what exactly does a torque convertor do and how does it work? A buddy told me my torque convertor is goin out on my AOD because it takes alot of throttle to go up a hill when startin out. Seems thers a lot of slippage. Also, it shifts real sloppy. I's wonderin what affect does the torque convertor do to a tranny.

 

Hello redneckdieselmechanic,

The torque converter provides two functions, like a clutch it disconnects the engine from the transmission (otherwise you couldn't stop), and secondly it provides torque multiplication.

Imagine two room fans facing each other. One fan is plugged in and running (like the side of the torque converter connected to the engine) and the other is "wind milling" from the air rushing past it. Even though it is just air propelling the "wind mill" side, don't poke your finger in there. Power is transferred.

Now, imagine a fluid used instead of air, yep ATF. Next, imagine instead of an open room where the wind just blows in a straight line, there is a "U" shaped housing that redirects the fluid from the wind mill side back to the driven side. This is what the torque converter looks like. Think of it like a hollowed out doughnut cut in half.

With fluid there is a much "stronger" coupling between the driven side and "wind milling" side. When the engine is turning slowly, there can be a lot of slipping between sides of the torque converter, this is what happens at idle. If you plant your foot on the brake, put the transmission in drive, and stomp down on the gas [DON"T DO THIS FOR MORE THAN A FEW SECONDS!], you'll find the torque converter "stall speed", the engine cannot overcome the friction of the shearing oil.

In between idle and stall speed there is a zone where the torque of the engine is multiplied by the torque converter. The fluid spinning against pitched vanes provides the torque multiplication. This is nice because it allows a higher gear ratio to be used in an auto-transmission than a corresponding manual transmission would need. Back in the way old days there was a GM transmission called the "Power Glide." It only had TWO forward gears. Torque multiplication was the only way that would work.

There is a problem with torque converters, there always is a slippage. This produces heat from the oil shearing and lowers fuel economy. To overcome this problem, today's automatic transmissions actually have clutches that "lock" the two halves of the torque converter together. You can see this happen on your tachometer when you go into overdrive. It first shifts up into OD, you see the RPMs drop and then it drops some more when the torque converter locks-up.

So, the problem you mention with your truck sounds like your stall speed is much higher than normal. This is a possibility, although torque converters are pretty simple and reliable contraptions. You may also have worn clutches inside your transmission that allow excess slipping. A third problem could be low fluid level, or a plugged line that isn't allowing sufficient fluid pressure to the clutch mechanism. Automatic transmissions are pretty complicated. I would have a reputable shop diagnose the system before blindly changing that torque converter.

I hope this helps.

Rich
2002 F350 V10 4x4 SCab

 

I realy appreciate it man. How bout another question? Would a AOD out of a 89 f 150 302 fit my 84 f 150 302 2v? Would i have to change the tv cable out with my tv rod or is there other complications? I found a rebuilt AOD for 300 bucks in a wrecked 89 f 150 in the paper. Seems like a good deal to me.

 

It could also be a stuck stator. At lower speeds it needs to freewheel, and then lock close to stall speed. If the power is down on pull-out, but seems to be okay at higher speeds, this could be the problem.