Transmission problems

You tried checking the Ujoints or maybe the drive shaft? Its entirely posible that one of them is worn, broken or damaged.

 

Rotten motor mounts? Throughout bearing recommended interval from Eaton is 50k for linehaul. I doubt it’s dried out. Maybe a rubber bushing, Torque rods, spring eye bushings, Especially if any are soaked in oil. My left motor mounts shot after a year of slow oil leak on it. Ride height, wheel bearings, any bushing, Cab mounts, linkage. Vibrations are hard to find. Safety issues most important. Don’t need and wheels or driveshafts flying off the Truck. Good Luck. Grinding while driving slowly is normal, forward of reverse. Mines had a popping noise in the driveshaft/ rears, that comes and goes. I’ve thought it was fixed several times. Hadn’t heard it in a while till last week. Once I get rolling over 10 mph, it goes away. Feels like a u joint binding up. I’m pretty sure it’s caused by lack of grease in the slip yoke. I’ve had it pumped with lots of grease, even took it apart and packed the spline shaft. Seems to be the problem. Chevy P/U Trucks had a problem with that in the 90’s. Slip yoke would dry out and bind. I doubt Speedco takes the time to pump it up good. It takes a lot of grease on initial greasing. I’ve added almost a whole tube once. Try greasing both slip yokes on driveshafts. Maybe?

 

Have you checked the ride height? AG380 on my truck only has to be out 1/8” or so and you get an awful racket out of the back of the transmission.

 

Just to clarify, no noise in 10th/11th? Assuming this is a 13 speed?

10th/11th on a 13 speed is usually direct in the main box. None of the countershaft gears are under load. Making me suspect a bearing/gear issue on the countershafts.

 

That’s how mine was. Lots of noise in every other gear, besides direct. Countershaft bearings were shot. Pretty bad. but I was able to run it another 400 miles to deliver. Seems to be the weak point on a 13. Or maybe runs low on oil, if levels slightly low? Mine wasn’t low, but given the height of the counter shaft, one is higher than the other. The higher one went bad on mine. I love the 13, but a 10 being simpler, seems to be a more durable trans. I don’t really know, except the origin warranty on a new Truck 10 spd was always 500k, while 13 spd was only 350, or maybe 375k I forget exactly, but makes me wonder. It’s enough to make me shift very carefully, Lol. Especially when heavy. I think a lot of failures on trans and rears are from abuse, more so than neglect as far as fluid changes are concerned. Just from my own experience. They’re very forgiving, but the flat out jamming and grinding gears I see so often Cant be good, One mistake loaded heavy, can bite off a tooth. That’s why Im the Guy winding it up real slow and easy, Lol. Plenty of time to hammer down, once it’s all rolling smoothly,

 

maybe it's your low high range gear box.cant remember name.Just Jack up make sure both rears aren't spinning that's free