Strange cyclical vibration on the highway

[600$04Ranger]

My 2004 4wd Ranger has 265,000 miles on it. I bought it with 200,000 and a blown 4.0l. I rebuilt the engine completely and have swapped in many new parts since I brought it home. It's a reliable rig but I have a mysterious issue. There is vibration that's noticeable at speeds above 55mph. It gets more intense as speeds increase but the frequency and rhythm don't change. I have newer tires and new front and rear driveshafts. The vibration is slow and sounds like it rises and falls. It's pretty consistent. I haven't changed cv joints since I bought the truck. I swapped in a used transmission and transfer case but I'm pretty sure the vibration was there before that. The alignment is good and tires are wearing evenly. I am stumped. Hopefully some of you have a few ideas!

 

[scotts90ranger]

If you rotate the tires does it change any? Does it feel like it's at a tire? That speed is usually an out of balance tire or a bad cord in a tire but there's other things too. Does it have a one piece rear driveline or two piece with a carrier bearing? I believe it should be one piece aluminum but have been wrong before...

Have you tried putting it in 4hi to see if it changes anything? Sometimes having load on things smooths it out if it's in the driveline somewhere.

 

[600$04Ranger]

I'll try that. Pretty sure it's not the tires. Maybe it's time for a rotation though. It has the one piece rear driveline. Had one built at a local driveline shop. Also has a double cardan front driveline from the same shop. Have a Detroit Tru Trac in the rear with 4.10 gears.

 

[scotts90ranger]

On my '00 Explorer I got some used tires from a Jeep that were scalloped that make a some vibration around that speed, nothing you can do for scalloped tires either which sucks but I still got like 35k miles out of those $500 tires...

 

[Robertmangrum.rm]

Did they balance the drive shaft? Im sure they did. But maybe it's 180° out. I just changed my center support/ carrier bearing out on my 2 peice. Think I may have got my front shaft 180° out. I have picked up a slight vibration. Just an idea.

 

[scotts90ranger]

Getting it 180 out isn't a thing, that would be fine, getting it 90 out would be a problem or even a tooth off can be...

 

[19Walt93]

I'll try that. Pretty sure it's not the tires. Maybe it's time for a rotation though. It has the one piece rear driveline. Had one built at a local driveline shop. Also has a double cardan front driveline from the same shop. Have a Detroit Tru Trac in the rear with 4.10 gears.

When did the vibration start and has it changed over time? The 2 piece driveshafts were used to reduce U joint angles and decrease vibration. If the truck is lifted that would increase driveline angles and if the vibration cycles it's driveline related, not tires.
Get it up on jack stands and run it up to speed. Assuming the vibration is present, have someone else bring it up to speed while you slide under and feel the transfer case and rear end to see where you feel the vibration strongest. At the worst end of the driveshaft install a worm clamp around the shaft, then bring it up to speed again to evaluate the vibration. Next rotate the clamp 1/2 turn and repeat, then turn it 1/4 turn, followed by another 1/2 turn. If it's a balance problem one position should improve the vibration and one should make it worse. If 2 adjacent positions seem to help, try moving the clamp 1/2 way between them. This procedure came from a vibration diag manual Ford released after the Fairmont was introduced.

 

[19Walt93]

Did they balance the drive shaft? Im sure they did. But maybe it's 180° out. I just changed my center support/ carrier bearing out on my 2 peice. Think I may have got my front shaft 180° out. I have picked up a slight vibration. Just an idea.

He said it's a one piece shaft so it can't be out of phase. Good suggestion for a 2 piece shaft, though except that 180 out wouldn't be a problem, any other mismate would be.

 

[RayInStl]

Does it seem to change/lessen when making gradual turns on the highway? It sounds like you need an alignment to me.