203 to a 208 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

milner · 01-15-2005, 12:49 AM

I was wondering what everyone thought about switching a full-time 203 out for a newer 208? I know the auto hubs aren't that strong but I don't do any heavy wheeling with the truck and was wondering if the swap would help out my mileage any? What do you guys think? Thanks.

1972 · 01-15-2005, 01:59 AM

I don't like 203 cases because I have had too many of them go bad. Usually the chain wears out because it is always going. I don't know if the swap would help your mpg that much or not. If you swapped in an OD tranny with the 208 it could help depending on what gear ratio and tire size you have. I would swap to a 208 because it will save wear and tear on your front driveshaft, differential, and axle joints. I wouldn't run the auto locking hubs either, they won't lock in when you need them to (when you are stuck). Manual hubs from MileMarker or Warn would work real nice.

Do you know much about the mechanics of the swap - adapters, driveshaft lenghts, shifters, etc...?

1969 GMC · 01-15-2005, 02:19 AM

Your truck does not have auto hubs if it came with a 203. theyre drive flanges

milner · 01-15-2005, 08:53 AM

Quote:

Originally Posted by 1969 GMC

Your truck does not have auto hubs if it came with a 203. theyre drive flanges

I know, I was talking about the 208.

72 CustomCamper · 01-16-2005, 12:54 AM

Just because you switch to a 208 case you don't need to install auto hubs. My 86 came factory with a 208 and manual hubs...

Chuck

milner · 01-16-2005, 11:09 PM

I know, I would probably install manual hubs also. I was just wondering if it would be worth it to do the swap. How much do you think it would affect the mileage? I am only getting around 8.5mpg now which isn't that great.

1972 · 01-17-2005, 01:23 AM

Quote:

Originally Posted by milner

I know, I would probably install manual hubs also. I was just wondering if it would be worth it to do the swap. How much do you think it would affect the mileage? I am only getting around 8.5mpg now which isn't that great.

I have never done a swap like this, but I would guess that it would only be 2 or 3 mpg at the very most. Is it worth it? Depends on how many miles a year you drive and how much $$$ you can do the swap for. You will need the t-case, adapter, possibly a new transmission output(I'm not sure on this), shifter assembly, and driveshafts.

72 CustomCamper · 01-17-2005, 10:40 PM

My old 74 K5 had the full time 203. I put hubs and a part time confersion in the tcase and it really didn't help the milage. Either way it got about 2 gallons per mile...

Chuck

milner · 01-18-2005, 12:14 AM

Quote:

Originally Posted by 72 CustomCamper

My old 74 K5 had the full time 203. I put hubs and a part time confersion in the tcase and it really didn't help the milage. Either way it got about 2 gallons per mile...

Chuck

Well I don't feel so bad at 8.5,lol. Before I put the 383 in I was only getting 6.4 with the tired 350.

1976Scottsdale · 01-21-2005, 12:39 AM

My old 76 is getting about 12-16mpg with a built 350 600CFM carb, th350, np203, and 3.42 axles.

**special-K** · 01-22-2005, 07:17 AM

Is your truck still full-time,I take it?I would suggest the swap.I wouldn`t expect much life out of that 203 with a healthy 383 up front.Find a donor with 700R4/208 to complete what you started with your drivetrain.It`s a common package,should give you what you`re looking for,mileage & more of them.

milner · 01-22-2005, 09:34 AM

Quote:

Originally Posted by 1976Scottsdale

My old 76 is getting about 12-16mpg with a built 350 600CFM carb, th350, np203, and 3.42 axles.

My 79 has a mild 383 with a Q-jet,th350,np203 and 3.42 axles but has a 2.5" lift with 33s. I know that it isn't an economy package but would like to at least get double digits in the mileage.

milner · 01-22-2005, 09:36 AM

Quote:

Originally Posted by special-K

Is your truck still full-time,I take it?I would suggest the swap.I wouldn`t expect much life out of that 203 with a healthy 383 up front.Find a donor with 700R4/208 to complete what you started with your drivetrain.It`s a common package,should give you what you`re looking for,mileage & more of them.

Yup,still full-time. I like it for around here when it snows and freezing rain like yesterday.

01-15-2005, 12:49 AM	#1
milner Registered User Join Date: Jun 2003 Location: Mandan,ND Posts: 268	203 to a 208 I was wondering what everyone thought about switching a full-time 203 out for a newer 208? I know the auto hubs aren't that strong but I don't do any heavy wheeling with the truck and was wondering if the swap would help out my mileage any? What do you guys think? Thanks.

01-15-2005, 02:19 AM	#3
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	Your truck does not have auto hubs if it came with a 203. theyre drive flanges __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

01-16-2005, 12:54 AM	#5
72 CustomCamper huh ??? Join Date: Nov 2002 Location: Fredericksburg,Va. Posts: 3,368	Just because you switch to a 208 case you don't need to install auto hubs. My 86 came factory with a 208 and manual hubs... Chuck __________________ 90 Blazer Silverado 350w/ 700R4 and 32" Kelly's "I am a bomb technician. If you see me running try to keep up!"

01-17-2005, 10:40 PM	#8
72 CustomCamper huh ??? Join Date: Nov 2002 Location: Fredericksburg,Va. Posts: 3,368	My old 74 K5 had the full time 203. I put hubs and a part time confersion in the tcase and it really didn't help the milage. Either way it got about 2 gallons per mile... Chuck __________________ 90 Blazer Silverado 350w/ 700R4 and 32" Kelly's "I am a bomb technician. If you see me running try to keep up!"

01-22-2005, 07:17 AM	#11
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Is your truck still full-time,I take it?I would suggest the swap.I wouldn`t expect much life out of that 203 with a healthy 383 up front.Find a donor with 700R4/208 to complete what you started with your drivetrain.It`s a common package,should give you what you`re looking for,mileage & more of them. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

01-15-2005, 01:59 AM	#2
1972 Majician Join Date: Nov 2004 Location: In the Middle Posts: 329	I don't like 203 cases because I have had too many of them go bad. Usually the chain wears out because it is always going. I don't know if the swap would help your mpg that much or not. If you swapped in an OD tranny with the 208 it could help depending on what gear ratio and tire size you have. I would swap to a 208 because it will save wear and tear on your front driveshaft, differential, and axle joints. I wouldn't run the auto locking hubs either, they won't lock in when you need them to (when you are stuck). Manual hubs from MileMarker or Warn would work real nice. Do you know much about the mechanics of the swap - adapters, driveshaft lenghts, shifters, etc...?

01-16-2005, 11:09 PM	#6
milner Registered User Join Date: Jun 2003 Location: Mandan,ND Posts: 268	I know, I would probably install manual hubs also. I was just wondering if it would be worth it to do the swap. How much do you think it would affect the mileage? I am only getting around 8.5mpg now which isn't that great.

01-21-2005, 12:39 AM	#10
1976Scottsdale Registered User Join Date: Aug 2004 Posts: 76	My old 76 is getting about 12-16mpg with a built 350 600CFM carb, th350, np203, and 3.42 axles.



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