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| | | | Joined: Jul 2014 Posts: 22 'Bolter | | 'Bolter Joined: Jul 2014 Posts: 22 | My 59 is a 3 speed. Neighbor has an sm425 4 speed. If I use the 4 speed do I need a different driveshaft ? | | | | | Joined: Apr 2005 Posts: 2,097 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,097 | If you are referring to the SM420 (granny gear 4 speed) the answer is yes.
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: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | If a 465, also need new driveshaft.
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: Jul 2014 Posts: 22 'Bolter | | 'Bolter Joined: Jul 2014 Posts: 22 | Yes a 420. Thanks guys. I was afraid of that. | | | | | Joined: Apr 2005 Posts: 2,097 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,097 | The SM420 is a good HD trans and would be great for hauling loads but is no improvement for normal driving.
If you are looking for better highway speeds, install an overdrive. The SM319 is a factory overdrive, it is a bolt in and no driveshaft or any other mods are needed. There are electrical components and a cable but that's it.
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
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