Vibrating at 2500 to 3000 rpm

[Dfather99]

Hello-

My 1995 k1500 has a bad vibration at around 2500+/- rpm. This happeneds under load at all speeds as long as I am on the throttle. All the following check out good:

U joints front and rear
Transmission and motor mounts
There was no play in the output shaft at the transfer case (np241c)

The trans shifts fine. I jus looking for were else to look. Again only vibrates/shutters when on the gas and around 2500 rpm

Thanks

 

[deadbeat]

Did you jack it up to remove pressure before checking play in the u-joints? After jacking it up, is there play in the pinion?

 

[Jglew82]

Since it's rpm related and not speed related, you can eliminate everything behind the transmission/Tcase and focus on checking everything in front (including torque converter and trans pump). Think of everything that spins in sync with the engine and isolate the rest.

 

[Dfather99]

Did you jack it up to remove pressure before checking play in the u-joints? After jacking it up, is there play in the pinion?

I had actually replaced the u joints and checked the pinion. all were good

 

[Dfather99]

Since it's rpm related and not speed related, you can eliminate everything behind the transmission/Tcase and focus on checking everything in front (including torque converter and trans pump). Think of everything that spins in sync with the engine and isolate the rest.

Good point I'll check the trans fliud level. how do you go about checking a TC and pump?

 

[Jglew82]

Process of elimination really, without pressure gauges and such it can be difficult to narrow down. Can you reproduce the vibration in park or neutral at 2500 rpm (put a load on it by turning on AC and all headlights/high beams). Can you do a stall test and reproduce the vibration (trans in drive, Parking brake set, foot on brake, press accelerator to stall for a few seconds)?

 

[deadbeat]

Thats a good point on the stuff that turns, in my mind for some reason I wasn't thinking. Will it vibrate in neutral, that would narrow it down a lot?

 

[Supercharged111]

Are all your bellhousing to engine bolts tight? How about the aluminum lower bellhousing and the rods that bolt from it to the motor mounts?

 

[Schurkey]

If all else fails, drop the torque converter pan, disconnect the torque converter bolts, and push it rearward away from the flexplate. Run the engine.

If it still vibrates, it's the engine or accessories. If it doesn't, it's the trans--which probably means a failed torque converter.

ALL of this assumes this is RPM related, not speed related. Does it vibrate at the same RPM in first gear? Third? Neurtral?

What is your scan tool showing for misfire history?

 

[Dfather99]

Does not make the vibration in neutral or in park. There is slight vibration when at a stop In drive.

No check engine light in.

Are all your bellhousing to engine bolts tight? How about the aluminum lower bellhousing and the rods that bolt from it to the motor mounts?

I'll check these they should be tight