Speedometer gear ratio tooth 2,73 axle ratio

[Chriss]

Hi

I have a CJ7 with AMC 360 and T-176 gearbox and Dana 300 .
Now I have 33" tires. But the axles still have the ratio 2,73.
The speedometer doesn't show the right speed.
The problem is that I can't find a speedometer gear for this axle ratio.
All the charts stops at ratio 3,07. Somebody told me that speedo gears with 31 or 32 or 33
tooth will fit. But which is the right??
Would somebody help me?
Cause I won' t pay one more police ticket.
Regards
Chriss

 

[gutthans]

You'll definitely be below 26 teeth, which is the count for 32" tires and a 3.07, and yea I'm looking for the lower chart spec too...

 

[gutthans]

Speedometer Gear Applet

This links to the algebraic equation to calculate the actual ratio (teeth required). Just plug in the variables to get the final number.

 

[PaRenegade]

I was in the same predicament. Mine originally had 2.73 gears and I switched to 3.73's and am running 33" tires. Here's the place that I got the correct speedo gear from. Look at this page and then click on the Dodge & Jeep page to get gears for the Dana 300 . Make sure you have the right gear housing too, there are 2 different ones based on the speedo gear you'll need. Also, get a new O-ring too.
Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4

 

[wm69]

I know running 2.73's with 31's required a 24 tooth gear. Using the formula

New gear* new tire = old gear * old tire

X * 33 = 24x31
X *33 = 744
744/33= X
X= 22.55, so I would say a 22 or 23 tooth gear would be what you need.

I have never seen lower than a 24, and the 24 and 25 tooth gears require a special housing for 21-25 tooth gears. I guess the fact that the housing is for 21-25 tooth gears means that they did make 21, 22, 23, but I've never seen one for sale. The 24 and 25 gears, and the housings, are hard to find.

And good grief man, regear that thing. My 2.73 Jeep with 31's is a dog, but I only use that one running the kids around town. Can't imagine how bad one would be with 33's and 2.73's.

 

[JR74CJ5]

Other options:

If you have a GPS smart phone, you can get a apple or android app that is a GPS speedometer. They (at least the one I was using) are pretty accurate.

I agree you should re-gear, but it if works for you...

There are also adjustable electronic speedo gauges, so you could adapt one in with a phaser on the tcase, but to make this option look good you would be buying a new gauge set and redoing your dash... Not the most ideal option.

the smart phone app is by far the quickest, free option. (If you already have a smart phone)

I took the belt clip case for my iPhone and vel-crowed it to my dash. My phone clips in and out. Works like a charm. Does drain the battery rather quickly...

 

[ThisGuyUKnow]

I know running 2.73's with 31's required a 24 tooth gear. Using the formula

New gear* new tire = old gear * old tire

X * 33 = 24x31
X *33 = 744
744/33= X
X= 22.55, so I would say a 22 or 23 tooth gear would be what you need.

I have never seen lower than a 24, and the 24 and 25 tooth gears require a special housing for 21-25 tooth gears. I guess the fact that the housing is for 21-25 tooth gears means that they did make 21, 22, 23, but I've never seen one for sale. The 24 and 25 gears, and the housings, are hard to find.

And good grief man, regear that thing. My 2.73 Jeep with 31's is a dog, but I only use that one running the kids around town. Can't imagine how bad one would be with 33's and 2.73's.

That equation is all you need? That doesn't seem to account for the axle ratio. Wouldn't your rear output on the tc would have to spin at a different speeds in order to maintain the same tire speed with the same sized tires but different axle ratios. Right? Not saying your wrong and Im right, just trying to understand.

 

[ThisGuyUKnow]

Other options:

If you have a GPS smart phone, you can get a apple or android app that is a GPS speedometer. They (at least the one I was using) are pretty accurate.

I agree you should re-gear, but it if works for you...

There are also adjustable electronic speedo gauges, so you could adapt one in with a phaser on the tcase, but to make this option look good you would be buying a new gauge set and redoing your dash... Not the most ideal option.

the smart phone app is by far the quickest, free option. (If you already have a smart phone)

I took the belt clip case for my iPhone and vel-crowed it to my dash. My phone clips in and out. Works like a charm. Does drain the battery rather quickly...

i did this for a while because my jeep didnt come with a speedo cable and it wasnt a top priority for me. When i finally installed the cable I found that the speedo reads about 5 mph faster. I just opted to leave it be and mentally note the difference.

 

[zzzhopperzzz]

https://itunes.apple.com/us/app/gps-speedometer/id339748125?mt=8

 

[JR74CJ5]

i did this for a while because my jeep didnt come with a speedo cable and it wasnt a top priority for me. When i finally installed the cable I found that the speedo reads about 5 mph faster. I just opted to leave it be and mentally note the difference.

Yeah with my new dash and gauge project, I'm fixing mine as well

It has never worked, so I'm not sure what the speedo gear will do when I get it working. I'll have to check accuracy.

 

[wm69]

That equation is all you need? That doesn't seem to account for the axle ratio. Wouldn't your rear output on the tc would have to spin at a different speeds in order to maintain the same tire speed with the same sized tires but different axle ratios. Right? Not saying your wrong and Im right, just trying to understand.

Well, that's using the assumption that the old speedo gear with old tire size give you the correct reading at the speedo head.

I know a 24 tooth gear is correct for 2.73's and 31's, so used that as a base. I found that info years ago on the applet listed above, which used to have a CJ specific chart with CJ gear ratios, tire sizes, and speedo gears.

My 2.73 equipped Jeep came from the factory with a 26 tooth gear and 235's (28.8 inches)

X * 33 = 26 * 28.8

x * 33 = 748

x = 22.69

Same answer, 22-23 tooth gear for 33's, running 2.73's.

 

[ThisGuyUKnow]

Well, that's using the assumption that the old speedo gear with old tire size give you the correct reading at the speedo head.

I know a 24 tooth gear is correct for 2.73's and 31's, so used that as a base. I found that info years ago on the applet listed above, which used to have a CJ specific chart with CJ gear ratios, tire sizes, and speedo gears.

My 2.73 equipped Jeep came from the factory with a 26 tooth gear and 235's (28.8 inches)

X * 33 = 26 * 28.8

x * 33 = 748

x = 22.69

Same answer, 22-23 tooth gear for 33's, running 2.73's.

Ok so then following your equation, if you were to change axle gearing, I'd guess it would look something like this

(X)*(new tire size)*(new gear ratio)= (original tooth count)*(original tire size)*(original gearing)

Where X is your new tooth count needed.

This is of course assuming that the factory tooth count provided an accurate speed to begin with.

 

[wm69]

Yep, that only works if you had the original (assuming the original was correct) gear and tire size.

 

[tinhorn]

I like the GPS idea. Last summer I paid about 30 bucks for a used Garmin GPS for this exact purpose. Well, it was for a boat, but same principle. (My phone screen goes blank after several seconds.)