shaking under acceleration

[87mustang]

03 f250. 6.0 fx4
whole truck shakes when accelerating under normal circumstances and smooths out around 50-55 mph.

-ball joints are not the problem, they are new
-brakes are not the problem, they are new
-front sway bar has new polyurethane bushings on mounts and links.
-rear driveshaft has newer u-joints. these are moog installed about 40k ago and are greased every 3-4 months.
-tires have been balanced and rotated every 5000 miles. i had this done when problem first started and it didn't change.

my suspicion is that one of the rear driveshaft u-joints is bad, but i don't know how to check them.

any help would be greatly appreciated.

[tbisme]

Take the shaft to a drive shaft shop if you suspect it is the cause and have it checked, some joints only have load issues and will not feel bad to the touch or feel unless they are in a torque load. Hope this helps.

[bigred_stroker]

I agree, you could have a shop look at it. If you want to do a quick check on your own, listen for the CLUNK sound when you put it in gear or go from reverse to drive. By the time the U-joints get to the point of vibration, you can hear the distinctive clunk sound. You could even have someone shift it in and out for you while you look at it and listen.

[87mustang]

found the problem. brand new u-joint is going bad already, how cute.

[87mustang]

so what would be a good brand of u-joint to buy so this don't happen again. i am pretty sure the last u-joints i bought for the rear driveshaft were moog, but i am not sure. whatever it is only lasted 30,000 miles, and were greased at every oil change.

[ImaPoser]

Originally Posted by tbisme

Take the shaft to a drive shaft shop if you suspect it is the cause and have it checked, some joints only have load issues and will not feel bad to the touch or feel unless they are in a torque load. Hope this helps.

Could this explain the shuddering I feel when accelerating up a hill in the 40-50 mph range only when towing a trailer? It never does it unloaded, and doesn't even do it when accelerating on flat ground while towing the boat.
I have never noticed a 'clunk' sound when going from drive to reverse, but I do feel what could best be described as slop in the drive train every time I come to a complete stop and then go.

If so. I'll add it to the list to be looked at this week. Second time towing the boat, second time it has to go to the shop. Last time was the HPOP, this time, it's a brake caliper hanging.

[87mustang]

so i figured out this one. the rear most u-joint didn't have a hole going to one of the ends for the grease, so only three sides of it were getting greased. completely wasted the one side, almost no needles left in it. it appeared that the hole was never drilled through the center of the cross on one side. i should have taken pictures, but that would have been smart.

i won't say whose u-joint it was but it was made in the USA, i did not buy an economy hong kong buffet part

[travsav]

So'd this fix your problem? My truck was shaking under acceleration, especially going up hills... and it was an injector that had gone bad.