How do I tell when my torque converter "locks up"?

[gdbontly]

I've read about automatic transmissions and torque converters, and I basically understand how they work. I think I understand that when the torque converter "locks up", the truck will pull harder and the transmission will run cooler. Is this correct? How can I tell if/when the converter locks and unlocks? And finally, does it only lock up in 3rd and 4th gear on the 48RE? Thanks.

 

[Matt400]

The converter will lock in 2nd, 3rd and OD based on various conditions such as RPM, Vehicle Speed, load, transmission temperature etc.



When it locks it feels like a shift and rpm's drop because you now have a direct connection between the engine and drive line.

Telling when it locks will take getting use to the truck. Some obvious points are pulling a grade while in 2nd gear and then you note an RPM drop because it locked or when on the highway under light accel passing through the 50 mph range you get a big drop in rpm cuz it locked while in OD.

 

[R.M.THOMPSON]

I think if you can watch the tach after increasing speed from a dead stop you will observe ;

1 ) first to secound //// 100 rpm drop

2 ) secound to third //// 100 rpm drop

3 ) lock-up at about 45 mph //// 50 rpm drop

4 ) O. D. thru 50 mph //// 100 + rpm drop



Odd thing is though , if you coast thru 50 the O. D. shift is very very smooth. Light accel thru fifty and the shift is to heavy for me. Now a medium rate of accel , I think Lock-up & O. D. hit at the same time or in conection with each other !!! I can't stand that 150+ rpm dump..... Last but not least favorable , is hard & full accel , in which case all shifts are appropriately spaced and rpm drops are closer togather and due to timing ,the mph point are not as listed above. O. D. may be as high as seventy+. I hope this helps in understanding the shift points. BTW , some of us have adapted or adopted a method of timing or training that 50 mph threshold as a place to coast thru or hard power thru while running unloaded or not towing . Wish there was a potentiometer on the dash to adjust that O. D. shift point and I think this trans would be almost perfect.

Mark T.