65mph 1800 rpm vibration/hum

[greenskeeper]

99 F250 CC 4x4 ZF6, 245k miles original drivetrain aside from driveshaft and clutch at 230k.

65mph 1800 rpms I get a wuh wuh wuh vibration or hum at the speed that you can read the spacing of the words.

If I push in the clutch, the vibration/hum goes away completely and the truck is "quiet" at 65mph idle.

Below or above 65mph 1800 rpms the problem isn't there either whether by downshifting to 4th or just driving faster or slower.....seems rpm related to me.

Can't tell if the vibration/hum gets better when turning versus driving straight at 65mph 1800 rpms which I would think could be an axle problem?

Harmonic balancer?

engine/trans mounts?

throwing ideas out there for help.

 

[79jasper]

They quit using the DMF prior to the SD'S? Can't remember.

So if I understand, only does it in gear? O/D or 5th?

This is a new thing? Or just never noticed it before?

This could still be something in the driveline.

Sent from my SAMSUNG-SM-G935A using Tapatalk

 

[greenskeeper]

They quit using the DMF prior to the SD'S? Can't remember.

So if I understand, only does it in gear? O/D or 5th?

This is a new thing? Or just never noticed it before?

This could still be something in the driveline.

Sent from my SAMSUNG-SM-G935A using Tapatalk

SMF

in gear, 5th gear (O/D) at 1800 rpms which is 65mph, it's loud too....actually thought it was something wrong with the intake or exhaust.

Push in the clutch and the truck is quite idling along while rolling at 65mph.

All the drivetrain components except engine are still turning at 65mph although no load at that point.

accelerating the problem seems to be there although less pronounced in lower gears, but always at 1800 rpm

I am wondering if it is an accessory to the engine....fan clutch.....harmonic balancer.....etc. I'm going to run the engine in N at 1800 rpms and listen. Then take the belt off and try again.

 

[Shadetreemechanic]

Check carrier bearing and u joints while you are there. Not likely to be u joints, but bearing is suspect.

 

[greenskeeper]

Check carrier bearing and u joints while you are there. Not likely to be u joints, but bearing is suspect.

new single piece driveshaft 5k miles ago

 

[greenskeeper]

at 1800rpms in the garage the vibration/hum is there although not nearly as intense (20%)

removed the belt and it seems to go away.

pushing on the fan there is lateral defection (front to back) at the clutch. I am assuming there should be zero play?

 

[IDIoit]

no movement in either of my fan clutches.

 

[greenskeeper]

no movement in either of my fan clutches.

Took the truck for a drive. No (or minimal) vibration drone at 65/1800, nor at 1800rpm during the upshifts to 5th gear, however the truck wasn't fully warmed up. Would this point to the viscous clutch on the fan?

 

[greenskeeper]

replaced the original 245k mile fan clutch. Noise is GONE!