I just finished reading this thread regarding the installation of a manual TC lockout switch (very interesting thread).

As a newby to all this, can someone give me a simple explanation about what the torque converter does, what the difference is between locked in and not locked, and how this affects driving characteristics and towing?

Thanks in advance.

 

A torque converter allows slippage between the engine and the trans. This allows you to come to a stop without stalling the engine. When the converter is "locked up", there is no slippage and the engine and trans are, in effect, locked together.
A lower stall converter (Goerend, ATS, DTT, etc) is a more efficient coupling than the stock converter. It won't "slip" as much as stock. It gives a more one to one feel, while driving. This is the exact opposite of higher performance converters for street/race cars. Their stall speed is generally higher to allow the engine to spin more freely up to its desired rpm band.
I am in no way an expert, btw...

 

Ok - I did some research and I think I understand the function. Now when driving, how can you tell whether your TC is locked up or not? Also, what is the function of the valve bodies?

 

You will feel your truck go into lockup around 50-55mph. You will hear and sorta feel it. Sorta feels like the tranny shifted but if you watch your tach...it doesnt go down like you shifted.

Valve bodies are a maze that pushes fluid. It makes your transmission shift


Heres some GREAT info how transmissions work

http://auto.howstuffworks.com/automa...nsmission1.htm

 

Mike,

You can tell when the TC locks up by a reduction in engine rpm and a feeling of direct drive, i.e. engine RPM and vehicle speed vary linearly. When the TC is not locked up you can put your foot on the throttle and the engine rpm will increase quite a bit, but increase of vehicle speed lags behind the RPM increase, it feels like something is "slipping" and in fact is on some level. In essence when the TC locks up the transmission becomes a direct mechanical link between the crankshaft and the rest of the drivetrain (ultimately the tires), just like a manual transmission when it is in gear. The most noticeable lockup event occurs after the tranny has shifted into overdrive, then it will lock the TC at around 48 - 52 MPH under light throttle conditions traversing flat ground. The engine RPM will decrease a ~500 RPM and you can feel a jolt forward as the TC locks up and direct drive is achieved.

I saw your response to my last post on that thread and agree that if abused the manual lockup could certianly cause damage, I don't plan to beat mine to death , I just want better control of the lockup. As one post suggested the lockup (in OD) happens around 48 MPH, I'd like it to lock up at 40 MPH. Plus I'd like lockup in 1st gear, at present the stock 48RE will not do this, don't abuse it and everything will be fine.

Hope this helps.

Eric

 

Thanks for the replies, I learned a lot today.

 

I've had some of this debate before - the 48RE WILL lock up in every gear if you manually shift it on the column. Try it. Go easy on the go pedal and watch what the RPMs do as you slowly accelerate. Since I tow in the mountains I use 2nd gear a lot and it locks up at 30 MPH. That keeps me from slipping as I pull the passes so everything stays cool.

I'd like the manual switch so I could force lock up earlier in 3rd. I believe that locks at 50.

 

Lots of misunderstanding of the operation of the torque converter. The "How Stuff Works" article is pretty good but lacks a little on the explanation of stall speed and lock up.

Think of the TC as three fans. The fan bolted to the engine is the "impeller". It is blowing fluid on the "turbine" which is the fan splined to the input shaft of the transmission. To increase efficiency and multiply torque there is a small third fan between the impeller and the turbine called the "stator". The stator's job is to redirect fluid exiting the turbine back in to the impeller.

Since none of the fans touch each other you can idle at a stop light without a manual clutch. Accellerating the vehicle allows the impeller to speed up before the impeller can catch up. The fluid that exits the stator is turned to the rotational direction of the impeller. This multipies torque. If accellerating hard enough, so much fluid will exit the stator and "load up" the impeller and the engine cannot turn the impeller any faster. This rpm is the "stall speed". For best performance, the "stall speed" should closely match the peak engine torque rpm. The easiest way to adjust " stall speed" is to change the diameter of the torque converter. Think of a weight at the end of a string. If the string is short you can swing it faster. There isn't as much centrifugal force. Lengthen the string and the centrifugal force becomes greater and harder to swing as fast. Race cars use small diameter converters to get the engine up in the power band quickly. Our trucks make large amounts of torque at low rpm's so lower stall speeds are desirable. The problem is you can't easily go bigger on the torque converter diameter because of tranmission design. The aftermarket guys tweak the angle of the stator blades (or add multiple stators) to try and lower the stall speed.

The differential of speed between the impeller and turbine is converted to heat. The potential large speed differential while in overdrive makes it necessary to connect the turbine and impeller in OD. This is the reason they add a mechanical clutch to the torque converter (lock up) is to reduce heat in overdrive. The problem with locking the converter in lower gears is the lack of torque multiplication (Admittedly, this is more of a concern with gas powered engines) and a small clutch that is only designed to hold while cruising (low torque). Aftermarket guys beef up the lock up clutch so it will hold easier at higher torque levels. This allows engine torque to accellerate the vehicle (Horsepower!)

Now,I don't think our trucks have the ability to lock the clutch up in first gear. This is to prevent stalling the engine if the lock up soleniod fails. Manual gear ranges do NOT bring on the lock up clutch. They lock up the "one way" clutches inside the transmission that would normally just freewheel on decelleration.

 

good explanation Nice car list.