speedometer gear

[Mopar85]

i have a 727 with 3.73 gears and 31x18.5x15 tires. i just bought a universal speedometer cable and autometer ultra lite gauge. what gear do i run for the speedometer to be accurate?

 

[fishy68]

For a stock speedometer I'd guess either a 31 or 32 tooth gear (could go either way) but I'm not sure since the speedometer is aftermarket

 

[John at CRT]

:read2:

727 Push Button = 8 Drive Teeth
727 Non Push Button = 13 Drive Teeth
904 Non Push Button = 13 Drive Teeth
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Drive Teeth x Rear End Gear Ratio x Tire Revolutions Per Mile
1001 = Gear Teeth
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tire Revolutions Per Mile = 20168 _
Tire Height
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tire Revolutions Per Mile Quick Reference

24” = 840.3 Tire RP Mile
25” = 806.7 Tire RP Mile
26” = 775.7 Tire RP Mile
27” = 746.9 Tire RP Mile
28” = 720.3 Tire RP Mile
29” = 695.4 Tire RP Mile
30” = 672.3 Tire RP Mile

example

13 x 4.56 x 683.7 (20168 ÷ 29.5 [tire height] )
Drive Teeth Rear End Ratio Tire Revolutions Per Mile

Divide Answer by 1001, Gives number of teeth needed on gear.

 

[fishy68]

:read2:

727 Push Button = 8 Drive Teeth
727 Non Push Button = 13 Drive Teeth
904 Non Push Button = 13 Drive Teeth
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Drive Teeth x Rear End Gear Ratio x Tire Revolutions Per Mile
1001 = Gear Teeth
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tire Revolutions Per Mile = 20168 _
Tire Height
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tire Revolutions Per Mile Quick Reference

24” = 840.3 Tire RP Mile
25” = 806.7 Tire RP Mile
26” = 775.7 Tire RP Mile
27” = 746.9 Tire RP Mile
28” = 720.3 Tire RP Mile
29” = 695.4 Tire RP Mile
30” = 672.3 Tire RP Mile

example

13 x 4.56 x 683.7 (20168 ÷ 29.5 [tire height] )
Drive Teeth Rear End Ratio Tire Revolutions Per Mile

Divide Answer by 1001, Gives number of teeth needed on gear.

Cool!! An actual formula to nail it down. Thanks John.

 

[6pk2goDemon]

:scratch:....hmmm. I have alot to learn.

 

[64physhy]

I must have done something wrong. I came up with 1.348 teeth first time ant 1.47 teeth the second time.

OK, I came up with 39.7, so I guess either a 39 or 40 tooth gear.

 

[64physhy]

Next question; where can you get them?

 

[oldkimmer]

.............Theres no way u need 39 teeth.........id say 33 at the most......kim......

 

[64physhy]

Let me try this again

Axle Ratio Rear Tire Diameter
24" 25" 26" 27" 28" 29" 30" 31" 32" 33" 34" 35"

2.76 30 29 28 27 26 25 24 23 23 22 21 *
teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth
2.94 32 31 30 29 28 27 26 25 24 23 23 22
teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth
3.23 35 34 33 32 31 30 29 28 27 26 25 24
teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth
3.55 39 37 36 34 33 32 31 30 29 28 27 26
teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth
3.73 41 39 38 36 35 34 33 32 31 30 29 28
teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth
3.91 43 41 40 38 37 35 34 33 32 31 30 29
teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth
4.1 45 43 41 40 38 37 36 35 34 33 32 31
teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth
4.3 * 45 43 42 40 39 38 36 35 34 33 32
teeth teeth teeth teeth teeth teeth teeth teeth teeth teeth
4.56 * * * 44 43 41 40 38 37 36 35 34
teeth teeth teeth teeth teeth teeth teeth teeth teeth
4.88 * * * * 45 44 43 41 40 39 38 37
teeth teeth teeth teeth teeth teeth teeth teeth

* not available

Well, it's obviously not working the way I wanted it to. Looks good when I type it, but when it posts, it sucks, and the attachment is too big. You can get the idea; the tire sizes appear shifter to the left one column from where they should be. 24" tire with 2.76 gears should be 30 teeth.

 

[64physhy]

.............Theres no way u need 39 teeth.........id say 33 at the most......kim......

I found a chart that I'm trying to post right now. Says with 4.10 gears and 27" tires, 40 teeth.

 

[64physhy]

There's some a$$ hat on ebay selling the gears for $30.....plus $30 shipping.

 

[2 Darts]

There's some a$$ hat on ebay selling the gears for $30.....plus $30 shipping.

YO has aftermarket speedometer pinions for 19.95 + S/H or NOS for $69.95 + S/H. Guess ya payz yer bux and takes yer chances.

 

[oldkimmer]

I found a chart that I'm trying to post right now. Says with 4.10 gears and 27" tires, 40 teeth.

........That sounds about rite....although im going off my memory........kim.......

 

[Tony Fields]

Here's a chart I found

 

[Locomotion]

If anyone figures out they need a 25, 31 or 34 tooth speedo pinion, I have used ones for $17.00 including shipping!

 

[fishy68]

There's some a$$ hat on ebay selling the gears for $30.....plus $30 shipping.

They have went up a bunch in price the last year it seems. A couple yrs. back I could get them for $20 most anywhere. Now some places are charging as much as $75 for them. You may have to do some digging to find one that don't cost a fortune.

 

[Tony Fields]

Here's some on Ebay

According to the chart, looks like you need 32 teeth

http://cgi.ebay.com/ebaymotors/SPEE...r_Truck_Parts_Accessories&hash=item255e791937