I've got a new, low-pitched VIBRATION...

[KMeloney]

Hey all,

Maybe this is just another installment of my mystery tranny/driveline woes (not sure if they're all in my head, or related, or what)... But I've developed (within the last month) a very low-pitched vibration in the truck. I feel it through the floor as opposed to the steering wheel, and I think I can hear it as well.

I can duplicate it at a variety of speeds, but usually with the same throttle input. It occurs very early in the throttle range, like when it's just cracked at slower speeds, and through a longer range at highway speeds. I need to revisit to see if I feel it when coasting... But I'm sure I feel it with this early throttle input. Then, after that range, it seems to disappear.

As you may have read, I get a quick chugging sensation around 1000 rpms and 30 mph, also. Needless to say, this truck can find itself in 6th gear at that speed, which I think is absolutely absurd. Not sure if these things are all related.

Any thoughts on the matter? The vibration feels as though it's driveline related as opposed to engine related... But what do I know?

Maybe some of you might be aware of what could cause a very low-pitched vibration that can change with throttle input. Engine mounts? Driveshaft? I have no idea. And the last thing I want to do is turn the truck over to the dealership without being armed with a little knowledge on the subject.

Know how it feels when you completely lug an engine in a standard-shift car? That's the kind of low, body-sensing, tight vibration I'm getting. It's may not be noticeable to others, but my truck didn't feel this way a month or so ago...

Thanks, folks!

 

[STORMIN08]

two things come to mind...... axle shaft ujoints, and driveshaft u joints. sometimes when loaded just right , you find the natural harmony of components that spin, there is usually a slight humm from a properly setup ring and pinion while under light load / light throttle situations.

also, what are some parameters of the black bear tune..... i thought i read were they reduce torque managment on the trans tunes by like 70 %, and completely on the engine tunes. if so , this can add wear to the driveline joints, if improperly loaded when using the accelerator.

i recently drove a 6.2 denali, with 35000 miles.....it felt like the driveline was going to fall out. very loose feeling. every shift you could feel the drive train load up and clunk.

 

[gnarpow]

Not sure if this is what you are hearing but it falls close to the RPM range you are taking about.

http://www.sandyblogs.com/techlink/2011/02/fuel-linebracket-rattle.html

 

[LI99HOE]

Check the rear ujoint.... if you get even a small amt. of play when you try to move around the rear shaft while in park.....replace it.
This is what the vibration was for me...hope it helps

 

[KMeloney]

Not sure if this is what you are hearing but it falls close to the RPM range you are taking about.

http://www.sandyblogs.com/techlink/2011/02/fuel-linebracket-rattle.html

Thanks. I've bookmarked that link, but I don't think that's what I have going on here. But I appreciate the info.

---------- Post added at 08:40 AM ---------- Previous post was at 08:38 AM ----------

Check the rear ujoint.... if you get even a small amt. of play when you try to move around the rear shaft while in park.....replace it.
This is what the vibration was for me...hope it helps

I'm convinced that it's driveshaft/u-joint related. Thanks for the info. I'm thinking that this could be it.

---------- Post added at 08:42 AM ---------- Previous post was at 08:40 AM ----------

two things come to mind...... axle shaft ujoints, and driveshaft u joints. sometimes when loaded just right , you find the natural harmony of components that spin, there is usually a slight humm from a properly setup ring and pinion while under light load / light throttle situations.

also, what are some parameters of the black bear tune..... i thought i read were they reduce torque managment on the trans tunes by like 70 %, and completely on the engine tunes. if so , this can add wear to the driveline joints, if improperly loaded when using the accelerator.

i recently drove a 6.2 denali, with 35000 miles.....it felt like the driveline was going to fall out. very loose feeling. every shift you could feel the drive train load up and clunk.

Thanks, Shawn. I, too, have almost 35,000 on my truck, and I get the clunking as well. But I don't have the tune in the truck at the moment, so that's not it. But I DO think it's shaft-related...

 

[STORMIN08]

having the tune installed is irrelavent, once installed and allowed to add stress and wear, the damage is there. one of the main reasons behind torque management, is the low rpm, higher torque production of the motors,,,,working against smaller parts in the tranny. typically there wont be damage to the 1-4 clutches or drums, but the smaller 5-6 clutches are easily over powered by the torque that is being made at low speed, but in higher gears. one of the best things that can be done is to tune the trans to down shift by speed input and throttle position. i would be willing to bet , you are hearing the early stages of ujoint failure. it may be worth looking into having the yokes swapped out as well, and being able to run the larger SPICE JOINTS.

 

[felixgun]

My 08 Tahoe LTZ got that "chugging" at 1k rpm/30mph and it was SO aggravating. I could feel it every time and after I did the resonator delete I could hear it too. I never noticed any of the other things you are experiencing though.... I got a BB Tune in hopes that it would fix it but it did nothing for the chugging.

 

[KMeloney]

Felix -- Did you ever get the situation corrected? If so, what did the trick? Driving me nuts now.

 

[STORMIN08]

have you noticed if this " chugging " was upon decel , or during acceleration ? what i suspect is happening, is the right combos of throttle input, gear selection, and load are causing the trans to signal convertor lockup, it isnt seeing enough demand to fully lockup, so it gets somewhat confused. todays system are so tempermental, i would almost suggest unhooking the battery overnight, this will help clear the stored input into the ecm and tcm. thus allowing the vehicle to relearn your driving style. it sounds like what you are experiencing is the pulsation of fluid being pumped during lockup / unlock situatons, just so happens to be a sweet spot when it isnt sure if it needs to lockup for acceleration, or unlock for deceleration.

 

[KMeloney]

have you noticed if this " chugging " was upon decel , or during acceleration ? what i suspect is happening, is the right combos of throttle input, gear selection, and load are causing the trans to signal convertor lockup, it isnt seeing enough demand to fully lockup, so it gets somewhat confused. todays system are so tempermental, i would almost suggest unhooking the battery overnight, this will help clear the stored input into the ecm and tcm. thus allowing the vehicle to relearn your driving style. it sounds like what you are experiencing is the pulsation of fluid being pumped during lockup / unlock situatons, just so happens to be a sweet spot when it isnt sure if it needs to lockup for acceleration, or unlock for deceleration.

Shawn -- It's definitely on deceleration. When it happens, and I look at the gauges, the rpms are inevitably at or a tick over 1000 rpms, and the speedo is dropping through 30 mph. My truck didn't always do this, but developed the condition in the last 6-10 months, I'd say.

My truck has ALWAYS lurched/flared upon slowing somewhat abruptly, which I hate. This tranny is way too intrusive. Since my rpms flare up when say, braking to turn into my driveway, and since I think that's just not normal, I'm suspecting that other things that I am experiencing are also part of tranny issues. I just can't realistically get these things looked into without being armed with more info. Otherwise, I'm just going to be told it's "normal."

PS -- I'll try to the battery-disconnect idea to start with. Beyond that, what could be a cure for the situation?

Based on what YOU suspect could be happening here, what's the "fix?"