Universal joint broke

you didn't accidently hit the splitter button, and pulled forward in high range?

 

He already noted it's an automatic.

 

Your experience hits home with me.

My interaxle drive shaft cut loose at 70 mph westbound on I-40 in Texas last month. It tore up both front drive air bags, both shocks, and a lot more. It was an expensive lesson to never trust a shop do a proper job of greasing.

After setting out my triangles, properly placed (unlike 99% of drivers), then inspecting the damage, I walked back a quarter mile to get the parts of the IA drive shaft and put them in my headache rack. The yoke had no grease.

I did my own grease job last week. Those yokes need a LOT of grease. First you start pushing out filthy water, then used grease, then finally start pushing out new grease. Don't stop until new grease comes out all the points. This is probably why maintenance guys don't grease them. It takes a long time to do it right.

I'm still recovering from doing it the right way with a good hand operated grease gun. I'm going to buy an electronic grease gun before I do it again. I did anticipate the job would be filthy and used 40 gallon garbage bags and duct tape to make a body suit and laid absorbent pads on the ground. That made clean up easier.

Symptoms before my experience led me to believe my fifth wheel was going bad. I carefully checked it, but couldn't find the issue. Especially in low range there was a feeling like the kingpin was moving forward and back in the fifth wheel.

 

I say a shock load. Universals just dont bust off at the base like that for no reason. The ends are not turned blue so heat wasnt the cause.

 

Funny. After over 20 years being around trucks (10 of those as a mechanic) I have yet to see a u-joint on a heavy truck that is sealed. Every one of them that I have seen has had a grease fitting. Now the slip yoke is a different story. Some have a grease fitting, others are sealed. Seems to be about 50/50 on that.

 

Do you have any close up photos of the break? If the surfaces of the breaks are mostly rough and jagged, I would say it was shock loaded. If most of the break looks smooth, almost like rippled sand on a beach then it was likely fatigued before it finally let go.