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| | | | Joined: Jan 2016 Posts: 6 New Guy | | New Guy Joined: Jan 2016 Posts: 6 | I have a 1 ton, changing gears from 5.14 to 4.1
What do I need to have speedo register accurate speed?
Thanks | | | | | Joined: Sep 2001 Posts: 29,270 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,270 | What year? 1953 A ratio adapter for $75-$125 The Speedometer Shop (disappeared?) or Jim Carter Truck Parts
Last edited by tclederman; 02/09/2016 6:32 PM. Reason: corrected and provided a link
| | | | | Joined: Jul 2010 Posts: 592 Shop Shark | | Shop Shark Joined: Jul 2010 Posts: 592 | Go ahead and get the rear end installation done, then do actual measurements using either a GPS or follow a car that you know is accurate at very specific speeds. The Jim Carter website will give you instructions. If you know the true MPH and the incorrect reading on your speedometer, you can have an adapter made that will be very precise. You can test it using the same method after the installation.
Doing the math, you will need an adapter that increases the speedo reading by 20.23% if you do nothing else but change the rear end ratio. If you also plan to change tire sizes, this will make a further change. But calibrate based on the road test, not the math.
Check to see if your tranny already as an adapter on it. Some came from the factory with them (mine did). If so, I recommend that you take it off before you do your calibration testing so that you don't end up installing an adapter to an adapter. Calibrate with your speedo cable screwed directly into your tranny.
The good news is that once you get everything else done, installing the adapter is only about a five minute job.
Matt
| | | | | Joined: Sep 2001 Posts: 29,270 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,270 | mechanical ratio adapters scroll down - $88 Performance Transmissions and Parts $150 plus shipping | | | | | Joined: May 2001 Posts: 1,907 'Bolter | | 'Bolter Joined: May 2001 Posts: 1,907 | Also, make sure you have your final wheels and tires installed for best results if you use a GPS check.
1948 3/4-Ton 5-Window Flatbed Chevrolet 34 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: Nov 1995 Posts: 5,738 24601 | | 24601 Joined: Nov 1995 Posts: 5,738 | Another option: I use the DigiHUD app on my phone. It's free, too.
~ John A kid raised on Hotwheels, Matchbox and Tonka cannot be reasonably expected to own only one vehicle as an adult. 1949 Chevrolet 3804In the Legacy Gallery | In the Gallery Forum1973 IH 1310 Dump1963 Kaiser M38A12001 International/AmTran RE3000 "Skoolie"2014 Ford E-350 4x4 (Quigley) | | |
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