Did the 1974 K20 when equipped with an automatic, have a 203 transfer case and was the transmission a TH350 or TH400? Also would it be safe to put 33/12.50/15's on factory rally wheels, either BFG mud terrian or Super Swampers? Thanks
CK5
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Question Re: 1974 K20
- Thread starter smitty2
- Start date
Yup, '74 autos would likely have an NP203, and 3/4's would generally have a TH400.
The qualifiers are there 'cuz every now and again you'll find something weird, like someone special ordered the '205 as a PTO option or something ... and because, in the last three decades, drivetrains get swapped out and people put in all kinds of weird stuff.
The only way you're gonna know for sure is to look at the truck. Coupla good resources to help you with that...
http://www.chuckschevytruckpages.com/images/transpan.jpg
http://www.chuckschevytruckpages.com/drivetrains.html
And yep, I've put 33x12.50's on the factory 15x8 ralleys, ran on the street no problem. I never 'wheeled in that truck, so I can't say how they'd do aired down, but I'm pretty sure you'd be fine. Check with your tire vendor about the use of an 8" rim to be certain.
-- A
The qualifiers are there 'cuz every now and again you'll find something weird, like someone special ordered the '205 as a PTO option or something ... and because, in the last three decades, drivetrains get swapped out and people put in all kinds of weird stuff.
The only way you're gonna know for sure is to look at the truck. Coupla good resources to help you with that...
http://www.chuckschevytruckpages.com/images/transpan.jpg
http://www.chuckschevytruckpages.com/drivetrains.html
And yep, I've put 33x12.50's on the factory 15x8 ralleys, ran on the street no problem. I never 'wheeled in that truck, so I can't say how they'd do aired down, but I'm pretty sure you'd be fine. Check with your tire vendor about the use of an 8" rim to be certain.
-- A
All the 3/4 tons prior to 77 I've seen only had TH350s, IIRC it was 76 or 77 that started the TH400....
Mmm. My '74 sixpack was a C20 from the factory with a TH400, but both "3/4" and "1-ton" crewcabs have the thick/narrow-spaced frame of the one-tons, so maybe they got the TH400 when the single cabs didn't
-- A
Yep, '77 began the TH400 in the K-series trucks of 3/4 and 1 ton.
TH400 has been around forever, including older trucks, but only in 2wd version.
C20. That explains it right there. 2wd's got the TH400's.Mmm. My '74 sixpack was a C20 from the factory with a TH400, but both "3/4" and "1-ton" crewcabs have the thick/narrow-spaced frame of the one-tons, so maybe they got the TH400 when the single cabs didn't
-- A
Yeah should have been more clear, sorry....
'74 will have the TH350 tranny.
What kind of Ralley wheels do you want to put on the truck? The Ralleys that everyone is so familiar with are 6 lugs. A K20 is 8 lug.
A '74 will highly likely have 16.5" from the factory unless someone else swapped in 16" rims.How'd I miss that?
Yeah, a K20 would have 16" wheels from the factory, no?
-- A
Thanks for all the answers. Yes, I'm asking about 15" ralley 6 lug wheels for a K10. Is an 8" wheel wide enough for 33/12.50" tires?
As I said, I've done it, with BFG AT's, in fact. I'm pretty sure the 8" rim was fine for the BFG's; I don't know for sure about Interco though I imagine any 33x12.50 would also work.
You can check out the tire manufacturer's web sites to be sure; they list acceptable rim width ranges.
-- A
Yes an 8" wheel is wide enough for a 33/12.5/15 tire. 
The next time you're asking questions about two different vehicles in the same post you might want to differentiate between the two so people don't get confused.
The next time you're asking questions about two different vehicles in the same post you might want to differentiate between the two so people don't get confused.
My Dad bought a '76 C20 crew cab brand new off the lot, and that truck had a TH350 (which fragged at 67,000 miles).
That pic taken in Sept 1980 bringing home my first car.
Rene
That pic taken in Sept 1980 bringing home my first car.
Rene
Rene, Different up north maybe?
All the 1/2 ton 74s had the 203, even manual trans. The 3/4 ton should also have the 203 according everything I've read.
Of course anything could have been swapped over the years.
All the 1/2 ton 74s had the 203, even manual trans. The 3/4 ton should also have the 203 according everything I've read.
Of course anything could have been swapped over the years.
Can't see them being that different...although even back then I questioned why GM would use a TH350 in a Crew Cab Camper special. The only way it could have been dumber is if it had a big block.
Up til now i haven't run across any option differences between US trucks and Canadian trucks.
Rene
Up til now i haven't run across any option differences between US trucks and Canadian trucks.
Rene
My '75 K20 Suburban has a t350/203 combo factory. Yes, 33/12.50/15's will work fine on 8" rims. I have 33/12.50/15 BFG Mud T/A's on 8" rims on my '90 Suburban.
