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I live in south central Missouri and last Fall purchased a B-61 tandem axle Mack dump truck with the quadramatic transmission.  I have no experience with a vehicle like this but, wanted to own an American made truck, that helped build America, before I became too old.  I had  driven it very little this year and decided last week I should begin to familiarize myself with operating the twin gear shifts.  After traveling the highway a few miles a fire developed in the engine compartment.  The fire department, police and a tow truck all arrived on the scene and when the smoke cleared the tow truck operator said the brake air lines had been damaged.  There was no pressure registering on the gauge in the cab.  The tow truck operator used an air line and his truck to refill the reservoir on my truck.  The brakes still would not release.  At this point the police said the truck was a hazard to other drivers and insisted it be removed from the highway.  The tow truck operator said he would have to pull the truck with the brakes engaged.  I put the transmissions in neutral and the tow truck operator hoisted the front axle off the ground.  When he started to tow we noticed the wheels of the back axle were turning.  The operator then decided he would keep the front axle of the tandem from touching the pavement by chaining it to the frame.  This allowed him to tow the truck without "scubbing" the tires.

My question and reason for posting is can someone explain if there is a way to release the brakes when you have no air pressure?  Keep in mind, I'm not a mechanic and probably an explanations should be dumbed down so I can understand it.  Thanks in advance.

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  • 2 weeks later...

newer brakes canisters use a 2-chamber design.  One has a diaphragm which uses compressed air to actuate the brake.  The other chamber has a diaphragm with air going to one side and a compression spring on the other side.  This second chamber is the parking/emergency brake.  The 2nd diaphragm is pushed down to release by pressing the release valve in the cab.  If the air pressure drops, the spring will automatically apply the brake.  These brake units typically have a "caging" bolt which allows you to manually compress the spring and release the emergency/parking brake.

Many older trucks had "DD3" brake cans.  these were a Dual Diaphragm 3 function (service, park, and emergency) piece.  Get it...D-D-3?  They had roller-locking devices in them, and a "reserve" air tank, along with a host of plumbing and an "inversion valve".  If these locked, there was an override valve in the cab that you could push in which would dump air to the release side to allow the truck to move off the road before that tank was exhausted.  Seems like you had to hold the valve in and apply the brakes via the pedal to get the piston to disengage from the roller locks.  Couldn't get far, but maybe off the railroad tracks!

Even older stuff, including a lot of original B-models, had a simple lever-operated parking brake around the driveshaft.  Of course, lots have been upgraded over the years.  I do not know what system you have.

So, it kinda depends on how your truck is currently set up as to exactly how you can override the brakes.  I took the DD3 stuff off my old R600 and upgraded it to the modern spring brake design.  Worked better, and gave me the "caging" bolt option, just in case.

Anyway, I trust you got it home okay, and are well on your way to getting it sorted out.  Lots of people on here will help, once they know what you have to work with.

Oh, and welcome!

"Eagles may soar, but weasels don't get sucked into jet engines."

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I gotta say I learnt something here 

R models in Australia have a valve to push thats beside the air supply valve to the trailer 

Looks the same on the knob, black round but I think the writing is different 

Anyway I have never known what this valve is for and have asked plenty of people over the years 

I push it and never holds, just pops back out 

On my mates R model we were problem solving (having a drink and talking dribble) one night a few weeks ago and I noticed that at least one of the brake chambers is different to a normal maxi 

It looks like these DD3 when I googled it 

He had no idea as it never gave trouble and hasn't ever paid attention 

His R model is 83, so two years newer than Mrs Mack 

I wonder if that is what that valve ia for 

Must look into this another night 

 

Paul 

Edited by mrsmackpaul
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And now Ozark, I am assuming it is a S cam brake, if so you can just wind the slack adjuster off with a 9/16 ring spanner

Or if it is the normal maxi can you can just insert the "T" bolt thats on the side of the can and do up tight witha 3/4 spanner

https://www.teamrunsmart.com/articles/truck-smart/june-2014/how-to-cage-your-brakes

Paul

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Thanks everyone for your information.  When no one responded to my original post during the first week, I assumed my question was too elementary to warrant discussion and put BigMackTrucks on the back burner.  Also, I have been dealing with the insurance company, finding a place to move the truck and hiring a mechanic who is knowledgeable, reliable and honest,  along with my other obligations.

I will post some pictures so the system I have can be identified.  I want to learn what I can so I'm able to use the information when future situations arise and hopefully pass it along to help others.  Thank you also for the welcome.

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12 hours ago, mrsmackpaul said:

I gotta say I learnt something here 

R models in Australia have a valve to push thats beside the air supply valve to the trailer 

Looks the same on the knob, black round but I think the writing is different 

Anyway I have never known what this valve is for and have asked plenty of people over the years 

I push it and never holds, just pops back out 

On my mates R model we were problem solving (having a drink and talking dribble) one night a few weeks ago and I noticed that at least one of the brake chambers is different to a normal maxi 

It looks like these DD3 when I googled it 

He had no idea as it never gave trouble and hasn't ever paid attention 

His R model is 83, so two years newer than Mrs Mack 

I wonder if that is what that valve ia for 

Must look into this another night 

 

Paul 

on that system you had  enough air to release brakes one time but you had to hold the button in. intended to only get you out of the road

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