"Invisible Crowbar" Beneath Brake Pedal of 1970 300

[70bigblockdodge]

You have a wheel cylinder problem either stuck or minute leak, after winter slumber do you have to bleed the brakes. If so it is a leak, I had one so small in left rear it did not even get moist from fluid, assumed it was evaporating from brake heat. Finally started leaking more and new wheel cyl fixed for good. Brake hoses can create a number of madladys.

 

[fins2fuselage]

Hoses or wheel cyls. seems to be the consensus, 70bbd; I'll check 'em out as soon as I can.

Jeff

 

[cantflip]

Nobody knows how to troubleshoot.
Booster.

Unlikely with his symptoms... cant be ruled out entirely yet...but its not the logical conclusion.

I just remembered that the brakes do pull slightly to one side (to the left IIRC), but I can't recall a time when they didn't; maybe that's a clue.

That would be a huge clue... if you pull left, chances are something on the right isn't working... at this point you may have more than 1 problem, so try to eliminate and inspect to the failed items and replace as found. It pains me to see parts thrown at problems when there are ways to test first.

 

[commando1]

Unlikely with his symptoms... cant be ruled out entirely yet...but its not the logical conclusion.

That was before he mentioned the pulling....

 

[cantflip]

That was before he mentioned the pulling....

Gee wiz Stan... I didn't want to argue with you, I have been making a point of trying to not annoy you lately.

Now if you just want to debate an issue, I can enjoy a good argument...so long as everyone can finish as friends.

 

[commando1]

Im not debating anything with anybody anytime anywhere.
Do your Flipflap detailed technical manual synopsis of the situation based on your professional experience and training in wanting to help others, and I'll toss out my opinion based on diddly flucking around as a shadetree mechanic.
I'm not criticizing your classroom lectures.
For a lot of people they may be helpful and informative. Personally I find 75% of what you impart in your classroom lectures taken from the pages of Captain Obvious.
Tween everybody here, the original problem gets solved 99% of the time.
It takes a village...
Chill, dude.

And it's not the thermostat.

 

[Mopars & Missiles]

.........And it's not the thermostat........

Well that's a relief, and I was just about to suggest that!

 

[Big_John]

Yes, but are we sure it's not the thermostat?

One of the things I love about this site is most everyone really wants to help. Pros and amateurs alike. A lot of very good information is handed out here, free of charge, no strings attached.

 

[78Brougham]

Is this gonna be a 5 minute argument or the full half hour...

 

[rags]

should the pedal really ever get near to an inch off the floor in normal operation with everything adjusted right? frozen cylinders or clogged hydraulics would give a high pedal not a low one. sounds like pressure's bleeding by in the master. slam the pedal hard. good then? if it goes to the floor with a light steady push, it's the master. also i've seen situations where people will put a left side adjuster in the right side and vice versa. in this case they back themselves off instead of adjusting up. never seen a problem with a chrysler booster. fords were famous for it. don't rule it out though especially if it's a rebuilt. rebuilt with the wrong push rod length! good luck, SG

 

[Fury440]

I forget, but ìs the push rod adjustable. Maybe way back when it got turned a few times.

 

[fins2fuselage]

The booster on the car is the third one, including the original with which the problem began; they have all functioned identically.

I will re-check the pushrod length, but the braking action is immediate and sensitive to the point of "overkill" --- i.e. normal Mopar power brakes. The brakes operate normally under all circumstances except when going down a hill with a stop sign/light at the bottom; that's the only time when I feel the "crowbar".

Jeff

 

[rags]

brake action is immediate. that's how it should be. with this description it could be a frozen wheel cylinder. now three wheels doing the work of four. brakes overheating and fading requiring more pedal effort. sorry i couldn't be of more help. SG

 

[CanCritter]

The brakes operate normally under all circumstances except when going down a hill with a stop sign/light at the bottom; that's the only time when I feel the "crowbar".

after all you've done this would have me looking hard at the proportioning valve...weak or missing spring in the valve itself with a lose checkball?...only so many things that can go wrong...possibley wrong MC?...this stuff should be rechecked...brake switch on peddel jamming it up?

 

[live4theking]

The booster on the car is the third one, including the original with which the problem began; they have all functioned identically.

I will re-check the pushrod length, but the braking action is immediate and sensitive to the point of "overkill" --- i.e. normal Mopar power brakes. The brakes operate normally under all circumstances except when going down a hill with a stop sign/light at the bottom; that's the only time when I feel the "crowbar".

Jeff

I've been talking a lot lately with my 85 year old father that was a Chrysler mechanic for many years. He says that there sould be 1/2" of free play in the pedal. He said that he had a car that the free play wasn't enough and i caused all sorts of problems that he couldn't figure out for a long time.

 

[fins2fuselage]

CanCritter, I tend to agree about the metering valve.

John, I'll check the free play.

Now if the weather will just give me a break to work on brakes . . .

Jeff

 

[71Newp]

Is this gonna be a 5 minute argument or the full half hour...

This isn't an argument, it's just a contradiction...

 

[rkrochen]

There are a couple of other things that could be checked as well. First I would pull the drums and make sure that the top of the shoes are anchored fully when retracted. The parking brake cable may be partially on not allowing the brakes to fully retract. The cylinders would then have free travel until they come into contact with the shoe which would give some free travel in the pedal. Secondly make sure that the brakes are adjusted properly.