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Author Topic:   finding gear ratio
Pigpen
Dirt Maniac

Total posts: 141
posted September 15, 2004 06:51 PM  
I am trying to find the gear ratio on a three speed saginaw tranny, I know about the ring deal... I just want count the gears to make sure, how do you do this?....thanks in advance.

Deak-Jr
Dirt Forum Racer

Total posts: 81
posted September 16, 2004 11:28 AM  
(** EDITED **)

AFTER SOME HUNTING, I found this:
http://www.musclemotorparts.com/trannys.htm

It lists ratios based on no lines, one line, two lines or three lines on shaft.

Saginaw 3 Speed

No Lines on Input Shaft
2.85
1.68
1.00

1 Line
2.54
1.50
1.00

2 Lines
3.11
1.84
1.00

3 Lines
3.50
1.89
1.00

ALSO:
from "http://www.members.shaw.ca/cbkspeedway/contentpages/tech.html" ....

"Determining the ratio of each gear in your standard transmission is actually pretty easy. You will need a fine scribe or marking pencil that will leave a legible mark on the transmission housing and shafts and a friend to handle counting on the other end of the transmission.

First, make sure you have the transmission shifted into the gear you want to check. If you are not sure check all gear positions, then mark the case above the shifter shafts indicating their position for each gear. This will also help eliminate mistakes when setting up shifters later on.

Starting at the input shaft (engages the clutch plates) make a fine line along top of the shaft and onto the front bearing cover sleeve. Without turning anything go to the rear of the transmission and make a similar mark on the top of the output shaft and onto the tail housing.

You want both of these marks to act as indicators with which to count the number of revolutions each shaft makes. The finer the lines, the more precise you can be.

Slowly turn the input shaft at the front of the transmission, counting revolutions until the tail shaft completes one full revolution. The number of full and partial revolutions completed by the input shaft determines that gears ratio. For example if the input shaft made one and one half revolutions to turn the output shaft through one complete revolution, that gears ratio is 1.5 to 1.

The problem is that few gear ratios come out in such round numbers. To make determining the exact ratio easier, turn the input shaft until the tail shaft completes 10 revolutions. Divide the number of full and partial revolutions of the input shaft by 10 to get the ratio for that gear.

Say the input shaft turned 17 3/4 turns to generate 10 full revolutions of the tail shaft. Divide 17.75 by 10 to get a ratio of 1.775 to 1. If you really pay attention to the position of the lines you can easily tell the difference between a 1.73 and a 1.52 ratio. Sounds like a small difference here, but on the track it means a lot!"

[This message has been edited by Deak-Jr (edited September 16, 2004).]

cd2
Dirt Maniac

Total posts: 161
posted September 16, 2004 12:51 PM  
Pigpin,i takt it that you want the 2nd gear ratio. The best i remember is count the teeth on the main shaft & on the 2nd gear, if any dought put the plate back on an shift into 2nd remove plate & count.Then divide the large number by the small number. Hope that is what you want & is the right info. cd2

Pigpen
Dirt Maniac

Total posts: 141
posted September 16, 2004 07:12 PM  
I am trying to determine if this tranny is a 1.84 or 1.89 so trying to turn the input and count the output is out.... the input shaft gear has 18 teeth the countershaft teeth connected to it has 29 teeth the countershaft connected to 2nd gear main shaft had 24 teeth and 2nd gear on the main shaft has 21 teeth....so... near as I can figure I divide the driven gear by the driving gears and come up with 1.61 and 1.14, I multiply those two together and I get 1.83....but, all the charts say a 2 line (which is what I have) is a 1.84.... So, did I do something wrong or are the charts wrong?

cd2
Dirt Maniac

Total posts: 161
posted September 18, 2004 11:10 AM  
Pigpin,1.61X 1.14 = 1.8354 which rounds off to 1.84, you are right. cd2

Pigpen
Dirt Maniac

Total posts: 141
posted September 18, 2004 12:19 PM  
Thanks... the calculator I was using automaticly rounds off, guess it was wrong...thanks for the help..AJ

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