Strange Noise that has me baffled.
 

I am hoping someone can help me.
I have a strange noise I am having a heck of a time diagnosing.

The noise only starts after I drive the truck for at least 40 minutes on the expressway at speeds above 65mph. Its like a clicking noise and definetly in time with my speed. I slow down and the noise gets slower, and louder. I stop it stops. I shift the tranny into nuetral, no difference. Still makes noise. I throw it into 4hi on the fly and the noise instantly stops. If I crusie around town for 15 minutes the noise goes away at a stop, until I make the 40 minute trip on the expressway again. I think it is heat related, and I think it is in the front differential. It sounds like its coming from the passengers side, however I have replaced everything on the passengers side. CV shaft, hub assembly, and brake caliper. I thought this fixed the problem, nope.

Couple of clues are pointing me to the diff, however I am not positiveits in the diff.
Heat related.
4hi instantly stops the noise.
Nosie even with the tranny in neutral.

What in the diff could it be? If its not in the diff, what could it be?

RE: Strange Noise that has me baffled.
 

What kind of a click is it? Loud, medium, quiet? High pitch/low pitch?

Maybe your 4x4 actuator is slacking off...

RE: Strange Noise that has me baffled.
 

That's what I was thinking. Something in the front axle engagement actuator getting too close...

RE: Strange Noise that has me baffled.
 

Saw a thread with similar symptoms on another board, maybe U-Joints heating up/going bad?? just a shot in the dark.

RE: Strange Noise that has me baffled.
 

Its a hard noise to describe.
Its like a plastic noise. Kind of like putting a card in your spoke when you were a kid. The faster you went the higher the pitch, the slower you go the louder it gets and the clicking becomes more prononced.

I drive every day on the interstate for at least 8 miles and it doesn't make the noise. Then when its my day to drive the carpool, I do 55-60mph for the 30 miles on a back country highway and no noise. But when I get on the interstate for the 30 miles @ 68-70mph. I slow down and the noise starts instantly. Pop it into 4hi and it instantly goes away. [sm=headbang.gif]

I have been trying to break it, so I know what it is.

RE: Strange Noise that has me baffled.
 

Seems like it could be a Joint going bad. When you put tention on the front drive it goes away (hence not loose any more) but while its disengaged it has the free play to make the sounds again.
With the wheels chucked, truck in park and turned off. Get under there and try to move around the front drive shaft. See if you find any play and/or clicking.
Next I would check to ensure that the frontAxleis actually disengaging also. It might not be unlocking thefront axlelike it should, so you are slowly over heating the locker. With it doing this in N also, this would be my main check. Due to it might be trying to pull the Axle out of lock with the increased vacumm, but unable to due to its STUCK. This is a plastic retainer on the Axle with a Cable to the inside of the Pumkin.

RE: Strange Noise that has me baffled.
 

I would agree with MNHawk I read about this on another forum and the actuator is not disengaging the front axle, parts are worn internally in the front diff....

RE: Strange Noise that has me baffled.
 

Possibly drop the front drive shaft and see if the noise remains. Won't hurt a thing and it would help you narrow it down to the shaft or the front axle...

RE: Strange Noise that has me baffled.
 

Hanr3, You say when you put it in 4wd it stops, but you have not stated if when you put it back in 2wd if the noise re-occurs or not. Does it come back right away or does it need the drive cycle again? I am researching this problem on a tech. site, and will let you know if I find anything, but it does sound like the front axle actuator is allowing the front axle to slightly engage. Korey

Hanr3, I want you to pull vacuum from the front actuator. I read about the vac switch going bad and allowing a slight bit of vacuum to the front actuator. so if you pull vac to the actautor where it cannot engage at all, and see if the noise still comes on. If it does not then replace the vac switch on top of the t-case. Let me know what you find. Korey.

RE: Strange Noise that has me baffled.
 

Yes, if you go from 2wdr to 4hi to stop the noise and then pop it back into 2wdr it will make the noise. It will stop only after the truck runs at slowerspeeds for a while.

I'll take today for example.
I drove to work and we took the back roads, highway.
On the way home I was doing 70mph the whole way. Slowed up a couple times for traffic. Made couple90degree truns (reduced speed to 10-15mph). 25 miles of that, couple miles at 55 with a stop to drop off the carpool. Then8 miles at 74mph on the interstate with crusie control on, couple at 55, and the last 2 at 40. Not once did it start making the noise. Variety of speeds and engine rpms.

However, the vacuum bleed makes some sense. Since the vacuum for the t-case comes off the engine, longer periods of high rpms (2K) could be causingthe problem. Sound reasonable?Tomorrow I have to drive to the next town (town I work in) 40 miles for my sons track meet. Typically it will act up when I make this trip on the interstate (long period of high rpms). If/when it acts up, I'll pop the vacuum line off the t-case and see if that instantly fixes the problem.

Where should I pull vacuum for the vacuum test?
Thanks for the help.

To be honest, I am not looking forward to tearing into the front diff just to look and see. Plus the vacuum switch is a quick and easy fix. At least compared to tearing into the front diff.

Edited: I just reread your post. If I understand it correctly. Pull the vacuum line off the front actuator verse taking a vacuum reading. I can do that before our little trip tomorrow. Then if the noise doesn't come back (no vacuum to the actuator) most likely the problem lies in the vacuum switch. That makes sense.