C20 to C30 conversion? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Mr Handy · 02-07-2014, 10:06 PM

Hi all, my Buddy Steve has a 70 C20 that he is working on converting to a 1 ton. He is wanting to convert the front end to work with Dually rims, and convert to disk Brakes. He is looking for a parts truck and trying to figure out what year range will work. I know the heavy trucks tended to lag behind the model changes of the half ton stuff.

If anyone knows what years will work let me know, also is it a simple cross member swap like in a c10 or is there more to it?

hugger6933 · 02-07-2014, 10:38 PM

It would be the cross member swap just as if it were a C-10 just 3x's as heavy[in both senses

]. So with that being said anything in the 73-91 range on the one ton square should fit the bill, and if he were to find one rolling he'd be that much more ahead to grab the wheels and rear as well and pretty much be done. I know easier typed than done. Isn't that always the way? Jim

Mr Handy · 02-07-2014, 10:42 PM

Cool thanks I will pass on the info!

71swb4x4 · 02-07-2014, 10:48 PM

I think in 75 the front brakes became a little bigger so it may be of benefit to get 75+

mrolds88 · 02-08-2014, 12:55 AM

Do a double check. I have been thinking on this very same thing on my 72. As far as I can figure, you SHOULD just be able to swap rotors if your truck is disc now. If not, you should be able to do a spindle swap. On the back, I was looking at a D70 from a 73 up.

SS Tim · 02-08-2014, 06:15 PM

Unless he is starting with a Longhorn C20 he can't just bolt on parts and "make it" a one ton. The C30 frame is heavier and has a longer wheelbase than a C20 (non-longhorn). The difference is 6" and accounts for the bed forward stretch.
If all he wants is a 8' bed dually, then he can bolt on the parts up front as with a crossmember swap. Out back the rear will need a later wide track dually rear unless he wants to go with a tucked. However if you do that then it gets pretty narrow between the housings and there is still a little tire hanging from the conversions I have seen.

C Blazer
C10 115
C10 127 6.04" height 2.53" flange width 0.156" thick 2.98 section modulus

C20 127 6.11" height 2.46" flange width 0.194" thick 3.71 section modulus

C20/30 133 (Longhorn) 7.20" height 2.77" flange width 0.194" thick 5.05 section modulus

Mr Handy · 02-08-2014, 09:24 PM

His 20 is a longhorn. His bed was rotted out so he built a flat bed for it.

02-07-2014, 10:06 PM	#1
Mr Handy Registered User Join Date: Feb 2013 Location: Spring Hill, Florida Posts: 465	C20 to C30 conversion? Hi all, my Buddy Steve has a 70 C20 that he is working on converting to a 1 ton. He is wanting to convert the front end to work with Dually rims, and convert to disk Brakes. He is looking for a parts truck and trying to figure out what year range will work. I know the heavy trucks tended to lag behind the model changes of the half ton stuff. If anyone knows what years will work let me know, also is it a simple cross member swap like in a c10 or is there more to it?

02-07-2014, 10:38 PM	#2
hugger6933 Registered User Join Date: Oct 2008 Location: Marianna Arkansas Posts: 7,280	Re: C20 to C30 conversion? It would be the cross member swap just as if it were a C-10 just 3x's as heavy[in both senses]. So with that being said anything in the 73-91 range on the one ton square should fit the bill, and if he were to find one rolling he'd be that much more ahead to grab the wheels and rear as well and pretty much be done. I know easier typed than done. Isn't that always the way? Jim

02-07-2014, 10:42 PM	#3
Mr Handy Registered User Join Date: Feb 2013 Location: Spring Hill, Florida Posts: 465	Re: C20 to C30 conversion? Cool thanks I will pass on the info!

02-07-2014, 10:48 PM	#4
71swb4x4 Senior Member Join Date: Nov 2003 Location: Brookings, SD Posts: 10,497	Re: C20 to C30 conversion? I think in 75 the front brakes became a little bigger so it may be of benefit to get 75+ __________________ Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs.

02-08-2014, 12:55 AM	#5
mrolds88 Registered User Join Date: Jul 2011 Location: WV Posts: 946	Re: C20 to C30 conversion? Do a double check. I have been thinking on this very same thing on my 72. As far as I can figure, you SHOULD just be able to swap rotors if your truck is disc now. If not, you should be able to do a spindle swap. On the back, I was looking at a D70 from a 73 up. __________________ 72 GMC C2500 402/Th400 first truck (still have) 77 GMC C3500 CC dually Sold 70 C50 dump truck "Rusty" 87 K10 Suburban Sold 93 K2500 xcab 6.5TD 96 GMC K2500 Suburban 6.5 TD

02-08-2014, 06:15 PM	#6
SS Tim Registered User Join Date: Aug 2010 Location: Edwards, CA Posts: 7,503	Re: C20 to C30 conversion? Unless he is starting with a Longhorn C20 he can't just bolt on parts and "make it" a one ton. The C30 frame is heavier and has a longer wheelbase than a C20 (non-longhorn). The difference is 6" and accounts for the bed forward stretch. If all he wants is a 8' bed dually, then he can bolt on the parts up front as with a crossmember swap. Out back the rear will need a later wide track dually rear unless he wants to go with a tucked. However if you do that then it gets pretty narrow between the housings and there is still a little tire hanging from the conversions I have seen. C Blazer C10 115 C10 127 6.04" height 2.53" flange width 0.156" thick 2.98 section modulus C20 127 6.11" height 2.46" flange width 0.194" thick 3.71 section modulus C20/30 133 (Longhorn) 7.20" height 2.77" flange width 0.194" thick 5.05 section modulus __________________ Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID Blazer SPID Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders Do you have a 1972 Plaid Pickup? Plaid Blazer ** Plaid Suburban

02-08-2014, 09:24 PM	#7
Mr Handy Registered User Join Date: Feb 2013 Location: Spring Hill, Florida Posts: 465	Re: C20 to C30 conversion? His 20 is a longhorn. His bed was rotted out so he built a flat bed for it.



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