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#4548593 - 10/19/17 06:55 PM 99 suburban transfer case issues
99Burb454 Offline

Registered: 05/28/17
Posts: 47
Loc: Missouri
Hello everyone! Been a little bit since Iíve been on the forum but is good to be back. Iíve got a bit of an issue with my transfer case that has me dumbfounded. Or at least it has me confused on which way to proceed as Iíve read about several possible causes and solutions. First, the 4wd hasnít worked on my 99 suburban k2500 7.4L vin J since I bought it. It has the 4L80e transmission that I just replaced with a used one this summer while I rebuild mine(which I still havenít got to 😕) and I believe it has the np246 transfer case. So, it hasnít worked since I bought the vehicle but after replacing the transmission now all of a sudden it works except one little problem....itís stuck in 4hi and will not come out of it no matter what I do. I havenít tried to put it in anything but 2hi because Iím afraid it would just get stuck in 4lo or 4auto if I did. I have tried the R, N, D, N, R trick or at least I think I have but am unsure how fast Iím supposed to cycle through the gears or if Iím supposed to hold the 2hi button while doing so, I unhooked the VSS plugs and double checked that I had them plugged in correctly but it still will not go into 2hi. Iíve checked the case fluid and topped it off and that didnít work either. So I removed the front shaft until I can get it fixed. Ever since the 4wd magically started working a few days ago(its been months since I replaced the trans) my Burb drives very strangely, even with the front shaft removed. At about 30 mph a noticeable shudder starts and persists until around 40 mph where it turns from a large vibration to a violent shaking and it feels like the wheels are literally coming off the ground. But it doesnít do that all of the time, only after the vehicle is thoroughly warmed up( about 30 minutes). The steering becomes sloppy and seems to jerk itself to the left intermittently. It feels like 4wd steering when you turn at slow speed but the front shaft is removed and really sloppy, loose steering when turning at higher speeds. I can hear the shift motor operate and try to go into 2hi twice each time I press the button, sometimes violently, to the point that it lurches the vehicle some, especially when trying the R, N, D, N, R trick. Nothing I have done or can think of trying has helped it in any way and I need some guidance on where to start. I tried to purchase a new encoder ring but OReillys told me that there isnít one for my truck. I find that hard to believe, I think they just donít carry it. The part number I keep coming up with is an AC DELCO 600-120 but they said that that part number is only for 2003 to 2007 or maybe 2006. Not important. I had some other issues directly prior to the 4wd magically coming alive that may or may not help diagnose my problem. I was in the middle of a 2 hour drive to St. Louis when I busted a brake line and had to turn for home. The reservoir drained almost completely dry brfore I noticed the light on the dash and my pedal going to the floor. I was able to buy fluid and lump her home but Iím afraid sucked an awful lot of air into the master cylinder. I fixed the brake line the next day and bled the brakes. After fixing that I took a drive and everything was fine until it started the shudder I described earlier. Oh, forgot one detail, when I backed out of my driveway one of the wheels fell plumb off cuz I was lazy and didnít take wheels back off to check torque on the wheel spacer lug nuts when I repacked hub bearings with grease a couple months ago. Please help, Iím at a loss and this old girl is a show truck of sorts and Iím missing shows while sheís out of commission. Thank you. Hereís a pic of my old girl just because
1999 'Burb 2500 LT 7.4L 454-4" suspension lift, 35" Nittos, running boards and dents in the hood from idiots at work. Always ISO of mods. Lmk

#4548622 - 10/19/17 07:42 PM Re: 99 suburban transfer case issues [Re: 99Burb454]
eljefino Offline

Registered: 06/15/03
Posts: 32214
Loc: ME
As for the shudder it sounds like your front axle is engaging the hubs or maybe just one hub via vacuum.

#4548709 - 10/19/17 09:04 PM Re: 99 suburban transfer case issues [Re: 99Burb454]
Kuato Offline

Registered: 10/23/05
Posts: 7094
Loc: Colorado
Sounds like new/replacement/rebuild yours transfer case is required - if it won't shift there is something stuck inside. Agree with the possibility of vacuum engaging the front hubs, which, even if the driveshaft is disconnected, could cause some issues on dry pavement.
Thick vs Thin test: 15k / 43k miles complete

#4548774 - 10/19/17 11:17 PM Re: 99 suburban transfer case issues [Re: eljefino]
99Burb454 Offline

Registered: 05/28/17
Posts: 47
Loc: Missouri
Vacuum engaging the front hubs? Itís got an electronic actuator, where would the vacuum come into play? That intrigues me if mine truly does have a vac connection somewhere
1999 'Burb 2500 LT 7.4L 454-4" suspension lift, 35" Nittos, running boards and dents in the hood from idiots at work. Always ISO of mods. Lmk

#4551692 - 10/23/17 07:30 AM Re: 99 suburban transfer case issues [Re: 99Burb454]
wtd Offline

Registered: 06/25/02
Posts: 1873
Loc: southwest Mo.
That truck does not have vacuum operated front hubs. As far as your problem goes, I would say your transfer case has an issue.
2014 Mustang GT
1998 Chevy K3500
1998 Chevy K1500
(2) 1992 Cavaliers
1970 Monte Carlo

#4552256 - 10/23/17 06:02 PM Re: 99 suburban transfer case issues [Re: 99Burb454]
AVB Online   content

Registered: 05/20/12
Posts: 1104
Loc: Georgia
Normally it is the encoder motor that goes out, but it could be something else.