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Vibration that is RPM related .. or so it seems

4K views 4 replies 4 participants last post by  JCart 
#1 ·
Problem:

When cruising down the road approaching 1500 rpms in any gear you start to hear a faint howling sound and maybe even a buzzing like vibration in the floor and gas pedal. As rpms increase to 2000 it gets worse ( louder ). Once up to 2000ish rpms it fades maybe just a little but still very noticeable. This only happens when under load/throttle pedal down. If I get up to speed and cruise somewhere in the 1500-2000 rpm range and let off the throttle and coast the howling/buzzing goes away completely. I CAN recreate this at any speed.

I thought maybe it was the down pipe rubbing the firewall again but I dont think this is the case anymore after looking around at it again today. Unless there is significant movement while motor is under load and pushes it into it or the transmission or something. There is some space between the pipe and surround equipment but not very much at all.

Notable things:

Transmission was rebuilt 2.5k miles ago at reputable shop by previous owner so I don't know if this is a new thing or not.

EGBPV is still in place but no leaks and works as it should when cold

It runs great and will run with this but it is irritating after awhile
 
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#2 ·
#3 ·
Since the transmission has been out, I would advise checking your motor mounts. The 7.3 mounts can move forward and back, at which point metal to metal contact occurs, forward and rearward movement is prevented by the transmission mount.

Sometimes when changing the transmission the engine gets slid one way or the other, and when the motor mounts aren't put back to center, all kinds of funky noises happen.

Sent from my E6810 using Tapatalk
 
#5 ·
I’d also check to see if any of the firewall heat shield is touching the Down Pipe, one of my trucks took me a while to figure that it was just touching intermittently. Actually rubbed a hole in the DP, that heat shield is some robust material.
Cheers,
j
 
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