Sometimes when I let off the gas, I'll hear and feel this "clunk" under me. Like somewhere near the middle of the regular cab.

I can't tell which RPM because I don't have a tach, but I'm guessing around or above the 3k range.

It doesn't happen all the time, but a good number of times.

Any idea what it could be?

Thanks,

 

What kind of truck,transmission,engine,Etc....
It may be the transmission doing the clunk since it is in the middle of the cab...Front middle.

 

Whoops, yeah, I guess you need that.

'88 F150 XLT Lariat Automatic 4x2 99k miles.

I would gas it, and it downshifts nice to get the power, once I get to the desired speed, I let off the gas, and then the clunk.

Thanks

 

Check your spare tire underneath...sometimes as it slowly loses pressure (often with winter), the whole thing gets a little lose and will clunk on acceleration and stopping. If loose, fill it with air.

 

It can also be a u-joint. Get under the truck and twist the driveshaft. If there's play in the u-joint replace it.

 

Or it could even be the rear end itself. Mine does it also. It feels like its coming from the middle but its actually slop in the rear.

 

Worn gears. My truck does that when you put her in reverse,it makes a Clunk sound from the gears hitting one anouther. The "Twist the driveshaft." Isn't the best method to test the U-Joints. The transmission itself could have some play and allow the DS to move. Like mine,When you put it in park on a angle,when you let off the brakes,the truck moves back some 'till the transmission kicks in.

Have you ever changed your rear differentail fluid or checked the gears? How long until you last checked/replaced tranny fluid?

But it could very well be the U-Joints.

 

The twist method should be a great test for u-joints. If there's play in the trans then you'll see it. If there's play in the u-joint then you'll also see that. And if there's play in both you should also see play in both. Of course I'm speaking from my own experiences. My u-joint had lost all grease and they part of one of the caps broke off and all the bearings fell out. So the twist method was excellent. That puppy had tons of play. Not only did I have the clunk but on two separate occasions the drive shaft got bound up and the truck wouldn't move forward.

Do check all your fluids. I see you have an 88 F150. Also check the rear trans seal. Mine wore out and leaked real bad. It's real cheap and easy to fix. So are u-joints.

 

What was the final outcome? My '89 does the same thing and I only want to fix it once.
Thanks!

 

I would disconnect the driveline from the rear end and the turn the rearend yoke back and forth. It's hard to describe how much play you should have. If we use a clock, from 12:00 to 1:00 is the limit, anything over that is time for a mechanic to check it. A good motors manual might have a back lash spec.

 

When I twisted my DS,It did have play per se not slack. It did move,but not to terribly bad. Hell,90% of my truck is stock with all 197,8XX miles on it....

 

Yep, there is a little play in the trans and rear end and it could be all that Mr. Willf is hearing. As far as u-joints are concerned there shouldn't be any play, slack, or what ever you want to call it. Them babies should be solid as a rock. So when you're using the twist method you're looking for something that's just not right. A little bit of turn in the shaft at the rear of the trans is fine but if it were to move off center then that would be one of them things that just isn't right. And again, my Suburban will clunk real loud if shifting from drive to reverse (or vise versa) on a hill where there's a lot of weight resting on the trans. But there's almost no clunk otherwise.

As a vehicle owner you get used to what your vehicle is like and when something changes you're the best one to figure it out. I assume Mr. Willf has noticed something change in how his vehicle sounds and is looking for help. And again, u-joints should have no play in them whatsoever. I've replaced a couple sets of them so I am familiar with what they are like before and after a fix. As far as the trans and rear-end things, I'm just offering up the things I would think to do if it were my truck making a new clunking noise. I have never seen end play in either but it could happen.

 

How about adjusting the TV cable? Of course, this is my AOD. Is it better left up to a pro or can I get by with trial and error?
Thanks.