Shifting “thunk”

[optimusprime]

2008 Yukon Denali XL with around 160,000 on the clock. Often when shifting (usually when downshifting when getting on the throttle to pass on the freeway or when giving it throttle after slowing down) there is an audible and felt “thunk” as if it is being slammed into gear. Sometimes it does it cold when up shifting from 2nd to 3rd but it only does it cold. After that the clunk is usually felt when getting on the throttle. Tranny fluid was recently changed at the dealership and nothing strange was noted. It has been doing this for a long time. Any ideas what could be causing this?

 

[iamdub]

2008 Yukon Denali XL with around 160,000 on the clock. Often when shifting (usually when downshifting when getting on the throttle to pass on the freeway or when giving it throttle after slowing down) there is an audible and felt “thunk” as if it is being slammed into gear. Sometimes it does it cold when up shifting from 2nd to 3rd but it only does it cold. After that the clunk is usually felt when getting on the throttle. Tranny fluid was recently changed at the dealership and nothing strange was noted. It has been doing this for a long time. Any ideas what could be causing this?

U-joints or engine mount. Jab the throttle from a stop and see if it makes the same sound. You don't have to floor it, just immediately hit 1/2 - 3/4 throttle.

 

[OR VietVet]

What @iamdub said and might want to check rear diff fluid condition and level and age. Do the test as suggested and look for the engine to lift on one side or the other and check trans mount.

 

[optimusprime]

What @iamdub said and might want to check rear diff fluid condition and level and age. Do the test as suggested and look for the engine to lift on one side or the other and check trans mount.

How do I check if the engine lifts? Am I doing this in neutral?

 

[swathdiver]

2008 Yukon Denali XL with around 160,000 on the clock. Often when shifting (usually when downshifting when getting on the throttle to pass on the freeway or when giving it throttle after slowing down) there is an audible and felt “thunk” as if it is being slammed into gear. Sometimes it does it cold when up shifting from 2nd to 3rd but it only does it cold. After that the clunk is usually felt when getting on the throttle. Tranny fluid was recently changed at the dealership and nothing strange was noted. It has been doing this for a long time. Any ideas what could be causing this?

What Chris said is where to look first. If yours is AWD, the mounts for the front differential probably need replacing anyway by now. One of mine has a lot of play but doesn't cause any clunks, that was because of the driver's side motor mount.

 

[OR VietVet]

No, you need to have a person in the driver's seat and have the brake pedal on and the park brake and then while in drive and reverse, the driver just gooses the gas pedal and then lets off. The engine will torque up on one side or the other, depending on the gear selected, and if the engine just moves up a little slightly and acts like it is being "held back" then that is good but if it jumps up 2-3 inches, that is not good and means a failed motor mount. You can check the trans mount by crawling under and watching while the engine is torqued, very important to make sure the rig is held securely in place-may even want to block wheels as well as the park brake and foot on the brake. It will jump a little too but if you are strong enough, you can lay under there and push up, like a bench press, and see if the trans mount separates. While under there you can also watch the driveshaft and u-joints to see if they rattle or get sloppy when torqued in reverse or drive.

My biggest concern here is that since you had no idea of what this process was, I am worried about telling you to crawl under the running rig and torque it in gear.

In other words, "BE ******' CAREFUL!

 

[Doubeleive]

How do I check if the engine lifts? Am I doing this in neutral?

pop the hood open, get in and start it up, put your foot on the brake and put in drive, while holding the brake pedal give it some gas and watch the engine thru the hood opening, the engine will move normally but it should only move slightly and not clunk to one side, do the same while putting it in reverse. you can also get a flashlight and look at the motor mounts closely to see if any of the fluid has come out or if the rubber is torn.
you may also need to have the slip yoke lubed

 

[OR VietVet]

Yep, that slip yoke is a popular source for noises too. Good call @Doubeleive

 

[optimusprime]

pop the hood open, get in and start it up, put your foot on the brake and put in drive, while holding the brake pedal give it some gas and watch the engine thru the hood opening, the engine will move normally but it should only move slightly and not clunk to one side, do the same while putting it in reverse. you can also get a flashlight and look at the motor mounts closely to see if any of the fluid has come out or if the rubber is torn.
you may also need to have the slip yoke lubed

Thanks for the info. I’ll check the slip yoke too. For what it’s worth, when I shift the truck in reverse and drive, there is an Audible clunk coming from under the truck. Been doing that since 2016.

 

[optimusprime]

No, you need to have a person in the driver's seat and have the brake pedal on and the park brake and then while in drive and reverse, the driver just gooses the gas pedal and then lets off. The engine will torque up on one side or the other, depending on the gear selected, and if the engine just moves up a little slightly and acts like it is being "held back" then that is good but if it jumps up 2-3 inches, that is not good and means a failed motor mount. You can check the trans mount by crawling under and watching while the engine is torqued, very important to make sure the rig is held securely in place-may even want to block wheels as well as the park brake and foot on the brake. It will jump a little too but if you are strong enough, you can lay under there and push up, like a bench press, and see if the trans mount separates. While under there you can also watch the driveshaft and u-joints to see if they rattle or get sloppy when torqued in reverse or drive.

My biggest concern here is that since you had no idea of what this process was, I am worried about telling you to crawl under the running rig and torque it in gear.

In other words, "BE ******' CAREFUL!

Haha thanks and don’t worry, I’m not going under there with the vehicle in drive. I’ll find another way to check it out.