NP 208 Transfer Case Issues

[ss396]

I have a 1987 K5 Blazer, 4" lift, 35" tires. 700R4 with 208 transfer case.

Recently I replaced the 3.42 gears with 4.10's, all new bearings and driveline yoke. I also replaced the open rear with an Auburn posi. Good pattern on rear gears, backlash to specs. U joints replaced.

Now back on the road. Driving under power at 60 mph, seems to be quiet, as soon as let off the gas, lots of noise until I hit 40 MPH. Seems to be getting worse.

Today I ran it in the garage on jack stands, 60 mph, deep growl appears to be from transfer case under power and off the gas. At first I am thinking i screwed up the rear gear setup, but rear axle is very quiet, all the noise is in the transfer case area. The transfer case did not appear to make any noise before the gear swap, now it sounds like it is ready to grenade.

My question is can an improper rear axle set-up transmit noise to the transfer case?

Or, is the new tight rear end, showing fault with the transfer case, the old rear had a lot of slop?

How can I tell if it's the transfer that's bad?

Sorry for the long post, sounds like it's time for a NP241, but I want to make sure the 208 is toast first. I don't understand why it is noisy now, maybe it's been on it's way out.

Cheers

 

[Stoopalini]

When is the last time you replaced the U-joints? If it's been a while, I'd start there.

Another thing that could cause that is if your driveshaft isn't long enough and isn't far enough in on the slip yoke on the NP208. Did you get the driveshaft extended after lifting?

Thomas.

 

[ss396]

I replaced the u-joints yesterday, they needed it, but it seemed to make it worse.

No I didn't lengthen the driveline yet, with the lift it only extended out 1", maybe that's too much.

I don't understand why I didn't hear any noise before the gear change, unless the sloppy rear was absorbing all the vibration.

Sounds like I should lengthen the driveline first. Not sure it it's overkill for a CV driveline, but the driveline is at a pretty sharp angle.

 

[Stoopalini]

The sloppy rear could have been absorbing the vib, no real way to tell.

If the driveshaft pulled 1" out, and you have a steep angle with no shims or rewelded perches to compensate, I would definitely start there. Something you could try is lowering the x-fer case by moving the spacers on the mounting bolts from the top of the frame rail to the bottom. This will drop the x-fer case about an inch and might help a lot. It will also allow you to test if the angle is the culprit by observing any changes in the noise/vibration.

Thomas.

 

[stevewix]

i have had the same vibration since i've had my blazer. it's only got a 2" lift, but it's also got a 14 bolt rear with rewelded perches. i recently put in a new slip yoke and u joints, and the problem in MINE is that the slip yoke is too short. can't find any longer ones, so i think i'll try lowering my 208 t case.


it seems to be wearing in, but try driving yours so that you arent accelerating or decelerating; no load on the drivetrain. mine is loud as hell when i take the load off the driveshaft.

 

[ss396]

stevewix, that sounds exactly like it.

I have the long slip yoke, but even from stock, it sets out too long. I tried all the shimming and TC drop when I lifted it to remove a definate vibration. I ended up removing taper shims on the springs and left the TC stock mounting to remove the vibration, it was fine until now.

I am going to drain the TC tonight, if the TC is bad, the oil should have some metal in it.

Looks like I need to lengthen the driveline, get the slip yoke further in the housing.

 

[stevewix]

i'm thinking it's due to either

a. worn output shaft bushing
b. not enough slip yoke in transfer case
C. both

maybe it's the high angle of the rear u-joint?

 

[ss396]

stevewix, I agree with you. Since I need to get a driveline built anyway, I think I will go with a CV slip yoke design.

Thanks for you comments.