Rear end vibration on highway

[masospaghetti]

I have some low frequency vibration coming from the rear of the truck at cruising speeds. Worst around 60 mph.

Whats the best way to determine if this is driveshaft (unbalanced or u-joints?), inside the rear diff, or wheel bearings? without tearing it all apart?

I plan on changing the gear oil which is probably the factory fill but I doubt this will help. 96 XLT 5.0, 148,000 miles. Thanks all.

Right now it's AWD but the front driveshaft has been removed.

 

[rs2k]

Easy way to check the wheel bearings is to jack up the wheel and push try to move the wheel side to side and up and down. If it moves at all the wheel bearings are shot. Sounds like you only need to check the rear, but if you decide to check the front it can be a little more difficult to check the front because anything loose in the front end can make it look like the wheel bearing is moving.

I had a Ford F350 break a rear axle because of a bad wheel bearing. :/


You should be able to check for u-joint wear buy hand with the truck in neutral and rear tires in the air. Use chocks and be very careful if you try this.

It could be an out of balance tire. I don't know how to check that. It's cheap to get tires balanced though.

 

[masospaghetti]

I checked the rear wheels for play, I couldn't move them in any direction. Also I changed the axle fluid with new 75w-140 LS synthetic, no change.

I just bought the tires this week so hopefully they aren't out of balance. New Coopers.

When you say check the u-joints, you mean feel for play?

 

[rs2k]

Yes, the only way I know to check u-joints is to look for play in all three axes and in the rotation. That really should be done with minimal load on the joints so you can check it by hand. The joints should be tight. There was another user who had a vibration that was resolved by replacing his u-joints here: http://www.explorerforum.com/forums/showthread.php?p=3203282


How bad is the vibration?

 

[DjDom]

I'm thinking something simpler, like sway bar links/bushings and rear shocks.

Especially the fifth shock.

 

[rs2k]

If it was one of those items I would expect the vibration to change depending on the quality of the road. Do you have a good and bad road to test at 60 MPH?

 

[masospaghetti]

I replaced the shocks and end link bushings in the rear (sensatrac load adjusting) although I have not replaced the 5th shock.

I will have to check my u-joints. The vibration isn't that bad but its certainly there - definitely a difference over my other rig (2000 Sport).

 

[rs2k]

Did the vibration exist before replacing the tires?

 

[masospaghetti]

No idea. The old tires were horrible and made all kinds of other noises.

 

[rs2k]

Where did you get the new ones? It might be a good idea to tell them you think the new tires are out of balance and you want them checked. I know when I bought new tires I got life time rotation and balance. Did you get something similar?

 

[Flash]

Easy way to check the wheel bearings is to jack up the wheel and push try to move the wheel side to side and up and down. If it moves at all the wheel bearings are shot.

The way the rear axles are retained allows for some lateral movement.
My '97 XLT had a lot of movement and it bothered me but I don't drive it now.

@masospaghetti. Try jacking both rear wheels off the ground then engage a gear and watch the wheels and shaft spinning to see if you can determine the source of the vibration that way.

 

[masospaghetti]

Thanks for the suggestions. I don't think its tire related. It's the same type of resonance that I had in a previous vehicle (Camaro) that had both a bad differential bearing, and bad wheel bearing.

I really would like a way to isolate the differential as the problem before I spend money installing repair bearings into it, if possible.

@Flash: Good idea but I would not feel safe running the vehicle up to 60 mph on jackstands.

 

[rs2k]

@Flash: Good idea but I would not feel safe running the vehicle up to 60 mph on jackstands.

Why not?

http://www.youtube.com/watch?v=G-Nunm3Sbzo

 

[JusTheUsual]

switch or rotate tires. My brother got brand new tires before for his 01 sport and one of the belts inside of tire was bad. If vibration in back, switch back tires to front and front to back, if vibration in front then, well obviously then its the tire

 

[Flash]

@Flash: Good idea but I would not feel safe running the vehicle up to 60 mph on jackstands.

I've run more than one car at 80mph on stands.
But then I didn't get out to look underneath.

 

[MCP]

I have some low frequency vibration coming from the rear of the truck at cruising speeds. Worst around 60 mph.

Whats the best way to determine if this is driveshaft (unbalanced or u-joints?), inside the rear diff, or wheel bearings? without tearing it all apart?

I plan on changing the gear oil which is probably the factory fill but I doubt this will help. 96 XLT 5.0, 148,000 miles. Thanks all.

Right now it's AWD but the front driveshaft has been removed.

Did you ever figure out what the problem is?