How do I tell when I'm in transmission "lockup"?

usa591 · **Posted:** Mon Aug 09, 2010 2:41 pm

NooB question here: how can I tell when the Tranny's locked up? I remember seeing a post somewhere but can't find it... :oops:

The search engine on this site makes it challenging to find info sometimes as it is ignoring the term "up" in "lock up" as it is too short.

-p

boilermaker2 · **Posted:** Mon Aug 09, 2010 3:44 pm

If I understand the question, the easiest way to see if your torque converter locked out into overdrive is to watch the tachometer. It will drop to ~1675 at 49-50mph and again to ~1650 at 60. RPMS increase to just over 2000 RPM before it locks and drops.

On the flip side, if the torque converter refuses to lockout, you will also see RPMS climb. If I remember correctly, it will climb to about 2500 RPMs at 60mph. This will happen during manual lockout ("tow" button on shift stick), ignoring the transmission shudder and just taking off driving or if your alternator was knocked-out while you waited for a water pump :banghead:

and their is not enough electricity flowing through the system (voltage is required for torque converter lockout to occur evidently) for lockout to occur..

flash7210 · **Posted:** Mon Aug 09, 2010 4:34 pm

The shift pattern works like this...

O/D Off
1st - 2nd - 3rd - 3rd+lockup (@ about 36-38 mph)

O/D On
1st - 2nd - 3rd - 4th - 4th+lockup (@ 51mph) - 5th+lockup (@ 62mph)

If you are at a speed where you think you should be at lockup (i.e. 55mph), watch the
speedo and the tach closely. When you accelerate, the speedo will move up proportionally
with the tach. When the torque converter in unlocked, you might see the tach hold a steady
rpm while the speedo slowly catches up.

Example:
From a steady speed of 40mph (O/D On) accelerate and try to maintain the tach at 2200rpm.
Notice how your speed increases while your RPM stays the same.
Then, once you reach 51mph, lockup occurs and RPM drops. Acceleration will continue but
you will notice that while your speed increases, the RPM increases at an equal rate.

Your three most important gauges are your speedometer, tachometer, and your butt.
Pay close attention to all three and you will soon have it figured out. :mrgreen:

stoutdog · **Posted:** Mon Aug 09, 2010 7:49 pm

To add to what flash said, you are in lockup when your RPMs change with your speed rather than with your foot. In other words, 75mph = ~2200RPMs regardless of whether or not you are pressing the pedal more to go up hill or have your foot completely off the pedal coasting down.

You will come out of lockup, momentarily, if you gun it to pass someone. Once you let off the pedal some, you will reenter lockup.

usa591 · **Posted:** Tue Aug 10, 2010 2:42 am

Dumb question, but what's the purpose of an overdrive gear? Is this responsible for the "roll-off" I see/feel on the tach when going up a hill at, say, 70mph once I get the Libby to the speed I want?

...so say you go from 1-2-3-4-5 then add an "overdrive" gear in 5th (5.5?), you'll be using less fuel than when "locked up" ? ...but the trade-off is less responsive acceleration, especially when towing?

KaspinCRD · **Posted:** Tue Aug 10, 2010 1:03 pm

an overdrive gear is just any gear that spins the output faster than the input. On our trucks, both 4th and 5th gears are overdrive gears. When you turn off O/D with the button on the shift lever, the truck will only use 1st through 3rd gears.

kdlewis1975 · **Posted:** Tue Aug 10, 2010 2:22 pm

Overdrive is for fuel economy. On some level, it is probably for longevity too since the engine has to turn fewer RPMs to travel a specified distance compared to that of no-overdrive. If you need to accelerate or climb a hill, turn of the OD and mash-it. If you're cruising on mild grades or level ground, you can leave it in OD.

stoutdog · **Posted:** Tue Aug 10, 2010 7:57 pm

kdlewis1975 wrote:

Overdrive is for fuel economy. On some level, it is probably for longevity too since the engine has to turn fewer RPMs to travel a specified distance compared to that of no-overdrive. If you need to accelerate or climb a hill, turn of the OD and mash-it. If you're cruising on mild grades or level ground, you can leave it in OD.

The only time I drop out of OD is if I need to accelerate uphill, in the mountains. Otherwise, the Jeep holds speed just fine, 75mph on mountain grades... shouldn't be dropping out of OD every time you climb a decent sized hill.

Joe Romas · **Posted:** Wed Aug 11, 2010 7:05 am

Nobody has mentioned it yet BUT TC lockup won't occure untill the transmission has gotten up to operating temperature or if the transmission fluid is overheating.

mikey1273 · **Posted:** Wed Aug 11, 2010 6:20 pm

Joe Romas wrote:

Nobody has mentioned it yet BUT TC lockup won't occure untill the transmission has gotten up to operating temperature or if the transmission fluid is overheating.

Very very true... I have realized this since I live less than a mile from interstate 83 and the south on ramp is with in a 1/2 mile. when I leave the house and get on heading south I have to drive a few miles before lockup happens.

How do I tell when I'm in transmission "lockup"?

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