I have a 1991 f150. 4x4, 302, e4od.

There is a slight clunk when I accelerate after coming to a complete stop. Just a quick clunk that I can feel.

Here's the fine print. It only happens when it's cold outside after my truck has been outside all day while I'm working. After it does it once on my drive home it will not do it again until the next day when my truck has sat outside all day again at work in freezing/sub freezing temperatures. I mean cold as in the air temperature...not cold as in the actual truck engine temperature.

It will not do it in the mornings because I park in a garage so my truck isn't sitting in temperatures as cold as when I'm at work. It will only do it once and it seems that the cold temperature has something to do with it. After it does it once it will not do it again for the entire drive home.

I've been under the truck. Everything feels solid and normal. All fluids are as they should be. U joints are greased.

Any suggestions? Maybe the splines? If so, what type of grease should I use in the splines and how much?

Any input is highly appreciated. I'm afraid if I don't find it that I'll cause more damage.
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Spray WD-40 into the leaf springs to drive the water out so it doesn't freeze the leaves together. For a smoother ride, jack the truck up, pry each leaf apart, and squirt in some chassis grease. You'll be amazed.

 

Thank you. I'll try that tomorrow. I never thought of that. I suppose that it makes sense that the springs could freeze and then the clunk is the sound of them freeing up... We'll see if it works. I hope so. It's warming up slightly where I live so I won't be able to verify until it drops below freezing again.