Partial engagement front axle while in 2wd???

[Torskdoc]

2002 CC 4.3/4L60E/3.42/ZR5/255-70R15


I was driving from Baltimore to Frederick this evening(50 miles or so). Got to within 3 miles of destination and heard sound like extreme tire noise on road from right front. It was definately speed related. As I slowed down the frequency of the sound went down and stopped when the truck stopped. Below 20mph it sounded like 2 gears grinding against each other. I took a look for loose stuff, found nothing and took off slow.

The noise stopped. About a mile down the road it started again. Stopped the truck at the light and the noise stopped. Started up truck again. No noise. Went about 2 miles and the noise started up again. This time I took a shot and engaged 4wdHI at about 40. NOISE STOPPED. Shifted back to 2WD and the noise stayed off for the rest of the trip (3 more miles). WTF!?!?!?

On the way home, it started up again. I shifted btwn 2wd and 4HI and back and the noise stopped. Had to do this 4-5 times. Slowed down to 40mph on interstate to do the shiftConditions to aggravate above problem.

1.) Moving in fwd gear accelerating or maintaining strain on drivetrain (not slowing down or coasting)
2.) 2HI engaged.
3.) Slight upgrade, enough to keep 1/3 to 1/2 throttle and maintain speed.

Problem does not start while on level ground or downhill.

I did do a quick listen for actuating of the TC and axle while sitting, engine oon, trans in neutral, e-brake engaged.
1.) Shift from 2HI to 4HI creates 1clunk
2.) Shift from 2HI to 4LO creates 2clunks.
Shifting back to 2HI sounds same.

It sounds like to me that the slider gear in the front axle is being partially engaged(pulled far enough to grind on the shaft gear to lock the axle.)

This leads me to a couple of ideas? All vacuum related. I didn't see any vacuum hoses disconnected or partially torn on quick inspection and diminishing light (5:30pm)

1.) vacuum ball has a leak....(I don't think so as my HVAC system vacuum actuators work ok. No delays on change from AC to Heat to Def)
2.) vacuum hose to front axle shift actuator has a leak....
3.) Front Axle Shift actuator diaphram has a leak....
4.) Actuator cable end is damaged allowing gear pack to partially engage.

Gonna Check the vacuum lines in the morning. I'll post further then.

You think I'm on the right track??? Anyone have anything like this happen to their truck????

Thanks

Larry

[HenryJ]

Front axle partially engages *solved*

[Torskdoc]

thanks HenryJ. I'll check it when I get back from the "boat"(volunteer on a WWII Diesel Sub in Baltimore) later today.

Larry

[Torskdoc]

Checked all the vacuum lines with gauge and pump. All hold 20" for 10 min. Vacuum actuator holds same.

The vacuum hose connection on the t-case appeared to have backed off some, so pulled it off and re-seated in correct orientation.

Cable was notchy (dry?) so I ran some cable lube down the end. Now smooth.

Put it all back together, ran it on I-97 from Balt to Annapolis and back. NO BUZZ, GRIND, etc. So think it's ok for now. Will keep an eye on it and call it cured if it works right next week on trip to Norfolk and back.

Thanks for the help.

Larry

[Torskdoc]

5 weeks later, 1600 miles, Ice, Snow, Idiots and Morons that don't know or don't care that traction on snow and ice is about non existant. WHAT FUN! Honda's and Jeeps going 70 in the snow....SIDEWAYS and backwards!!! (But officer, the speed limit is 65......)

Anyway, the problem hasn't raised it's ugly head. There might be something to add to your regular maintenance program. Disconnect the Vacuum can from the Diff Cable and lube the cable with PB Blaster and then a shot of 3 in one oil or a very light weight multi. 0W-20? Also reseat the Vacuum valve on the Transfer case. As it's a press fit and the vac. lines are taped together and not much slack, movement of the engine laterally could cause the connection to come loose.

Will keep an eye on it and report any further problems.

[Rich K.]

This thread is old but I thought I would query for any further input. I'm having problems with my 4 wheel drive and I am wondering if this is a part of the problem.

Ever since I installed my 2" BL, my 4X4 is intermittent. I narrowed it down to the front differential and suspect the actuator cable. The vacuum actuator functions, but the front diff may or may not engage right away, but will engage eventually. The cable is not strained even though I reattached the actuator to the original location after the BL, but Iv'e seen stranger. I checked to make sure my front drive shaft is rotating after engaging the 4hi or 4lo so I know the transfer is engaging.

All this said, I have an intermittent "buzz" coming from the transmission/front differential area. It isn't there constantly, but when it is there it "buzzes" consistently with the shifting of the transmission. It started after I returned from a long trip to OK City. I didn't hear it all last week, but then I had to engage my 4 wheel drive one morning and later that day the "buzz" started again and hasn't quit since. Another thing that concerns me is that the "buzz" doesn't go away if I engage the 4 wheel drive.

One day I will plan on installing the manual shift cable to replace the actuator, but I am saving up for the Boise springs for now.