Speedo Correction on a Bronco II.

[engdept]

I need to get my speedo correct on my Bronco II. According to the article in the Tech Library, I had a 19 tooth gear. I did the math and it came up to a 21 tooth gear. I installed a red 21 tooth gear and now my speedo reads 10 mph fast.

Did I install the correct gear?

What would I need to get it down that 10 mph and do they make it?

http://www.therangerstation.com/tech_library/Speedogear.html

 

[MAKG]

Gears are multiplicative, not additive.

Obviously if your speedometer is wrong, it's the wrong gear.

You count teeth by, well, counting them. How you could identify yours from any article is a bit of a headscratcher. It is what it is.

 

[kunar]

I need to get my speedo correct on my Bronco II. According to the article in the Tech Library, I had a 19 tooth gear. I did the math and it came up to a 21 tooth gear. I installed a red 21 tooth gear and now my speedo reads 10 mph fast.

Did I install the correct gear?

What would I need to get it down that 10 mph and do they make it?

http://www.therangerstation.com/tech_library/Speedogear.html

why is it wrong? did you change gears or tires?

(old ratio) / (new ratio) = (old speedometer gear) / (new speedometer gear)

its the same for tire diameter as it is for gear ratio....

 

[engdept]

So is tech article wrong MAKG? I identified both gears based on the colors noted in the tech article.

I have new gears and tires.

 

[kunar]

So is tech article wrong MAKG? I identified both gears based on the colors noted in the tech article.

I have new gears and tires.

what were your stock gears and tires, and what are your new gears and tires? what was your original speedometer gear tooth count?

 

[engdept]

The stock gears were 4.10's and the stock tires I have no idea. New gears is 4.56 and new tires are 31's

 

[Hahnsb2]

Have a friend pace you to get a good idea how far off your speedo is, take however many percent it's off and add that percent to your current speedo gear teeth. I hope that makes sense. You're going to need a larger speedo gear for sure, not sure if they have more than 21 teeth though... Personally I'm using a 21 tooth (red) gear in my b2 with 4.10s and 31s, if I was still using my 1350 I wouldn't need a such a big gear, but the internal 1354 gear was different and made it read even faster (it was around a total of 25% off!).

 

[engdept]

I installed the transfer case output gear from my factory transfer case to the transfer case in the truck. The stock worm gear is the red one.

I know for a fact that it is 10 mph off across the board. I used my GPS to get actual speed.

 

[Hahnsb2]

That is simply impossible. So when you're doing 1 MPH your speedo reads 11MPH?

 

[engdept]

when the speedo is reading 15, I am doing 5. When the speedo reads 55, I am really going 45. I readit that way from 15 to 70.

 

[mhughes165]

thats impossible, speedo gears will be off exponentially, if its not then theres probably a issue with your speedometer itself...

 

[kunar]

thats impossible, speedo gears will be off exponentially, if its not then theres probably a issue with your speedometer itself...

somebody had the needle off and put it back on wrong....

 

[engdept]

somebody had the needle off and put it back on wrong....

It is hard to put the needle back on wrong in a Gen 1. When no power is on the speedo, it will be setting on 0 mph.

I will check it again tonight just to make sure I was reading it right.

Is there a certain way the worm gear has to go on the t-case output shaft or is is the same both ways?

 

[rickcdewitt]

what they are saying is if its the speedo gear off it will be like this example-

60mph -10 off

30 mph-5 off

15mph-2.5 off

it increases with speed

 

[mhughes165]

It is hard to put the needle back on wrong in a Gen 1. When no power is on the speedo, it will be setting on 0 mph.

I will check it again tonight just to make sure I was reading it right.

Is there a certain way the worm gear has to go on the t-case output shaft or is is the same both ways?

the speedometer gets no power at all, it reall sounds like what metal mcguyver has said, the only way for it to be off like this is the needle being moved, either reposition it, by moving it to 10 mph, takin it off and puttin it back on at 0, or replace the gauge cluster...

 

[engdept]

Whenever the truck is stopped, it is on 0 mph; I am 100% positive of that.

Like I said, I will check it again whenever I get off today.

 

[Earl43P]

You will discover that at rest, the needle has to have tension against the peg.

Use forceps to rotate the shaft to compensate out the erroneous 10 mph, then place the needle back on, so that tension occurs. It will probably take several tries to get it spot-on.

 

[engdept]

Alright, I checked the needle at rest and it is right on 0 mph. Below is the speed numbers I got using my GPS. The first number is what the speedo is reading and the second is what the GPS was indicating.

Speedo = GPS
20 = 16
30 = 24
55 = 45
65 = 53
75 = 61


Anyone got any advice for which gear to use? I have a red speedo cable gear with a red t-case output shaft gear in it now.


EDIT: I just counted the teeth on the speedo gear and it only has 16 teeth. I was going by the Tech Library's info that the red speedo gears have 21 teeth. I will go order a 21 tooth gear tomorrow at the local Ford dealership and see if that works.

 

[rickcdewitt]

i say use the 20 or 19 tooth,it comes out closer.i get a little over 19.5 for you

you bought the wine colored gear it looks like.

 

[engdept]

I am going to get the 19, 20, and 21 tooth gears; at just a few cents over $5, I don't see why not. That will give me the chance to experienent with it.

I will let you know which one I use.