1977 gmc grande sierra k25 350 th350 np203. front drive train clunk !!!help!!!

[ruedger455]

Hey guys, i have a big problem. Today i started messing with my 4x4 on my 77 grande sierra. And when i went in reverse in 4hi it started making a loud metal clunking noise! I have the np203 t-case and i also have locking hubs. How do i know if the previous owner put in the part time kit? Now i unlocked the hubs and put it in hi-loc and now it clunks when shifting into reverse or drive. And it clunks when i get on the gas and stopping while driving. Could my tcase be low on fluid? Or could something be broken? This has me very upset i just bought this truck last week. Let me know what you guys think.

 

[ruedger455]

Also when the hubs are unlocked if i put it in 4 hi it goes no where and the front drive shaft clunks hard and spins and it sounds like a train wheel on the track. That metal to metal sound.

 

[ruedger455]

No one can help me out?

 

[Stroked]

I have absolutely ZERO experience with 203 transfer cases, so I'm not much help. But if it won't move with the hubs unlocked in 4-high then that tells me it doesn't have the part time kit installed.

Can you tell if the sound is coming from the axle or the t-case?

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[ruedger455]

Im almost 100% postive its coming from the u joint by the tcase i went out and moved the drive shaft and it was very sloppy lots of play in the u joint. Then i drove it in 4 wheel cause the 203s are supposed to be full yime 4x4 and i rechecked the drive shaft and now theres no play or wiggle. So im thinking maybe the u joint is seized?

 

[bucket]

If the hubs are unlocked and the truck will only move in a 'loc' position because the front driveshaft spins, that tells me it has not been converted. If the driveshaft does not spin, something must be broken. If you have bad u-joints, you probably should start there.

 

[ruedger455]

How do i know if my front drive shaft is a custom length or if its the stock length?

 

[Stroked]

I would assume it's a standard length driveshaft unless your truck is lifted a significant amount.

 

[ruedger455]

Its lifted 6 inches ill post some pictures of the drive shaft.

 

[89Suburban]

Hey guys, i have a big problem. Today i started messing with my 4x4 on my 77 grande sierra. And when i went in reverse in 4hi it started making a loud metal clunking noise! I have the np203 t-case and i also have locking hubs. How do i know if the previous owner put in the part time kit? Now i unlocked the hubs and put it in hi-loc and now it clunks when shifting into reverse or drive. And it clunks when i get on the gas and stopping while driving. Could my tcase be low on fluid? Or could something be broken? This has me very upset i just bought this truck last week. Let me know what you guys think.

Also when the hubs are unlocked if i put it in 4 hi it goes no where and the front drive shaft clunks hard and spins and it sounds like a train wheel on the track. That metal to metal sound.

In the pics that looks like the factory drive shaft with the double Cardan joint on it. Very possible that double Cardan joint is wore and sloppy. Especially being run on a lifted truck, they take a beating. Check the other U-joints for slop and replace if necessary. That is quite a bit of an angle looking at that lift, I am guessing it is a 6"?



When you unlock the front hubs and drive it in LOC it will have some slop in the drive line giving it gas and letting off the gas so that is normal for a unit that old. It will have slop in the drive line that normally you would not feel driving it in "All Wheel Drive" like it was designed for.


When you have the hubs unlocked and don't have it in a LOC position it will spin the front drive shaft and not move the truck because the differential in the transfer case is sending power to the shaft with least resistance on it so that is also normal.

I would also check the fluid level in the transfer case to be safe.

 

[ruedger455]

It clunks even when the hubs are locked and in 4hi. And now there is no wobble in the u joint like before when i checked it. Its all stiff and no wiggle. Ive been driving it with hubs locked and in 4 hi since yesturday, as thats the way its meant to be driven with the np203 not being converted.

 

[89Suburban]

If the wobble disappeared then there is probably some stress on the drive line hiding it. Put the T-Case in neutral and I bet it will show up again.

 

[ruedger455]

Ill try that ill post here after i check

 

[89Suburban]

Ill try that ill post here after i check

Make sure you set the parking brake or use wheel chocks hoss before you climb under there

 

[89Suburban]

Another thing you can do is just pull the front shaft and run it in 4 hi LOC and run it around in Rear/2WD until you get the joint fixed, IF that is the problem. I actually ran a Burb in Front Wheel Drive mode once for a few weeks.