F350 slip joint / pinion / drive shaft question

Just looking for guidance in figuring out a small issue with the 6.4 F350. It is not lifted, but does have a leveling kit on front.

Just over a year a go had the rear pinion seal replaced at a Ford dealership. Apparently it was done by a journeyman mechanic and they kept telling me how lucky I was. Anyway, a few months later the truck developed a little "bump" when stepping on the throttle from a stand still. Like the shaft spins a tiny bit before moving the truck forward. I did some reading and decided to check out the slip joint. Wanted to do it right so even bought the fancy Ford Blue Teflon grease for the job. When I separated the male/female parts of the slip joint I noticed that there was a machined slot in the female end, and a couple Red painted splines on the male end. To me it made sense that the red painted splines were to fit within the slot. They were not in this position when I separated the two. It was offset by a couple splines. Likely done by the mechanic. I cleaned, lubed and reassembled everything, making sure the two red painted splines were within the slot. Should the mechanic not have done the same?

Truck got better, but still has a little bump on take off. Trying to figure out what it might be. U joints are fine, with a couple being newer. Carrier bearing looks OK to me. Wondering if the mechanic didn't torque the pinion nut enough? Has damage occurred somewhere internally by the slip joint splines being offset like they were? Any thoughts on what it might it might be, where to look, or what to test would be appreciated. Truck is perfect otherwise and this little bump is driving me nuts!

Do you know if the driveline angles are correct???

When you had the driveshaft off, did you check for side to side and up/down play on the slip joint and splines while together? Also, how many km on the truck?

Caper11 said:

Do you know if the driveline angles are correct???

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Thought about that, but never had any issues till after the work was done at the dealer. Again, truck is not lifted, rear suspension is stock.

zal said:

When you had the driveshaft off, did you check for side to side and up/down play on the slip joint and splines while together? Also, how many km on the truck?

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No I did not. That would be a good test to perform. Just over 240,000km

I would look into that. Slip yokes and spine do wear out. Should not be any movement except in and out. At 240 ,000 km, I would think that is the issue. But you have to have the driveshaft off the truck and hold it in a vise to check.

As as for the splines lining up, the yoke ears on the slip and weld yoke should be parallel to each other.

I had an old Duramax that did the same thing, the rubber bushings on the front of the leaf springs were a little wore out, causing the whole axle and spring assembly to move just enough to cause the that light bump. Might be your issue, I sold the truck before I bothered to fix it though to guarantee that was the problem.

for the slip being wore if you test how previously mentioned make sure you do it at its running length. as for problem was noticied after pinion seal was replaced, that sounds more like pinion was not tightened since nut and yoke would of been removed, did you check for play there, those bearings should be under pre-load so no end play should be present. also should get slight noise from accel to decel if this was the issue. for slip alignment its done with yoke ear alignment but still could be out half a turn from original which would throw out balance. most tecks would not take apart slip to just do a pinion seal. suspension could also be issue as mentioned but easy test is put a load in truck and if suspension will feel different. who changed the u-joints for i have seen guys damage drive shafts and dent them doing u-joints or bending ears slightly causing even new u-joints to be loose