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Jul 21st, 2025 | | | | Joined: Jan 2006 Posts: 67 'Bolter | | 'Bolter Joined: Jan 2006 Posts: 67 | Hey Bolters,
I am planning on installing a 3:55 rear end in my 46 1/2 ton (currently have the std 4:11). Are there speedometer gears available for the 3:55 ratio? I have my transmission apart, so it would be the best time to change, if available. I have also read about adapters that go inline with the speedometer cable.
Thanks.
Larry
Larry
46 Chevy 1/2 ton stake - family truck for 78 years
USAF 75-81
| | | | | Joined: Sep 2001 Posts: 29,262 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,262 | Good luck finding gears, Larry I use an "inline" adapter on my Suburban. The company that made it for me seems to be gone. You calibrate/calculate the ratio with a GPS or by measuring miles on an interstate. Maybe someone who has had one made recently will post information? ?? http://www.clarkbrothers.net/ratio_adapters.html. ?? | | | | | Joined: Mar 2010 Posts: 843 Shop Shark | | Shop Shark Joined: Mar 2010 Posts: 843 | Good morning Larry.
I did the same conversion on my '36 Chevy pickup and then the speedometer and odometer were off by 17%.
A 17% overdrive adapter from Mr. Speedometer in Canada solved that problem. His adapter goes on the back of the speedometer head.
The '36 is much more pleasant to drive with the 3.55 gears.
Ray
| | | | | Joined: Jan 2006 Posts: 67 'Bolter | | 'Bolter Joined: Jan 2006 Posts: 67 | Thanks for the tip Ray. I will contact your source.
Larry
46 Chevy 1/2 ton stake - family truck for 78 years
USAF 75-81
| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | Or one can just remember your speedo is 11% fast, or whatever, pretty simple.
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: May 2009 Posts: 11 New Guy | | New Guy Joined: May 2009 Posts: 11 | Google PATC transmission parts, They can make you an adapter. I had mine made a couple of years ago and it works great for a sm420 with 3:55's. I think it was around $80. They are in Louisiana, Tom | | | | | Joined: May 2001 Posts: 1,878 'Bolter | | 'Bolter Joined: May 2001 Posts: 1,878 | Anybody ever take one of these apart? I was looking at the gear ratios available from Clark Bros and it seems like they can't be getting these by changing tooth counts. Do they just use 2 wheels of different diameter? Just wondering.
1948 3/4-Ton 5-Window Flatbed Chevrolet 33 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | They are toothed gears, positive engagement.
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: Jan 2006 Posts: 67 'Bolter | | 'Bolter Joined: Jan 2006 Posts: 67 | Thanks for the info delwrench. I will check them out.
Larry
46 Chevy 1/2 ton stake - family truck for 78 years
USAF 75-81
| | | | | Joined: Mar 2008 Posts: 374 'Bolter | | 'Bolter Joined: Mar 2008 Posts: 374 | Larry, I am planning the same 3:55 upgrade in my 46 1/2 ton as well just south of you in Northeast Florida.
Good info to know regarding the speedometer. Good luck!
Todd | | | | | Joined: Jan 2006 Posts: 67 'Bolter | | 'Bolter Joined: Jan 2006 Posts: 67 | Very nice truck Todd!
Hopefully, in six months or so mine will look similar (other than I have a stake bed). Updating everything mechanical first, then on to paint and body.
Larry
46 Chevy 1/2 ton stake - family truck for 78 years
USAF 75-81
| | | | | Joined: Mar 2008 Posts: 374 'Bolter | | 'Bolter Joined: Mar 2008 Posts: 374 | Thank you Sir! Good luck and keep us posted! | | |
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