Hey there

Whenever I apply the gas pedal or take my foot off there's this knocking sound. It's stronger when I'm in a lower gear. It's not in the engine.

 

"This knocking sound"

Oh, you mean THAT knocking sound.

I kid, I kid. Can you be more specific? Trans? Tcase? Driveline? Diff? Anything loose? You are sure its not the engine? Does it do it in neutral? With the clutch pushed in?

See where I am headed with this? Basically, its impossible to diagnose a noise on your truck from behind a computer screen.

 

Could be play from loose or worn universals. Try jacking one rear wheel while in gear turn the wheel from lock to lock. You will see how much play is in the drive train and maybe able to locate the noise. You will need to chock the front tires.

 

It kind of sound like it's coming from the rear differential. It's hard to describe it other than a knock but the image I get when I hear it is like if there are two gears and one's smaller than the other and when you hit the gas the teeth of the smaller one is knocking against the other's. Sorry that's not very clear I know, haha, but that's the best way I can describe the knocking sound. I don't know where but I heard someone say to replace the U joint.

 

im guessing its ur rear differential could be blowing your rear gears

 

I guess you have to determine if it is a driveshaft universal problem or a gear problem in your rear differential. For the driveshaft take a screwdriver or anything metal and give your driveshaft a tap not enough to dent it but a good solid tap about the midpoint. Remember that sound! Most of the time when you have a worn universal joint its the rear one and when you put your truck in gear and start out you will hear a clunk accompanied by that ringing sound. If one of your universals is that far gone, put your truck in neutral block the wheels, crawl under it and twist the driveshaft back and forth, you should be able to see some movement in the universal. Remember that the universal is under constant torque so any movement will result in a lot of movement when you are driving down the road.
If you think that it is a gear problem, chock your front wheels jack the back of your truck up off of the ground put in neutral and twist your drive shaft back and forth. There should be some play between the pinion gear and the ring gear but it is minimal. (When you are setting up a differential it's around.008") If yours is clunking or knocking as you describe it then it's time to investigate further. Your gears may be toast or they are okay and it's time for a rebuild.

 

Yeah, quit imagining things and check the driveshaft out. I thought I had a bad motor mount, same noise you have btw. There is more torque applied at a lower speed so it clunks louder. I was messing around yesterday and found the carrier bearing to be most of the problem.