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Ford F150 drivetrain

I recently experienced an extreme vibration while driving my 2004 F-150 truck. I assumed it was the universal joints which I told my mechanic. After inspecting it he said it was probably a bent shaft on the pinion gear in the rear end. He took the driveshaft off and replaced the rear with an auto salvage yard unit. He says now the universals are worn also and should be replace. He started (but without my go ahead) by taking one out which was difficult but it seems to have been held in with pins instead of the usual expanding “c” clip so he cut that one out with a torch. Briefly getting back to the rear end, he showed me as he rotated the flange that connects to the driveshaft that it did not travel in a true circular path but had a high spot like a wobble and leaked oil from the center. My question is was my differential really damaged to the point that it would cause this extreme shaking or could it be the universals? Question 2-the universals were pressed in an held there with pins instead of the typical “c” clips. Is this a new method?

History- The truck was used several times carrying a large load which sent the bed down to the axle however it wasn’t recent and the truck drove fine until now. The truck has 92k miles on it and in relatively good condition.

Can you give me some insight?

Although I’ve only seen it on GM products some universal joints have plastic injected around them from the factory that fills a channel around the u-joint and holds it in there.

The ends of this plastic really looks like little pins are in there that must be taken out. The fix is to heat the yoke and after a bit the melting plastic expands and shoots out the holes; care must be taken as I’ve had the u-joints get overheated while doing this with the result of the u-joint cap being blown off and flying across the room. The replacement u-joint has the c-clips with which you’re familiar.

As to whether the u-joints would have fixed the problem in the first place I can’t tell you; it’s possible that they were worn bad enough to cause your vibration but it’s also possible that the rear end was the problem also.