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Ratio adapter speedometer #1182871 Fri Sep 16 2016 07:43 AM
Joined: Dec 2006
Posts: 1,154
W
WHO, ME ? Offline OP
Shop Shark
SM420 transmission 1:1 final with 3:38.1 ring pinion 27" dia. Tires 1954 3100 PU. At 35mph on speedometer actual speed 40 mph about 5/6 mph difference. We need a ratio adapter for the transmission any suggestions or model numbers. Don't want to fool around with the speedometer itself a ratio adapter would be an easy fix and easy to remove.
Thanks!

Re: Ratio adapter speedometer [Re: WHO, ME ?] #1182877 Fri Sep 16 2016 12:04 PM
Joined: Sep 2001
Posts: 29,260
tclederman Offline
Boltergeist
Some people just use a GPS for their new and accurate Speedometer.

Jim Carter used to provide ratio adapters - he might still do that.

The Speedometer Shop is where I have obtained ratio adapters - they seem to be out of business.

Bob's Speedometer Shop supposedly makes them ($!50).

A Google search of "speedometer ratio adapter" gives these results.

Maybe someone who has obtained one in the last year will post information?


Tim
1954Advance-Design.com
1954 3106 Carryall Suburban - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic - part of the family for 15 years
Z-series (54/55) GMC 350 (2-ton) COE - now part of Dave's family
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engine are not "splash oilers" - this is a splash oiler.
Re: Ratio adapter speedometer [Re: WHO, ME ?] #1182886 Fri Sep 16 2016 01:21 PM
Joined: May 2005
Posts: 1,630
B
beltfed Offline
Shop Shark
Would a one tooth change in the driven gear from the tranny, less than $15, not work?


Six volt guy living in a twelve volt world
Re: Ratio adapter speedometer [Re: WHO, ME ?] #1182891 Fri Sep 16 2016 01:59 PM
Joined: Feb 2000
Posts: 4,053
J
Joe H Offline
Shop Shark
You will need to check it at 60 mph for the best reading. Most all of the cable driven speedometer are calibrated at 60 mph, 1000 rpm of the cable is 60 miles per hour.

Here is a good link to really check yours.
https://www.hotrodhotline.com/calibrating-speedometer#.V9vrrjtT5Tc

Trans gears are a easy to change, but you still need to know how far off it is at 60.

Re: Ratio adapter speedometer [Re: WHO, ME ?] #1182920 Fri Sep 16 2016 06:42 PM
Joined: May 2009
Posts: 13
D
delwrench Offline
New Guy
I got a ratio adapter custom made from PATC Transmission Center in Louisiana. I figured out my percentage with a GPS and multiple test drives and then called them up and it works great

Re: Ratio adapter speedometer [Re: WHO, ME ?] #1182956 Sat Sep 17 2016 02:44 AM
Joined: Jun 2011
Posts: 3,105
E
EdPruss Offline
Shop Shark
I'm sure there is a speedo shop in Redding, even Sacto where
you can get an adapter, even look for one in a wrecking yard, speedo shop should be able to fix you up.

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.
Re: Ratio adapter speedometer [Re: WHO, ME ?] #1182960 Sat Sep 17 2016 03:56 AM
Joined: Dec 2006
Posts: 1,154
W
WHO, ME ? Offline OP
Shop Shark
I wrote to Novak transmission and gave them my numbers. Turns out I'm about 11% off the mph. They directed me to an ebay supplier for said ratio adapter. Novak excels at after sale customer service.
Thanks to you all!

Re: Ratio adapter speedometer [Re: WHO, ME ?] #1182975 Sat Sep 17 2016 12:58 PM
Joined: Sep 2010
Posts: 82
D
Darling Offline
Shop Shark
I affirm "delwrench"s comments! Works great on my 1946 Chevrolet truck original speedo.

Re: Ratio adapter speedometer [Re: WHO, ME ?] #1182977 Sat Sep 17 2016 01:30 PM
Joined: Sep 2001
Posts: 29,260
tclederman Offline
Boltergeist


Tim
1954Advance-Design.com
1954 3106 Carryall Suburban - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic - part of the family for 15 years
Z-series (54/55) GMC 350 (2-ton) COE - now part of Dave's family
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engine are not "splash oilers" - this is a splash oiler.

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