1964 GM PD4106 Service Brake Stuck on

[djanspach]

Hi -
I'm new to bus's but pretty good with old cars.  We have a newly acquired 1964 GM PD4106 (2095) that has been running and driving great.  The previous owner upgraded to the "spring brakes" and added a Haldex air parking brake and Anti Compounding Valve.  Everything was working just fine.  Last weekend we came back from a trip and parked in the driveway.  Since we hadn't tried the air wipers yet we decided to give them a run.  The wipers need some help but worked.

This weekend we fired up the bus and went to leave but the brakes were stuck and literally the brake lights are stuck on.  Everything sounds like it is working.  The parking brake push pull makes air release noises.  The brake pedal also feels and makes air release noise as well but the brakes and brake lights never change.  The bus will not move.  You can feel it surge when shifting into gear but will not move even with a little throttle. 

Air pressure is normal for our bus and gauge (100-105psi).  I even used the shop compressor to air up the system a bit to 120psi just thinking maybe we had a leak somewhere.  I couldn't hear a leak even with the engine and external compressor turned off. 

I'm at the point where I think some debris from the wiper motors(?) may have gotten into the system.  I know I happened across a brake system plumbing diagram somewhere around (service manual I'm assuming).  I haven't really been under the rear of the bus and have been cribbing and using proper support when under the front of the bus.   

Any advice on what to check?  I thought if I started at the anti compounding valve and see if I can determine where the air pressure is and where it isn't.  I can see that the brake light switch is in one of the lines near the anti compounding valve.

Thanks!
Don

Previous owner spring brake video:
https://www.youtube.com/watch?v=3I2f9UhURD8

[Dave5Cs]

Just an Idea but did you have it in Neutral and then when aired up put 100 lbs of pressure on the service brake pedal to release them and then go forward or reverse?

[djanspach]

Yes -

Our bus is a 6V92T Detroit with the Allison V730 automatic.  So its always in neutral when parked.
We tried a couple different combinations of foot on the brake - put it in gear.  Off the brake - put it in gear.  To the most extreme in gear off the brakes and giving some throttle.  I did this in both drive and reverse. 

I am hoping its something simple.  ;-)

[Runcutter]

Don, this may be different because your brakes have been changed out.  I can't tell from your post whether you have followed the normal procedure for later coaches (after Johnson bar hand brakes were phased out).  It shouldn't matter whether or not the bus is in gear, but parking brake release is normally pushing the park brake valve (down, in, whichever), then making a full brake application.  Your description makes me wonder if you've only done a light brake application, or you've done the required full application.  The brake lights are on because the brakes are on -- not vice-versa.

Arthur

[djanspach]

Thanks Arthur. 

It appears that the ICC, Johnson bar and high idle solenoid have all been removed.  I have determined that I have proper application valve operation but the double check valve isn't letting the service port air release when the application pedal is released. 

So I find the service brakes stuck on - not the air over spring parking brake.

When I'm at the rear service brake relay, I find air on the service port at the top, even though the application pedal is off.  Once I relieve this pressure by cracking the fitting at the top of the service brake relay the brakes release.

I have to figure out how the double check valve should be releasing.  First I need to figure out what all these valves under the driver actually are.

[Coach_and_Crown_Guy]

It occurs to me that whoever "removed" the ICC brake valve may not have done a clean and complete job. The ICC "emergency brake" operation was essentially designed to apply FULL service tank air pressure to the rear brake chambers using existing service brake lines. This was an exceedingly harsh, very fast, and scary brake application that mostly caused more troubles than it solved. It went around the foot valve and obviously had to have various check and other components to work properly, in parallel to, and supersede/overrule the foot valve. 

Like the most favorite trick was for drivers to use it as a Parking brake..... which was fine until the air pressure leaked out and the brakes released and the bus rolled uncontrollably, which caused some truly spectacular nastiness. My thoughts are that any hidden check valves etc. may not have been removed and re-routed/capped properly, plus you're certainly experiencing some of the results of age and lack of maintenance of these possible components.

Finding and deleting these complicating components would be a good use of your efforts in order to restore the totally clean air lines with only the service brake foot valve with only the minimum required check, relay, or other regulator valves as if the ICC functionality or components were never installed. A clean and simple service brake air circuit is what you eventually want. Good luck.

[luvrbus]

Changing to spring brakes there should be a anti compound/ quick release relay in the system that has probably gone bad it is the relay that has 2 lines running to each can mounted some place. That is where I would check because you have a fully applied parking or service brake or it would move