How does it work ?

[theoldwizard1 2]

I know a few things about automotive electronics. I even know a bit about manual transmissions and typical automatic transmission from cars and trucks, but I don't know anything about how the "automatic" transmission on a Wheel Horse works !

I have studied some of the exploded drawings on the Toro Master PartsViewer and seem to have more questions than answers. Looking at the drawings from a C-121 automatic

• [*:3ab6pusl]The "pump" in this example seems to actually be 2 pumps. A swash plate pump and a gerotor pump. Why ?[*:3ab6pusl]The swap plate seems to be controlled by the trunnion shaft, but how does it change the swash plate angle ?[*:3ab6pusl]The part called the "Automatic Transmission" appears to be just a swash plate "motor", but how does the fluid get transferred in to it from the pump (I would assume it is from the swash plate pump not the gerotor) ?

Is there any "How does it work" tutorials ?

[can whlvr 993]

i cant answer your questions but i tore one apart and ended up taking it to a profesional,it was worth it in the end

[Trouty56 567]

Wizard,

Have you seen theses diagrams??? This explains the fluid routing.

Neutral

Forward

Reverse

[theoldwizard1 2]

Trouty - Those diagrams help a lot.

Now answering some of my own questions.

The "pump" in this example seems to actually be 2 pumps.

[mavfreak 11]

I ave a auto trans, is there anything that is usable inside one? its missing the pump and strainer and one axle is shot do to a loos hub and key way. I have no use for it but was wondering if some parts can be used by others before I scrap it

[Trouty56 567]

Mayfreak,

The housings could maybe be used by someone. I've seen many cracked ones. The right side of mine is not cracked but where the pin goes though for the hitch it is broken. I haven't had the need to remove that hub yet (seal is still OK) but when I do i'll be looking for a right side. Not looking forward to the hub removal...I've read horror stories on here and have seen the pics to back the stories up!!

[mavfreak 11]

I really don't want to scrap it on the chance that someone may need something of of it, but its just in the way. I guess I could tear it down and just put it in parts bin

[theoldwizard1 2]

From the horse's mouth (thanks to trouty)

PRINCIPLES OF OPERATION

(Refer to the Neutral, Forward & Reverse Schematic Diagrams, Figs. 1 (Pg. 6), 2 (Pg. 7), 3 (Pg. 8). Power is transmitted from the engine through a belt and pulley arrangement to the pump shaft (shown at left of diagrams). Rotation of the input shaft causes the main pump cylinder block and the charge pump to turn, initiating the power transmitting function. Oil from the reservoir is drawn by the charge pump through the inlet strainer and forced, by way of the check valves, into the low pressure lines. Oil introduced by the charge pump fills the area in back of the cylinder block pistons, holding them against their swash plates in both the pump and the motor. When the pump swash plate is in neutral the pump cylinder block pistons do not move in and out. Thus, in neutral. no oil is being pumped from the variable displacement pump. low pressure oil from the charge pump fills the complete system, including the area around the acceleration valves. These valves are held open by the spring between them. The acceleration valves remain open until high pressure oil is introduced behind one of them. Which valve depends on the direction of rotation as determined by the position of the pump swash plate.

RELIEF VALVES

Pressure from 70 to 150 PSI is controlled by the charge pressure relief valve. This exhausts the excess charge oil not needed to make up leakage to the oil filterandcase reservoir. When an implement Is used, the maximum charge pressure, from 550 to 700 PSI, is limited by the implement relief valve. Some separated systems also incorporate a high pressure relief valve which serves to prolong the life of the hydrostatic unit. located on the left side of the tractor above the transmission, this relief valve has been factory adjusted and will reset automatically if triggered.

FORWARD TRAVEL

In forward position the pump variable swash plate tilts and, as the cylinder block continues to rotate, the pistons cross over a valving plate under low pressure and advance up the swash plate. This in turn pushes them into the block, forcing the oil from the block under high pressure. At the bottom of their stroke, the pistons pass again to the low pressure side of the valving plate and are refilled by the charge pump with ail returning from the motor through the low pressure line. The high pressure oil (shown in black) closes the high pressure check valve and travels through infernal passages to the inlet side of the piston motor.

In the motor, high pressure oil acting on the back of the piston forces the piston down the incline causing the block to rotate and turn the output shaft.

REVERSE TRAVEL

When the control handle is moved to the reverse position, the pump variable swash plate is tilted in the opposite position which changes the direction of oil flow. The high and low pressure circuits interchange causing the motor to rotate in the opposite direction.

ACCELERATION VALVES

The acceleration valves are placed in the circuit to limit vehicle acceleration to a safe rate. With the control lever in neutral, oil is under low pressure throughout the circuit. When the control lever is advanced, the circuit pressure increases, causing the oil on the high pressure side to bleed by the flats on the valve lands and into the low pressure side. This high pressure oil continues to bleed to the low pressure side,

by-passing ~he piston motor and holding the acceleration rate to: a safe level during the time it takes for the acceleration valve to close against its seat. The delay in closing the valve is due to the time it takes the high pressure oil to bleed through the small orifice in the acceleration valve metering plug and into the area behind the valve.

PUSH VALVE

When open, the push or free wheeling valve allows the oil to by-pass or flow from one side of the main circuit to the other. When pushing, the motor becomes a pump forcing the oil through the open valve and to the other side of the motor. The direction of oil flow depends on the direction the unit is pushed.

NOTE:: On "B" and "C" series tractors, and similar prior models, the hydrostatic pump and motor are bolted together as a single unit. For purposes I of description we will refer to such a transmission system as a "standard system".

On

[WheelHorse_of_course 99]

There is a Automatic Transmission Repair Manual PDF (~68 pages) you can download from the Toro site.

If you would like a copy of that PDF contact me via email.

Or, if you want a bound and printed copy of this, let me know, and I can sell one to you (special price of $11 including shipping for RS members).

cheers

Rolf :banghead:

[flyovrcntry 115]

How does it work? Push on the lever!!! :thumbs:

[Trouty56 567]

Now you can change the title of the thread to 'How it does work!'

:banghead: