08 Yukon Driveline "Slop/Slack"?

DrData

Member
2008 Yukon Denali,6.2L V8, AWD, Six Speed Trans, 3.42 Gearing. 141,000 miles.

Recently bought this vehicle, love it. But, it seems to have some slop or slack in the driveline. When shifting from reverse to drive (as when backing out of a parking space and pulling out forward), there is a one to two second delay for the driveline/trans to engage in drive. If I'm in a [modest] hurry, there can be a significant hard thunk as it catches up and engages. This also sometimes can occur when stopped at a red light then accelerating forward.

I have an appointment at my GM dealer next week but wondered if there may be a known issue or something needing servicing? (Also, would like to be somewhat knowledgeable on any "driveline' issue if possible.)

Any ideas or experiences will be appreciated. :smile:

PS: Trans fluid level looks ok, was changed w/filter by previous owner. Do not know if differentials have been changed, plan to do this soon.
 
OP
DrData

DrData

Member
Haven't received any replies on this......but, here's an update on what I've done/tried.
:smile:
Had my GM dealer check out Driveline/Trans. They could replicate the problem but could not diagnose problem without a full tranny teardown. Big $$$, so I had to decline further action, spent $98 on that basic diagnosis.

Researched and proceeded to try another remedy. Purchased Lucas Transmission Conditioner ($12.99/20oz bottle at Autozone). First called and consulted with tech support at Lucas. He recommended using the 20oz. bottle of Conditioner (vs. the stronger/thicker "Transmission Fix"). Also consulted with my very experienced Autozone manager who has used this product successfully and concurred with the use of the Lucas Conditioner. While the bottle says it's ok to add without draining some old fluid out, both of my trusty advisors suggested removal of about 15ozs of tranny fluid before adding treatment. Using a simple hand pump kit, ($14.99 at Autozone), pumped out ~16ozs. Then added 20oz bottle of Conditioner.

FYI-I am VERY guarded about using additives in today's modern vehicles but I do trust Lucas as I've been using their gas treatment for many years with good results.

Did a brief test drive and seemed to feel some improvement over 5 miles. Parked overnight, drove today and problem seems to have improved by reducing the 2 second lag to one second! Lucas guy had said, drive it about 200 miles to get desired results. I plan to drive that mileage tomorrow night. I'll post a results update.
 

Robbabob

Well-Known Member
Very surprised you didn't get a reply to your initial post! I am a regular, but travel a lot and miss many posts.

FYI - There have been a few comments in social threads saying, "If you cant help, don't waste the guys time with 'feel good' comments." I am also told that feel good posts can get a person in trouble.

So here I am, giving you a feel good post. At least you're being acknowledged for being here; you're actually visible.

Also, thanks for the follow up comment! I learned from it and others will too. Give us another update after the 200 miles, please.

Good luck!
 

Mounce

Well-Known Member
Really thought I replied to this after your first post. Must've been half asleep lol.

Anywho, in my experience all vehicles (that I've driven) have a second or two delay like that. To me, that's just the transmission shifting gears.

If you hold the brake and shift into reverse, you'll notice there's a delay between when you put it in reverse to when you hear the transmission engage (shift as I'd call it).

Sounds normal to me but it's hard to diagnose things through text. Definitely keep us posted.
 
OP
DrData

DrData

Member
Thanks for the replies guys. (I was starting to wonder if anyone was reading these after nearly a week.) Appreciate your thoughts.


Mounce, I hear what you're saying but this condition just has that feeling that something is not right. It's not just the one or two second delay, it's more about the "slam" effect that occurs when it is being called to go forward. Not that I'm pounding on it, it just seems wrong and potentially harmful to the trans/driveline. Also, I will be trailering with this new vehicle and am hoping to be confident in the tranny performance.

I will keep you guys posted with my results. (I may have to visit a psychiatrist soon, haha.) :crazy: :smile:
 

Mounce

Well-Known Member
If you gas it while it is transitioning from Park to Reverse or Reverse to Drive while stopped it will slam like that.

Has it always done this since you got it or is this new?




Also, I apologize for the wait, I seriously thought I replied to you. It's like I thought the complete situation through and thought out a reply then didn't post it. :no: (I think I'm the one that needs a psychiatrist! :rotfl: )
 

HARDTRAILZ

Moderator
If you do not hit the throttle during the 1-2 second pause does it go into gear with a thunk or nice and smooth?
 
OP
DrData

DrData

Member
If I DO NOT touch the throttle it will still thunk a little.
 

Mounce

Well-Known Member
Has it always done this or is it something that started happening recently? Still sounding like normal transmission engagement from my side of the Web.
 

Robbabob

Well-Known Member
Starting to think U-Joint issue causing the THUNK. Hard to describe or explain if the shift timing is normal or not.
 

HARDTRAILZ

Moderator
I have some thunking due to the locker, but in checking things out I found the tranny mount collapsed and replacing it took out quite a bit of the thunk and things seem much more solid. You might try checking it as well.
 
OP
DrData

DrData

Member
OK guys, I'm back at this post with updates/results. Thanks again for your previous comments.

So, Since March @141K, I did some towing of a 3500# trailer through the Kentucky and Tennessee hills without any notable problems. But, the driveline/transmission slack (thunk) continued. Back home, after consulting with some knowledgeable resources, I tried a bottle of the Lucas "Transmission Fix". Most said it's worth a try. Tried it but no improvement. Sloppy engagement delay has worsened over time and mileage (now at 147k). My next step will be a local trans shop who I have (moderate) trust in. Most people in the know seem to think it is truly in the trans itself. They use some term about some valve.

Any additional thoughts would be appreciated. I'll post updates as I proceed. May not be real soon due to the $$ involved. Fingers crossed for a simple fix to be found.
 

Blackwater

Well-Known Member
Anyone thought of the torque converter?
 
Im having the same issue with my 08 yukon as well started with a slight humming or whirling from the rear then slowly got worse now its to the point where i have a clunking noise driving, turning, when engaging gear. I took the differential appart and didnt see anything abnormal didnt check behing the casing where the pinion gear is at tho, I have a feeling that is my culprit.. If you get any futhur information please send a shout out ...
 

Mooseman

Moderator
This is an old dead thread so doubt you'll hear anything from anyone in it.

I would imagine you checked your U joints? Also add some grease to the transmission/transfer case output slip yoke. What kind of mileage does it have? Maybe it's wear in the diff gears. Is there a lot of play in the pinion backlash?
 

Mooseman

Moderator
Also add some grease to the transmission/transfer case output slip yoke.
That. I had a mystery thunk when coming to a stop and grease in the slip yoke fixed it.
 

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