Soft Peddle

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parishpbs

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I did a complete rebuild of the manual drum brakes on my 67 Dart GT. Wheel, and master cylinder, shoes, drums and rear line.

The rears bleed nice and clear with no air. When I bleed the front it runs clear for maybe 30 seconds and then starts running air bubbles. I have kept the master full and run at least 2 reservoirs of fluid and still get air.

I have tried the vacum, gravity and a pumper methods and still have little or no peddle. When I have another pump the peddle up it runs clear till the peddle hits the floor and then it starts pushing air?

I have checked all of the fittings, pulled drums and found no leaks.

I'm thinking I have a bad Master? It was a re-man
 
I assume you adjusted the shoes pretty tight. If not, you would have a lot of lost travel. I always bleed with vacuum and my wife slowly pressing the pedal. I usually see bubbles, but they are from outside air sucking past the bleed threads. You can see that even without vacuum from the venturi effect, i.e. the fluid falling down the drain tube sucks a vacuum at the top.

I don't know how a bad MC could entrain air, as long as you keep the reservoir full. Problems would be it either leaks or doesn't build pressure from seal leaks. New MC's can be bad. I had a fairly new rebuilt one fail. Took it apart and found a cut seal because the rebuilder machined the bore and left a sharp edge on the side ports.
 
Usual reman master its bad I did 5 of these to one car before buying new and fixing the problem.
 
BillGrissom said:
I don't know how a bad MC could entrain air, .
Click to expand...

You can reach a situation (possibley defective residual valve?) where the pedal retracts fast enough that it sucks air in past the rear cup on "rebound."
 
Thanks so much for your input and feed back. Yes I did bleed the master. I have the shoes adjusted to about 1.5 rotations with tire on, do they need to be tighter?

I was thinking the same thing, pulling air around the bleeder valve, but I still can't get any peddle to speak of.

I guess a NEW master is in my future. Anyone know of a reputable supplier for NEW?
 
parishpbs said:
Thanks so much for your input and feed back. Yes I did bleed the master. I have the shoes adjusted to about 1.5 rotations with tire on, do they need to be tighter?
Click to expand...

You need to adjust until you feel a slight drag when rotating the wheel.
 
67Dart273 said:
You can reach a situation (possibley defective residual valve?) where the pedal retracts fast enough that it sucks air in past the rear cup on "rebound."
Click to expand...
X2. When you bleed the brakes, let the pedal up SLOWLY so it will draw in fresh fluid from the reservoir and not air around the rear seal. Also, I never push the pedal all the way to the floor. Half way on a new/reman unit is fine and only 1/4 pedal on a used master cylinder.
 
Are there residual pressure valves in an A body's braking system, or could they be suspect for trapping air if installed? My '72 has issues with what feels like air in the system (pedal can be "pumped up"), but every time I bleed it, no bubbles. I took it to a local Firestone and the braking effect was better, but it still gives a couple state inspectors fits because it doesn't start slowing down the moment they start applying brakes.
 
took it to a local Firestone and the braking effect was better, but it still gives a couple state inspectors fits because it doesn't start slowing down the moment they start applying brakes.
Click to expand...

You need to adjust the rear brakes if disk & drum, and all four brakes if all drum.

That extra pedal travel is a result of having to push the shoes too far before making contact with the drums. Adjust them up until there is a lot of drag, step on brake pedal hard to center shoes, and re check adjustment. The shoes will seat themselves in a mile or two.

Another problem with drum brakes is not having shoe & drum radii the same. If a drum has been turned over size, a new shoe will not make full contact its entire length making for excessive pedal travel, soft pedal & long stopping distances.

Your car’s drums maybe within acceptable tolerance, but the shoes don’t quite match the drums radius. Keep adjusting the brakes over a period of a few weeks until the shoes wear in.

In the old days there was a machine that could grind a new larger radius onto the shoes to match an oversized drum. Fortunately those devices are hard to find, and brake systems now have to be renewed to OEM specs, by installing new drums.
 
Yeah, it's all drum-when I pump the brakes, it actually stops pretty well. If I get the chance this weekend, I'll adjust them in accordance with what you're telling me. Thanks!
 
I want to thank all of you for your input. I have been adjusting every couple of drives and the peddle is getting much better. I know I have a drum that is maxed out and can't be turned but I'm in the process of looking for an 8 3/4 so I don't want to put money into these right now.

I think adjusting is the secret. Good peddle now.
 
The way to adjust drums is to adjust them up until you can NOT turn the wheel. This "seats" the shoes in place. Then back off and count the "clicks." When the drum is "just scraping" it's probably about right. Try to do the other wheels the same way, then test drive, jack it back up and see if they still "scrape" when spun. If not, tighten em up a couple/ three clicks.

You should NOT have to pump drum brakes, to get a good solid pedal.
 
Yeah, I know I shouldn't have to-that's what made me think I had/have air in the lines, but if I bleed it, no bubbles. I'll adjust them and report back...just not today-I gotta sleep...:sleepy1:

I also have to take it back to the exhaust shop Tuesday morning. I really hope they can put all my pieces together for those tight tube headers up over the steering parts.

67Dart273 said:
The way to adjust drums is to adjust them up until you can NOT turn the wheel. This "seats" the shoes in place. Then back off and count the "clicks." When the drum is "just scraping" it's probably about right. Try to do the other wheels the same way, then test drive, jack it back up and see if they still "scrape" when spun. If not, tighten em up a couple/ three clicks.

You should NOT have to pump drum brakes, to get a good solid pedal.
Click to expand...
 
Adjusted the drums all the way around about two turns...that should say something in and of itself. I sincerely thought they were good when I bled the brakes-evidently not. Needless to say-the brakes are much better. I get way better response now-probably about 1/4 pedal travel before the car starts noticeably slowing-thanks!
 
Glad to hear it's better now. One last point. Keep an eye on the fluid level in the Master Cyl. If it starts to drop significantly, it means a leak somewhere(even if you don't see any fluid. I had a M/C leaking into the Booster and never saw fluid anywhere. I also went through 2 rebuilts to get a good one.
 
Will do-I don't have to worry about it leaking into the booster, but I do keep an eye on it.
 
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