Brake Issue

[Tennessee_Farmer]

I need an expert to figure this one out.  I am working on an Eagle that the brake system seem impossible to bleed.  I have a lot of Eagles and have bleeded a lot of brakes so the common solutions are not going help.  I had this car in storage and unused for about 20 years.  I have replaced the front calipers, the rear brake cylinders and the master cylinder with new ones.  I have tried bleeding the system with a vacuum bleeder and the old fashion two-person work the pedal system until all air is removed, but the brake pedal still goes to the floor.  There are no leaks.  I even sealed off the ports to master cylinder to see that it is working and the brake pedal is stiff.  The only thing I have not changed is the combination valve but I can see no reason as to why this would effect brake action.  When the pedal goes to the floor there is a little brake action.  I thought maybe it was because the rear brake shoes were not adjusted out, but I have even removed the drums and wrapped the shoes with a belt fastener with no change.  When the engine is running, the brake pedal goes to floor with no resistance.  I am frustrated and need some ideas. 

[rmick]

Try reverse pressure bleeding https://www.brakebleeder.com/solutions/bleeding-brakes/how-it-works/

[Tennessee_Farmer]

Still can't figure it out.  I tried a different combination valve and no effect.  I bypassed the combination valve and no effect.  I blocked it off at the combination valve going to the passenger front brake and brakes worked.  Tried replacing the the brake hose and front left caliper but no effect.  Reverse bleeding had no effect.  This is a real mystery

[AMC of Houston]

If the pedal goes to the floor with no leaks anywhere; has to be either power booster on master cylinder.  Nowadays about 20% of "old-style" new master cylinders are bad right out of the box (personal experience speaking).   I saw that you capped the MC lines for a test; but the results may be different if the MC pistons could move a little further with the test (and get to the possible bad spot in the bore where it'll bypass).

[johnbendik]

I hesitate to even mention this because it sheds a glaring light on my own ineptitude.  Nevertheless...

I had the same symptoms after completely replacing everything that you have replaced.  The pedal traveled too far, and brake action was minimal (although I could lock up the rear brakes with a hard stab at the pedal).  Another weird symptom is that I could not get the brake light to go out.  I finally gave up and took it to a mechanic for a professional 'bleeding'.

Long story short, it turns out that if you switch the front brake calipers (left to right) AND invert them (turn them upside down), everything will match up and install properly and even look mostly correct.  However, the brakes will never work right and will exhibit all the symptoms you've described.  That's what I had done.

I have always had a problem with 'spatial relations' and this was a prime example of it.  I'm not even going to suggest that you might have done the same thing, but I'll throw this out there just in case.  The one sign that should have clued me in was that if you make this mistake, the bleeder valves will be above the brake line instead of below.

The mechanic has a good laugh at my expense, and I invite anyone reading this to do the same...

JB

[Tennessee_Farmer]

Thanks for the new information.  I would not put it past myself to install things upside down, but in this case the front calipers are correct, just like in my other Eagles.  The bleeding ports are on top.

I have spent many days and quarts of brake fluid trying figure this out.  Here are some of the things I have done.

I have tried replacing the master cylinder many times with old ones and new ones.  The one on the car right now is an old one with a rebuild kit.

I have done many measurements with the power booster and I don't see any problem.  There is an adjustment on the push rod from the power booster to the master cylinder.  The length is the same as other power boosters I have laying around the shop.  I tried adjusting it out and all I succeeding in doing is having brake drag from the brakes continuously being partially applied.

On the master cylinder, when I block the port for the front brakes leaving only the rear brakes, the brake pedal holds fine.

Behind the power booster there is a T fitting for the front brakes.  The T is fed by the master cylinder port for the front brakes.  The T then goes in two directions.  One side goes directly to the driver-side front brake.  The other side goes to a steel brake line that follows the firewall to the combination valve attached to the lower wall of the engine compartment.  From the combination valve another port goes to a steel brake line that connects to the rubber hose that goes to the passenger-side front caliper.  A second steel brake line goes from the rear brake port of the master cylinder across the fire wall to a port in the combination valve.  Another port leads to a single steel brake line to the rear brakes.  This eventually branches for the left and right rear brakes.  The only purpose of the combination valve is to measure a failure in either the front brakes or rear brakes.  There is a shuttle in the valve that will go off center if there is a failure sending an electrical signal to the brake light on the dash.  With that said, I tried the following:

At T for front brakes, block off the line going to passenger-side front brake.  This leaves the driver-side front brake working as well as rear brakes.  The pedal works fine.

At T for front brakes, block off line going to driver-side front brake.  This leaves the passenger-side front brake working as well as rear brakes.  Pedal goes to the floor.

Repeat the above, but block off rear brake port as well.  Pedal goes to the floor.  The problem now seems to be isolated in the front passenger-side brake.

Reconnect all the brake lines.  Now, go to the combination valve and block off the exit port to the passenger front brake.  Brake pedal holds.  Now the problem appears to be either the front passenger brake hose (which looked fine) or the caliper.

Change front passenger side brake hose.  No pedal.

Install new front passenger brake caliper.  Still no pedal.

Writing all this is simple.  But, at each step of the tests the brakes have to be newly bled, thus the reason for using a lot of brake fluid.

There are no leaks in the system so I can not figure out where the gremlin is.  I have bled this car so many times with so many different systems I don't think the problem is air in the system.  Although I don't know where the gremlin could possibly be. my only thought is someplace in the system there is enough free motion that when everything is put together this motion uses up the brake pedal - like what would happen if the rear brake shoes were not adjusted out to near touching the brake drums.

I have tried letting the car sit with the hope the problem would disappear with no luck.  I have been working on another restoration and had absolutely no problem with brake work. 

   

[vangremlin]

This is a real head scratcher!  You've been going about this the right way, very methodically and testing each component.  And I don't envy you having to re-bleed the brake system that many times.

In reading through this, it sure sounds like something to do with the front passenger brake.  Could it be the steel line that runs from the combination valve to the front passenger brakes and then connects to the rubber hose?  Seems like you've tested everything else!

Good luck!

[Tennessee_Farmer]

When I have time to get the car back on the lift, I am going to fabricate a copper line (easy to bend) to run from the master cylinder to the steel brake line on the right wheel and see what happens.

[mo.eagles]

The problem with a copper line is it can expand and give you the same issue. I would look real close at the R/H caliper while the brake is applied. See if you can spin the wheel (with it off the ground). Check the flex hose as well. Could be expanding?

[Tennessee_Farmer]

I connected a bypass going directly from the master cylinder to the steel line that connects the rubber hose to the right front caliper (i.e. just after the combination valve.)  This eliminates the left front brake as well.  With that, the front right brake works.  Thus, no progress.  I am going to try rebleeding the wholes system, and when that likely fails, I will trying installing yet another master cylinder.

[packotobacco]

Hi I don't know if you're still dealing with this I had a post running for years trying to fix a very similar issue finally solved it, search for mysterious brake issue and skip to the end, not the mysterious power brake issue post. Not sure if this is your issue but it should be quick to verify.

[vangremlin]

Hi I don't know if you're still dealing with this I had a post running for years trying to fix a very similar issue finally solved it, search for mysterious brake issue and skip to the end, not the mysterious power brake issue post. Not sure if this is your issue but it should be quick to verify.

I believe this is the thread packetotobacco is referring to:

http://forums.amceaglesden.com/index.php?topic=45769.30

[Tennessee_Farmer]

The problem is solved.  I worked on this issue many hours last year and finally gave up.  I just pulled the car out again and gave it some fresh thought.  I tried extending the adjustment screw on the rod between the booster and the master brake unit.  I extended a little at a time and I got good break action but found the front brakes were pretty much locked on.  Then I thought maybe the pads on the new brake pads I had installed were too thick.  I measured everything and they all were the same thickness as my supply of new brake pads.  Then I decided to reinstall the old pads.  They were still useable but worn.  Problem solved!  However, as I examined the brake pads I had removed, the right side were new and the left side a little used.  I must have tried to economize when replacing the pads.  However, one steel ear on one of the pads was seriously bent.  How it got that way I don't know, but that had to be the problem all of the time.

[vangremlin]

Great to hear the problem is solved!  Go out and drive that Eagle!