[greenskeeper79]

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.

 

[greenskeeper79]

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.

 

[greenskeeper79]

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?

 

[greenskeeper79]

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?

 

[Gator5713]

It could be the fan clutch or even the water pump. It's been several years ago so memory of specifics is fuzzy but it seems I recall a similar vibration that I couldn't find then one day one of my drivers called saying "I think the fan just fell off the front of the motor". Sure enough the shaft had sheared off right at the pump and upon inspection I could tell it had been cracked for a while. New pump and no more strange vibration!

 

[greenskeeper79]

since it does it intermittently I am leaning towards the fan clutch. Water pump was replaced about 10k miles ago with OEM motorcraft.

 

[Gator5713]

When did the hum/vibration start? Before or after the new water pump? A cracked fan blade could also cause this.

 

[greenskeeper79]

When did the hum/vibration start? Before or after the new water pump? A cracked fan blade could also cause this.

within the last 50 miles. there is play in the fan clutch itself laterally. haven't bothered to change it out yet but it's prime suspect #1

 

[7.3hoarder]

Whenever i have a vibration ike that at a high speed its usually a Ujoint going out. Just a thought. Doesnt vibrate until im in overdrive

 

[greenskeeper79]

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