Transfer Case Grinding in 4WD

[truckster]

I just got my Blazer running again after 8 years. I took it out for a drive today - everything seemed good in 2HI, but in 4HI and 4LO there's a grinding noise coming from the transfer case. It's a 350/350/NP205 drive train. The transfer case worked great before I parked it due to a thrown rod. I did disconnect the driveshafts to move the transmission and transfer case while I was working on it, but I didn't disconnect the transmission from the transfer case.

Any ideas?

[franken]

Gear lube in the TC??

[truckster]

Originally Posted by franken

Gear lube in the TC??

It's topped off with ATF, which is what the manual calls for.

[Getter-Done]

Is the linkage adjusted correctly??

This is the main issue on a Transfer case.

Especially since you know it worked good Before








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[57taskforce]

I’ve always run 80/90 in the 205s I’ve had. Sounds to me like maybe you’ve got an issue with the front output shifting mechanism or maybe even shift fork. I would first check to make sure the front output shift rail is fully into the 4x4 detent position when in 4hi or 4lo. If it’s not fully engaged you’ll get issues like your having. The rail circled below controls 2x4/4x4 operation by engaging and disengaging the front wheels. The upper shift rail controls HI/Neu/LO ranges. Report back what you find on the shift rails and we can go from there.

[MJN]

Originally Posted by truckster

It's topped off with ATF, which is what the manual calls for.

Figured I'd open this can of worms- what manual are you referencing? The 1981 GM Light Truck Service manual is the oldest I'm aware of that references using Dexron-II for the transfer case when the NP208 came out. The 1972 10-30 truck owners manual states using 80w or 90w GL-5 for the transfer case on page 52. Not saying this is your problem but maybe worth looking into.

[gmc684x4]

I agree dex 3 is too light a oil for an old school np205
If you ever look at the bearings there large and course and made to be lubricated by gear oil using an auto fluid your most likely starving your gears and bearings of oil

[sick472]

I've read some about this oil vs ATF debate (or can of worms that MJN mentions) and apparently the manufacturers switched the NP205 to the ATF to boost mpg at the cost of transmission life. My conclusion, either will work. Gear oil is probably best for longevity, but produces more heat and costs some mpg's.

[truckster]

I think Getter-Done and 57TaskForce are steering me in the right direction. I didn't check the linkage when I reinstalled the transmission. I'll probably be able to get under it tomorrow and take a look.

[truckster]

I think that was it. The upper shift rod was stuck. I tapped it gently with a deadblow hammer and it went into place. I re-read my shop manual; somehow I must have gotten it wrong. I'll drain it and replace the ATF with gear oil tomorrow. I should have it back on the road by early next week (waiting for other parts) and I'll report back.

[57taskforce]

Glad you got it pointed in the right direction. I’ve seen those rails get sticky before. Once you run it around some and get oil slung back up there it should get easier to shift.

[truckster]

UPDATE: So after I cleaned the shift rails and replaced the fluid (75-W90, as per the factory repair manual - OK, I don't know how I misread that one), it was shifting easier, but still making noise. I noticed that the noise was only on deceleration, which made me start looking outside the transfer case. I had dropped the front driveshaft, and thought I might not have gotten the U joint in square, but that wasn't it... Then I noticed scratch marks on the exhaust. I cut 1.5" out of the vertical part of the exhaust and welded it back up, and no more noise. Sometimes it's the stupidest things.

[Getter-Done]

Good Deal .
That you got it fixed

Glad to see your update.

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[57taskforce]

That’s about the best case scenario there. It happens, my mufflers were rubbing the rear driveshaft when I bought my truck. Mufflers??? I don’t need no stinkin mufflers... (I have mufflers again... too loud)

[gmc684x4]

Glad you got it sorted out

[Accelo]

I am sure automatic transmission fluid will hurt anything.
Early Dodge 4 speeds required automatic transmission fluid.
Nothing I know of that was built in the last decade uses 90W.
Even the differential requires synthetic in my 21 year old Silverado.
However, using the 90 will reduce the leakage. The speedometer fitting is a know leak.
Glad you got it figured out.