Brake Mystery Please Help.

[SSteve]

I know I'm new here but we've had this problem since we've owned the 1969 Charger SE.  The car has power brakes.  We live in Colorado Springs so the vacuum isn't great here but that should not be the problem. I had 3 shops try to fix it and no luck.  Trying to stop we really have to stand on the brakes to get any stopping power. Like when you have no power braked. It's almost worse when we are going slow. Drums all around. We have replaced everything at each wheel. Bled them numerous times. Replaced the power booster. the proportioning valve.  Now it's even WORSE!  When we drive it 5 miles the right rear brake starts dragging to where it will lock up.  We can get it to turn if we bleed it a little.

No one can figure this out.  Help.

[birdsandbees]

Your push rod is possibly set too long (without the FSM free play clearance) between the booster and the master cylinder, so it's not fully releasing causing a wheel cylinder to stay extended. That or a sticky brake pedal, like I use to have. If I didn't lift the pedal with my toe the RR brake would drag.

Why you have bad brakes, that's another ball of wax.

AND.. there is no "proportioning valve" on a 4 drum brake system in '69. That block is simply a "tee" with a shuttle spool for brake failure warning.

[green69rt]

I agree with bird.  Here's a picture of the push rod that connects the booster to the MC.  This screws in and out then locks in place with a locking nut.  It must be adjusted correctly.  Too far out and keeps your brakes on all the time.  Too far in and you cannot get full travel on the MC and may not have good braking ability.

After this, I would check the vacuum at the booster.

[Hard Charger]

Would this screw adjustment have anything to do with having the pedal to sensitive. That is slight pressure to where you cannot feel the pedal and the brakes are working.

[BLK 68 R/T]

Another thing to check for the rear brake dragging is the rubber hose that goes to the rear axle housing. If it's old or getting kinked it could be stopping fluid from returning to the master cylinder and keeping pressure on the brakes. How much vacuum does your engine make? did the new booster come with a check valve or did you reuse the old one?

[b5blue]

  All of the above plus brake hardware, return springs can look good but not pull strong. Small pads on backing plates need checked for flatness and lubed if okay. An inline vacuum reserve can can help store a bit of boost, I used one when I had a 509 cam. (Low vacuum.)
  The last time I had a booster fail I just swapped to manual with very happy results. Later I swapped out front drums to 11 3/4 Mopar disks and retained manual. 

[Alaskan_TA]

When we drive it 5 miles the right rear brake starts dragging to where it will lock up.  We can get it to turn if we bleed it a little.

As mentioned above, this part my be due to a rubber line failure.

They can come apart internally & let pressure in, but the rubber flap from inner de-lamination closes like a one-way valve & will not let the line pressure return to zero as fast as it should.

It would be a good time to replace the rubber lines up front also if they are old.

[igozumn]

This.  Replace the flex line from the body to the rear axle housing.  Had it happen to me when I put discs on the front with an adjustable prop valve in the rear line.  Brakes acted like there was no vacuum assist from the booster.  Thought it was a big cam low vacuum issue.  Even put a big electric vacuum pump on and still acted like no assist.  But then I smelled the hot rear brakes one night.  It'd boil water on the aluminum wheels.  Brakes were dragging from the flex line being collapsed internally.  Replaced the $15 line and everything worked like it should.

Had it happen on a '68 VW Bus.  RH rear flex line collapsed internally.  RH rear drum got so hot it burned the paint off the wheel.  



Bought my first '69 Charger in spring of '89.  Big block, but small block suspension, 10" manual drums.  And leaking rear axle seals, so the rear brakes were soaked.  So, basically no brakes.  You could stand on the pedal at 90mph and it would almost speed up, LOL.  Replaced the axle seals and rear brakes and it worked better.  Put some 11" drums on the front (still 10" on the back), and it worked a little better.  Got my R/T SE and it was stock power 11" drums at 4 corners.  It worked a little better.  But putting discs on the front, other than maybe fuel injection, was the best thing I ever did.