1999 Suburban Trans Vibrations???

I own a 1999 Suburban 4 X 4 with 120K miles and has original transmission. I just replaced u-joints on front drive shaft since I was getting some noise and vibrations. While underneath the truck I noticed transmission oil on the truck underside. It is located directly above the transfer case and looks like it's new. Didn't see any trace of oil anywhere else not even on the transmission. When I took it out on the highway I could feel a small vibration coming from the transmission at about 50mph. This vibration comes and goes but if I step on the gas to go faster or when going uphill it's worse and consistant. Now I'm awaire GM has problems with these transmissions and one common problem is a valve inside. I've read that once you feel this vibration it's usually too late to repair and a rebuild is the only way to fix. Oh yes, my check engine light is on and will have a code reader put on it. Anyone out there who can help me or educate me please? Thanks for any help.

Sounds like what a bad planetary gear does, I had the same thing happen and it cracked the rear of the trans case.

Thanks for the info. Now my 4x4 doesn't work in 4Hi or 4Low but it works in 4 Auto and all the lights are working. I can hear it engage especialy in 4 Low but it stays in 2wd. And yesterday to top it off after driving 12 miles on the highway, I got to a stop and all my drives where dead. No 2wd, no 4wd forward or reverse. So I turned off the engine waited a few minutes and restarted it. Everything was ok on 2wd but still dead on 4wd. I'm thinking also the transfer case so I'm gonna take out the T-case and put it on my work bench. Time to open it up to inspect and rebuild, unless it's damaged beyond repair.

T-cases are pretty solid,On the NP241 check for bent shift forks, some are stamped steel and they bend easier than the cast ones, If its rebuildable think about a thicker chain upgrade & a slip yoke eliminator ( requires drive shaft mods though) Hope you figure it out.

Ok, thanks for the good tips. But I have the electronic shift T-case ( Auto-Trac ) and maybe you would know why I can get it to work in 4 WD Auto but not in 4Hi or 4Low. In 4Low I hear the clunk when I press the button while in neutral slightly rolling. I also read somewhere in another thread that these switches especialy around my year (99) go bad quite often. Anyway winter is around the corner here and they put so much salt on the roads that vehicles get a beatting. I'm gonna have it parked for a while so I can do some work on it and do things right.

There is a code for trans slipage. And usualy means a new valve body is in your future. Does anyone know if GM actualy improved the design if you buy a new valve body?

possible solution here check this out

http://forums.vmag.com/suvsuburban0501/messages/1602.html

OR

http://www.atcdg.com/TechBulletins/bull_152.htm

I am having this same problem in my '99 3/4 ton. I hit about 65-70 mph and the vibration comes in strong, but only under a load. When I let of the throttle it diminishes alot. When I bought the Burb there was a chattering noise coming from the transfer case, kind of a loose bearing noise. The people I bought it from had it fixed so I dont know the details of the repair. That same noise is starting to come back AND the vibration is much worse now. I think they had the output bearing replaced on the Trans. case but Im not sure. I doubt any major work was done to because it was repaired in a day or two (before I picked it up).

Anyway, Ive been reading all the threads about vibrations at 65+ mph and this thread hit home.

GMCMudBogger - you mentioned planetary gears and a cracked case...My Trans Case has a repaired spot on it that I noticed a year or so ago. Its a crack towards the rear of the case about 5-6 inches from the output shaft, mid way up the case. It had been repaired with JB weld or something like that.

Is it possible my transfer case has had a broken chain or gearset? Maybe bearings that never got replaced when and if these things had happened in the past?

Sub5 - Did you ever solve the problem with yours?

I am glad I found this post cuz this problem has been bothering me since the week after I bought this car.

Thanks

I am having this same problem in my '99 3/4 ton. I hit about 65-70 mph and the vibration comes in strong, but only under a load. When I let of the throttle it diminishes alot. When I bought the Burb there was a chattering noise coming from the transfer case, kind of a loose bearing noise. The people I bought it from had it fixed so I dont know the details of the repair. That same noise is starting to come back AND the vibration is much worse now. I think they had the output bearing replaced on the Trans. case but Im not sure. I doubt any major work was done to because it was repaired in a day or two (before I picked it up).

Anyway, Ive been reading all the threads about vibrations at 65+ mph and this thread hit home.

GMCMudBogger - you mentioned planetary gears and a cracked case...My Trans Case has a repaired spot on it that I noticed a year or so ago. Its a crack towards the rear of the case about 5-6 inches from the output shaft, mid way up the case. It had been repaired with JB weld or something like that.

Is it possible my transfer case has had a broken chain or gearset? Maybe bearings that never got replaced when and if these things had happened in the past?

Sub5 - Did you ever solve the problem with yours?

I am glad I found this post cuz this problem has been bothering me since the week after I bought this car.

Thanks

If your transfer case chain was broken, for one, four wheel drive wouldn't work that's for sure, you would hear all kinds of snap crakle & pop. I have heard of cracked bell housings on newer Burbs, I wouldn't think it wise to use JB weld to fix a tranny housing that's like a band aid on a bullet wound!

If your transfer case chain was broken, for one, four wheel drive wouldn't work that's for sure, you would hear all kinds of snap crakle & pop. I have heard of cracked bell housings on newer Burbs, I wouldn't think it wise to use JB weld to fix a tranny housing that's like a band aid on a bullet wound!

To clear things up, No, the chain is not broken now. I would know that for sure, but I have been trying to piece together a likely reason that the transfer case would have a repaired crack (i.e. JB weld spot). Thats the mystery here. I did not put the JB Weld on to fix it, I assume the previous owner did. Thats all I was saying. The Burb runs good as far as 4 X 4 goes. It just has that annoying vibration at 65-70 mph. Regardless of whether Im in 4WD or 2WD.

I have been trying to isolate the problem for a while, when I have time to. I had the drivelines checked and balanced. Everything was good there. Brand new set of Michelin LTX tires. Vibration still there. I am curious if I may have a loose yoke on the transfer case output shaft. What do you think? If there is any play (side to side or back and forth) in the output shaft, could this cause a vibration like this? Is there an acceptable level of play for the output shaft? Or should everything be tight?

You mentioned a bad planetary gear earlier in this thread. Could this vibration I am having be in the transmission and not the transfer case?

YOur 3/4 ton does it have a 246 transfercase? Just had mine out. There is a oil pump in it that put a whole in the tail shaft mid way up closer to top side. CHevy needs to address this anyway you should get a new back half to the case and as far as the vib Check your steering pitman,and idler arms! My 99 3/4 454 4x4 had all your same problems. Let me know what you find or have found.