Yugo Workshop Manuals
Yugo L4-1300cc 1.3L (1991)
Transmission and Drivetrain > Automatic Transmission/Transaxle > Component Information > Technical Service Bulletins > Technical Service Bulletins for Automatic Transmission/Transaxle: > Page 800
Technical Service Bulletin # ATRATB8923
A/T - Math Formulas Part I
TSB: 89-23 (Aug)
Transmission math formulas are not reserved exclusively for engineers. Understanding some basic mathematical formulas can be one of your most
The following information contained in this bulletin will discuss various basic formulas dealing with:
Take the time, now, to understand these relatively simple concepts.
You will be saving yourself many problems, and considerable frustration, and also dollars, in the future.
Shift Speed and Pressure
SHIFT SPEED AND PRESSURE
To figure the area of a circle (valve or servo):
Radius (which is 1/2 the diameter) x Radius x 3.14159 = Area
EXAMPLE: A 1" diameter circle has a radius of 0.5"
0.5 x 0.5 x 3.14159 = 0.785
Therefore a 1" diameter circle has an Area of 0.785 sq. inches
Pressure x Area = Force
EXAMPLE: 100 psi line pressure, on a servo with an area of 2 square inches = force
So, 100 psi line pressure x 2 sq in = 200 pounds of force.
Force divided by Area = Pressure
EXAMPLE: 200 lbs divided by 2" = 100 psi
Force divided by Pressure = Area
EXAMPLE: 200 lbs divided by 100 psi = 2 inches
THINGS WE CAN DO WITH THESE FORMULAS:
EXAMPLE: A 700 R4 has 62 psi of line pressure at Idle.
The tip (reaction end) of the PR valve has a diameter of 0.365" (0.365 divided by 2 = 0.1825 radius) 0.1825 x 0.1825 x 3.14159 = 0.1046" area
We want 75 psi of line pressure at Idle
First, let's see if those numbers add up, using: Pressure x Area = Force
62 psi x 0.1046 = 6.48, or 6 1/2 lb PR Spring
We want 75 psi:
What if we put in an 8 lb Spring? Force divided by Area = Pressure
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