2002 denali front diff failure/vibration

[mhaywoodcz]

GM Gurus, I have recently been working to solve a vibration in my 2002 Yukon Denali. Heads up this has been a fun 1. SO, 6 months or so ago I replaced the transmission with a reman from Performabuilt with a FTP torque convertor 2000stall. (just adding this to the history, you will see why soon.)

Probably 1 month later I started to notice issues with vibrations above 50mph. Feel it in the floor and lil in the steering wheel.Reached out to Performabuilt, they asked about the flex plate. Since I reused mine they wanted me to replace it incase its bent or damage. So I pulled the tranny back and replaced it. no change.
Since then I have
Rebalanced wheels and tires
Swapped wheels and tires with a friend
Pulled the drive shafts, had them rebalanced/new U joints
Pulled transfer case, rebuilt it myself
Pulled rear axles, replaced bearings/fluid, inspected (all good)
Installed a different torque convertor
Reinstalled Old transmission( it wasn't bad, use this for pulling camper so wanted a built version)
Reinstalled Performabuilt transmission and FTP torque converter
Replaced transmission mount
Replaced front wheel hubs
Replaced front CV axles
Just did a big brake upgrade (2023 calipers, rotors, wheels and tires)
Full front end rebuild 10k miles ago, tie rods, ball joints, sway bar links etc.
All this has been done with the vibration not changing, if anything it's starting to get worse.

Rebuilding this piece by piece is not too hard, this vibration just bothers me.

Long story short after all of this I decided to put all 4 wheels up (full time AWD) and put it in gear, this could help me see everything turning.
I noticed the passenger wheel wasn't turning like the others in drive.
I rotated it, helped it along, and noticed the bolts that pass through the frame (front Diff mount, passenger side) move about 1/4 of an inch towards the driver side. This only does this at a certain point in rotation. I crawled under it and say the entire front Diff shift 1/4 inch to the driver side when the passenger wheel turned.
I started to do some thinking that its the bushings in the mount. Either the bracket on the passenger side or 2 bushings on the diff on the driver side. I looked them over, they aren't cracked or damaged, they look fine.
Sorry for the long post.
So my question is my diff the cause? Vibrations above 50mph and now the movement during passenger side wheel rotation.

 

[mhaywoodcz]

Forgot to add, the vibration is while rolling, neutral, or in any gear at the higher speed. It kinda drones also, kinda humm, humm, humm. Hope this helps someone decipher this and anyone else in the future

 

[Sam Harris]

If I’m understanding your post, the actual front diff moves 1/4” at certain times..? I guess I’d be checking the diff mount points, to determine why that’s happening. I may be confused by what you wrote, but it sounds like you’ve already identified the problem.

 

[Donal]

GM Gurus, I have recently been working to solve a vibration in my 2002 Yukon Denali. Heads up this has been a fun 1. SO, 6 months or so ago I replaced the transmission with a reman from Performabuilt with a FTP torque convertor 2000stall. (just adding this to the history, you will see why soon.)

Probably 1 month later I started to notice issues with vibrations above 50mph. Feel it in the floor and lil in the steering wheel.Reached out to Performabuilt, they asked about the flex plate. Since I reused mine they wanted me to replace it incase its bent or damage. So I pulled the tranny back and replaced it. no change.
Since then I have
Rebalanced wheels and tires
Swapped wheels and tires with a friend
Pulled the drive shafts, had them rebalanced/new U joints
Pulled transfer case, rebuilt it myself
Pulled rear axles, replaced bearings/fluid, inspected (all good)
Installed a different torque convertor
Reinstalled Old transmission( it wasn't bad, use this for pulling camper so wanted a built version)
Reinstalled Performabuilt transmission and FTP torque converter
Replaced transmission mount
Replaced front wheel hubs
Replaced front CV axles
Just did a big brake upgrade (2023 calipers, rotors, wheels and tires)
Full front end rebuild 10k miles ago, tie rods, ball joints, sway bar links etc.
All this has been done with the vibration not changing, if anything it's starting to get worse.

Rebuilding this piece by piece is not too hard, this vibration just bothers me.

Long story short after all of this I decided to put all 4 wheels up (full time AWD) and put it in gear, this could help me see everything turning.
I noticed the passenger wheel wasn't turning like the others in drive.
I rotated it, helped it along, and noticed the bolts that pass through the frame (front Diff mount, passenger side) move about 1/4 of an inch towards the driver side. This only does this at a certain point in rotation. I crawled under it and say the entire front Diff shift 1/4 inch to the driver side when the passenger wheel turned.
I started to do some thinking that its the bushings in the mount. Either the bracket on the passenger side or 2 bushings on the diff on the driver side. I looked them over, they aren't cracked or damaged, they look fine.
Sorry for the long post.
So my question is my diff the cause? Vibrations above 50mph and now the movement during passenger side wheel rotation.

Looks like you have already checked or replaced the common failure items. So, maybe check the welds where the diferential mount are welded to the frame and all the frame welds. The front suspension may have to be loaded normally. Tires on ground type loads. So jack up the vehicle and sit the front tires on blocks so the you can check for the loose connection. Use a pry bar to check for movement in welds and joints.

 

[nonickatall]

There is always imbalance in the drive. It doesn't matter if the tires aren't perfectly round and balanced or the drive shafts or brake discs or whatever don't run perfectly.

Normally this unbalance is compensated for by the axle. On the one hand, because the axle holds the wheel firmly in position and avoids vibrations by restricting the freedom of movement and, on the other hand, because there are rubber bearings there that absorb these vibrations.

For example, it is typical for BMW vehicles when they have axle play, that they start to flutter in the steering at around 110km/h, which is the resonance speed if you have 16 or 17 inch tires.

If you have already replaced everything that has to do with the axle and these vibrations also cause a hum, I would, as others have already written, check the differential, especially in its mounting points, because the differential should not normally move.

Because if it did that there would be constant slamming during load changes.

When should the oil in the front differential be changed anyway, so I would unscrew the drain plug and see if there are any chips and change the oil in one.

And check the mounting points...

 

[mhaywoodcz]

thanks for all the replies guys, the fluid is definitely glittery, so I ordered a reman diff from powertrain products. With 170k on the original, it's possible it's at its end. I know when I first got the Yukon it had 150k on it, diff fluid was brown glittery, so I figure it hadn't ever been changed in the past. Keep everyone posted on the progress

 

[nonickatall]

thanks for all the replies guys, the fluid is definitely glittery, so I ordered a reman diff from powertrain products. With 170k on the original, it's possible it's at its end. I know when I first got the Yukon it had 150k on it, diff fluid was brown glittery, so I figure it hadn't ever been changed in the past. Keep everyone posted on the progress

Better than changing the gearbox and differential, is to change the gearbox and differential oils, before you have to change the differentials and gearbox....

 

[mhaywoodcz]

Update, I checked all the mounting points and everything is good. Replaced the front diff, driving wise its smoother but I still have the vibration. Ive pulled the front and rear drive shafts, going to take them to a different shop tomorrow (drive line specific). I believe the last place I had U-joints install and them balanced that they didn't follow thru on the balancing portion.
Keep y'all posted...

 

[mhaywoodcz]

Update, the other shop rebalanced the drive shafts, they ended up removing weights and adding some others. Seems the first shop didn't do a good job. Either way it's a whole lot better. When I did the big brake upgrade (2023 pads/rotors) I got a newer set of wheels. The tires are new but are load rated at 113 vs 117. So I guess it's time to pull these firestones and go for higher load rated Michelin. Everyone says they are the best, time for me to see for myself....