MACK321 Posted March 22, 2023 Author Share Posted March 22, 2023 So I replaced all my drums and shoes replaced slack and cam on the axle that is locking nothing changed still locking Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527629 Share on other sites More sharing options...
Joey Mack Posted March 22, 2023 Share Posted March 22, 2023 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... 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527630 Share on other sites More sharing options...
MACK321 Posted March 22, 2023 Author Share Posted March 22, 2023 I will take a picture of it tomorrow I don't know what type of valve it is Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527633 Share on other sites More sharing options...
MACK321 Posted March 22, 2023 Author Share Posted March 22, 2023 I lowered the height of the suspension too was siting little high Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527634 Share on other sites More sharing options...
fjh Posted March 22, 2023 Share Posted March 22, 2023 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!! 😅 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527656 Share on other sites More sharing options...
mechohaulic Posted March 22, 2023 Share Posted March 22, 2023 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... 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527661 Share on other sites More sharing options...
mechohaulic Posted March 22, 2023 Share Posted March 22, 2023 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 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527662 Share on other sites More sharing options...
fjh Posted March 22, 2023 Share Posted March 22, 2023 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 ! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527665 Share on other sites More sharing options...
Joey Mack Posted March 22, 2023 Share Posted March 22, 2023 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. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527666 Share on other sites More sharing options...
Mark T Posted March 22, 2023 Share Posted March 22, 2023 Still no looking at pilot pads on hub ? Interesting point about the air chamber too. Any of those good ones usually aren't a very good product. Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527668 Share on other sites More sharing options...
MACK321 Posted March 22, 2023 Author Share Posted March 22, 2023 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527673 Share on other sites More sharing options...
mrsmackpaul Posted March 22, 2023 Share Posted March 22, 2023 Slack adjuster to push rod angle looks like it's past 90 degrees Maybe just camera angle Paul 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527679 Share on other sites More sharing options...
Joey Mack Posted March 22, 2023 Share Posted March 22, 2023 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.. Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527680 Share on other sites More sharing options...
Hayseed Posted March 22, 2023 Share Posted March 22, 2023 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..! Quote "Be who you are and say what you feel...Because those that matter...don't mind...And those that mind....don't matter." - Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527691 Share on other sites More sharing options...
Mark T Posted March 22, 2023 Share Posted March 22, 2023 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 ? Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527694 Share on other sites More sharing options...
Joey Mack Posted March 22, 2023 Share Posted March 22, 2023 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... Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527695 Share on other sites More sharing options...
mrsmackpaul Posted March 22, 2023 Share Posted March 22, 2023 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 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527696 Share on other sites More sharing options...
Hayseed Posted March 22, 2023 Share Posted March 22, 2023 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..!! Quote "Be who you are and say what you feel...Because those that matter...don't mind...And those that mind....don't matter." - Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527697 Share on other sites More sharing options...
Mark T Posted March 22, 2023 Share Posted March 22, 2023 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. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527699 Share on other sites More sharing options...
MACK321 Posted March 22, 2023 Author Share Posted March 22, 2023 Paul i am taking this seriously I show all the messages to my mechanic and we checked everything as you guys saying 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527703 Share on other sites More sharing options...
MACK321 Posted March 22, 2023 Author Share Posted March 22, 2023 Mark T chamber is brand new put it in 2 weeks ago Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527704 Share on other sites More sharing options...
MACK321 Posted March 22, 2023 Author Share Posted March 22, 2023 Hayseed only place is the dealer and they won't take my truck it's deleted and the start crying if I bring my truck to them Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527705 Share on other sites More sharing options...
Joey Mack Posted March 23, 2023 Share Posted March 23, 2023 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... Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527706 Share on other sites More sharing options...
MACK321 Posted March 23, 2023 Author Share Posted March 23, 2023 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 Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527708 Share on other sites More sharing options...
Joey Mack Posted March 23, 2023 Share Posted March 23, 2023 I know,,, I'm sorry.. at this point, I guess we will just pray that someone figures out your issue.. It's hard to do this one from 1200 miles away.. Quote Link to comment https://www.bigmacktrucks.com/topic/72584-rear-passenger-axle-locking-when-braking/page/3/#findComment-527709 Share on other sites More sharing options...
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