1977 K20 Drain Transfer case Plug

• Nov 27, 2020

• #1

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pleary36

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1977

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K20

Engine Size

350

I am looking for the drain plug on my 1977 K20 transfer case. I only see one plug and it looks like a fill plug. the only thing I can think of is to remove the inspection cover, and that looks to high. Any input would be appreciated.

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• Nov 27, 2020

• #2

PrairieDrifter

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350, 350, 350, 350, 350

Remove the lowest hanging bolt, either on the pto cover(side cover) or the rear cover, and let it drain out the hole, all the bolt holes should pass through the case.

 

• Nov 27, 2020

• #3

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pleary36

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As you can see it was the first time trying to post pictures, I only meant to post two. I can usually figure out how to turn a wrench but not so much with a computer. I will give it a try in the morning and let you know how I make out. I am not sure what kind of oil I am thinking gear oil but I will know when I drain it
Thanks for the help.

 

• Nov 27, 2020

• #4

PrairieDrifter

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350, 350, 350, 350, 350

That looks like an np203, correct? Try cleaning up the hole and bolt of oil and may want a dab of rtv on the threads.

 

Last edited: Nov 27, 2020

• Nov 27, 2020

• #5

Goldie Driver

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https://www.gmsquarebody.com/thread...ncludes-blazer-and-suburban.6137/#post-152998

From a 1979 manual, but full time 4wd transfer case uses 10W30 or 10W40 motor oil .

FYI!

 

• Nov 27, 2020

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Octane

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.

 

Last edited: Nov 28, 2020

• Nov 27, 2020

• #7

Grit dog

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You need that brace for the transfer case too if you’re planning on any heavy use.
Probably no problem with that pipe plug, but I always make sure the fill plug comes out fine before draining the oil out of anything old or questionable.

 

• Nov 28, 2020

• #8

75gmck25

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The NP203 uses 10w30 motor oil, and you want to fill it right up to the bottom of the fill hole. It holds up better with good lubrication.

While you are under there, unbolt the front driveshaft and put it on the bench. Check all the universal joints to see they are lubed well and don’t bind or click. The two on the double cardan joint (CV joint) take the most abuse. If you replace them, use sealed joints that do not require periodic lubrication. Also shoot some grease into the fitting on the driveshaft and then push and pull the slip joint to make sure it’s not frozen. It won’t ever move really easily, but it does have to slide smoothly.

Bruce

 

• Nov 28, 2020

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Octane

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• Nov 28, 2020

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Octane

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I did all that on my k10 also, and replaced a leaking pinion seal.

 

• Nov 28, 2020

• #11

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pleary36

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I have the other crossmember and the skid plate, I had them off because I took the motor and transmission out, it is out of Death Valley CA. the truck ran well but everything leaked. I have been driving it for two years and just put in a new driveway so it was time. I rebuilt the motor and sent the transmission out to be rebuilt. Nothing needed to be done but I figured if I have it out I should go through it.
Going out to the barn now to finish the transfer case and all that will be left is putting on the AC, alternator, PS pump and carburetor.
Thanks for the input, you guys are great, I would of tried to take the bearing retainer cover right off and it would of been more work.

 

• Nov 28, 2020

• #12

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pleary36

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Bruce,
I looked in the 1977 factory service manual and it said, part time Transfer case SAE-80W or SAE-80W-90 GL-5 gear lubricant(SAE-80W in Canady) Full time transfer case use motor oil.
I do not know what is what but since I have locking hubs I assumed it was part time transfer case and I used SAE-80W-90 GL-5. If I got it wrong let me know and if it is full time I will have to change it out.
I did replace the universal joint before I reinstalled the drive shafts. the other problem I have is after re-installing the transfer case I saw the breather hose pulls right out and won't stay in place, I will have to try poly or tap it to 1/8" NPT.
thanks, Pat

 

• Nov 28, 2020

• #13

highdesertrange

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pleary you have a 203 full time transfer case. it uses 10-40 engine oil. if it has hubs it has a conversion kit in it but the transfer case still uses 10-40. and yes you remove the lower bolt on the front output shaft rear bearing retainer. highdesertranger

 

• Nov 29, 2020

• #14

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pleary36

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Thanks, I will drain out the gear oil and replace it with 10-40 and run it while I break in the motor and change it again when I change out the break-in oil.
How do you determine the difference between a full tine and part time transfer case.
Thanks, again

 

• Nov 29, 2020

• #15

highdesertrange

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looking at the rear of the case a 205(part time) has a cover that has 3 bolts holding it in place that is the idler shaft. it's located about where your fill plug is. a 203(full time) does not have that. I don't have a 205 pic handy, maybe someone will post one. highdesertranger