MACK321 Posted March 9, 2023 Share Posted March 9, 2023 (edited) Hello I have a 2011 Mack CXU613 I'm having a problem when I brake bobtail or driving empty my passenger rear axle locks up making it very hard to stop and I don't hard brake just a little tap to the brake makes the axle lock all my speed sensors are new brakes are new I replaced the brake chamber for the rear axle as my mechanic thought that was the problem turned out not to be anyone have had this issue before? Edited March 9, 2023 by MACK321 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted March 9, 2023 Share Posted March 9, 2023 when ever i delt with a rogue brake acting erratic, findings were things such as brake can (you changed ), wrong size brake line compared to the others from can to quick release valve; oil /grease on shoes, . when you say shoes are new; brand new or resent install. has this happened since shoes changed?? someone put new shoes have wrong grit block?? slacks must be autos; is the adjustment same as rest or a slack over adjusting ?? 1 Quote Link to comment Share on other sites More sharing options...
MACK321 Posted March 13, 2023 Author Share Posted March 13, 2023 My mechanic said that the shoes and drums look new I never replaced them Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted March 14, 2023 Share Posted March 14, 2023 Was anything changed leading up to this Slack adjusters have different holes for different applications Are they all in the same hole at each back wheel Are the other brakes working properly or at all Measure how much the rod travels out of each can, they should be pretty much the same Are the rods all the same length to ensure all slack adjusters travel the same distance Are the slack adjusters going past 90 degrees If you back the brakes off at the slack adjusters so there is no contact with the drum, then when the park brake is set are the rods at 90 degrees to the slack adjusters, this is important Are all S cams spinning freely and not binding I dont live in a part of the world that uses salt on the road, and even I have to pull S cams out occasionally to properly degrease and clean all the crap out and start again, I can only imagine this would be much worse if you live were salt is used Paul 1 1 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted March 14, 2023 Share Posted March 14, 2023 Amen Paull...Exactly !!! Quote Link to comment Share on other sites More sharing options...
MACK321 Posted March 14, 2023 Author Share Posted March 14, 2023 Paul thanks I will show this to my mechanic they just trying to play the guessing game first they said might be the brake chamber replaced that and nothing changed Quote Link to comment Share on other sites More sharing options...
Popular Post mrsmackpaul Posted March 14, 2023 Popular Post Share Posted March 14, 2023 I was taught to not play the guessing game, always prove the problem before changing parts Times have changed Paul 3 Quote Link to comment Share on other sites More sharing options...
MACK321 Posted March 16, 2023 Author Share Posted March 16, 2023 Hey Paul I did what you said to do checked it with the mechanic everything checked out good would anything with abs wires. sensors can cause that issue Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted March 17, 2023 Share Posted March 17, 2023 ABS and that stuff I know nothing about sorry I assume this is a bogie drive truck Maybe hook a air pressure guage up at each can to see if the pressures are equal I still would be leaning towards a mechanical issue All rods need to travel the same distance and slack adjsuters should be on the same angles at rest and when brakes are applied Paul 1 Quote Link to comment Share on other sites More sharing options...
MACK321 Posted March 17, 2023 Author Share Posted March 17, 2023 Okay thank you I will take it to another shop just to make sure Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted March 17, 2023 Share Posted March 17, 2023 I wonder if the ride height is too high and causing the rear axle to have a light load on it. He did say "Bobtailing". -Paul asked if the S-Cams moved freely. -Mechohaulic mentions slack adjusters and adjustment. and air line size.. I hope all 8 drive tires are the same size.. I think you should check what Paul and Mech, said, as well as the ride height adjustment.. jojo 1 Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted March 17, 2023 Share Posted March 17, 2023 I wonder if the ABS isnt working on this wheel , I doubt it would have any effect unless under hard braking But if the wheel locks, shouldn't the ABS release the brake and stop it rrom skidding ? As I said I really dont know about ABS Paul 1 1 Quote Link to comment Share on other sites More sharing options...
Mark T Posted March 17, 2023 Share Posted March 17, 2023 Drum's not round for some reason. Is it an aluminum hub ? If the pilot pad is rotted there's nothing to pilot the drum weather it's new or in good shape. If you're at the point of throwing parts at it ? drum and linings on that wheel end. 1 1 Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted March 17, 2023 Share Posted March 17, 2023 37 minutes ago, Mark T said: Drum's not round for some reason. Is it an aluminum hub ? If the pilot pad is rotted there's nothing to pilot the drum weather it's new or in good shape. If you're at the point of throwing parts at it ? drum and linings on that wheel end. Could just swap drum to another wheel and see of the problem shifts with it Paul 2 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted March 17, 2023 Share Posted March 17, 2023 Yes Paul... Good Call... Hell, that's poetic.. 1 1 Quote Link to comment Share on other sites More sharing options...
Mark T Posted March 17, 2023 Share Posted March 17, 2023 Something still has to pilot the drum on the hub. If it is the drum though, Paul's idea would indeed work. 1 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted March 17, 2023 Share Posted March 17, 2023 I have seen this happen with incorrect drums.. like putting hub piloted drums on a budd wheel hub.. many years ago... I dont remember the inner diameter, of 2 types of drums.... 1 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted March 18, 2023 Share Posted March 18, 2023 Mark has a good point also,,, I have seen guys run a tire up on a hub using one lug nut (rather than 2 opposing lug nuts half-and-half) and it pulls up really hard and can damage the pilots that keep the drum spinning true.. MACK321,, I wish you were doing this diagnostic... so that you could see the parts and possible damage to cause this issue.. jojo 2 Quote Link to comment Share on other sites More sharing options...
Mark T Posted March 18, 2023 Share Posted March 18, 2023 Could be a nice high quality Chinese drum too 1 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted March 18, 2023 Share Posted March 18, 2023 Oh Hell..... Quote Link to comment Share on other sites More sharing options...
MACK321 Posted March 18, 2023 Author Share Posted March 18, 2023 Drums are webb drums and haldex shoes so yeah if I am bobtailing it does it and if I'm driving empty too when I have a load on there seems like it's not locking up Quote Link to comment Share on other sites More sharing options...
MACK321 Posted March 18, 2023 Author Share Posted March 18, 2023 Tires all the same size Quote Link to comment Share on other sites More sharing options...
MACK321 Posted March 18, 2023 Author Share Posted March 18, 2023 ride height adjustment How do I know if it's to high and can I adjust it Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted March 18, 2023 Share Posted March 18, 2023 You can use a tool like this one. you need to know the brand of suspesion, Mack dealer should be able to tell you, buy just for the heck of it you can use thie measurement on this tool. you can use a tape measure to get close. also if you use the measurement on the tool and find the frame rail is much higher, its a good chance you are too high.. Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted March 18, 2023 Share Posted March 18, 2023 your truck is a 2011.. So it has a Volvo frame. behind/below the fifth wheel on the left side is a larger hole with a screwdriver slot in the middle. the bolt next to the hole is the bolt that holds the suspensiion adjuster in place. that is where you make the adjustment. Let us know if you are going to make an adjustment. I dont want to type all the info yet. jojo 1 Quote Link to comment Share on other sites More sharing options...
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