Rear driveshaft slip joint

[gw33gp]

Recently, I have been noticing a kind of hum or weird vibration at speeds above 55 mph or so. I checked out the drive train and the only thing I found was a slight looseness in the rear driveshaft slip joint. It is not loose in up and down movement but there is a rotational looseness. It is not a lot, but I don't recall any play before. I know there is backlash in the differential and transmission, I don't think there should be any in the slip joint.

Is this normal? Could that possibly cause the hum?

I am thinking the only repair would be to replace the entire driveshaft. Does anyone have any other ideas on this?

 

[sgtsandman]

Mine doesn't have any slop in the drivetrain other than the backlash in the differential.

 

[dvdswan]

Did you rotate the tires?

Did you check for any mud on the inside of the rims?

As @sgtsandman said there shouldn't be any rotational movement on the slip-joint.

I would suggest taking the driveline down to a driveline shop and have it checked/rebuilt.

 

[gw33gp]

It is not the kind of vibration that is caused by tires being out of balance. It is more like running a tire with a very aggressive tread like a mud tire. The only difference is, it is more of a feel thing rather than hearing it. I do have BFG mud tires but the ones I have on there now are Michelin LTX M/S tires. They have always been very quite and smooth.

I have been considering just buying a new driveshaft, but a rebuild would be less expensive. I will check into that.

 

[Eddo Rogue]

I greased up the splines, also I heard of people using white loctite on the splines.

 

[19Walt93]

Don't put locktite on the splines, Ford has a special blue grease that works good for that. Before replacing the driveshaft, I'd pull it out and flex the u joints around because I think you have one that's beginning to bind up. I prefer greasable joints, just remember to locate the grease fitting on the compression side of the joint and to orient the fittings so they're lined up so you can grease them both without rotating the shaft.

 

[gw33gp]

I agree, no Loctite on the spines. There should be free movement there.

I did relube the slip joint at around 100K miles. I used a DuPont Krytox grease that has moly disulfide in it. With near 269K miles on it, a relube could be needed but I think it is too worn for a relube. Yesterday, I got under it again and got into a position that I could better detect side movement in the slip joint. I was able to feel a some slight side movement there in addition to the rotational backlash.

Good call on checking the u-joints. They are still the original ones and I keep checking them because I can't believe they have lasted so long considering all the abuse I have run them through. I had the driveshaft out for some other work a month ago and they were still free rotating without play.

I decided to go ahead and order a new drive shaft. I found a Black Friday discount online from a Ford dealer. It was already the lowest price I could find online and the shipping was very reasonable. They didn't charge tax either. Rebuilding presented some problems for me. Once I got the driveshaft out, I didn't have a good way to get it to a place for rebuilding. Here in SoCal, that kind of work is expensive. With the discount on the new driveshaft, I don't think I would have saved much money. Now, I will have a new OEM driveshaft that will surely outlive the truck.

 

[Eddo Rogue]

Forgot to mention I used bel ray waterproof grease (the blue stuff). Also replaced the u joints with greasables.