PD4106 park brakes won't release...

[Busted Knuckle]

Bob some breaks won't release until about 90 PSI.
I have 2 buses that are that way a '95 Setra and '97 Dina both have to have between 90-100 psi to release the first time, but don't reset them selves until around 60-70.
DOT rules and the standard is 60 min. for the reset for lose of air pressure.
FWIW  BK  

[robertglines1]

BK ,I reread his post and he said the parking brake was popping back up at 90.  Isn't that to high? shouldn't be around 60?  Bob

[wildbob24]

Billy,

The zerk on the chamber should be next to the lock port, where the closest hose to the mounting bracket is attached.

In looking at your pictures, it appears that your chambers do not have them. Must be older versions.

Later installations(like my buff) had a mechanical release on the end of the shaft where it attaches to the slack adjuster.
If yours doesn't have these(and it probably does not), the only way I know to release them would be to unbolt the chambers from the brackets. You would need to have the bus jacked up and the wheels removed in order to safely do this.

PM me your email and I'll send you a couple of scanned pages from my manual with pictures of the zerk location and the mechanical release. The files are too large to attach here.

Bob

[Busted Knuckle]

Bob in a perfect world yes. But there are variables that could effect it. Could be someone has changed out the release valve itself. Or any other valves in the system. Problem with these old coaches is if you don't have a knowledgeable mechanic and parts man working together sometimes the parts guy will tell you "this will work, it's the same thing only newer!"
It takes someone like Luke (and a few others) who knows the difference, and will take the time to find you the right part.
 BK  

PS also his system could be gummed up.

[Rick 74 MC-8]

Billy
With the coach aired up if you push in the parking brake knob doing nothing else will it hold psi or do you hear air leaking ?  It should hold air might drop a little from charging the brake system but it should hold once that happens with no air escaping

                                                           Rick 74 MC-8

[wildbob24]

BK ,I reread his post and he said the parking brake was popping back up at 90.  Isn't that to high? shouldn't be around 60?  Bob

That is high. DOT requirements are that the warning alarm sounds at around 60psi and the emergency brakes apply at around 40psi The problem here is old DD3 systems are plumbed differently than modern spring brakes. Plus, we're dealing with a modified system that may or may not be correct.

In a typical DD3 system(like my Buffalo), the parking brake control is sensing the pressure in the parking brake reservoir, which is isolated from the rest of the system by a check valve. The pressure gauge reads from the accessory tank, so the 2 are not necessarily going to be in sync. So, the accessory tank pressure can drop to 0 and the parking brakes will not apply. The warning buzzer will come at about 60psi, though.

The fact that Billy is losing pressure while his foot is on the brake indicates a leak somewhere. My approach, at this point would be to get the bus up in the air and observe and search for the leak(s) while a helper operates the brakes.

I would also check and make sure that there is pressure at the lock port when the parking brake is released. The double check valve or the inversion valve could be stuck and preventing the proper flow of air.

Bob

[bwze]

Well here I go with another video....they say picture is worth a thousand words...well a video definitely trumps that....

GM PD4106 - Trying to release park brake.....

I followed RJ's procedure to a tee quite a few times, but nada....I do hear air escaping while the park brake is depressed until it gets to around 90 psi and then the valve pops back up...

I got a feeling I bought myself a big ole polished up turd....

[Busted Knuckle]

Billy,
I wouldn't discount it as a "big ole polished up turd" just yet!
Most likely it will be a simple fix.
But even if you have to replace both DD3's and a valve or 2 you will have a nice coach to enjoy for a long time to come!
  BK 

[robertglines1]

just a old girl that needs a little tlc! soap and water time. or change parking brake valve .squirt a little soap water around it to see if it is leaking.  Good luck. once she gets into a good mood you will be happy also.

[Rick 74 MC-8]

Billy

         Find out where the air is going when you release the brakes and you may have found the problem




                                                                                       Rick 74-MC-8

[brando4905]

Billy,

 Try not to get discouraged, it's not a turd!   I definitely know how you feel though. I have an older GMC as well, there have been times that I wanted to burn it to the ground, but once you get all this little stuff sorted out your gonna love it. It seemed like for awhile there every time I got in my bus I had to have something replaced or repaired, it can be very frustrating to say the least.

Hang in there.

Brandon

[bwze]

Just went out and pressurized the air system with my garage compressor again. Stepped inside and pushed the park brake valve down and then started my search for escaping air. Found it at the back of the driver's side rear brake chamber...right where the push rod leaves the chamber itself. With this new discovery, it seems I may become acquainted with a DD3 rebuild......for both sides.....



I also checked for air leaks with the valve in the park position and found it leaking at this frayed hose that I noted earlier, so I guess I'll be replacing that also....



Anybody got any suggestions on where to get a rebuild kit for these?

[fortyniner]

II was just writing up something to have you check for escaping air at the cans. I had a similar problem with DD3s (4905) which turned out to be a hole in the service brake diaphragm. The symptom was difficulty releasing the parking brake and air escaping from the DD3 unit while service brake is applied. Yours looks like a hose. Replace them all while your at it.
 
Your fortunate to have DD3s on a 4106 as many just have a simple system that can leave you with NO BRAKES if air pressure is
lost.
.
The DD3s do have an emergency disable mechanism where the rod connects to the arm. It completely disables rear brakes. I assume the fronts would still work but dont know for sure.
.
That would allow you to move the bus and perhaps get it on some ramps so you can work on it. I you have yet to put your bus on ramps and block it up ( this refers to blocks between axle/bump stop) that is a whole new discussion.  Its safe when done right but extremely dangerous otherwise.
.
Tom P.

[eddieboy]

I also have a 4106 (1962).  Mine only came with the hand brake for parking.  The ICC will hold it fine, but I don't want to depend on it for any length of time do air pressure going down will have me chasing her down the road.  I am looking into changing to the sprin brakes.  They don't seem to be very expensive for brad new.  Is it possible you also have the hand brake?  That was stock on mine.  It is a drum brake attached to the drive shaft.  Just to be extra safe, I will keep both systems when I get done. (if ever)
Ed

[gmbusguy1]

Billy, most of the advice in this post is Great.

However YOU NEED a 4106 service manual and supplement as the DD3's are in there

safety first!!! your bus is heavy and  NEVER go under it (not even for a minute) until it is properly blocked from falling and Killing you should you lose an airbag or line. this has happened and we have lost busnuts to this.

if you are not familiar with air brakes my advice is to get the bus to a qualified BUS technician these vehicles are heavy and the brakes need to work right

from the photos you posted and the leaks you can find if it were me I would replace both rear brake cans with rebuilt units from Luke at US Coach along with all new hoses to the cans

Merry Christmas

Chris