Need some help. 1971 K-20
 

Hey Folks,
Im new here, and trying to get some info on a truck I recently bought. It has supposedly an original 350 in it. And it looks that way, as it cosmetically leaves a lot to be desired. But runs really good. Shifts nicely too. Ive already changed the oil and filter and just am trying to get some help identifying the other majors. Im thinking this is the SM465 in there, and then Im assuming this is the GM 10 bolt rear end. But the low line fill port on the diff cap kinda threw me off. Just trying to see some opinions on what everyones take is on it. I want to check all my differential and transfer case fluids, but want to make sure I have the right stuff on hand before cracking open the check ports.

Also notice in the one, where the speedometer cable is going into the transfer case, It looks like there is a good bit of seepage going on, and I am hoping that is where a lot of the minimal loss is coming from. Is this a common leak, do you have to replace the entire cable. Haven’t owned one of these style trucks since I was a kid, and then I surely didn’t know what the hell I was looking at. It was a 2WD as well so a lot of other things to make sure and keep tabs on. Just looking for some guidance,

Re: Need some help. 1971 K-20
 

a couple more

Re: Need some help. 1971 K-20
 

Neat ol truck. Looks like keeper.
Speedo cable should have an o ring. Just thread it off and peek. Looks as though things have been out somewhat recent. New u joints a plus. Maybe the trans and transfer got a gasket kit and the o ring got over looked, who knows.
Hows that thing ride? Thats a big stack of springs!!
Oh and the rear from what i see is an eaton

Re: Need some help. 1971 K-20
 

That an Eaton rearend. Ho52 or ho72, not very familiar with them. I'm almost positive there is an o ring on the speedometer cable housing, should be able to replace o ring and stop leak. Sweet truck!

Re: Need some help. 1971 K-20
 

Looks like a 205 case, sm465 trans. , eaton ho52 rear, should be a Dana 44 up front.(laking cosmeticly!?!) I don't have my quad focals on but she looks very nice in the picture!!! Enjoy it

Re: Need some help. 1971 K-20
 

Agree with doo142. If it is an original K20 the best you could do is a 350 and that is definitely an HO52 which came on the 3/4 tons. The 1 tons had an HO72 but they are basically the same. There is a serial number on the top of the diff on the passenger side front. If it has one of the following codes it is an original 4x4 1971 HO52: TJH, TJJ, TKB, TKC, TKK,TKL,TKS, TKT. If it is the correct rear axle, the HO52 between 1968 and 1972 all used a 4.10 gear ratio with the 350 and an automatic. It should have a Dana 44 up front. If you look on the long tube side on the front of the axle there is a BOM (Bill of Materials number) stamped on it. The proper BOM numbers for a 1971 K20 are: 603352 -1 & -3 & -10 are all Standard, 4.55 gears, 603352 -4 Trak-Lok 4.55 gears, 603325 -8 &-9 & -11 are all standard 4.09 gear sets. Hope this helps. By the way, I like the truck.

Re: Need some help. 1971 K-20
 

What? Two posts and no one said:


:welcome2::welcome2::welcome2::welcome2::ennyd:

Oh yeah...another K20:metal:

Thanks guys I knew you all here would be able to help. I will be posting some other questions that id like to help me decode this ol girl. There were sone things that stood out to me that the seller just really didnt know about. I will check those numbers too. Im itching to get under there, but ive got a go kart im rebuilding for my oldest kids bday and getting tight on time.
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Re: Need some help. 1971 K-20
 

You can pickup new seals and gaskets for the 205 from offroaddesigns.com but becareful or you'll spend a freakin fortune on that site.

Re: Need some help. 1971 K-20
 

Welcome aboard this crazy train! Thats a nice truck for Virginia(im a native of north west va)and another K/20 to boot! Love the dual spots.

They both shine bright too
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Re: Need some help. 1971 K-20
 

Welcome aboard! That's a very nice looking K20! Agree with all that's posted above.... only other thing I noticed was the incredibly stout rear spring packs. I'm not sure they came stock with that many leaves, it must ride.... well, like a truck! And it has the best kind of overloads, I don't think you can find those anymore.

Re: Need some help. 1971 K-20
 

Yes I meant to respond to the first post. Those springs make it stiff as a wedding di#$. But it drives well. Im thinking this one rolled out of flint michigan minus a bed. It has some kinda pto literature on the dash and visor. Making me think it could have been a wrecker????. Then there are red and white spot lights mounted behind the grill. Fire truck??? I do know the bed is a donor and could stand to loose a few springs
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Re: Need some help. 1971 K-20
 

:chevy::chevy::chevy:

Re: Need some help. 1971 K-20
 

Yay! Another K20.

Fixed it for 'ya...

Re: Need some help. 1971 K-20
 

Bet your on the right track. Could of been a water truck or similar for a local fire dept.
how about a pic of the spid inside the glove box? Mine had all the pto stuff still attached that I removed, still a mystery as what it was for..

Re: Need some help. 1971 K-20
 

I will post those spids, and I didn't mean the truck was lacking cosmetically. Just the engine is not the best looking. But she runs like a top

Re: Need some help. 1971 K-20
 

So if you all could just confirm with me, Based on the NP205, What is the recommended fluid here. I am sure that opinions will differ so I would just like to see them and then make a decision based off all the data that rolls in. As far as I know its the original transfer case and likely fluid, so I want to know the SAFEST way to approach and add to it. And on the picture, I am just looking for reassurance that the Fill port is just that, and I should be able to reach in with a finger and contact fluid if so its good, if no I need to add. So I just want to know what to add??

Re: Need some help. 1971 K-20
 

The good news is the NP205 runs on just about any lubricant. While the transfer case didn't change, GM recommended gear oil and later ATF.

Re: Need some help. 1971 K-20
 

Uh not so much, it is more like this:


https://www.youtube.com/watch?v=8Q7FFjUpVLg

Re: Need some help. 1971 K-20
 

As posted above, it's not too picky. Mine calls for 80W90 but there was a bad seal between the transmission and the t-case, so ATF got pumped into it. No harm done, got the seal fixed and am running 75W90 full synthetic now.


That is correct.

Re: Need some help. 1971 K-20
 

Thanks Stocker, So lets just say for example: I check and shes low, without knowing what is currently in the transfer case, it sounds that the NP205 is versatile enough that a mixture of fluids is not going to have adverse effects, or would it be safer to drain down and replace with all ATF. Just seriously would hate to jack it all up because of not being informed. Its one thing to burn it up cause of wear and tear. But don't wanna add some potpourri of oil in there and cause a problem.

Re: Need some help. 1971 K-20
 

Since you just bought the truck and don't know what previous maintenance was done, I would change most (or all) of the fluids as a preventive measure. Including but certainly not limited to both differentials and the transfer case. For simplicity if nothing else, I used 75W90 synthetic in all three. You shouldn't have any issues with ATF in the t-case, though, if that's your preference. But yes, drain it and fill with fresh fluid.

Incidentally, if all you want to do for now is top it off, as long as you can reach any fluid, it's easy enough to tell if it's ATF or gear oil just by looking at and smelling the stuff.

Re: Need some help. 1971 K-20
 

Spid picture

Re: Need some help. 1971 K-20
 

A no-spin inside that Eaton diff -- kinda rare, quite desirable!