hot. I stopped at a gas station for gas [yeah, it was a cadillac] and afterward the car just wouldnt' move at all! I had to adjust a little play back into my master cylinder rod and all was good again.
All this is assuming your brake shoe adjustment is ok.

 

Let's start with the brake adjustment. I have Lincoln style brake drums and shoes. I have a tight spot at one point in the rotation otherwise just minor drag like you should have. NEW BUILD. When I apply the brakes they will not realease. It is in the front brakes not the rear brakes.

 

I meant when I apply the brakes and let off they will not release.