How does a 4 speed automatic gear box work?

The torque converter is an oil filled donut (steady Wayne) that offers varying resistance between the engine and the gearbox. It uses a series of vanes and a turbine with an impellor driven by the engine. It has a number of other jobs and that is a bit of an over simplification but it's probably all you need to know :-). On a ZF 4 speed it has a "lock up" mode where the flow of oil is reversed activating a direct drive clutch feature, effectively locking the torque converter. This normally happens at between 50 and 60 MPH depending on the gearbox and TC.

An oil pump (driven by the torque converter) provides hydraulic pressure and a series of valves and hydraulic "logic" circuits operate one or more clutches inside the gearbox to transfer power from the input shaft to the output. These valves and logic circuits are located beneath the gearbox where the selector and kick down cable go in. The clutches are very similar to motorcycle wet clutches if you are familiar with those. The combination of "kick down" cable position, gear select position, the oil pressure and a centrifugal "governor" on the back of the gearbox are used by the logic circuits to determine which gear should be selected.

The power is transmitted from one end of the box to the other via shafts, clutches and sun gears, it's effective route and gearing being determined by which combination of clutches are operated. (the sun gears allow the input shaft to rotate faster than the output shaft - the clutches can be used to "lock" the sun gears.)

Any the wiser ? :-)

I have a copy of the Land Rover "Service Product Training" manual that, one day, I will get around to converting into a PDF. If you REALLY want to know how the box works, see if you can get hold of a copy...

cheers

Dave W.

Taken from hotrodders.com: "as far as how does a torque convertor work? picture two fans facing eachother. the fan with the power on will drive the fan without power. now switch the air being blown to trans fluid and you've just mastered basic torque convertor theory. the engine drives the "fan plate" which inturn drives the transmission. hope I didn't totally screw you up with that bit of misinformation. but I understood it. call me crazy......."

But for more information see here:

Don't you just love the Web?

HTH David.

Oh, just realised, try this:

David

Just read through it again myself - crikey, who designs these things? It's a bloody nightmare! Hats off that they work at all!

Mark> Hi all, I am about to fit a 4 speed Auto box to my Mark> defender. I like to know how things work, so are there and Mark> good sites that will tell me:-

Mark> How a 4 speed auto works? What is a Torque converter and Mark> how does that work, why do I need one? What is difference Mark> to a 3 speed, apart from the obvious?

Mark> I know how manuals work as I've rebuilt a couple but I have Mark> not the Mark> foggiest how autos do their thing.

--

+-------------------------------------------------------------------------+ |Andy Cunningham aka AndyC the WB | andy -at- cunningham.me.uk | +-------------------------------------------------------------------------+ | - Everything you wanted to know || about the P38A Range Rover but were afraid to ask. |+-------------------------------------------------------------------------+"And everything we want to get/We download from the InternetAll we hear is/Internet Ga-Ga/Cyberspace Goo-goo" -- from "Radio Ga Ga"/"We will rock you"

In message , Mark Hale writes

Ask any female driver - You press the accelerator and it goes. You press the brake and it stops.

Ouch!! -SWMBO has just read this post over my shoulder.