Unfortunately, most people don't think of others, so they don't post their solution when they figure it out.

But, yukonxl78666 explained how he fixed his a few posts back.

Tell your son to carefully read through this topic and to try all the suggestions. Or just take it to a trusted mechanic.

 

The only post I saw where a real fix was found involved the front drive shaft on a 4WD model. This one is 2 wheel drive.

The other "fix" involved eliminating the 4 cyl / 8 cyl cycling. Really not a "fix" in my opinion. Of course you are entitled to disagree.

Just drove my son's vehicle again. It does not do it when in "tow" mode. Also does not do it if you manually downshift to "3" before you get down to 25 mph. Drive shaft still has a load on it in both of those situations. Also, engine is still loaded in both of those situations, so if it were a motor mount, I would expect the same shudder in tow or with a manual downshift.

Good, bad or ugly, I will report back.

Seeing how many of the folks in this thread already took their vehicles to a trusted mechanic, I think I will pass on that.

 

No, I said the post by 'yukonxl78666'
This one ...

All models have suspension (which could be sagged out), universal joints (common wear point that people often neglect), and motor mounts.
These are all easy to check. It takes a few minutes.
You can check mounts pretty quickly and easily with a crowbar, or by just shifting the transmission in and out of drive with the hood up.
All these things are suspect at 250k
But they didn't come back. So maybe they got it fixed.
You could get it solved in a day, or you could spend days asking on a forum, from people who have never seen or driven the vehicle. Your choice.

 

That's true. But tow mode and manual shifting both offset the shift points, so the load could be different .

I'm not saying it's isn't his transmission. In fact, odds are it is, based on miles. They don't often last to 250k.

I'm just saying that you should always check off the low hanging fruit, before jumping to the most expensive solution. At this mileage it would be a transmission replacement for around $3,500

 

A full spectrum scan is step one. Not just P codes but all 4 code families of P, B, C and U need to be checked as a first step for any clues for any system issues like a wonky sensor.
Could be binding U joint but only check is to drop both driveshafts and feel them. Had a front shaft U joint binding in my old '99 Yukon and it surprised me as only used 4wd in winter in snow.

 

Old thread but still no concrete answers to the pesky shudder. I have an 08 2wd Suburban at 339000 miles. The second engine is now at 215k miles. Remanufactured tranmission 2 weeks ago. New U-joints, motor and transmission mounts 6 months ago. All new suspension front and back maybe 6k miles ago. Supposed to be stock suspension ( moog ) and quick struts and it ended up raising the front just over 1 inch. Not sure how. Rear end was taken apart and showed no wear so all good. New plugs and wires recently. New coils and injectors. New wheel bearings. No codes popping. I still have the shudder when slowing in the 20 mph area. It does go away in tow mode. So just seeing if anyone came up with something new in the past year. Thank for any input, Marcus in Kissimmee Florida

 

Check torque converter. This a common issue with Tahoes, Suburbans, Yukonsand Denalis.

 

I suspected the TC but since I had nearly 340k miles on that tranny we threw a new one in. So I'm thinking it must be something else causing it. Only happens when unloaded at that specific speed. Can the driveshaft be unbalanced at lower rpm's and not at highway speeds?

 

Sorry I had to correct what said above. The only time the shudder/vibration appears is on deceleration loaded only in Drive. Around 20 to 15 mph. It does not happen when tow mode is on. No vibration when in 3rd, 2nd, 1rst or neutral. Does not happen when accelerating. Appling brakes does not change anything. Engine and mounts are good. New transmission with TC didn't change anything. Diff checks out and new U-joints. New wheel bearings. New front and rear suspension. Tires still in good shape. Lot of stuff was done in the past 10k miles. Had to with 350k+ on the clock. Nothing is out of whack. Only the vibration and a cracked dash.