Slart

Hi,

I've been trying to learn how our transmissions work. Can someone explain what the boost valve does?

I think when it's activated it alters the pump's fluid return system (restricting it) so it makes more pressure. Is this correct?

My main condition is under what conditions it activates, and if it's all or nothing activation, or a variable thing.

Thanks!

Steve

Slart

Oh, I should add I am specifically talking about a 4l60e, but am eager to learn about any model if someone is willing to share knowledege.

TeamTripp

Pressure is regulated by pump displacement. The pump rotor and vanes sit inside a pump slide so that volume (and pressure) can be adjusted by reducing pump capacity. The pressure regulator valve controls how much fluid is directed to the "decrease" side of the pump slide to change its output. This pressure regulator valve is spring loaded for a minimum idle pressure. As throttle position and engine load increase, pressure needs to increase as well. Fluid is directed from the pressure control solenoid to the Boost Valve, which puts increased pressure on the regulator valve, to reduce the amount of decrease fluid going to the slide, which will increase pressure.

In a nutshell, the Boost valve acts on the pressure regulator valve to increase pressure in related to engine load.

Slart

Thanks!

I think I understand.

The pressure control solenoid (in the valve body) controls the action of the boost valve. The boost valve (in the pump), which actually controls pump pressure?

In my atsg manual it says the pressure control solenoid varies pressure to the pressure regulator valve. Is the pressure regulator valve the boost valve?

On a 4l60e, the pressure control valve is the EPC thing that I've been turning to adjust pressure, and on a 700r4 it's the throttle valve?

TeamTripp

The pressure regulator sits on top of the boost valve and is seperated by springs. Movement of the boost valve creates more tension on the pressure regulator valve to increase pressure.

Line pressure flows through the Actuator Feed Limit valve and becomes AFL fluid. This AFL fluid then goes through the EPC. The EPC regulates how much fluid goes through it by the PCM and becomes Torque Signal fluid (in theory, this pressure increases relative to engine torque). Torque signal fluid is responsible for movement of the boost valve.

In the 700R4, the Throttle Valve did what the EPC does now. There is no need to crank on the EPC solenoid to firm up shifts. Sure, its cheaper, but there are better ways to acheive a better performing transmisison.

Slart

Thanks for the info! A little above my head, but I get the jist.

Steve