Prof

Ok, I am still trying to get to the bottom of a clunk in what I think is the rear end of my truck. Bottom line, I get a clunking sound when I turn at low speeds, and it appears to come from the rear of the truck.

Sound reminds me of the clunk I had for a while when my spare tire was loose, but that is tight right now and clunk is happening.

I had the truck up at a tire place, asked them to do a shake test, nothing.

So, now I am wondering if it is my differential. I was having some chattering taking off about 25k ago, so I changed the diff fluid adding the Motorcraft friction modifier in the proper amount, and hadn't had a problem till recently.

So, is it possible that the fluid and friction modifier is no longer working, requiring a new change?

This is a daily driver, 2wd, no hard driving, no off reading, no towing. Any other ideas? It has the original tie rod ends and front end as best I can tell.

AKSCREW

How do the u-joints in the driveshaft look? If you just changed the fluid in the rear end, then it is not bad already. I would suspect you have something failing internally. How did the oil look when you changed it out the first time?

ceasefire49

which wt did you put in. You know there is a service bulletin out on this that says I believe to put 90-140? with Ford friction modifier in.

corey_lax

check some easy stuff like the tailgate as well. I had a clunky noise coming from the back and ended up being the tailgate. I thought it would be something worse. I packed the tailgate hinges with grease, and lubed the latches and it went away.

Prof

Hmmm...I will check on the fluid. When I changed the differential fluid, I removed the whole cover, so I could get to the bottom of the pumpkin, and it was clean - no particles what so ever.

Hadn't thought about the tailgate, I will check that...

ceasefire49

Yep they(fomoco) discovered the original recommended oil was to light. The person I got the truck from had it(rear end) rebuilt. When I get a vehicle the first thing I do is change all fluids. When I pulled the rear cover I noticed that the cover was showing burn. I checked and thats when I found the 85 140 or 90 140 deal as a service bulletin. Full syn with that x4 modifier. I have put a good 50 thou on it and it sounds good. I used the valvoline full syn. The front Diff did not change wts. I change all fluids underneath every 60,000 so I will be due shortly.

nrivera04

You shouldn't have to do another diff service at 25k, so I would rule that out.

Something obvious and dumb... is there anything in the bed that may be moving around?

What about tight u bolts and or leaf springs?

Prof

Thanks for the responses...

Ok, the fluid I used was Amsoil 75/140; is this too light? Where the hell do I find 90/140?

I have been up under the thing, and I can't see anything that is loose, leafs are tight, spare is tight, bed appears to be tight. This only happens when I turn too, not on acceleration or deceleration, which I think rules out u-joints, doesn't it? I can't see or hear anything in the tailgate that would lead me to believe it is that, but I am going to get in there and grease it up anyway. Now, I have a POS ARE brand cap, that I guess could be moving around when I turn, but all the bumpers appear tight and I see no unusual wear...so I am still stumped.

ceasefire49

It is 75 140 and thats not even close to being to light. Make sure you put the ford friction modifier in and not the stuff you get at the parts store. Sorry about the confusion. I thought you world check the service bulletins.

ceasefire49

http://www.fordproblems.com/tsbs/F-150/2004/ Try this. Its a paid deal but here is another

http://www.ford-trucks.com/tsbs/?tsb...tsbmodel=F-150 also you can google anything on the internet.