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Rear passenger axle locking when braking


MACK321
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Sir... we tried to keep you from spending a bunch of money on this..  I'm sorry..  a lot of this should have been diagnostics and tests.. do you know what type of valve is delivering the 'service air' to the brake chambers? all 4 brake chambers should be plumbed to the same valve through 2 ABS valves, one on each side, unless you have a butterfly valve set-up centrally located on a cross member..  can you post pics of the ABS valves?  I'm trying, as-is others here to help you..  I sure hope whoever adjust's your brakes....  know's how...  

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Just something to try ! If the wheel has spring brakes try caging the offending wheel ! just thinking a little out side the box here! an intermittent protrusion of the spring pot may cause issues as well specially with auto slacks! If the wheel has no spring brake disregard this comment!! 😅

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with all the $$$$$ spent ,one item was slack adjuster that kinda eliminated the rusted clevis ; I think! makes you want to take a trip to physically see the truck. so  many $$$ based on maybe .  find your self racking brain cells as to what else is left . some thing sooo simple is being over looked : don't know what... 

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when all was apart, slack was off - did anyone spin the cam see if movement was free and easy; or spin it 180??? I'd put added return spring on slack as in earlier picture . brake can reported as being new= same size as others 30-30/ 24-30. was the  service brake line  from valve to can removed and check for failing inner rubber lining??? is the line same size as rest ??? 1/2 in 

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1 hour ago, mechohaulic said:

when all was apart, slack was off - did anyone spin the cam see if movement was free and easy; or spin it 180??? I'd put added return spring on slack as in earlier picture . brake can reported as being new= same size as others 30-30/ 24-30. was the  service brake line  from valve to can removed and check for failing inner rubber lining??? is the line same size as rest ??? 1/2 in 

He was talking tractor brakes and showed a trailer axle I was confused by this, first were working on a tractor then a trailer Which is it! Any way !   Leave no stone un turned at this point !!! The Parts canon has  already fired!  might just as well load a new brake pot in it and shoot too new clevise and all  ! also check the cam for freeness while your there! I'm tapped out don't know what else to suggest! The group here has Touched on almost every scenario !

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All of these points seem good to me.. I'm grabbing at straws.. I wonder if the front drive axle is not braking good enough, causing all the brake effort being sent to the rear axle.another question I have is,,,,. Do the brakes grab hard and fast with a slight push of the pedal?  Which would indicate a bad treadle valve.  I would also like to see pictures of the brake chambers mounting position, along with slack adjuster length.. I hate to question another mechanic that I don't know personally, but it seems odd that so many new parts have been installed and the problem still exists.  

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That rubbed spot on the push rod tells me that the slack adjuster may be to short, or the chamber is not mounted in the correct holes for the slack adj. Length.  When the brakes are released the clevis would have to be angled upward, therefore rubbing on the hole in the brake chamber.   Paul, it does look like it is passed 90 degrees.. 

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2 hours ago, Joey Mack said:

That rubbed spot on the push rod tells me that the slack adjuster may be to short, or the chamber is not mounted in the correct holes for the slack adj. Length.

^^^^^^^^^Plus One to This^^^^^^^^^^^

2 hours ago, mrsmackpaul said:

Slack adjuster to push rod angle looks like it's past 90 degrees 

Me Too, Mrs..!

"Be who you are and say what you feel...
Because those that matter...
don't mind...
And those that mind....
don't matter." -

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Sometimes when someone changes a air chamber they just measure what's sticking out of it and cut the new one to that length which may not be correct, then nothing there works right.  That chamber doesn't look very old. Did this issue start after that was replaced ? 

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yes Mark..  thats true, but the rub mark means that when the yellow button is pushed in and the rod pulls back, there is stress on it..  then each brake pedal push, just grinds away at the rod..  just sayin'... I know you are very smart about this,  I value your thoughts...  

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Need to sort the basics out first, do what has been suggested 

If it was my truck I would 

1) pull all 4 brake drums and brakes apart

2) pull all 4 S cams right out and clean bushes etc out spotless 

3) compare all 4 sets of shoes rollers etc to compare if all are the same 

4) reassemble brake assemblies making sure all cans are in the correct holes for slack adjusters 

5) make sure all slack adjusters are of the same length

6) make sure all rod angles to slack adjust ratios are correct 

7) measure drums etc and make sure the match the shoes

😎 reassemble and adjust, before the wheels go on

 

If the truck is aired up, release the brakes and you can pull rods on the maxi cans by hand to see how much travel is actually there

You can also feel if anything is binding by doing this 

For all I know the other brakes aren't even working due to been out of adjustment and the reason this one locks is it is the only brake still working 

Truck would be in my open air work shop right away until I got this sorted

Of course it isn't my truck 

Mack 321 you really need to start looking into this more seriously 

Paul

 

 

 

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17 minutes ago, mrsmackpaul said:

For all I know the other brakes aren't even working due to been out of adjustment and the reason this one locks is it is the only brake still working

Fair call ,Paul..

 

Mack321, Can you find a Shop with a Roller Brake Tester.? & find out exactly WTF is happening when you put your Foot on the Brake Pedal..!!

"Be who you are and say what you feel...
Because those that matter...
don't mind...
And those that mind....
don't matter." -

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25 minutes ago, Joey Mack said:

yes Mark..  thats true, but the rub mark means that when the yellow button is pushed in and the rod pulls back, there is stress on it..  then each brake pedal push, just grinds away at the rod..  just sayin'... I know you are very smart about this,  I value your thoughts...  

IDK  this one is another one that makes you wish you were there.  The little pin looks funky. Is it the right clevis ??   picture looks almost like a welded on clevis. (  IDK why, I can't zoom in on the picture )  I'm starting to think something with that air chamber.

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so there are no local shops that know how to work on big trucks? I get the part about being deleted...  That started years ago, I used to work at a Mack dealership..  we didnt touch them..  sorry...  

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Joey there is local lots of local shops but don't think anyone of them have a Roller BrakeTester and most the local shops are busy they would keep the truck for weeks before looking at it and not the same as you think now a days most of them just want your money not fix your truck 

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