Grinding/rattling while decelerating or coasting at highway speed.
Below are the traits:
-2015 Mack with automated trans
-only happens when empty
-occurs while coasting or decelerating at highway speed (mostly in 12th, less so in 11th gear on a 12 speed)
-can feel grinding in my feet
-will smoothen out once the truck begins to accelerate again
-putting the truck in neutral causes it to stop
-rattle often progresses to a grind when the truck is giving the slightest bit of throttle so that the engine starts to minimally build but not enough for the truck to start pulling/ accelerating again
-sometimes when hitting throttle to accelerate, it will hesitate and grind for a split second before engaging and smoothing out
- doesn’t happen every empty trip, but has been occurring more frequently by the week and now occurs 60+% of empty trips
-rattle sounds almost like an older roller coaster being pulled up the initial hill by the rattling/clunking chain
-grinding has a higher frequency similar to a vibrator plate
-all of it sounds/feels like metal to metal
I am thinking maybe flywheel, trans, driveshaft joints/yokes or rear differential?
Any thoughts? I have a dealership appt this Wednesday but am hesitant to bring it in without a clear direction of where to look or a guarantee that they will be able to duplicate symptoms.
Thank you,
Pat
Grinding/rattling while decelerating or coasting at highway speed
Discussion in 'Trucks [ Eighteen Wheelers ]' started by PJM41, May 4, 2021.
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Look at the air bags on rear drive axles if they are too hi or to low that's what's making it sound off ?
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Definitely check ride height. It can make some crazy sounds if it's off and in my experience it usually does it when coasting or steady speeds
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thanks guys. The leveling valve was replaced at the Mack dealer in late december and they specifically stated they spent a couple hours making sure the ride height and drive line angles were in spec, so I assume they are still good but will be double checking.
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could be bad differential , hopefully not the idler gear
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