Interesting drum brake problem

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justthatguy

justthatguy

Josh(69 Valiant)
Joined
Jul 6, 2012
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Location
Danville, VA
I got a 72 Duster a few months back, but due to 2 feet of snow haven't been able to get anything done. I want to get this car to the point of a summer daily, but one problem is holding me back.

The ***king brakes on this thing.

The master cylinder was replaced by the previous owner, and it looks like the lines are new too, so no worries there. I'm working on setting the correct pressure on the front shoes, and on the back, the right side is fine, but the left side keeps dragging even though i've taken the drum off, and cleaned the hell out of it. I set the brake just to where it starts to drag, but it locks every time I touch the brakes, and usually ends up smoking. Also, I get a brake light intermittently and it feels like I don't have the pressure I should, or going on my 69 Valiant, it feels like I should have a lot more pressure instead of locking the brakes when the pedal hits full travel. It doesn't go to the floor, do they need to be bled?

Not really in a hurry but I need to get exhaust run on it soon.
 
You need to check the rubber brake hoses. These will fail and allow brake fluid through the hoses when the brake is applied but not release the pressure. If you haven't replace the three hoses, you should.
 
I just went through this with a Honda. I had weak brake return springs and the rear drums would drag. Replaced with a new spring kit and all is well again. I've never had the problem before, and it drove me nuts. Check for that if you find nothing else wrong.
 
Oklacarcollecto said:
Bingo!!! I have been there a few times myself.
Click to expand...

Yup, Just had it happen to me on my 69 Dart rear brake hose. The think just sits in my carport covered up and when I took it out a couple of months ago, I came back with the rear brakes smoking and stinking.
 
I sprayed the hell out of all brakes with cleaner, then cycled them a few times, I think I have them all too tight now, but wow, I actually have decent braking now. Now just need to get some new tires on there so I can stop skidding all over the road. I'll go through all the lines though. I lost brakes on my Valiant and ran off a hill into trees. I learned my lesson.
 
Ditto again on the old brakes lines; this will cause the brake dragging every time. The inside liner breaks down, and a chunk pushes into the passage and blocks the return flow of the fluid; it is amazing how much pressure this can hold on the cylinder or caliper.

In reading of your brake symptoms and the occasional brake light, I am highly suspicious that the former owner did not properly bench bleed the new master cylinder before installing. I would be taking it off, bench bleeding it throughly, and starting all over in a complete bleed of the other lines.

BTW, you ought to be putting a bit of lube on the backplates where the edges of the brake pads rub.

Have you put on any new spring kits, especially on the back where the one brake has been seizing up?
 
You may also have a wheel cylinder sticking. Had to do my 64 Belvedere drum brakes a few times. take apart,clean everything, put back together.never saw anything, dirt, pitting etc but something was making them hang up. worked good after, for a few years. I guess from sitting mostly only put 5000 miles on it in 9 years.
 
Ditto on the rebuild. Wheel cylinders, springs and hoses, all 4 corners. Not worth chancing it on iffy parts. Brakleen will only help the brakes grab better, but it sounds like you've got too much grab. The piece of mind is worth it, especially in a panic situation.
 
Over machined (oversized) drums will cause this also.
It can cause the shoe to "cam in" on the drum and lock up.
 
If the problem manifests on one side of the car only (I.e. left side locks up while right side doesn't), then I would also double check the brake lines into the proportioning block to ensure the front brakes are both on the rear reservoir of the master cylinder (since the lines were replaced by a previous owner and may have been done incorrectly). Of course there would be a problem with whichever rear side locked up too as both rears share the same hard line.
 
After I get the front brakes done on my DD Caprice, I'll dig into this thing. I'll probably do a rebuild on the back brakes, I believe the front brakes have been rebuilt because they look clean, but I'll look at them just in case. I'll check and probably redo all the lines. It would seem it's a wheel cylinder problem, I looked at the springs, and they looked fine. While I'm at it, I'll stick a 4 barrel on it too.
 
Had this as well
69 Dart drum on all corners.... The prob turned out to be, the drums were at there machining limit maybe even a little more. New shoes helped but as soon as some wear on the shoes took the tolerances down.. the front breaks lock up.
I see one of the other members also mentioned this. Springs, cylinders etc become over extended as well as the piston in the master, thus the reason we tend to think master issues. Once I installed new drum (ones that meet spec) new shoes need and cheap anyway POOF all groovy again!
 
i had this problem as well on my 72 dart with drum brakes. i replaced wheel cylinders, shoes, drums, brake hoses, master cylinder, cleaned the proporting valve, blew the lines out. replaced brake hardware. after it was said and done, the backing plate was bent or warped. replaced with another, good to go.
 
My bosses collection Lambo had to be driven around the block every 6 months (bad job eh? ) pulled into the complex to park it and the rear driver brake locks up. We had to drag that poor tire 70 feet to get it back into the garage. Got it on casters and pushed it back into its place and ordered a brake line. His mechanic cut the hose at both ends and got a nice blast of fluid when he cut the cylinder side. We then proceeded to slice this line until we came to the blockage. it was 10mm of solid rubber, the hose swelled up choking the passage and the cylinder didnt have the pressure to purge its fluid, but enough to lock the tire.
I had a brake shoe on my truck lose half of its lining and it was wedging, locking the brake but it would release properly.
 
A somewhat far-fetched but plausible scenario:

Drum brake systems use a residual pressure valve in the line. When these cars were built, the RPV was in the outlet of the master cylinder. Later on, Mopar changed to putting the RPV in the rear wheel cylinders. It is at least possible that the cylinder on one rear wheel was changed to the later type out of ignorance. I don't know for sure what the effect would be, but a failure to release pressure seems a possibility.
 
Drum brakes? Does it have the right master cylinder? Both wells should be the same size.

I'm adding my 2¢ to those who are recommending new hoses. Look for crimps in the steel lines along the driver side rocker panel area and across the top of the rear axle housing. You'll need to bleed the brakes; RR, LR, RF, LF. Using a different sequence can cause you to chase an air bubble in the lines.

FWIW: The self-adjusters in the brakes will not loosen a brake that is set to tight. It will, when working properly, tighten a loose brake. To use the self-adjusters, locate a large open area where contact with other things is minimized. Back the car up to approximately 15 mph. Slam on the brakes hard. Drive forward about two car lengths and stop to evaluate adjustment. Repeat as necessary. If no improvement noted in three repetitions, something other than brake adjustment is wrong. For this to work properly, the brake shoes must be making contact with the drum when the brakes are applied.
 
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