Motor mount, slip yoke or Diff? Clunk!

[dwinters14]

So here's my dilemma. I've had a nasty clunk with my yukon since I bought it. Happens every time I got from P to D to R, every time I accelerate hard, every time the transmission shifts and every time I slow down. I've been putting it off but I've been slowly narrowing my list of what it could be.

When I first got the truck I got it inspected and the mechanic said my motor mount was bad. I assumed that was the main root cause but I still looked at and replaced other things around it to be safe. I replaced both my U-joints in the drive shaft, checked my transmission mount, greased the yoke and now replaced my driver side motor mount.

The clunk is still there. I checked the slop in the pinion bearing with my hands and it seemed fine, and I did a fluid flush and peaked inside. None of the gears were worn excessively and there wasn't large chunks of metal shavings in the fluid.

The only things I have left that I think it could be are:

Passenger side motor mount
Differential
Slip yoke.

I honestly think it's the diff, as my driver side motor mount was still in one piece when I replaced it and looking at my passenger it looks about the same, especially considering how violent the clunk is. I'm not ruling anything out, just would like some advice on maybe ways I can diagnose the issue better before I continue replacing parts.

 

[Teamiez]

I do know the slip yoke has been a culprit in many cases for this issue, thanks for reminding me of mine I forgot about it lol!

 

[Joseph Garcia]

I went through a very similar situation. I changed the slip yoke, I changed the universal on the rear drive shaft, and I confirmed that my existing motor mounts were good. But the clunk was still there. My clunk ended up being the differential mounts. I replaced both of them (each one comes complete with the metal arm and bushings on each end), and the clunk disappeared.

 

[dwinters14]

I went through a very similar situation. I changed the slip yoke, I changed the universal on the rear drive shaft, and I confirmed that my existing motor mounts were good. But the clunk was still there. My clunk ended up being the differential mounts. I replaced both of them (each one comes complete with the metal arm and bushings on each end), and the clunk disappeared.

Is your truck 4wd? Mine is 2wd and I don't believe I have diff specific mounts. It's my rear pumpkin that integrated into the axle.

 

[swathdiver]

Is your truck 4wd? Mine is 2wd and I don't believe I have diff specific mounts. It's my rear pumpkin that integrated into the axle.

Yes, Joe's truck has a front differential. Check your control arm bushings, sway bar bushings and links and ball joints and tie rods and don't forget to check the rear control arm bushings. If you subscribe to the shop manual on AllDataDIY, you can get the specs to check and see how much movement you have on the various components and learn if they are out of spec or not.

 

[OR VietVet]

More Information for ACDELCO 45D10160

More Information for ACDELCO 45D10231

Leaning to these or too much gear lash at the diff.

Put the rig on 4 jack stands supporting the rear axle with two of them and level. Have a trusted friend run the engine and do the shifting with his/her foot on the brake. Get under there and listen with a mechanic's stethoscope. Even better if you can have it n a drive on rack and see what is the problem.

 

[dwinters14]

More Information for ACDELCO 45D10160

More Information for ACDELCO 45D10231

Leaning to these or too much gear lash at the diff.

Put the rig on 4 jack stands supporting the rear axle with two of them and level. Have a trusted friend run the engine and do the shifting with his/her foot on the brake. Get under there and listen with a mechanic's stethoscope. Even better if you can have it n a drive on rack and see what is the problem.

Interesting, the RCA’s can cause a clunk like that? I replaced my traction bar and inspected them. They were tight, and the bushings looked fine but i didnt get in there with a breaker to really see how tight they are.

Im probably gonna get it up on a lift and have someone sit by the pumpkin/yoke underneath and see where the gearshift clunk is coming from.

Anyone know where i can find the updated slip yoke? Not getting much luck on google as im not sure what the specific part number is.

 

[OR VietVet]

If it is on a lift the suspension will sag and not give you true results. A drive on rack or jack stands under the rear axle and under the front control arms close to the ball joints will help duplicate the load on the suspension. Every time you shift gears, the rear axle will attempt to twist a bit and that effects the rear arms. The noise is less likely at those arms but should be inspected under a load. I think it is in the diff but getting under there with that stethoscope will help pin point the problem.

 

[dwinters14]

If it is on a lift the suspension will sag and not give you true results. A drive on rack or jack stands under the rear axle and under the front control arms close to the ball joints will help duplicate the load on the suspension. Every time you shift gears, the rear axle will attempt to twist a bit and that effects the rear arms. The noise is less likely at those arms but should be inspected under a load. I think it is in the diff but getting under there with that stethoscope will help pin point the problem.

Interesting, I'll see if I can get that done, but I'll probably start at the yoke/diff first as the more I drive the truck and the timing of the thuds is making me think the yoke. The new mount I put on is stiffer than the OE and I notice the transmission shifting more, as well as more vibration overall. The clunk only gets bad when I really step on it, but otherwise it's just a faint feeling as the tranny shifts.