Here's the truck in question and a nice picture to go along

85 f150
Decently built 300
Np435
Bw1345
8.8 open rear
Dana 44 with aussie drop in locklocker, new carrier bearings and new quality u joints.
35 inch tires.

The last few days the truck had a rare slight vibration/dragging that went with wheel speed. I was leaving work tonight and had to make a 3 point turn to leave the parking lot. I started my turn and it seemed to be still in 4x4 but hard to tell due to the ice in the lot. I made sure the shifter was in 2wd and finished pulling out. Hit the pavement and it was for sure in 2 wheel, I hit the gas and between 2nd and 3rd gear, there was a seriously loud bang. I stopped and unlocked the hubs, a quick peek underneath and everything looked fine. It had a clunk the wgile way home, increasing with wheel speed. I won't push it past 50kmh/30 mph.

I got underneath with a flashlight:
-Both driveshafts and u joints are intact and look good.
-The front axle shafts are fine and not loose.
-With the hubs unlocked and transfer case in 2wd I can turn the front driveshaft smoothly and the axles turn accordingly.
-Can't see any damage or anything out of place, but it is dark out.

Another 2 months ago I installed the drop in front locker. I pulled the carrier and the bearings were very bad.
I took it to my college and pressed new Yukon bearings on, keeping the old undamaged shims on their correct side. New cups/races were installed. The housing is smaller than the carrier to have bearing preload, and is usually installed with a case splitter. In order to get the carrier into the diff housing I heated the housing warm to the touch on my wood stove and a few light hammer taps had it in.
Because the old shims were used and I used Tha same carrier, the gears should be "set up" the same. The front diff may not have been what went bang anyway but theirs the story behind it.

I'm wondering if anyone here has had this happen or any guesses as to what it could be.

 

Wow... I guess you weren't able to discern a general location from where the noise originated?

 

It seems to be in the front end, definitely not the back. Can't tell which side if it is a specific side.

 

When you first heard the bang, you were in 2WD but with the hubs locked, right? Then you unlocked the hubs and drove home, but still had vibrations and noise. I wonder if the internals of the hubs had frozen so at least one stayed locked, even with the **** turned to free. If one hub hadn't released, could that have caused the locker to act up?

Later you crawled underneath and reported you could freely turn the front driveshaft. In 2WD and with the hubs unlocked, that's exactly what you should see. However, was the truck now inside the garage with that nice woodstove blazing? If so, a frozen hub could have thawed out and fully released by then.

Not sure what kind of hubs you have, but most manual types don't directly lock/unlock when you turn the ****. The **** merely loads or unloads a spring that controls the actual locking mechanism. Once you roll a short distance and the splines line up, the spring-loaded mechanism takes over and they lock or unlock, as requested. The downside is if the locking mechanism can't move freely (frozen moisture, for example), nothing happens even though you'd turned the ****.

That's my story and I'm sticking to it...

Have you driven the truck since confirming you could turn the front driveshaft by hand? If the problem is now gone (still in 2WD), that would support my frozen hub theory.

 

That's a good idea about the frozen hubs.

Maybe the locker unlocked very harshly as I was shifting and one manual hub is frozen. I'll investigate tomorrow morning. Everything seems to be working but it was clunking all the way home, and it's fairly colder tonight than the past week or two.

The truck hasn't been in the heated garage on weeks, the stove was used to expand the third member enough to get the carrier into it 2 months ago when I assembled the locker and front end.

I apreciate the input.

 

Karl is correct in his description of the spring and how those things lock/unlock, you have to roll a bit after turning those *****.

 

The mystery depens.

I took the truck out for a quick drive and it had the clunk to it. As I drive it for a while 20-30min it quieted down and was nearly gone. 4x4 still works properly. However I now get a rattling/ticking whenever I hit the gas, regardless of what gear, 2hi or 4hi. It sounds like it's coming from the tranny or transfer case. Both diff oils and yhe tranny are full, I will check the transfer case tomorrow.

 

Are you sure that rattling/ticking isn't the engine pinging?

 

Are you sure the noise is new? Or could it be something that was always there but now you're listening in hyper vigilant mode? Been there, done that...

For the noise, try applying gentle pressure on the shifters and see if that quiets it down. Don't do that all the time, as it will wear down the shift forks, but it's fine for some quick troubleshooting.

 

I will tell of a strange thing that happened to me but nota Ford truck but to show the strange part.


At times when making tight turns like in a parking garage looking for a spot to park I would get a binding like the truck was in 4x4 mode but was not. No way to un-lock hubs as you flip a switch on the dash for 4x4 and it locks 2 side front axle.


I would have put money it was a front CV joint, yep not Ujoints. Dealer found a bad CV joint on the front drive shaft the cause. Because 1 side of the front axle stays connected the drive shaft turns all the time. I think when making a turn the shaft turned slower or faster to make it bind.


Some thing to think about if the hubs not unlock and front drive shaft keeps turning.
Dave ----

 

It's definately not the engine pinging...

I'm uploading a video of the noise, will post shortly, it seems to me my np435 has seen its last drive...

 

The engines drowns the sound a bit bit you can clearly hear it if it uploaded properly.

Just after I stopped recording I went to turn down my street and it began bucking and banging really hard. I barely made it the 5 car lengths in granny gear to my spot. It banged really loud about every second shaking the truck every time. I'm thinking the trannys toast.

I'll have it towed the 20 km to my garage pull the tranny and see what happened.

 

Are you sure that's the transmission? It sounds more like a rod knock or wrist pin.

That would be easy enough to isolate, by revving the engine while stationary with the clutch pedal down. I'm assuming you already tried that? I kept trying to read the gauges in your video. Is the factory oil pressure gauge inop? Either that or you've got very low oil pressure. I saw the three gauges below the dash but couldn't read the labels.

 

I disconnected the factory water and oil guages and used the holes in the block for aftermarket guages. I stopped it at a few frames and the oil was reading 45 psi, which is where it normally sits while driving.

The engines running smoothly. Shortly after starting it I had it revved up a bit to warm it up before recording that. I didn't notice anything wrong with the engine. The trucks misbehaving when in gear and on the gas. Throttle amount doesn't matter.

I'm thinking it isn't the locker or hubs as it would do it when turning corners or cruising in neutral. When in 2wd the front driveshaft is free to turn.

I don't think it is the transfer case. It only misbehaves under throttle.

 

I'll start it up tonight and check for a rod knock as mentioned.

The transfer case was still working properly between 2hi and 4hi on a snowy road.

I appreciate the input guys.