Transfer Case Grinding in 4WD - The 1947 - Present Chevrolet & GMC Truck Message Board Network

truckster · 02-03-2021, 10:58 PM

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 · 02-03-2021, 11:19 PM

Gear lube in the TC??

truckster · 02-03-2021, 11:30 PM

Quote:

Originally Posted by franken

Gear lube in the TC??

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

**Getter-Done** · 02-03-2021, 11:38 PM

Is the linkage adjusted correctly??

This is the main issue on a Transfer case.

Especially since you know it worked good Before

.

57taskforce · 02-04-2021, 12:01 AM

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** · 02-04-2021, 10:27 AM

Quote:

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 · 02-04-2021, 02:00 PM

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 · 02-04-2021, 02:23 PM

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 · 02-04-2021, 02:50 PM

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 · 02-05-2021, 08:32 PM

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 · 02-06-2021, 02:22 AM

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 · 02-15-2021, 07:42 PM

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** · 02-15-2021, 09:50 PM

Good Deal .
That you got it fixed

Glad to see your update.

This is (one ) of the many Reasons I enjoy this Forum

(The Most of Us)
Share the ( Good / Bad / & Ugly )

.

57taskforce · 02-15-2021, 11:07 PM

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 · 02-16-2021, 12:45 PM

Glad you got it sorted out

**Accelo** · 02-16-2021, 02:27 PM

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.

02-03-2021, 10:58 PM	#1
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 7,981	Transfer Case Grinding in 4WD 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? __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

02-03-2021, 11:19 PM	#2
franken Registered User Join Date: Jun 2013 Location: Somewhere Posts: 3,128	Re: Transfer Case Grinding in 4WD Gear lube in the TC??

02-03-2021, 11:38 PM	#4
Getter-Done Senior Member Join Date: Dec 2009 Location: TN. Posts: 8,442	Re: Transfer Case Grinding in 4WD Is the linkage adjusted correctly?? This is the main issue on a Transfer case. Especially since you know it worked good Before . __________________ ________________________________________________________________________________________ ____________________________________________ 84 Chevy K-20 63 Impala (my high school car) http://67-72chevytrucks.com/vboard/s...Crew Cab Build

02-04-2021, 12:01 AM	#5
57taskforce All about them K’s Join Date: Jun 2014 Location: Land of Entrapment Posts: 6,504	Re: Transfer Case Grinding in 4WD 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. Attached Images __________________ Tyler '57 3100 http://67-72chevytrucks.com/vboard/s...d.php?t=813888 '72 K20 Cheyenne: 5” lift, 35’s, front dana 60 blah blah blah… http://67-72chevytrucks.com/vboard/s...d.php?t=662879 ‘69 K10 SWB: 4” lift 33”s… in a million pieces http://67-72chevytrucks.com/vboard/s...d.php?t=805206 '98 Silverado LT K2500HD ECLB Vortec 454/4l80E: 6" lift 35x12.5x20’s

02-04-2021, 02:00 PM	#7
gmc684x4 Registered User Join Date: Jul 2012 Location: Whitehorse yukon Posts: 1,218	Re: Transfer Case Grinding in 4WD 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

02-04-2021, 02:23 PM	#8
sick472 Registered User Join Date: Jul 2015 Location: Sedalia Mo. Posts: 1,131	Re: Transfer Case Grinding in 4WD 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. __________________ He who is without oil shall throw the first rod. Compressions 8.7:1 1972 C10 1976 C10 (parts truck) 1985 K20

02-04-2021, 02:50 PM	#9
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 7,981	Re: Transfer Case Grinding in 4WD 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. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

02-05-2021, 08:32 PM	#10
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 7,981	Re: Transfer Case Grinding in 4WD 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. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

02-06-2021, 02:22 AM	#11
57taskforce All about them K’s Join Date: Jun 2014 Location: Land of Entrapment Posts: 6,504	Re: Transfer Case Grinding in 4WD 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. __________________ Tyler '57 3100 http://67-72chevytrucks.com/vboard/s...d.php?t=813888 '72 K20 Cheyenne: 5” lift, 35’s, front dana 60 blah blah blah… http://67-72chevytrucks.com/vboard/s...d.php?t=662879 ‘69 K10 SWB: 4” lift 33”s… in a million pieces http://67-72chevytrucks.com/vboard/s...d.php?t=805206 '98 Silverado LT K2500HD ECLB Vortec 454/4l80E: 6" lift 35x12.5x20’s

02-15-2021, 07:42 PM	#12
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 7,981	Re: Transfer Case Grinding in 4WD 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. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

02-15-2021, 09:50 PM	#13
Getter-Done Senior Member Join Date: Dec 2009 Location: TN. Posts: 8,442	Re: Transfer Case Grinding in 4WD Good Deal . That you got it fixed Glad to see your update. This is (one ) of the many Reasons I enjoy this Forum (The Most of Us) Share the ( Good / Bad / & Ugly ) . __________________ ________________________________________________________________________________________ ____________________________________________ 84 Chevy K-20 63 Impala (my high school car) http://67-72chevytrucks.com/vboard/s...Crew Cab Build

02-15-2021, 11:07 PM	#14
57taskforce All about them K’s Join Date: Jun 2014 Location: Land of Entrapment Posts: 6,504	Re: Transfer Case Grinding in 4WD 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) __________________ Tyler '57 3100 http://67-72chevytrucks.com/vboard/s...d.php?t=813888 '72 K20 Cheyenne: 5” lift, 35’s, front dana 60 blah blah blah… http://67-72chevytrucks.com/vboard/s...d.php?t=662879 ‘69 K10 SWB: 4” lift 33”s… in a million pieces http://67-72chevytrucks.com/vboard/s...d.php?t=805206 '98 Silverado LT K2500HD ECLB Vortec 454/4l80E: 6" lift 35x12.5x20’s

02-16-2021, 12:45 PM	#15
gmc684x4 Registered User Join Date: Jul 2012 Location: Whitehorse yukon Posts: 1,218	Re: Transfer Case Grinding in 4WD Glad you got it sorted out

02-16-2021, 02:27 PM	#16
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,301	Re: Transfer Case Grinding in 4WD 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.



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