A0 High Speed Gears - Speedometer Dip Switch Adjustment

simp5782

Feo, Fuerte y Formal
Supporting Vendor
8,972
1,701
113
Location
Memphis, TN
Ok. Logical question is to consult the TM first. if that is no help. Then here we go.

I am going to assume you could calibrate it as you would a 10 switch VDO gauge using pulses per mile vs actual miles driven? Speedos all have the same if not near the same calibration per federal law. Especially these styles from what I have read. Easiest way would be a place that is certified for calibrate speedos. Since they have a roller they could put it on and do it all without leaving the shop.

http://www.nsifleet.com/pdf/OldElecSpeedo.pdf

This seems to kinda run the way it should. I don't know the exact make of the speedo on these things.

According to the TM it would 34754/35180 = 0010011010 for a stock setup.
 
Last edited:

Rebuilder

Member
96
3
8
Location
Minnesota
Ok. Logical question is to consult the TM first. if that is no help. Then here we go.

I am going to assume you could calibrate it as you would a 10 switch VDO gauge using pulses per mile vs actual miles driven? Speedos all have the same if not near the same calibration per federal law. Especially these styles from what I have read. Easiest way would be a place that is certified for calibrate speedos. Since they have a roller they could put it on and do it all without leaving the shop.

http://www.nsifleet.com/pdf/OldElecSpeedo.pdf

This seems to kinda run the way it should. I don't know the exact make of the speedo on these things.

According to the TM it would 34754/35180 = 0010011010

That's very helpful. So based on the chart the stock LMTV speedo is set at 0010011010 which is 34754-35180 pulses per minute. In my truck 50mph on the speedo is about 63mph +/- on the GPS which is a 26% gain. Does that mean we should program in a 26% lower pulses per minute which is roughly 27777 or 0010101111? Does that sound right?
 

simp5782

Feo, Fuerte y Formal
Supporting Vendor
8,972
1,701
113
Location
Memphis, TN
That's very helpful. So based on the chart the stock LMTV speedo is set at 0010011010 which is 34754-35180 pulses per minute. In my truck 50mph on the speedo is about 63mph +/- on the GPS which is a 26% gain. Does that mean we should program in a 26% lower pulses per minute which is roughly 27777 or 0010101111? Does that sound right?
I would start at 30341s binary and see where you stand.

Gps on the phones can be off. Mine is 2.2mph off from my garmin gps and 1mph off from my other android using the same gps app.

Or find a Honda civic at night with the center dash speedo display and pace it!
Sent from my SM-G935P using Tapatalk
 
Last edited:

Rebuilder

Member
96
3
8
Location
Minnesota
Does anyone know the proper dip switch sequence on the back of the A0 speedometer to adjust for high speed gears? Thanks
I finally got around to figuring this out. Took a few hours of messing around and basically just guessing but it worked out in the end. I tried the test in the VDO doc listed above but it didn't work so I just started switching and testing. Side note... you have to turn the truck off and back on for the switch to take effect so driving around and flipping switches doesn't work.

If the pics ever disappear the correct setting is 1101101001 (1=up/on 0=down/off)

Speedo dip switch settings.JPG
 

Ohiobenz

Active member
Supporting Vendor
349
41
28
Location
Seville, OH
@Rebuilder When playing with the settings did you happen to find one that indicated about 10% faster than actual speed with the 307's??? I went to 14x20 tires which has my speedo off by 5mph at 60 compared to GPS.
 

Rebuilder

Member
96
3
8
Location
Minnesota
@Rebuilder When playing with the settings did you happen to find one that indicated about 10% faster than actual speed with the 307's??? I went to 14x20 tires which has my speedo off by 5mph at 60 compared to GPS.
My memory isn't that good haha. I'd probably start testing 1 at a time and then different combinations of 7,8,9,10.
 

coachgeo

Well-known member
3,151
223
63
Location
North of Cincy OH
Does anyone have pictures of diffs from Bryce with the Detroit locker setup?
looks pretty much like any other differential with a detroit locker put "inside" a differential carrier.

examples:
https://www.pirate4x4.com/forum/gen...-how-install-detroit-locker-your-14-bolt.html
http://www.off-road.com/trucks-4x4/project/project286.html

any further discussion on this needs to go in one of the existing threads about installing gears and lockers so not to muddy this one up about speedo adjustments.
 

Awesomeness

Well-known member
Steel Soldiers Supporter
1,266
261
83
Location
Firestone, CO
I finally got around to figuring this out. Took a few hours of messing around and basically just guessing but it worked out in the end. I tried the test in the VDO doc listed above but it didn't work so I just started switching and testing. Side note... you have to turn the truck off and back on for the switch to take effect so driving around and flipping switches doesn't work.

If the pics ever disappear the correct setting is 1101101001 (1=up/on 0=down/off)

View attachment 732867
I tried these settings and it was about 10% low for me (e.g. shows about 60MPH at 65MPH actual speed).

Has anyone tried contacting Medallion and getting the actual settings guide?

If we assume these switches are a binary number, for pulses per mile (or some multiple, such as this binary number * 100), we would have two options... read the binary number right to left (#10 switch is 0 or 1, #9 is 0 or 2, #8 is 0 or 4, and so on), or read them left to right (#1 is 0/1, #2 is 0/2, ...). Right to left is most common, so lets start there.

The original settings: 1101100101 = 512 + 256 + 64 + 32 + 4 + 1 = 869
High speed gear settings suggested above: 1101101001 = 512 + 256 + 64 + 32 + 8 + 1 = 873

They wouldn't really be very far apart (0.5%).

A possibility would be...

The original settings: 1101100101 = 512 + 256 + 64 + 32 + 4 + 1 = 869
Old to new gear ratio results in traveling this much further per pulse: 3.90 / 3.07 = 1.27035830619
Cut the original number down by new gearing ratio difference: 869 / 1.27035830619 = 684.058974358
My first proposed setting: 1010101100 = 512 + 128 + 32 + 8 + 4 = 684

If we read the binary digits left to right instead (less common, but maybe they are doing it in order of the dip switch numbers, which are left to right)...

The original settings: 1101100101 = 512 + 128 + 16 + 8 + 2 + 1 = 667
High speed gear settings suggested above: 1101101001 = 512 + 64 + 16 + 8 + 2 + 1 = 603
667 / 603 = 1.10613598673
This 10% change seems more in line with what I'm seeing out of this new setting (from the picture above). It gets me part of the way there, but not all the way. So let's go on.

The original settings: 1101100101 = 512 + 128 + 16 + 8 + 2 + 1 = 667
Old to new gear ratio results in traveling this much further per pulse: 3.90 / 3.07 = 1.27035830619
Cut the original number down by new gearing ratio difference: 667 / 1.27035830619 = 525.048717948
My second proposed setting: 1011000001 = 512 + 8 + 4 + 1 = 525

I think I'll give this second proposed setting a try next, followed by the first.

It's also entirely possible that some of these switches do something else and aren't part of the math, they aren't binary at all, or they are some other kind of number (for example you take a base of 100,000 pulses/mile and DIVIDE by the binary number these create, or there is a decimal point in between the binary digits of this number, etc.). What makes me wonder is that in the VDO guide posted above, the largest possible number (1111111111) results in the smallest Pulses/Mile range (3906-3927), and the smaller binary numbers result in much larger value ranges. Also, if you look at the ranges, they start small (3906-3927 is a range of 21 numbers) and end big (101494-103322 is a range of 1828 ), so it would have to be some kind of multiplier, at least for that VDO brand of gauges. Could it also be an inverse binary number (flip the 1's to 0's, and 0's to 1's)?
 
Last edited:

Awesomeness

Well-known member
Steel Soldiers Supporter
1,266
261
83
Location
Firestone, CO
If we assume these switches are a binary number, for pulses per mile (or some multiple, such as this binary number * 100), we would have two options... read the binary number right to left (#10 switch is 0 or 1, #9 is 0 or 2, #8 is 0 or 4, and so on), or read them left to right (#1 is 0/1, #2 is 0/2, ...). Right to left is most common, so lets start there.

The original settings: 1101100101 = 512 + 256 + 64 + 32 + 4 + 1 = 869
High speed gear settings suggested above: 1101101001 = 512 + 256 + 64 + 32 + 8 + 1 = 873

They wouldn't really be very far apart (0.5%).

A possibility would be...

The original settings: 1101100101 = 512 + 256 + 64 + 32 + 4 + 1 = 869
Old to new gear ratio results in traveling this much further per pulse: 3.90 / 3.07 = 1.27035830619
Cut the original number down by new gearing ratio difference: 869 / 1.27035830619 = 684.058974358
My first proposed setting: 1010101100 = 512 + 128 + 32 + 8 + 4 = 684

If we read the binary digits left to right instead (less common, but maybe they are doing it in order of the dip switch numbers, which are left to right)...

The original settings: 1101100101 = 512 + 128 + 16 + 8 + 2 + 1 = 667
High speed gear settings suggested above: 1101101001 = 512 + 64 + 16 + 8 + 2 + 1 = 603
667 / 603 = 1.10613598673
This 10% change seems more in line with what I'm seeing out of this new setting (from the picture above). It gets me part of the way there, but not all the way. So let's go on.

The original settings: 1101100101 = 512 + 128 + 16 + 8 + 2 + 1 = 667
Old to new gear ratio results in traveling this much further per pulse: 3.90 / 3.07 = 1.27035830619
Cut the original number down by new gearing ratio difference: 667 / 1.27035830619 = 525.048717948
My second proposed setting: 1011000001 = 512 + 8 + 4 + 1 = 525
I got a chance to try these out today. I tried both of my proposals above, and neither was correct. The first setting (1010101100) showed about 2x actual (GPS) speed on the speedometer. The second setting (1011000001) was about 1.5x actual (GPS) speed displaying.

So I started troubleshooting, and noticed these "rules"...
  • Setting dip switches to off (0) makes the speed registering on the speedometer increase. So if it's reading slow, turn some off (0), and if it's reading fast, turn some on (1).
  • Switches toward the left (lower numbered switches) make smaller adjustments. Switches toward the right (higher numbered switches) make bigger adjustments. (This means that reading the digits left to right is the correct method.)

Speedometer Setting Change Effects.jpg

The troubleshooting process I took then went like this...
  1. Drive and see if the speed on the speedometer is faster or slower than actual speed (on GPS).
  2. If it is faster, find the rightmost switch that is ON, and turn it OFF.
  3. If it is slower, find the rightmost switch that is OFF, and turn it ON.
  4. Drive and test again.
  5. If it is now instead the opposite (too fast/slow) of step #1, return the switch modified in step #2/#3 to its original position, and instead make the same change to the next switch to the left of the previous change that is the same setting. For example, if you previously changed position #9 from ON to OFF, return #9 to ON, if #8 is OFF skip it, and then if #7 is ON then set it to OFF. (Basically, the setting change went too far, so change a smaller value instead.)
  6. If it did not change enough, loop back to steps #2/#3.
  7. Loop back to step #1.

Hopefully those instructions are easy to follow, even if they don't make sense. The idea of it is to change the biggest values first, and work your way to smaller settings, narrowing in on an ideal value.

Doing this I came up with...
1101001001 = 1 + 2 + 8 + 64 + 512 = 587

This works extremely close for me. I have two different speedometers, and I checked it on them both, and it works very well. At 65MPH (GPS) it reads 64-66MPH on the speedometer. I'm not totally sure why this value works yet, but I'll probably keep messing around with the math, or try to get info from Medallion.

Speedometer Settings for 3.07 MRAP Axle Gears - 23Jun2019.png
 
Last edited:
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks