I see you live in Canada. It's probably very cold up there like it is down here now correct? What can happen, if you drive around in the slush or in the snow in 2wd, none of the stuff up front turning, snow and slush can get up on the driveshaft and in and around the axles. It can then turn very cold and freeze and stick to the axles and the driveshaft. Then when you suddenly decide to use 4x4 all kinds of things happen when the parts with frozen snow start turning. I have also had water get into the lockout hubs like someone else mentioned and freeze.

Frozen snow and ice can also get caught up in the front calipers and rotors.

The only way to test this theory is find a place inside where it's warm that you can park it, and let it thaw and melt off.

 

I'm a little hesitant. It takes a LOT of abuse to kill a transmission like an NP435. And if you do manage to finish one off, I'd expect more of a grinding type of noise, not the bucking/knocking I heard. Before condemning the transmission, at the very least I'd want to drain the gear oil through some cheesecloth (or similar) and look for chunks of metal. Brass dust in the oil is normal.

Any chance of a rod knock or similar fault that only shows up under load? Is that possible? If so, it may not be obvious when revved in idle. Just thinking out loud, and trying to connect the dots towards a more likely scenario instead of assuming it's a part not very prone to failure. Not saying that's impossible, but rather I'm thinking of probability.

 

It has been the coldest of winter the past few days about 0*F. I started the engine and gave a few punches to 4500, and not a sign of trouble, just running smoothly. I won't rule out the engine, as it is a completely stock bottom end, with a 4 barrel carb, comp cam, headers, dual exhaust, port and polished etc. meaning the stock bottom end is taking some abuse. (I bought a built 300 a while ago and it damaged a piston so I swapped out the bottom end in a hurry.)

All winter I've kept the manual hubs locked and would help keep things moving. But water could get in anything and freeze overnight or while parked. Once I get it into the garage I think Ill pull the hubs, brakes, and maybe front axle shafts and have a peek in the diff.

I also agree it would be very difficult to break a np435. There's many claims online of people running them in upwards of 900hp and not breaking them....

Something is seriously broken with the truck though. After I recorded that video I thought I wasn't going to make it down my street idling in granny gear, it was a violent banging and jerking coming from something.

I'll see if I can rig something up to drain the oil into and see if any debris comes out. The gear oil is so thick in this cold it felt like jelly when I was checking it earlier.

 

One more thought. If all seemed well revving the engine with the clutch pedal down, try it with the transmission in neutral and your foot off the clutch pedal. Make sure the truck doesn't try to move as you let up on the clutch pedal, just in case something is jammed inside the transmission.

Neutral with the clutch pedal up will spin the transmission input shaft and cluster gear. This will help determine if the transmission is the source of the problem. It doesn't spin everything, but does get two of the three major components.

If that checks okay, put the transfer case in neutral and shift the transmission through all the gears. Let the clutch pedal up in each gear and see if the fault returns. Now you'd be spinning the transmission output shaft (and the transfer case input shaft). It's possible a fault now could be caused by the transfer case input shaft, so don't automatically assume it's the transmission. Please be aware the transmission may be difficult to shift like this, as the output shaft is normally restrained by the rest of the drivetrain, so don't let that alarm you.

Also, I'd be very hesitant to rev the engine so high, especially unloaded. I don't think I've ever taken mine over 2000 unloaded, and 3500 under load. High revs with no load is murder on the rod bearings and wrist pins.

 

I haven't thought of trying that, it might bring interesting results. I will tomorrow.

Thanks again.

 

More late night thoughts:

Playing the probability game, think about the bearings for the front differential carrier. Those bearings broke once, so it's possible the same root cause (twisted housing?) is still present and trashed your new bearings, too.

I had been thinking one of your hubs wasn't releasing, but what if it's the other way around? Maybe one isn't locking? You may not notice the lack of traction because the locker still sends full power to the locked side.

I'm not sure how a locker would behave with the transfer case in 2WD and a mismatch between the front hubs. Backdriving a locker from just one side could cause some erratic behavior, but I'm not really sure.

Anybody else got any ideas?

 

I wonder if I pull the front driveshaft and try to turn the axle shafts with the hubs off, if that will work. There is a way of testing the locker with the tires in the air but it's half in a snowbank. I'll probably have to try once I get it towed to my garage.

 

The transmission can be driven through all gears smoothly with the transfer case in neutral.

 

Groovy, you are making good progress. There's a slim possibility of a transmission fault that only occurs under load, but those odds are very slim, so put that on a far back burner.

I'm still leaning towards a problem with the front axle. Please indulge me for a moment with my crackpot frozen hub theory. I'm not sure where your 'spend time vs. spend money' indicator is currently pointing. Maybe you're tired of messing with the cold and just want the truck towed to your nice warm garage.

But if you're cheap like me and hate spending money for a tow, not to mention having to admit defeat, here's another option. If you're willing to gamble a little effort, your locking hubs should be easy to remove. It's been a while, but I think it's just six bolts and a snap ring. Then you'd know 100% that the front wheels are not backdriving the front axle and you could do a test drive. Obviously you won't have 4WD, and I don't know if that's required to get home.

Your call, just another thought.

Anybody else got any ideas? I don't want to monopolize 'Operation Help A Canadian'.

 

Im 20 and heading back for another semester of college at the end of the city startong tomorrow, and I sure hate spending money.... I'll try to have a look after work at the hubs. Perhaps if the hubs are fine and the shafts spin free I'll try pulling the rear driveshaft, drive it on the front a few feet and see of it messes around again.

 

The problem is consistent it seems regardless of 2wd or 4wd, and only when power I'd applied. For all I know the rear end has a problem. Pulling the rear driveshaft may solve it.

I'll try pulling the hubs apart and the rear driveshaft. If nothing works I'll tow it to my heated garage, put it on jack stands and try to diagnose more.

Thanks for the help this far!

 

Disconnect the rear driveshaft and try and drive it via the front driveline.

 

I found the problem before I even got to the truck. Drummmmmm roll please....







As I was walking up I seen the puddle of gear oil. You know it's oil when it hasn't frozen and it's -20c outside.

My uncle is searching his lovely junkyard for another axle. I'll post the damage whenever j get that cover off

 

Looks like you found it.

Here is from when my brother's mid-90s Bronco axle let go:

 

Circumstantial evidence at best. I'm still holding out for my fabulously thought out frozen hub theory. Are you sure the truck didn't roll while parked and that oil actually came from the front axle?