np203 vibration


I have a 78 3/4 ton 4x4 and has the ol np203 that was converted to part time shortly after it came off the dealers lot in 79. Anyway, When driving the truck which has the 400 cuin with turbo 400 tranny, above 60, the transfer case shift lever begins to vibrate, the faster over 60 the worse the vibration gets, and I am wondering if there is something about to crap out in the transfer case. The 4wd still works good, no problems to speak of, I am just not sure about the vibration. Is it normal? Do i just need to accept the fact that driving over 60 is just not a good idea in my truck??<br>anyone with real knowledge of what i am refering to please get back with me..<br>-abe<br>

Alan Addict
I'd go looking at U-joints first. In particular that &quot;Cardin&quot; (I think that is the name) double joint right ahead of the case. The front drive shaft freewheels even with the part time conversion and with no torque load on it the joint could be loose and shaking. Try leaving your hubs locked and shift in and out of 4wd at the speed you get the vibration. Don't leave it in too long but see if the vibration changes appreciably when you load the front shaft. Check the whole drivetrain for anything loose or stuck. My son had a vibration start in his 97 from a u-joint that was frozen from rust. His ended up taking out the transfer case housing from the strain of the frozen joint.


Senior Member
Alan has the right Idea, Check the U-joints. Also make sure you check the front drive shaft. The constant velocity joint on the front drive shafts can cause this type of vibration. Also the splined shaft can get very sloppy. I would concentrate my efforts on checking the rear drive shaft U-joints. I would remove the shaft and check it that way.


Yes Alan, it's a Cardan joint. Yes yortengel, the slip yolk spines do get worn. Being that Abe has a 78, the rear driveshaft has a slip yolk on it as well. The driveshaft is bolted in on both ends. Unlike newer models, where the slip yolk is where the rear driveshaft slides into the t case.<br>Check for &quot;side to side&quot; play at the slip yolks. DO NOT ENGAGE 4WD at the speed the vibration occurs (you said 60 mph?).<br>I can say that my splines are worn on my 80 GMC's front driveshaft. Doing 60 on the highway, the shifter does vibrate. The hubs are unlocked. There's a but here..... it has the NP 205 t case in it. This leads me to believe that the front shaft has worn u joints, slip yolk, or the shaft itself is unbalanced. I wouldn't worry about it if everything seems to be ok. If parts are worn, replace them.<br>Alan, I replaced most of my front end, trying to find a problem that turned out to be the right front axle u joint being siezed.<br>New centerlink, ball joints upper and lower, tie rod end, drag link, steering box, then found the u joint locked up. Funny, the problenm I had was in 2wd, doing 20 - 40 mph. For no reason, the truck would pull hard right. I couldn't stop it. Then I could go again, it may happen 10 minutes later, an hour later, or a minute later. That one was fun to diagnose!!<p>~Chuck<p>----------<br>Chuck's Chevy Truck Pages - Snowplowing Central<br>


Junior Member
I had the same problem, I shimmed the gear with rubber donuts but the gear shift soon loosened. I probably have to get down there and tighten again.


Well, I appreciate all of your responses, sorry it has taken me so long to get back and tell you all what has happened, but I took a vacation and when I returned I decided to take a closer look at my drive train.<p>I checked the drive shaft for play, no slop<br>checked front shaft, no slop<p>decided to remove rear shaft just to take a peak and see if there was a froze knuckle or something, and to have drive shaft rebalanced if necessary.<p>Pulled off shaft and found the front u joint, the one at the transmission, one knuckle was missing all bearings and was in need of replacement, so I purchased both new u-joints and reinstalled shaft, problem solved.<p>YOU ALL WERE RIGHT!! THanks for directing me to the problem!!!<p>-ABE

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