Have a 96 f150 302 4x4 3.54 front end. 3" lift 35" tires. Been having an issue I will try to provide as much info as possible. ANY help would be great.

Ok. A couple months ago I was on the highway going from 60mph to 70 mph I hear a knocking thinking it is the transmission I immediately let of the gas. As soon as I'm under 65 it stops. I hit the accelerator and get above 65 and it comes back. Let off the gas and fall below 65 it goes away. I finish my trip at 65 and all is good. It gradually gets me to 60 mph over the next couple of weeks. After reading a couple posts and playing with it a little I begin to think of u joints since it gets worse when I let off the gas and goes away when I accelerate as long as I stay under 60 it went away. I replace main drive shaft as well as the front drive shaft. Nothing changes.

I am driving one day last week and my manual hub locks up. I limp it home and shred everything down to the spindle. A couple of junkyards and parts stores later I get a new half shaft and spindle and put it all back together. The issue remains. Same symptoms same speeds. Until Thursday. That's when all the sudden it begins to knock no matter what speed. No matter if it is in neutral or drive. The side I replaced is locked up at the half shaft. Soooooo. I tow it home. Pull it apart. All bearings intact. So I pulled the drivers side off. Maybe a slightly crunch u joint all other bearings intact.

I am thinking if is the front differential. There is very little play on the passenger side. None at the forward shaft.

Please let me know your thoughts. Also any help finding a new differential.

Thanks.

 

If your manual hubs are unlocked and your transfer case is in 2H, your front end shouldn't be turning at any speed.
Try blocking the front end up and spinning the wheels by hand to see if you can track down the source of the noise.
Or try removing the front drive shaft to see if it goes away. Then remove the hub locks one at a time to see if it goes away.
That's all just to make sure it is in the front driveline for sure.
Or get all 4 wheels off the ground so you can put it in 4x4 and trace down the noise.

 

Great advice. Over the last couple days I pulled both sides down to the axles. I pulled both and re packed everything fresh. I put new Warn premium manual hubs on. Thought maybe I was binding and holding those axles in. I had it broken down so I figured I might as well take that off the list. Got the wheels back on and took it for a spin. Still knocking and feels like it it thumping and like it is binding as well. I try your idea. Everything is locked up int the front. Front drive shaft is froze. Along with front axles. I try to remove the front drive shaft to isolate the differential. I get it off and out of the bind....😁. Pull out and still doing it.

Feels like maybe the drive shaft. I had replaced the u joints. I even used a press for the first time. I had to replace the rear flange yoke. I plan to pull the rear drive shaft. Should I look for any thing?

 

If the front driveshaft is removed (or even if you were just in 2H) and the hubs are unlocked there shouldn't be anything keeping the truck from free wheeling and driving nice just like a 2WD.
Jacked up, your wheels should spin freely. If they don't, your hubs aren't unlocked.
Again jacked up, hubs unlocked, 2H, you should be able to turn your front driveshaft by hand. If the driveshaft is out, you should be able to turn the yoke on the diff by hand. If you can't, you either have a seized diff or your driveshafts are jammed (seized).

 

I jacked it up and it turns. All easily by hand.

So when I went to pull the drive shaft it was seized. As soon as the driveshaft released the front moved freely. I drove it again and same noise and feel. A strong "ka-chunk-ka-chunk" as the truck moves. When in forward or reverse. And it increases in sound when foot off the gas. That is all at 10mph or less.

Dropped the rear shaft and the rear joint is a little stiff. I jacked up the rear end put in neutral and worked them back and forth. Maybe a little crunch but not too bad. Barely noticeable. I am thinking of pulling the cover this weekend and checking it out. I am still baffled. Doesn't sound like trans mission? The transfer case? Does it move when in two wheel drive?

Thanks again Chris for the good advice.

 

Ok so the little crunch wast a broken pinion gear. Wow! So I replaced the ring and pinion and all the seals and bearings. What a tough job.

Truck has smoothed out a bunch. But still has the vibration/noise above 65mph. Could it be the tie rods? The sound is almost like exhaust brakes?