av8roc

Yes the truck is 4x4 and I have a 6.5' bed. The forward drive shaft is 2 piece with a rubber boot covered slip yoke. I dropped and greased that thinking it was the culprit. It was well greased however and thus not the problem.

My rear shaft (transmission to rear) is solid one piece. The manual stated there is a slip yoke where it mounts to the tranny.

I was wondering if that may be the problem and if the TSB still applies to a one piece solid rear shaft.

Thanks for all the help guys.

HoustonRider

SB is for more recent vehicles, re-greasing it will be a band-aid, there is too much play in the yoke to begin with (on newer trucks). You need to use a heavy moly based paste that won't go away so quickly to start.

Yes, the 4x4 is the once piece shaft. The u joint usually isn't the culprit, its the yoke.

VTX1800N1

Yes, the TSB I linked to is specific to the rear drive shaft. You will have to register on that site (free) to see it. It involves inspection and lubrication of the slip yoke at the rear of the transfer case (rear drive shaft).

sglover

Good video but watching, was it hitting the tail housing or just a slack in it. I could not tell.

I used the suggested ford grease but I did notice the original grease was thicker like a dope more so. Is it a problem or just the removal and re-install causing it? Have you seen any better luck with another type grease?

VTX1800N1

The slip yoke is designed to move fore / aft to accommodate changes in drive shaft geometry relevant to the rear axle as the axle moves through its suspension travel. What is happening is that a lack of grease on the slip yoke causes it to bind until there is enough force fore / aft that it overcomes the binding suddenly. This results in an instant release of the binding and that is the thudding / knocking you are hearing. If you use a glove in the yoke and see what looks like very tiny glitter in the grease, that means the nickle coating is wearing off the yoke (because of the binding) and you need to replace the entire drive shaft (according to Ford, I don't know if a slip yoke is available separately and can be swapped out).

sglover

Not sure if you wrote that or it was a copy from the TSB Good Stuff! I had read A TSB on the yoke before but not that. Very best way I have seen it explained and made me go I wasn't seeing things in the video, I did have the silver in mine and the frsh grease added just thick enough layer to prevent the bind. The should Definately come out with a seperate yoke but that would cost Ford the sale of a D.S., I have read the u-joints arent replaceable but mine have the retaining clips so I was thinking they must be.

VTX1800N1

Combination of me summing up the TSB and I'm just mechanically inclined and have an understanding of the problem. I would say that if you saw the metal flakes in the old yoke grease, it's only a matter of time before the problem comes back. Moly paste (not grease) is probably the best way to prevent this. With metal flakes already present in the old grease, that indicates abnormal wear and the clearance between the transfer case output shaft and the slip yoke teeth has increased. This will allow the slip yoke to cant (angle) more than the design was meant to. The thicker layer of grease or paste will fill in the increased clearance gap for a while, but eventually it will get squeezed out of where it needs to be and the problem will likely come back.

The TSB says that this was the result of the slip yoke not being greased on the assembly line. IOW, this was a defect that was always present in the truck from the date of manufacture. Too bad Ford (and other manufacturers) don't warranty things like this for the life of the vehicle. It's clearly a screw-up on the assembly line.

sglover

Absolutely agree with you, guess I will try and find a Molly Paste until I buy a D.S.
Thanks for the write up though and to (Houstonrider) for the youtube post. I initialy as most thought it was a turning/slack type clunk, thought that would be a throttle up or down noise, not a delayed reaction as we get. Now to worry about how much of that metal is getting in the T.C. gears. Im glad there is a seal between it and the tranny.

VTX1800N1

I got this in the mail today. This is what Ford recommends to use for the slip yoke. You are supposed to use all of it. I don't know if this grease contains moly or not.



About moly, it's easily the best lubricant for extreme high pressure applications like this. The problem is whether there is any potential for that moly to mix with the transfer case fluid. I wouldn't think it would, because the fluid would wash the grease away eventually if the two mixed under normal operating conditions. If moly grease or paste did get in the transfer case, it would be bad. The TC has a wet clutch that spins up the front drive shaft when you select 4x4 operation. If moly got on that clutch, it would cause slippage.

sglover

I went to Ford for the Slip Yoke grease and got a Motorcraft tube of blue grease that I had read on anothe TSB nothing like that. I think I will be checking into again, my truck quit completely when I used the blue grease and just started doing it again every now and then not all the time, yet!