swodo

Perhaps a stupid question, but assuming a stock 2200 RPM at 60 MPH wouldn't a 3000 rpm stall speed converter be "slipping" at the same speed?

imp

No question is ever stupid; some answers thrown out sometimes are. "Stall Speed" associated with a torque converter refers to the average engine speed which will be attained with the transmission in gear, brakes locked, and throttle held in wide-open position.


In operation, a torque converter is always "slipping" a bit, so long as it is transmitting power from the engine to the transmission. Slip is the difference in speeds between the engine and transmission input shaft. Slip creates heat, generated by friction within the fluid. Heat represents burned fuel, thus the slip present affects fuel economy. This is why torque converters have seen a mechanical clutch placed within them in recent years, which "locks-out" the slip, thus increasing fuel economy.


Your example of 2200 engine rpm at 60 mph reveals nothing about the amount of slip present given those numbers, as many factors affect that engine speed, such as throttle opening, whether the vehicle is at a constant speed, or possibly climbing a hill. Upon releasing the throttle to coast, the slip works in reverse, the car's motion being transmitted through the torque converter backwards, to drive the engine at some much lower speed.


Cruising on level roadway, with constant throttle opening, the transmission input shaft speed would be a few % lower than the engine speed, so at engine = 2200, transmission = about 2100. The slip under those conditions would be 100 rpm. imp

Buck Sergeant

swado, the quick answer to your question is "no." The torque converter is one of the most misunderstood items in the automobile. IMP is correct in his analysis. My experience has shown me that if you can FEEL slippage at any RPM, then there is a problem with the tranny or torque convertor. As I am implying, while cruising, you should NOT be able to feel the 100 RPM drop. Of course, under drag racing conditions, a 100 RPM drop is very noticeable, and very undesirable.

P51C

This is a multiplate lockup torque converter and will be fully locked on the highway to prevent slip and overheating the fluid and trans parts. Back in the days before plate-style clutch converters, a high stall converter would be brutal on the highway and kill the transmission in short order. Stall speed just refers to the maximum flash rpm when not moving that the engine jumps to when you accelerate aggressively. This is the same as on a stick car when you rev it up and let the clutch out. YOU determine "stall speed" in those circumstances. In an auto, it does it for you.

Buck Sergeant

P51C, I totally agree.

swodo

Makes sense now. Thanks to all.

imp

I don't know how your type and style of torque converter was so easily determined, since I did not see a reference to year, model, etc. Important thing is whether you follow and understand "slip" or not. imp