Dan Peters
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• Brookfield, WI, USA |
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• Registered on 1/13/2003 |
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• 1 post |
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 Posted:8/23/2003 00:11 |
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does anyong know what equation or numbers i need to put in my speedometer. I have a 94 ford bronco AOD it has the digital speedo that i can easily reprogram the problem is i don''t know what number to use i have 35 in tires and 5.13 gears. Any help appreciated.
Dan |
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Meixter
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• Almost Heaven, WA, USA |
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• Registered on 5/27/2003 |
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• 2 posts |
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 Posted:8/23/2003 21:17 |
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I don't know the answer but I was also wondering if anyone knows how to calibrate the speedo on a '91. |
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LOCKED UP
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• Baton Rouge, LA, USA |
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• Registered on 9/29/2001 |
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• 1,256 posts |
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Posted:8/24/2003 00:18 |
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Might want to try bigbronco.com. Wish I could help but mine was a 90 
That or maybe a hatnes/chilton/ FSM would be able to tell you
MY WEBSITE / DELTA 4X4 CLUB
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Bob Kennedy
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• Olympia, WA, USA |
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• Registered on 9/19/2001 |
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• 93 posts |
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Posted:8/25/2003 01:16 |
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Confirm the tranny first. Momma Ford never put the AOD behind the PSOM (digital odometer).
It was usually the E4OD.
The 91. on teh other hand did not have the PSOM and should have a mechanical odometer. If it does, it'll be a matter of selecting the correct teeth count for the speedo cable.
Bob K
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Al Stu
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• NOYB, OR, USA |
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• Registered on 10/13/2001 |
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• 13 posts |
• 1 Vehicle
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Posted:8/25/2003 23:00 |
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First thing to do is measure the tire rolling circumference. The way I do this is to put some grease or something on one of the tread lugs then move the vehicle one full tire revolution to transfer the grease to the surface. Vehicle load and tire inflation can affect rolling circumference considerably so make sure they are "normal".
Armed with this information you can easily calculate the PSOM conversion constant by hand or use my nifty online calculator located at http://www.superford.org/registry/vehicles/detail.php?id=641. NOTE: The tire sizes (Rev. Per Mile, Rolling Circumference, Rolling Radius & Diameter are the actual in use loaded effective measurements, not brochure spec numbers.
To calculate buy hand you can use the formula located at http://www.off-road.com/ford/bigbroncos/tech/psom.html.
Highly recommended to double check the value by hand before programming the PSOM. Also by working the formula backwards from the current PSOM conversion constant to see if it gives the correct previous tire size. This should ensure the formula is correct for your PSOM.
BTW, since the PSOM is driven by the ABS ring on the rear axle only tire size requires reprograming. Gear changes should have no effect on the PSOM calibration.
This information is worth less than you paid for it so use at your own discretion and risk. YMMV
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