Clunk when accelerating after coasting at 80 km/h, and clunk when reapplying gas after coasting from 40 km/h to 60 km/h

[kurt87]

Hello,

I own a 2008 gmc yukon and am experiencing some drivetrain issues.

First of all, when I am coasting at 80 km/h and floor it my yukon makes an alarming clunk in the front end. If I accelerate not as aggressively the clunk doesn't happen.

Also, when I take my foot off the gas going 40 to 60 km/h and let the rpms drop then re-engage the gas peddle I here and feel a slight clunk. I think of it as teeth grabbing after spinning or something like that.

My yukon has 244k kms and i already changed both rear u-joints. I did the engine mount check and they seem to be absolutely fine. Engine does not move around too much at all.

I also have the following engine codes:
P0430
P0455
P1153
Should I be fixing these? Are they pressing?

Not too sure what it could be, any ideas?

 

[donjetman]

Front differential mount bushings wear out.
https://www.tahoeyukonforum.com/threads/no-more-klunk-yeah.134250/

 

[Geotrash]

Welcome! You didn't say whether yours is an AWD Denali or not, but if so then Don is spot on. To his comment I'll add motor mounts - most likely the drivers side. They're fluid filled and when they go, they leak a corrosive fluid that stains the area below them orange. You can check them by putting your left foot firmly on the brake and jabbing the throttle with your right foot, with the hood up so you can see the engine through the gap. Do it in both forward and reverse. If the motor jumps more than a half inch, one or both of them are bad.

 

[petethepug]

Denali
Standard or XL
2WD or 4WD

You’re mentioning km so I assume you’re up North with 4WD or AWD. Verifying will make an easier diagnosis.

 

[kurt87]

Denali
Standard or XL
2WD or 4WD

You’re mentioning km so I assume you’re up North with 4WD or AWD. Verifying will make an easier diagnosis.

Yes it is a standard denali and AWD.

 

[petethepug]

Cool welcome from SoCal, deff what others have mentioned on front diff mounts / dog bone bushings. Inspect motor mounts for being popped / leaking dampening fluid, front sway bar bushing and bar attachment hard mount points.

Lube the driveshaft yoke too …

Lube Slip Yoke - AWD

Ok...so I've read, and read, searched, and searched, and I'm still not clear on the topic fully. I know that all the late model GM SUV/trucks have a slip yoke on the front of the driveshaft, and over time/miles it gets to where it doesn't slip so well and results in a bit of a drive line clunk...

www.tahoeyukonforum.com

Change out your emissions carbon canister asap. If it hasn’t released carbon pellets onto your fuel system yet, you dodged a bullet.

 

[kurt87]

Cool welcome from SoCal, deff what others have mentioned on front diff mounts / dog bone bushings. Inspect motor mounts for being popped / leaking dampening fluid, front sway bar bushing and bar attachment hard mount points.

Lube the driveshaft yoke too …

Lube Slip Yoke - AWD

Ok...so I've read, and read, searched, and searched, and I'm still not clear on the topic fully. I know that all the late model GM SUV/trucks have a slip yoke on the front of the driveshaft, and over time/miles it gets to where it doesn't slip so well and results in a bit of a drive line clunk...

www.tahoeyukonforum.com

Change out your emissions carbon canister asap. If it hasn’t released carbon pellets onto your fuel system yet, you dodged a bullet.

Okay will do. If it did release carbon pellets into my fuel system what does that mean? Like will it hurt my engine?

 

[petethepug]

They are too big to migrate to the motor. They’ll get into the rest of the fuel system though. It forces 100k fuel system maintenance most have never done.

 

[Geotrash]

Okay will do. If it did release carbon pellets into my fuel system what does that mean? Like will it hurt my engine?

First symptom will be difficulty getting fuel into the tank without the pump handle constantly clicking off.

 

[kurt87]

Hello,

I own a 2008 gmc yukon and am experiencing some drivetrain issues.

First of all, when I am coasting at 80 km/h and floor it my yukon makes an alarming clunk in the front end. If I accelerate not as aggressively the clunk doesn't happen.

Also, when I take my foot off the gas going 40 to 60 km/h and let the rpms drop then re-engage the gas peddle I here and feel a slight clunk. I think of it as teeth grabbing after spinning or something like that.

My yukon has 244k kms and i already changed both rear u-joints. I did the engine mount check and they seem to be absolutely fine. Engine does not move around too much at all.

I also have the following engine codes:
P0430
P0455
P1153
Should I be fixing these? Are they pressing?

Not too sure what it could be, any ideas?

Sorry I have a correction to make. The sound doesn't come from the engine bay, it comes from behind the drivers seat sort of around the transfer case location. Do you have any ideas what would make the clunking noise around there?