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Brake pedal is way too stiff
https://slantsix.org/forum/viewtopic.php?t=44390		 Page 1 of 1
Author:  ESP47 [ Thu Apr 07, 2011 3:11 pm ]
Post subject:  Brake pedal is way too stiff
I asked this question on FABO a while back and couldn't figure out a fix so I thought I would ask you guys.

The car is a 67 Valiant with a 225, 9" manual brakes and power steering. From day 1, the pedal has been hard to push down, doesn't travel very far and is hard to keep held down while sitting at a light.

The idle is sitting fine at around 550-600rpm in gear. There is nothing visually wrong and no strange sounds that I can hear.

I swapped out the master cylinder for a new non-remanufactured Raybestos master cylinder for the same year (non power) and that didn't really help. Bled all the brakes and they bled out fine. There are no kinks in any of the brake lines or rubber hoses at the wheels.

A guy on FABO suggested it could be a bad contact between the shoes and the drum(s). Makes sense if only 50% of the shoe is touching the drum to stop the car. I pulled the drums off and they look fine. The shoes also look great. Just to be sure, I swapped the drums from my Duster on there and tried it out. Brakes felt the same.

Then I thought I figured it out. I was trying to adjust the starwheel and it was kinda hard to turn. I noticed the spring on the bottom that connects one shoe to another wasn't the correct type and had way too much tension. I swapped the springs off my Duster and figured for sure that the brakes would feel better now. Took it for a run and that only made it feel about 10% better.

I also removed the self adjusters a couple months ago to run the brakes a little looser to see if that would make a difference. That helped ever so slightly but the brake pedal pressure still isn't even in the ballpark for what it should be.

Does anyone have any other suggestions? Could it be a faulty wheel cylinder that takes way too much pressure to push the shoes out?
Author:  Joshie225 [ Thu Apr 07, 2011 3:26 pm ]
Post subject: 
Many modern brake shoe linings are much harder than the asbestos based linings originally found on our cars. If you buy 'premium' brake shoes you almost certainly have long life and hard linings which require more pedal pressure than the original shoes. If you can still buy cheap brake shoes try them. If not find a brake and clutch friction shop and have your existing shoes relined. You may need to explain what you're trying to achieve, but this can be made better. A quick search turned up Capitol Clutch and Brake. Might give them a call. http://www.ccbparts.com/
Author:  Reed [ Thu Apr 07, 2011 3:44 pm ]
Post subject: 
Unless I am mistaken, the self adjusters are a necessary component of the drum brake system and the car should not be driven without them present.

Do your brakes drag, pull, or pulse? Does the car stop correctly or is it hard to stop?

I would put the self adjusters back into all four drums and take the opportunity to verify that the drum brakes are assembled correctly and that the wheel cylinders all function correctly. I would also check for bent or damaged hard lines.

You might also have a problem in the metering block.
Author:  wjajr [ Thu Apr 07, 2011 5:01 pm ]
Post subject: 
Sometimes glazed linings will cause poor stopping performance. Glazing can result from ridding the brake with left foot, brake fluid contamination, or a lot of rust & crud coating the shoes.

One other possible reason is perhaps the drums were turned past their maximum cut, and someone, when replacing the shoes, did not contour the new shoe to fit the radius of the drum, resulting in a small contact area with brake drum.

You may have stuck or stiff wheel cylinders, or collapsed soft lines. Drum brakes are designed to self energize when driving forward. In other words, as the shoes are pushed to the drum, they tend to dig in on their own due to the way the shoes are suspended making for easer stopping.

To see or feel the difference between forward and reverse stopping power at the peddle due to self energizing, back up your drum brake equipped car briskly, that is, if you are capable without crashing, and apply the brakes. See if twice the effort, and twice the stopping distance are the result compared to the same speed going forward.
Author:  THOR [ Thu Apr 07, 2011 5:21 pm ]
Post subject: 
What diameter is the bore on the new master compared to a stock unit? A diameter than is too small will cause the brakes to be hard to push.

As others have mentioned, the rubber lines can become blocked internally. I had this happen on my old '71 Dart and I wound up replacing the soft line to the rear axle.

All went well after that.

~RDE~
Author:  ESP47 [ Thu Apr 07, 2011 10:24 pm ]
Post subject: 
Josh, the fronts and rears have the cheaper Napa brand shoes. The same type I run on my Duster. They are in great shape with no to very little glazing at all.

Reed, I didn't even know what self adjusters were until I got this car a year ago. Up to that point, the only car I had ever worked on was my Duster and it had no self adjusters on there when I bought it. I had no idea they even belonged on a car lol. The brakes don't drag, pull to either side or pulse at all. It's hard to stop as well. It's one of those situations where they stop good enough (with a ton of pedal pressure) most of the time. But its that 1% of the time where you have to slam on your brakes on the freeway or something that scares me, because it just doesn't stop as quick as I want it to.

wjajr, the shoes are really clean and I feel like I kind of ruled out the drums themselves as being the problem since I put my Duster's on and that didn't help. New shoes and my Duster drums rules out the shoes and drums in my book. I know the soft lines aren't collapsed so I'll have to check out the wheel cylinders more. I wish I had some spare ones on hand because they are too expensive to buy just to try out.

Thor, I measured the bore diameter when I got it and it was stock. I can't remember what it was when I checked....I believe 15/16"?

Is there a technique for blowing out all the brake lines? Should disconnecting the soft lines and blowing air through the lines from the MC down to the wheels be good enough?
Author:  lancer61 [ Fri Apr 08, 2011 6:22 am ]
Post subject: 
Quote:
blocked internally
has nothing to do with dirt in the hoses, the rubber gets bad and there is nothing to do about that but replace them.

The break hoses can get bad from the inside and cause all kinds of weird behavior, they can stop fluid from returning back to the master cylinder and things like that, if they are old it could be worth a shot and replace them and see if that helps.
Author:  KBB_of_TMC [ Fri Apr 08, 2011 8:54 am ]
Post subject: 
When my old drum brakes had a very hard pedal, I found that a couple of the slave cylinder's pistons had simply gotten stuck in place - I only had 1 of the 4 pistons actually doing anything.

After many years, they can corrode and take thousands of pounds of force to break free.
Author:  SlantSixDan [ Fri Apr 08, 2011 9:04 am ]
Post subject: 
Quote:
What diameter is the bore on the new master compared to a stock unit? A diameter than is too small will cause the brakes to be hard to push.
Other way round. Smaller-bore master cylinder = longer pedal travel with less effort. Larger-bore master cylinder = shorter pedal travel with more effort.

It's worth looking to see if arc of the brake shoes is substantially different to the diameter of the brake drums (this will be obvious by checking the contact/wear pattern on the shoes; if there's only contact at the center or at the ends, that'll explain the lack of brake force), but my vote goes to a problem in the hydraulics: seized wheel cylinder(s), blocked hardline(s) or valve, and/or dead flex line(s)...though I suppose a faulty master cylinder could be causing it, too; exactly what master did you install?

I can understand your removing the pre-'69 self-adjustors; the '69-up types work well and save a lot of hassle in periodic brake adjustments. Direct retrofit and all the components are still available.
Author:  THOR [ Fri Apr 08, 2011 9:38 am ]
Post subject: 
Thanks for the correction Dan, don't know how I mixed that up.

:)

~RDE~
Author:  ESP47 [ Fri Apr 08, 2011 12:46 pm ]
Post subject: 
Don't quote me on this because I'll have to check the box when I get home, but I'm fairly certain I got a Raybestos MC36221. Should be the type with a flat cover and single bolt that holds it on in the center.
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