: Questions about a Stall Torque Converter ???



Young DeVille
10-17-04, 01:00 AM
Today at work I heard some guys talking about cars and I heard one of them mention a Stall Torque Converter. One of the guys laughed and walked out of my department. So my question is what exactly is a Stall Torque Converter and how does it work??? Also would this be useful in a 97 Deville??? :want:

eldorado1
10-17-04, 12:56 PM
http://cadillacforums.com/forums/showthread.php?t=22294&page=2&pp=20&highlight=torque+converter

BeelzeBob
10-17-04, 03:50 PM
I think you mean they were talking about a higher stall speed torque converter. All torque converters have a stall speed designed into them. That is the engine RPM at full stall against the torque converter. If you hold the brakes firmly and floor the throttle in drive the engine will rev up against the torque converter to a certain RPM. That is the stall speed. Torque converters are often modified by aftermarket companies to raise the stall speed to allow the car to accelerate harder off the line. The modified converter will allow the engine to rev higher at full stall so that it gets into the power band sooner.

Factory converters are designed with a lower stall speed to optimize fuel economy, efficiency, minimze temperture inside the transmission,maintain adequate durability, etc.... A modified converter with a higher stall speed will slip more in normal driving so it will adversely affect fuel economy, temperature inside the trans, durability of the trans potentially, etc. A high stall torque converter in an automatic transmission is probably the single most bang for the buck for performance if you are looking for acceleration off the line and it can be driven daily if used intelligently...i.e...don't hold the torque converter in a high slip mode when climbing hills, add an auxilary trans cooler, etc....

Probably the guys laughed because they didn't know what a high stall converter was or did and pretended to be wise and laugh and walk away or they thought the idea of putting one in a Cadillac was funny. A Deville is not generally thought of as a street racer so putting a high stall converter in the trans would be kind of an oddity....but it would improve the off-the-line performance considerably.

dkozloski
10-18-04, 01:35 AM
Why would it make any difference what amount of slippage there was in the converter, within reason, if the converter has a lock up system anyway like TCC? Don't some automatics have a lockup shift in every gear?

BeelzeBob
10-18-04, 01:36 PM
Why would it make any difference what amount of slippage there was in the converter, within reason, if the converter has a lock up system anyway like TCC? Don't some automatics have a lockup shift in every gear?


You are right. A lockup clutch in the torque converter negates any slippage and would theoretically negate the impact of a higher stall/higher slippage torque converter....once it locks up. Most transmissions with a lockup torque converter have a minimum lockup speed for driveability reasons of 35 to 45 MPH. Many of them do not lockup the torque converter at speeds below 55 mph even. I don't think many of them (if any....) lockup the converter in first and second gears....I would doubt it as it makes driveability difficult as the engine cannot flare if more throttle is requested which makes the car feel very "flat" for performance reasons. It also makes the shift quality much more difficult to calibrate in the trans if the torque converter is locked. In addition, if the torque converter is locked, it generally unlocks the instant any throttle is requested to improve the performance of the vehicle so the added slip of a higher stall speed converter would be evident. In most cases the torque converter runs "open" a great deal of the time and it only locks up at cruise conditions which is where the greatest fuel economy benefits are.

Rob Benham
10-19-04, 02:46 AM
I just spotted in my 94 SLS hand book that the STS has the same gearbox, but the converter is described as a Torque converter clutch as opposed to a Viscous converter clutch. They are both 4T80Es Got me beat, but is this what they are getting at?

BeelzeBob
10-19-04, 04:59 PM
The torque converter clutch is a lockup clutch that locks the turbine wheel to the housing of the torque converter thru a clutch plate to eliminate any slippage in the torque converter. This is inside the torque converter and , in effect, just makes the torque converter a solid connection when it applies.

Typically this is called a TCC for torque converter clutch.

In the FWD Cadillacs the lockup mechanism is the same but there is a viscous coupling inside the torque converter clutch mechanism so that the lockup is not purely solid but thru the viscous coupling that allows some slight slippage or creep to insulate the driveline from chuggle. Chuggle is that feel you get when the driver of a manaul trans gets the RPM too low and the engine starts to run rough or lug...or chuggle. When a TCC locks up the driveline cannot slip so it can chuggle, especially in FWD cars with transverse engines.

The VCC or viscous converter clutch is basically the same thing and same function as a TCC...but it has the extra isolation of the viscous coupling to prevent th chuggle.

Search in the archives using "TCC" and "VCC" and "torque converter clutch" and "viscous converter clutch" and read my posts for more info.

The Northstar 300 HP engine with the 4T80E trans was TCC equipped in 1993/94/early95. It was running changed to a VCC in mid model 1995. So....a 1994 STS would have a TCC and a late 1995 STS would have a VCC.


TCC or VCC has nothing to do with the stall speed of the torque converter.