atlas
New Member
:yaayy:My 67 New Yorker came with a small set of 14in wheels and tires. I switched to a set of 70series 15's now my speedometer is way off. How do I figure out the right gear for the speedo?
speedometer
- Thread starter atlas
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MrMoparCHP
Old Man with a Hat
The Factory Service Manual has a chart, tire size and rear end gear but you will need to convert the tire size.
Alan
Alan
Mopars & Missiles
Well-Known Member
Better method: GPS and math.
1. Driver maintains constant speed at 20 mph per passenger operated GPS unit.
2. Driver tells passenger what speedometer reads and passenger records that data relative to 20 mph GPS data point.
3. Repeat steps 1 & 2 for a number of other speeds (ie. 30, 40, 50, 60, etc.) to generate a data set.
4. Drive back home.
5. Calculate speedometer error versus GPS speed from recorded data. You will find a fairly consistent error percentage, either faster or slower than the actual GPS speed.
6. Remove speedometer pinion gear from transmission to determine what size pinion gear you presently have.
7. Calculate the number of teeth for the new pinion gear that are needed to correct the speed from the error percentage determined in step 5. Example, if 10% slow, then you need 10% LESS teeth on the pinion gear than you have now.
8. Get and install replacement pinion gear with correct number of teeth as per calculation in step 7.
9. Drive and enjoy!
1. Driver maintains constant speed at 20 mph per passenger operated GPS unit.
2. Driver tells passenger what speedometer reads and passenger records that data relative to 20 mph GPS data point.
3. Repeat steps 1 & 2 for a number of other speeds (ie. 30, 40, 50, 60, etc.) to generate a data set.
4. Drive back home.
5. Calculate speedometer error versus GPS speed from recorded data. You will find a fairly consistent error percentage, either faster or slower than the actual GPS speed.
6. Remove speedometer pinion gear from transmission to determine what size pinion gear you presently have.
7. Calculate the number of teeth for the new pinion gear that are needed to correct the speed from the error percentage determined in step 5. Example, if 10% slow, then you need 10% LESS teeth on the pinion gear than you have now.
8. Get and install replacement pinion gear with correct number of teeth as per calculation in step 7.
9. Drive and enjoy!
commando1
Old Man with a Hat
Or
MrMoparCHP
Old Man with a Hat
I've done the just add/remove a tooth method and drive/check. Or like now, ignor speedo and use GPS (Polara speedometer is sticky, bang on dash it might more to correct reading)
Alan
Alan
jtalberts
Member
Damn it. This has me thinking this is why the speedo was probably disconnected in the Fury when I bought it. Add another thing to figure out.
atlas
New Member
thanks to everyone for this very useful information
BuzzBee
New Member
This is just one of the reasons I am redoing my dash panel with Auto Meter electronic speedo.
For some reason ( which can't be resolved with a new cable, gear and thorough cleaning of
the speedo mechanism ) the speedo bounces every now and then at different speeds. It's
not accurate and I can barely see it with night driving. Lucky for me I had two spare units
so I don't have to destroy my original.
For some reason ( which can't be resolved with a new cable, gear and thorough cleaning of
the speedo mechanism ) the speedo bounces every now and then at different speeds. It's
not accurate and I can barely see it with night driving. Lucky for me I had two spare units
so I don't have to destroy my original.
commando1
Old Man with a Hat
You should start a thread on your I.P. makeover.
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