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Mod | | | Forums66 Topics128,196 Posts1,057,395 Members48,469 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
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| | | | Joined: Mar 2015 Posts: 24 New Guy | | New Guy Joined: Mar 2015 Posts: 24 | I'm looking to reduce rpms on the highway....I have a 1956 gmc with a 270....I have been told it has a 390 rear and would like to keep the original rear end in the truck ....but maybe change the ring and pinion to lower rpm's at highway speeds....anyone have any experience with this issue?? | | | | | Joined: Sep 2001 Posts: 29,270 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,270 | | | | | | Joined: Sep 2011 Posts: 1,462 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,462 | GMC should have a Dana 45, not as easy to find as the G.M. corp axle or the Dana 44, threads on forum regarding the 45.
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: Sep 2001 Posts: 29,270 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,270 |
Last edited by tclederman; 04/21/2016 5:23 PM. Reason: 1955 GMC guide added
| | | | | Joined: Apr 2005 Posts: 2,102 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,102 | Apparently not all of them. My friend has a 56 GMC Suburban Carrier, 316 Pontiac, hydro and it has the same 3.90:1 corporate rear end as my 56 Chevy 3100. Everything is original as far as we can tell.
Fred
1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine
| | | | | Joined: Sep 2011 Posts: 1,462 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,462 | What series is your '56 (i.e. 100, 150) and what rear axle does it have?
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: Mar 2015 Posts: 24 New Guy | | New Guy Joined: Mar 2015 Posts: 24 | thanks for the response guys….I have a 1/2 ton 100 series..I'll be under the truck this weekend…not sure how to identify if it is a spicer or gm….lot's of conflicting info on the web…manual says it should be spicer 45….headed to Carlisle this weekend …..thanks for the help…... | | | | | Joined: Sep 2011 Posts: 1,462 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,462 | The G.M. corp axle will have a round cover on the rear & the carrier bolt into the same shape opening in the front of the axle housing. Dana / Spicer axles have a 10 bolt cover with straight vertical sides.
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: Mar 2015 Posts: 24 New Guy | | New Guy Joined: Mar 2015 Posts: 24 | Well we took the cover off and found it to be a Dana 45.....with a 307!!! so I took off the 205 tires I had on just as project tires ....and swapped them for 31 10.50's and what a difference in RPM drop.....never thought there would be that much of a difference just in tire size....now cruises at 55-60 no sweat.....thanks for the info guys......by the way found a spare tire mount for a short bed stepside out at Carlisle...been looking for one for a long time.....swapped it for a front bumper from a chevy 3100...great find..........
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