how do I diagnose knocking in 4x4 system?

[bhawk]

94 ranger 4x4, manual trans with manual hubs. Ever since my son got the truck we get knocking sounds in the driveline when the front hubs are locked. The knocking noise is most prominent when the truck is cold and you first get going. It knocks when cold even without the transfer case engaged. The knocking sound reduces considerably when the truck has been driven for 10 miles or so (this is when the hubs are locked but the 4x4 transfer case is not engaged).
Once the knocking is not very noticiable with hubs locked but TC not engaged, the knocking returns loudly when we engage the TC in 4x4 mode. The knocking is always there with the TC engaged in 4x4 mode, but as I say, if the TC is not engaged it is reduced considerably after the truck is driven some miles.
I have replaced all 3 U joints in the front axles, no change.
I replaced the double cardan U joint near the transfer case, no change. ( I will say that 2 of the 3 front U joints were in bad shape and the double cardan joint was poor as well before replacement).
How is the best way to isolate and find the source of the sound????
I am thinking of things like----raising all 4 wheels off the ground on jacks and running the system??? dangerous??---or taking the front driveshaft off and running the truck cold to see if the knock is affected??---
I did try driving with one wheel hub locked and the other unlocked. The noise is gone with only the one hub locked and the TC not engaged. But when I engage the TC in 4x4 mode, the knock returns even with only one wheel hub locked. Help!

 

[bhawk]

Well, an update.
I crawled under the truck a few minutes ago and find the front drive shaft near the double cardan U joint makes a knocking noise when I lift the shaft up and down. Should that joint make a noise when I lift it up and down?
Anyway, I removed the front drive shaft and drove the truck with the hubs locked. The knocking noise is gone.
So, another question arises.
Q. Can I engage the transfer case in 4x4 mode without a front driveshaft hooked up?
I would like to do this to see if I get any noise when the transfer case is turning the front output shaft.

 

[rkneeshaw]

What about the stand alone u-joint in teh front drive shaft? did you change that?

The front drive shaft should have 3 ujoints total: 2 in the double-carden joint, 1 directly behind the front differential.

If you grab the drive shaft and push it up or down while it is all bolted into place there should be no play in it at all.

 

[bhawk]

I got the front shaft on the bench now and the ball and socket setup in the middle of the double cardan U joint appears shot, again. So, I'm going to find a complete used shaft and swap it in see what happens.

 

[cmattina]

I am hoping to bump this thread as I am having the EXACT same problem on my 93. I DO NOT want to spend as much time chaning u-joints for no reason. I'm surprised that my symtoms have been described right to a T.

 

[ab_slack]

I am hoping to bump this thread as I am having the EXACT same problem on my 93. I DO NOT want to spend as much time chaning u-joints for no reason. I'm surprised that my symtoms have been described right to a T.

Have you gone underneath yet and manually rotated the front drive shaft and the two side shafts out to the wheel? Made sure all turn freely (while TC case in 2WD and hubs unlocked)? Pushed against them laterally and made sure there is no obvious play?

Those are the first and easiest checks to do.

 

[randyw]

Ok so instead of starting another thread with related issues I'm bumping this one.

Problem- I aswell experience a popping sound from the front when locking in the 4wd, but mine doesn't seem like it's locked in while it's popping. The truck will kinda jerk alittle then after a few minutes of that it will stop and be fully locked in, but every once in a while it will pop and what seems to be popping out of 4wd.

It's a 94 4.0 5spd with the original automatic hubs, after searching the issue I'm thinking the auto hubs could be the problem. Hoping for just a ujoint(s) being the issue I wanted to see if anyone else had experienced this or had any thoughts. It's too cold and to much snow to try to crawl under it to inspect the ujoints and shaft right now.

Again just asking if anyone else has experienced this before I get frost bit layin in snow trying to track down this problem and thacks for any help and advice.

 

[cmattina]

For my problem...

I ended up being the radial arm plate. I wasn't super surprised because after changing one of the front U-joints no difference was made. I took it to my mechanic who is pretty good (been doing it for 40 years), and he said it took him a while to find the problem. My bushing were good, by the way, the metal was worn into an oval.

They replaced the plate under drive's side underneath the floorboard. Being in 4x4 simply exasperated the problem.

They told me they found the problem by parking the truck and phsically rocking it.