Technical Having trouble getting drum brakes working right

I have run out of ideas on this one, and no one I have spoken with can figure this out. The HAMB has the experts, so here I am seeking advice.

The car is a 1954 Chevy 210 with a 350 and automatic. The problem is with the brakes, specifically that the stopping power is poor. Every component in the braking system is new, and I am using the stock manual 4 wheel drum system except I have a Walton firewall pedal assembly with a new dual reservoir master cylinder (1 inch bore) from a 69 Impala 4 wheel drum car.

When I push the pedal the brakes engage, but I have a lot of pedal travel and the stopping power sucks. I cannot get the wheels to lock up no matter what I do. I have owned lots of drum brake cars, and these brakes are not normal.

The brakes shoes are adjusted correctly. I have swapped out the master, checked the clearance on the master cylinder push rod (it is fine), and bled the brakes a bunch of times. Pumping the pedal does not make a difference in pedal feel. I have good pedal, although a lot of travel, and almost no stopping power.

The entire system is plumbed with very small diameter brake line (looks like 1/8"). Smaller than the 1950 Chevy I used to own. I don't know if this is a factor, but perhaps it is. I bought the car this way, so it has never had good brakes since the system was replaced before I owned it.

One last note. When bleeding the brakes, opening one bleeder results in the pedal going all the way to the floor. In my experience, a dual master should not do this, but this one does.

Any advice is appreciated. I am out of ideas.

 

how did you do it? new drums or did you cut the old ones? have the shoes been contoured to the drums?

 

Are the front/rear plumbed to the right ends? Rear of M/C generally feeds front, and this could be the problem.
Have you had wheels/drums off? Examine shoes' position, 'working' shoe must contact rigid anchor pin in forward direction. (this year Chevrolet was pre-Bendix)
This would account for inability to 'lock-up' wheels in a 'panic stop'.
Smaller line diameter, if 'extreme' in difference to OEM could have an effect, that would be insufficient hydraulic advantage...

 

54 chevys have bendix brakes, not Huck....

The end of the master cylinder should not make any difference, the pressure is the same at both ends, because it's not a step bore master cylinder.

The long pedal travel is due either to air or brakes not adjusted properly (could also be due to the shoes not having the same arc as the drums, but not as likely)

High pedal effort can also be due to lots of metallic in the shoe compound. Different shoes have different feel, some are more "grabby", some are more "hard". But more likely, it's the pedal ratio, if the aftermarket pedal was designed for a power booster.

 

Squirrel has it figured as usual


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1951 and up for Chevrolet Bendix brakes.
As usual I agree with Squirrel there's smelting off with pedal ratio and possibly throw.

 

Right again! to add: I'd suspect either the front or rear circuit has air, not both. Otherwise pumping would build pedal. That's also why the pedal goes to the floor when bleeding one circuit or wheel.

 

is there a different hole for the brake pedal to change ratio. one for power one for manual.

 

'53-'54 Chev used 7/8'' master cyl., so figure that into your diagnosis ...

 

When you installed the fire wall pedal assemble you did not cut the length of the brake pedal to make it shorter , because this will change the mechanical advantage designed into the pedal system. Good Luck. Slim

 

The Walton pedal looks to have a ratio of about 6:1 from my assessment of the pic on their website.
http://www.waltonfabrication.com/19chcarmad.html

I'm suspecting it's the master cylinder bore, but am curious as to the reference to 1/8" brake lines.

Chris

 

If your not using the booster in this set up then the ratio is wrong.its intended to use the booster.you probably need to drill another hole in the arm to get the ratio right.pics of the setup?

 

I had the Walton Fab power fire wall mount pedal assembly in my 51 Chevy and it was the single greatest improvement to the entire car. Do you have the Firewall mount or the under floor pedal assembly ( they offer both)? Are you using a booster or doing manual Brakes?

I plumbed my entire car with 3/16 brake lines, it had 4 wheel drums, factory Bendix on the front and 10 bolt chevy drums on the rear, and it would stop on a dime.

Do you have residual pressure valves in the lines? yes some say you don't need them when on the firewall, but I put them in everything. If it was like this when you got it, and its manual brakes, it may be that it is a pedal set up for a power booster and they eliminated to booster, which will have the wrong ratio for the pedal. that what it sounds like.

 

Thanks for all the responses guys. Lots of good questions. Here are my answers.
- Yes, It has Bendix brakes.
- The Walton pedal assembly is a firewall mount, and I am not using a booster.
- The drums have been cut. I noticed that the self-adjusters are adjusted out quite a bit for having new brake shoes. If I adjust the shoes to be tighter (too tight) against the drums, the brakes improve but are still poor.
- Neither master I have tried had residual pressure valves. I added a 10lb Wilwood valve to the rear, but it made no difference. Due to that I did not install one to the front.
- I have not modified the Walton pedal. It was installed when I bought the car, but the car had never been driven.
- There is only 1 hole in the pedal arm.
- I am confident there is no air in the system. I have bled it many times.

I did not realize the Walton pedal was designed for a booster (the web site does not show a booster). That may very well be the problem, but I'll need to research this more. The web site states manual pedal assembly. I also suspect the 1 inch bore master is a problem, but I have not been able to find an application for a dual master with a 7/8 bore. Does anyone know which car may have come with a dual manual master with a 7/8 bore?

Thanks again, and if you have more ideas I'd like to hear them.

 

the 7/8 bore would make the problem worse.
maybe the master is defective?

 

Just because you have new parts doesn't mean you have good parts. Trust me on this. Had a similar brake problem with new wheel cylinders that were absolute junk.

 

This almost sounds like the floating piston in the M/C is bottomed out and jammed [ giving only 2 wheel brakes]
Or a proportioning valve is faulty

 

I had a similar issue with a similar setup. It came down to the master cylinder push rod. Does yours thread into a clevis? Is it adjustable? You need to adjust modify or whatever until you get to the point where your pedal is as high as possible and the push rod and clevis are as long as possible where the clevis pin/bolt aligns and slides through the hole on the pedal rod. This will maximize your throw which might solve your problems.


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-Clean up the linings with steel wool.
-Check the anchor pin adjustment, this is very important yet many have never heard of it.
-Lining material can make a tremendous difference is stopping power. Porterfield brake pads and shoes are some of the best.. https://www.porterfield-brakes.com/

 

This may be a help. I would try to extend the rod where they lock up when hot. There you have the other extreme condition. Then back the rod off, go like 1/8" (or count full turns) at a time, but write down what you do.

 

The firewall mount pedal assembly is meant to be used with a booster. If you do not have one, your pedal ratio is off, which will do exactly what you are saying is happening. You can either put a booster on it or pull the pedal out and drill another hole in the pedal above the existing one about an inch to inch and a half, to increase the ratio. The 1 inch master should work just fine. I would look into putting a booster on it. that's not a light car and the booster will help, I used an 8 inch dual diaphragm booster, with a 1 inch Vette style master and it worked great. also had 10lb residuals in front and rear lines.

 

Great advice everyone. I'll start by trying to extend the push rod, although I have already extended it a bit. If that helps, I'll pull out the pedal and drill a new hole. If neither helps, I'll go with the booster. That is an interesting thought about poor quality linings. I'll think a bit about that one.

Thanks again for the help. I'll be out of town for a week, but when I get back I will try these suggestions and write back to the thread.

 

Are your primary and secondary brake shoes in the correct location?

 

Are the shoes arced the same as each drum? If they aren’t the shoe may flex as it tries to stretch out to the drum. Pull the drums and see if there are any unscuffed spots on the shoes. You can sand down the high spots, because finding an actual brake shoe arcer is rare nowadays.

 

The primary shoe is to the rear on each wheel, but the difference in length between the primary and secondary is small, maybe an inch. That seems odd to me. I believe the arc is the same, but I will take a look. I did not see any obvious sings of high spots.

Thanks guys.

 

The short primary shoe lining should be to the front of a Bendix servo drum brake, and can be a different material than the longer secondary lining.

 

Yes, that is how I have it. I thought the primary was the longer shoe, but in any case, the longer shoe is on the rear.

 

Thanks to the help of those on this forum, the brakes are fixed. I checked the pedal assembly, and it is made for manual brakes, so I moved on from that. While under the dash I got to thinking about the length of the pedal push rod and the thoughts raised here about leverage. I had left a tiny bit of clearance from the end of the pedal push rod to the master cylinder piston when I installed the master cylinder. The clearance was very small, but it did exist.

I tried extending the push rod about 5/16 of an inch, which eliminated the clearance and put a small amount of pressure on the piston. That fixed it. It seems that despite the long pedal travel, the piston was not being fully compressed, thus the brakes could never be fully actuated. The pedal travel is far shorter now, and the brakes lock when I jam them. I checked for any drag on the brakes, and there is none. After a long test drive today, all is well.

I am still a little unclear as to why the pedal was firm and did not go to the floor before I made this change, but perhaps it was just too much travel for the arc of the pedal assembly.

Thanks for all the help.

 

Be careful - if you tightened it to the point of not uncovering the return port in the cylinder, when the brake cylinders heat up in use, the brakes won't release

 

You might want to put a return spring on that pedal to.