Weird vibration/sound and RPM jump (1 Viewer)

[schradec]

Was driving today and noticed a strange noise/vibration from the front end of the LC when going around 30-40 mph. Only happens under acceleration, and pretty randomly. Also noticed ones a weird erratic jump of the RPM. Didn't notice the engine actually jumping or revving, and didn't feel as though the trans was slipping....but the gauge jumped quickly and then was fine. Almost as it if lost power to "signal" from the motor. No codes thrown or anything of that nature. I would describe the noise as similar to when you hit the snooze bars on the side of the road on the highway...just not as aggressive a vibe/sound.

Just returned from a few hundred mile trip with no issues or symptoms until today. Only things I have done recently was lube U-joints and front drive shaft last night.

Only other thing I noticed was that the front diff was leaking (has since I bought the truck) and I crawled under it last night and tightened down the bolts on the back of the housing...was able to tighten all of them a touch. Possible I threw enough diff oil out from my trip to cause it to become low and cause this vibe? I will check the level of the diff tomorrow and see what it looks like....it was fresh and full before leaving as I had just drained and filled them before hand.

I searched around but wasn't really seeing anything that seemed related...figured I would post an ask here.

Appreciate your help all!

CS

 

[schradec]

After doing a little more digging I'm suspect of the u-joints on the front shaft, as well as the front wheel bearings (specifically the drivers side). Pinned down the MPH range slightly more to almost 35 on the dot, while under load/acceleration. It is very hit or miss though as to when/if it will happen. It sounds as described above, or when you have something in high wind vibrating...makes a buzzing type sound. I can feel it most prominently through the drivers side floor, where my left foot rests.

Any insight is greatly appreciated!

 

[mod5csi]

Mine could be a different issue. But my indicated RPM jumps and/or drops a couple hundred RPMs. Usually around 2500 RPMs, my highway cruise RPM. For me it's the mechanism in the guage cluster. There's no actual change in RPM, according to my Torque App.

I never noticed until I heard a weird sound also. My sound turned out to be a bad bearing in the AC idler pulley, when the AC kicked on at the same time my indicated RPM jumped.

I notice the indicated RPM jump often anymore. At least once per highway drive. AC on or off. Only around 2500 RPM. It is not the torque converter lock up. Torque App says RPM remains same and relativly smooth.

 

[schradec]

Mine could be a different issue. But my indicated RPM jumps and/or drops a couple hundred RPMs. Usually around 2500 RPMs, my highway cruise RPM. For me it's the mechanism in the guage cluster. There's no actual change in RPM, according to my Torque App.

I never noticed until I heard a weird sound also. My sound turned out to be a bad bearing in the AC idler pulley, when the AC kicked on at the same time my indicated RPM jumped.

I notice the indicated RPM jump often anymore. At least once per highway drive. AC on or off. Only around 2500 RPM. It is not the torque converter lock up. Torque App says RPM remains same and relativly smooth.

Ok def will look into this. Yea my app is saying the same, smooth #s no drop. Mine has been doing it with the AC off, however I would imagine it is still spinning even when the AC is off right?