My truck makes a clunk noise when I put it in gear,but my truck also jolts when I give it gas.When im driving and I get back on the gas after letting the truck coast,you can feel like a jolt.I'm assuming theres slop in the differential.I don't want to fix it unless I have to,but since I tow stuff with my truck.I'd rather know what it is,and if towing will put more stress on that area of the drivetrain.Also all my u joints are tight.When Im driving on a smooth street I can hear a humming noise,but might be the ATs.Thats what Im assuming but I can only fix stuff.I couldn't diagnose I problem if my life depended on it.

Thanks in advance

Its a 77 150 351m with C-6 and part time 4x4 if it matters

 

Not sure if its going to help but this is taken from a Haynes manual for 1980-1996 trucks ( I know your is a 77, just trying to help).

Knock or Clunk when the transmission is under initial load (just after transmission is put into gear)

1. Loose or disconnected rear suspension components. Check all mounting bolts, nuts and bushings.

2. Loose driveshaft bolts. Inspect all bolts and nuts and tighten them to the specified torque.

3. Worn or damaged universal joint bearings. Check for wear.

I know the year is different but again just trying to help.

 

There is another thread with what appears to be the same thing you are describing. Maybe that will give you a couple of answers or good leads to follow.

https://www.ford-trucks.com/forums/6...-to-drive.html

 

jack up one of the rear wheels and rock it back and forth and see if there is a lot of play or if you hear the clunk. If not jack up one of the front wheels and do the same.

My 77 is a 2wd and a clunk came from the centerline bearing yoke binding due to a sloppy bearing. I replaced the bearing and lubed the yoke and the clunk went away.

About ten years ago I developed a pronounced clunk in the torque converter or the tranny. This thing would clunk when you let off of the gas and stepped on it again. It would also clunk when you decelerated to a stop and stepped on the gas to take off. I found out what it was by climbing under it and putting a wrench on one of the torque converter mounting bolts. You could rock the torque converter back and forth about 15 degrees and hear the clunk. Take your spark plugs out so the engine will turn a little easier. I had the tranny rebuilt and the problem went away. The tranny shop never told me what was wrong, but I did see on this forum where one guy said these early trannys had a plastic thrust washer that would break and fall out and would create slop in the tranny. Maybe that was the problem with mine.

 

"Centerline bearing yoke"

Is that the middle u-joint?

Thanks

 

Check your motor mounts and transmission mounts too.

 

btoohey44

Thanks for your suggestions
I check all my suspension components and there all tight.I also tightend the u joint straps on the yokes and they were all pretty tight too.My u joints don't seem to have play in them either,but then again I aint putting near as much muscle on thos u-joints as my engine is.

Whatever it it I just want to know whats causing it, so I thank both of yall for the help

 

Hey thats right Ive never thought about the engine mounts.Tomorrow Im just going to tighten ever bolt throughout the drivetrain to rule a loose component out of the puzzle.

Thanks for pointing it out lv2race

 

Yes, since you have a long bed there should be a yoke at the back of the tranny and another yoke behind the centerline (or center support) bearing. This was the one I was having problems with. Some people never lube them and they start jamming up. Sometimes the even get damaged due to the lack of lube.