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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!
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| | | | Joined: Oct 2012 Posts: 307 'Bolter | | 'Bolter Joined: Oct 2012 Posts: 307 | I saw a 1957 6500 truck for sale. It has a 283 and overdrive transmission. Does anyone know if these came with the R-11 overdrive?
1958 Chevy Grumman Olson step van
| | | | | Joined: May 2005 Posts: 8,878 . | | . Joined: May 2005 Posts: 8,878 | Being such a large truck it's not likely a BW overdrive unit like used on the small trucks and cars.
Could be a Clark 5 speed overdrive, or possibly a Spicer. Or could be an auxiliary transmission with overdrive after the usual 4 or 5 speed, If so likely a Spicer 3 speed, possibly 4. | | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | It could be a NP-540 series, 4 shift rails, Al top cover, or Clark, 3 shift rails, Ci topcover with rounded corners.
Both of these trans.' have high(OD) gear to the right and forward, direct is right and back.
Both of these trans.' have a big gap in ratios where they got the OD position from(3rd), which is really awkward with a load unless a two speed rear end is there.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Oct 2012 Posts: 307 'Bolter | | 'Bolter Joined: Oct 2012 Posts: 307 |
1958 Chevy Grumman Olson step van
| | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | IF you have a OD transmission, it's not a factory transmission. Chevrolet never put a OD trans in a 1957 big truck (only the 3100 & 3200 had a optional OD transmission). The 6000 Series Trucks were standard with the SM-420 4-speed with an optional New Process 5-speed (direct drive). This 5-speed has a shifting pattern that looks like this; 1...2...4...R ....3...5 Mike B  | | |
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