Bizzarre Vibration

[commercialcobb]

First Post, (1999 Yukon 4 door 200k old body style).. For a month or so I was getting a weird vibration in the GAS PEDAL.. It was slight at first but rather consistent while at any cruise speed when I am only trying to maintain speed (high and low 70mph and 25mph). If I give it some gas to accelerate or lift off to slow down it goes away. So as luck would have it, I got my oil changed last month and it now feels like I am standing on a womans vibrator on full blast (sorry for the lack of a better term) in the same cruise ranges. I don't think the oil change made it worse but it got worse immmediatley after I left the station.

Any thoughts on this? I am very knowledgeable under the hood but this has me stumped as I cannot duplicate it while stopped at the house and don't have a lift. It vibrates so bad now I can actually hear it like it's my phone ringing on vibrate (there's a better analogy)

Any help is greatly appreciated..

 

[oldsalt]

Wow. This is a weird one. If it happens only when rolling I would look at something drive train related.

When you are cruising your motor and transmission are basically resting and a vibration will travel. When you accelerate or decelerate you are introducing torque in the drive train and upsetting the vibration. Does that make sense? Did you do any work to the car before the vibration started?

Welcome to the forum.

 

[commercialcobb]

No modifications. Truck is totally stock. Yeah I am stumped too. Everything seems fine, tranny shifts fine, engine purrs minus that infamous exhaust leek that I assume is the header exhaust flange. Tire pressures are good and even tread wear so I know it's not coming from the road. A guy before said it could be a dirty intake/throttle body but that didn't make much sense to me.

 

[Ceejkay]

does it do it only when driving or any time its in drive? i would say look into your motor/transmission mounts. i had a jetta that had this problem, when under a load the gas pedal would *vibrate*. basically what was happening is when a load was applied the motor rotated to the right a little bit, due to bad mount and the vibration was not deadened by the mounts i could feel it in the gas pedal. hope this makes sense....

 

[Danny_Z56]

I would think either a bad universal joint or rear differential issues.

I was once riding in a Tahoe that had a bad vibration/humming.We were doing around 75-80mph on the expressway,i told my buddy,you hear and feel that right? he's like "yeah its probaly just a bad U-joint".I said naw i think its in the rear end,you may want to slow down some..... against my advice he kept on going fast,he then goosed the throttle to get around a vehicle and then BAM!!!! I told him to pull the f*ck over!! i got out and started looking under the vehicle.My first thoughts was that maybe the driveshaft dropped or the tranny tore it self apart lol. I went to the rear of the vehicle and seen that the rear diff was on fire............. I patted out the fire with a rag that was in the back.

Guess i was right when i told him i think that vibration/humming is coming from the rear end.Im guessing that the rear had NEVER been serviced and it was leaking,hence the outside of the diff being on fire.

 

[commercialcobb]

The vibration occurs at all speeds under speed control (I.E. maintaining speed) and not under acceleration/load or coasting/unloaded. I get it at 20mph and 80mph and everywhere in between with no increase or decrease in intensity from the bottom to the top of the speed range mentioned. Although it was only sporadic today I did get it from time to time. Seems like it's only when it has warmed up, which just adds to the confusion. I vibrates so badly that I can hear the pedal over the radio (which I don't blast it loud, but it's loud enough). Just blows my mind

 

[TigerEyz3]

Not discounting any of the previous suggestions, but check your axle bearings...given your vehicle mileage and comparing it to the things that I've discovered on my own vehicle, it's very possible your bearings have worn into your axles a bit (causing them to sing/vibrate).

 

[commercialcobb]

I have thought of that as well.... It's not the truck or the car beside me vibrating.. It's the gas pedal/accelerator pedal/throttle that is vibrating.. Other than the gas pedal being mounted to the firewall in some shape or form and only attached by cable and linkage to the engine's intake manifold, how can my gas pedal vibrate? The truck runs slick as snot on a doorknob and makes no sounds or vibrations. It only exists at the gas pedal.. Most bizarre thing I have ever encountered in 15 years working on cars (mostly my own 1966 Shelby Cobra -Replica-, 1983 Jeep CJ-7, 1973 Porsche 914, 1989 BMW 325i, etc.)

If there is no obvious remedy (which I knew there wouldn't be), how can I test the truck that only does it while in motion?? Take it to a shop? They cant do anything I can't outside of putting it on a lift and doing it that way..

Another thought, is there something going on in the engine that I am not hearing or feeling minus the gas pedal.. I know if something was going on in the drive-train that I would get some more common and obvious signs but those do not exist.. Everything is perfect, no screaming bearings, no hard shifts, starts on command, gets decent gas mileage, idles like a well oiled machine, horn blows, etc...

Somehow, some abnormal malfunction has caused the Yukon to make the gas pedal vibrate constantly (conditions mentioned previously) like a cell phone on vibrate..

If you have a response, and I hope you do that can help, please read above for the speeds and conditions for which this vibration occurs..

Thanks again for any help.. Ryan

---------- Post added at 06:39 AM ---------- Previous post was at 05:25 AM ----------

Just another thought before I hit the bed... The only thing wrong with my truck is GAS PEDAL vibration... It is only connected to the firewall through a mount then to the engine through a cable.. Axle bearings and u-joints would be felt and heard throughout the truck. It's not, only the gas pedal.. I don't mean to sound rude, believe me, I am at the mercy of the court here, but as stated previously the only condition is a madly vibrating gas pedal while maintaining speed or cruise.. Ya'll are helping me with suggestions and very much appreciated , my problem is, how did it get to my gas pedal and not the rest of the truck and where did it come from. U-joint I would hear and feel all over (I blew a u-joint in my jeep at 60mph and destroyed the tanny when it all fell apart) so I know what that sounds and feels like. Wheel/axle bearings would sing like a sixteen year old girl in the shower. Engine is pristine, it only got worse, immediately after an oil change. It's not their fault, the problem was pre-existing under Obama Care, but what ever they did made it 5 times worse..

 

[SunlitComet]

Perhaps the cable is not freestanding. In other words may be it is routed some way that it is touching a component it should not be. Or perhaps the pedal is getting worn along the linkage somewhere.

 

[youknowmyname67]

does it do the vibration when cruis control is on? only reason i ask is i went through a problem similar with my dads 02 le sabre.... peddle vibrated right between 45 and 50 only when pressin down the accelerator.... no problems in cruise control no problem when let off the pedal turned out to be the bearings on the end of the axle. took me awhile to figure it out