Pardon my thickness but what is locking out gears

[myredracer]

in a transmission all about? What is involved to do it? I don't even know if our '09 F250 can do it. We have a V-10 with 4.1 final drive, rated to tow 12,500 lbs and tow a 29' TT weighing about 7K lbs. We just had a run up about a 10% grade to 4,000 ft. I had tow haul on and it was fine and had it at about a steady 50 - 55 mph. Do I ever need to think about locking out a gear? Or have I got this all wrong and it's something you would do for downhill runs to improve engine braking?

[valhalla360]

Locking out a gear is simply turning off overdrive or moving the lever to a lower gear. In that situation, the higher gear ratios are locked out. With tow/haul mode, the transmission will generally handle things just fine.

But if you are going up and down short steep hills, the transmission will sometimes hunt for the correct gear bouncing back and forth frequently. If it happens occasionally it's not a big deal. If it's shifting every 30seconds, it's hard on the transmission. A simple solution is just to lock out the higher gear and run in the lower gear at slightly higher engine RPM.

Locking torque converters have been around for quite a while. A torque converter is basically a hydrallic pump that allows slippage. The slippage allows you to leave the vehicle in gear while stopped. The problem is that slippage doesn't stop while traveling down the road and it wastes energy. The solution is basically a clutch that locks the two halves of the torque converter together so there is no slippage. When at a stop light, the clutch releases and the torque converter operates as normal with slippage. Once up to speed, the clutch locks up and eliminates the slippage.

Early versions only locked the torque converter in overdrive. More recent ones can lock additional gears. An easy way to check if you are locked is to let off the gas or punch it for a second. If the RPM hold steady or gradually change with the speed, it's locked (there's no slippage so the RPM and speed are locked together). If the RPM jumps up or down quickly (much more so than the speed), it's unlocked and you are seeing the impact of slippage.

There can be a side benefit for towing if the tranmission locks in lower gears. When unlocked under heavy load, that slippage creates lots of fluid friction and heat. This can overheat the transmission. If you can hold a steady speed in a gear that is locked (without lugging the engine), there is no slippage so the transmission fluid doesn't overheat. This is why you don't hear about manual transmissions overheating.

[nomad297]

bid_time wrote:
Overdrive is not the same as Torque Converter Lockup. Overdrive is a gear with a higher than 1:1 ratio. Locking out a gear simply means it's a gear you don't allow your transmission to shift into. It's normally done with the gear selector lever.

Best answer.

Bruce

[bid_time]

Overdrive is not the same as Torque Converter Lockup. Overdrive is a gear with a higher than 1:1 ratio. Locking out a gear simply means it's a gear you don't allow your transmission to shift into. It's normally done with the gear selector lever.

[Dave_H_M]

Whoah Mr. Forest you gave some bad skinny on torque converter lock up.

Even my ole 99 F250 would lock up when it was out of overdrive. :h

I do not know anything about the trans arrangement in the OP's truck. On my 2012 F 250 locking out a higher gear would be toggling the switch on the shift lever down to the next lower gear. The gear selected that would be the highest that the trans could then go would be displayed on the dash.

[Camp__Forrest__]

It sounds like you're asking about torque converter "lock up". This is when the input shaft of the transmission is "locked" to the output shaft of the engine. Under normal circumstances, there is a slight amount of slip in the torque converter between the engine and transmission. To improve fuel economy, modern transmissions can lock the torque converter to prevent slippage. In most transmissions, this is indicated as "overdrive". Engaging tow/haul mode, turning off overdrive, or moving the shift lever from D(with circle) to D will prevent lockup.

[Old-Biscuit]

Turn off OD
Move shift lever out of 'D' to 2
ETC.