Low whine at 40 mph????

[CityGuy24]

Ok, I was driving the truck today and noticed a low whine around 40mph. It is really noticeable when running 40mph and slightly in the go pedal. If you let off the go pedal it continues for a few seconds as you cost but goes away. It comes back as soon as you get back in the go pedal. It goes away completely when you get up to speed and not cruising around 40 mph. Any clue what it might be? Thanks.

[ZeroOne]

Does the whine ever change pitch? If so, does the pitch change go in sync with speed? How about engine speed or transmission shifts? Do those affect pitch or make it go away? How about engine braking with tow/haul mode. When you're slowing using the engine, does it do it?

My first guess would be something in the rear drivetrain if it is speed related. Rear axle or driveshaft.

One other question... are your hubs locked?

[CityGuy24]

I only notice it around 40 mph, it does not seem to change with speed. The hubs are not locked. It only makes it when you are slightly on the go pedal, and continues a few seconds after you let out.

[ZeroOne]

If it's only doing it at one speed, doesn't change pitch, and the front drivetrain is not spinning... then its probably not the rear end. Maybe it's just a trait of the engine at that speed? Are you in over drive at this point? (Very low RPM).

[Greenhorn Diesel]

Is there any vibration involved? Just like previously stated, are you in overdrive when this happens? If so, perhaps torque converter shudder I had an escape that did that...I know I know not the same thing, but just a thought.

[elibenson]

There is a TSB about drive shaft noise. It is a harmonic vibration that they fix by replacing the drive shaft with one that has an extra vibration damper. Sort of like the harmonic balancer on the engine.

TSB
07-20-7 MOAN/DRONE AT 1500-2000 RPM - DANA 80 DUAL REAR WHEEL AXLE

Publication Date: September 24, 2007

FORD: 2008 F-Super Duty


ISSUE:
Some 2008 F-Super Duty 350 Chassis Cab vehicles equipped with a 6.4L engine and a Dana 80 dual rear wheel (DRW) axle may exhibit a 4th order engine moan/drone concern between 1500-2000 RPM.

ACTION:
Follow the Service Procedure steps to correct the condition.

SERVICE PROCEDURE

Replace the driveshaft with a revised part number per application. Refer to the 2008 Super Duty 250-550 Workshop Manual, Section 205-01, for driveshaft removal and installation procedures.

PART NUMBER PART NAME
8C3Z-4R602-EEA Driveshaft Asy - 140.8" WB/4X2/AUTO/DRW
8C3Z-4602-AHA Driveshaft Asy - 140.8" WB/4X4/AUTO/DRW
8C3Z-4R602-ADA Driveshaft Asy - 161.8" WB/4X2/AUTO/DRW
8C3Z-4R602-BMA Driveshaft Asy - 161.8" WB/4X4/AUTO/DRW
8C3Z-4R602-AMA Driveshaft Asy - 164.8" WB/4X2/AUTO/DRW
8C3Z-4R602-AVA Driveshaft Asy - 164.8" WB/4X4/AUTO/DRW
8C3Z-4R602-AFA Driveshaft Asy - 176.2" WB/4X2/AUTO/DRW
8C3Z-4R602-BDA Driveshaft Asy - 176.2" WB/4X4/AUTO/DRW



WARRANTY STATUS:
Eligible Under Provisions Of New Vehicle Limited Warranty Coverage
IMPORTANT: Warranty coverage limits/policies are not altered by a TSB. Warranty coverage limits are determined by the identified causal part.

OPERATION DESCRIPTION TIME
072007A 2008 F-Super Duty F350 6.4L Chassis Cab DRW Axle Dana 80: Replace The Rear Driveshaft Includes Time For Diagnosis And Road Test (Do Not Use With 1007D, 1007D7) 1.2 Hrs.

DEALER CODING
BASIC PART NO. CONDITION CODE
4602 D9

[CityGuy24]

Well, I had the dealer look at my truck. I talk to the technician and he is convinced the whine I am hearing is the turbo spooling up. He got in the truck, put it in gear and used the brake to torque the engine and it made the sound I was hearing. I don't understand while I only hear it at certain intervals. Can someone explain that to me?

[elibenson]

Hrm.. With the daul turbo set up that we have on these trucks, some times both turbos are not really working. The VGT turbo usually does the work at lower RPM's and the other one starts working when the VGT starts needing more air. It sort of pre-pressurizes the air a bit before it goes to the VGT to be pumped up to a higher pressure. I am guessing that at the RPM/speed that you mentioned you are starting to hear the two turbos together. Might be a harmonic interference between the two spinning turbos making the sound you are hearing. Don't know.. But either way, if it did it without the drivetrain moving (brake torquing) then it isn't your driveshaft.

[rollthecoal]

Mine did this for the first 30,000km. After that it disappeared