Hey guys I've had a problem with my '91 F150 5.0 4x4 for the past year where for instance I'll come to a complete stop and then start accelerating, I'll get a nasty what feels like a drivetrain clunk or pop and its so bad that I can't pinpoint where its coming from because it's so violent. More than likely it sounds like a bad u joint or mount somewhere but I have replaced u-joints, transmission mount, and went as far as putting a brand new LS carrier in the diff. While I was in there I saw no bad wear on the ring and pinion, it was in spec and made sure it was in spec when putting the new carrier in. I have seen posts of the newer trucks having a similar problem with the slip yoke binding up at the tcase and the solution to that was to grease the splines in the yoke which I did. Did not help my problem and since my truck is lifted 4" I thought this could be the culprit. The only way to dive my truck without such a violent clunk is to slowly ease into the gas and once I'm up to about 20mph I'll feel a slight pop almost like something in the drivetrain unbinds. Hope everything makes sense in the post I've been getting tired of this problem and really want to fix it.
Thanks

 

I feel your pain. We had a clunky squeak in the CR-V and it took us weeks to figure out what it was. Turned out to be a loose sway bar link bolt - just loose enough to make a racket but not loose enough to suspect the bolt wasn't tight when you looked right at it. Thought the wheel was going to fall off for a while.

Since you've gone to so many lengths already, I'll just throw out some ideas based on problems that I've seen on trucks over the years. You may have already checked these, but it's just brainstorming:
Two trucks have had loose motor mount bolts, one squeaked and one clunked. They were the single mount to frame bolt, not the mount to engine bolts.
Three different trucks had worn out motor mounts letting the fan hit the shroud occasionally - two shattered the fan shroud, one just rubbed it (sounded like a rod knock).
The truck I currently DD was missing two bellhousing bolts when I got it, and it had the wrong flywheel which caused the clutch to make a terrible scrapey sound.
Have seen shock mounts and spring perches rust but not completely break off and make noise. Front and rear. U-Bolts too. Body mounts too.
Radiator mounts rust out and the radiator hoses were knocking the radiator around...but never hit the fan.
A friend had a '95 with no 4X4 locknut on the front wheel (missing two pieces of the three).
That same friend's truck had a violent intermittent clunk that turned out to be the electric t-case shift motor engaging by itself. That truck had been in a flood, btw.
Had a Chevy friend with a clunk - it was loose lug nuts and they didn't figure that one out till it was too late. Sheesh.
A Dodge had such a worn out crank that the balancer/pulley moved 3/4" to and fro when revved.

That's all I can think of now. Just brainstorming of course. The single truck I've owned with an automatic (C6) had a terrible clunk in it, but only when you shifted into reverse or drive. A loud clunk with a ringing aftertone. After in gear it was quiet. That's the extent of my experience with autos. All my ZF's have been noisy, but most are. Never had any noises from an M5 trans. Anyway, hope my ranting helps somehow!

 

Since ideas are being thrown out, what about the drum shoes cable being stuck or the parking brake cable not adjusted properly. Little speed and it lets go and wheels are not up to speed. Sandy

 

Had a car that made a clunk when stopping and accelerating, found that the rear axle lower support arm on the left side had worn to the point that it allowed the axle to move 1/2 inch on that side.

 

Thanks for the reply. So far I've checked most of the rear of the truck checking for looseness in suspension/drivetrain, I will definitely check the motor mounts up front and see if the if there's slop. My engine runs good but there is a slight vibration at idle so could be a possibility.

 

​​​​​​Will check that out too. I haven't touched the drums since I've owned the truck. Thanks

 

There is a grease fitting on the slip joint where the two driveshaft sections meet. Load it up. That was my clunk under the same exact scenario.