Installing a lockup kit can provide great benefits, which is why it's a popular mod especially for people who tow.
A lockup kit:
reduces fuel consumption,
reduces transmission temperatures,
improves engine braking, and
gives better driving responsiveness.
This blog discusses various driving conditions and provides my recommendations on when to use the lockup kit, and when to switch it off.
Why is there a Torque Converter Lockup Clutch?
Firstly, I’ll talk about the intended design and use of the torque converter clutch and how it influences when to use the lockup kit.
The torque converter is a fluid coupling between the engine and the transmission gearbox. It’s a brilliant device which acts like the clutch of a manual gearbox, but automated.
Being a fluid coupling, it allows the engine to idle whilst stopped, and provides torque multiplication as you accelerate or are under load. But once acceleration has stopped and you’re driving at a constant speed, a fluid coupling can only be about 90% efficient. When you’re working the transmission hard its efficiency drops and it causes heat.
More transmission heat = wasted energy = wasted fuel
Therefore, every modern transmission has a lockup clutch inside the torque converter.
Normally, when in highway driving conditions, the lockup clutch can engage and it locks the engine and gearbox together to improve fuel efficiency (no slip = no wasted heat = no wasted fuel). When locked, it performs like a manual transmission.
Whereas the factory ECU optimises the use of the torque converter clutch for fuel savings when on the highway, our lockup kits are optimised for fuel saving, reduced transmission temperatures and better engine braking in a wider range of conditions.
The clutch in a manual gearbox is substantially larger and stronger than a transmission lockup clutch; in a manual gearbox the clutch is required to get the vehicle moving from stationary and to also cope with a wide range of driver skill levels (abuse).
The transmission lockup clutch is computer programed only to engage once there is low slip. Our SafeLock® feature also ensures this. Once locked, though, severe driveline shock loads should be avoided.
When should you use the lockup kit?
Many people only use it when towing or on the highway, but you can use the lockup kit all the time if you want. Personal preferences and various driving situations will influence your decision.
When should I turn it ON?
We say, if there is a benefit to you, turn it ON. If not, turn it OFF
Benefits can be for fuel savings, transmission temperature protection, and better engine braking. Maximum benefits are obtained when the transmission is working hard, such as when towing, climbing hills, or in sand.
But you can also get benefits when you’re not towing. Driving normally doesn’t work the transmission as hard and it’s unlikely to overheat. Although temperature reduction is less important, you can still get better fuel economy when driving at highway speeds.
In general, you’ll save fuel if the kit is locking the torque converter when the factory ECU would otherwise have it unlocked. It will also run cooler and extend transmission oil service intervals.
When “performance driving”, a lockup kit gives your car the responsive feel like a manual gearbox. As you accelerate and decelerate it remains locked and provides more responsive power delivery, so if this is something you like then leave the kit on.
If there is mechanical risk, turn it OFF
Risk in this context means you are likely to experience severe, dynamic driveline shock loads. It’s not uncommon to hear of CV joints breaking when driving hard and off road, and these are exactly the conditions I’m referring to.
Hitting obstacles with momentum in low range 4WD is another example, such as in this video.
The torque converter allows for slip between the engine and the gearbox which helps absorbs driveline shock loads.
You should treat your car with mechanical sympathy. Nothing is unbreakable… not even a HiLux ;-)
My Recommendations
Here are my recommendations noting that avoiding severe driveline shock as described above always takes priority.
Highway Driving and Dirt Roads (Turn ON)
These are perfect conditions to use the lockup kit. You get better fuel economy and reduce transmission temperatures. This is especially beneficial when towing. Our kits are fully automatic, so you can almost just set and forget, as they will lock and unlock when required.
But driveline and transmission protection is still a consideration if you need to urgently stop. Our kits detect if you are emergency braking and will immediately unlock the torque converter. If you are braking because of an upcoming potential impact (like a washout) unlocking the torque converter will help reduce any impact shock.
Mountain Roads (Turn ON)
Driving up fairly slow and winding hills puts a lot of load on the transmission, which causes high torque converter slip and high transmission temperatures. These are perfect conditions to gain the maximum benefits of the lockup kit, especially when towing as the vehicle and transmission are working very hard.
City and Daily Driving (ON or OFF)
When travelling at 60kph or under, using the lockup kit depends very much on your own driving circumstances. If you're in a hilly area you may gain fuel savings, but if on the flat, probably not. The transmission cooler should easily cope, so temperature protection is of less importance. But if you just like the manual gearbox responsiveness or are getting fuel savings, leave it on.
Sand (Turn ON)
Sand is a soft and forgiving surface. We recommend using the lockup kit to prevent the transmission overheating. Soft sand places a lot of load on the transmission and the high slippage in the torque converter can generate significant amounts of heat.
In sand the torque converter is both your friend, and enemy. If you suddenly hit a very soft section and start to bog down, the slip of the torque converter creates more torque and can keep the engine on boost to give you the power you might suddenly need to maintain momentum. The downside is the risk of overheating your transmission.
Locking the torque converter means you won’t get high transmission temperatures, but when you unexpected hit really soft sections the revs might drop quickly and you may lose turbo boost, just when you need the power to keep momentum.
Therefore, you should use SPORT mode and chose a lower gear in sand, to keep the revs a bit higher.
Muddy Tracks and Water (Turn OFF)
When mud driving and in water crossings it is difficult to know the terrain ahead of you. To avoid the risk of an unexpected impact shock we recommend you switch the lockup kit off. Mud and water covered tracks are typically on flat ground, so the risk of overheating the transmission is low anyway.
Steep Hills (Turn ON)
Those long, steep climbs like you find in the Victorian High Country are notorious for overheating the transmission. Switch the lockup kit on, use low range 4WD (4L / 4LLc) and in climb using SPORT mode in 2nd gear when possible – of course, use 1st when necessary, but with the AISIN transmissions (Landcruiser, Pajero NT+, Triton MQ+) it wont lockup in 1st gear (only 2nd and above).
When descending steep hills, you will get improved engine braking in 2nd gear, but in practice you’ll use 1st gear (which wont lockup), so having the kit on or off depends on the circumstances. For example, leaving it on for the downhills inbetween uphill climbs.
Vehicles with the JATCO transmission (Pajero NS, Triton MN, Challenger) will lockup in 1st gear and improved engine braking is a big benefit, but again, assess the conditions and only lockup if you’re not likely to cause excessive driveline shock.
4WD Off Road - rough tracks, creek beds and rocks (Turn OFF)
To avoid the risk of driveline shock I recommend turning the kit off, and instead just monitor your transmission oil temperature. If it starts to get hot (90-100 degC), switch the lockup klit on when the conditions are suitable to help cool it down.
In Summary
Whilst we've never had any reports of damage to a torque converter, there’s no substitute for using your common sense according to the road or track conditions; and to treat your car with some mechanical sympathy. Whilst our kits have many protection features built in, they can’t predict what’s ahead of you!
So, use the lockup kit when it provides a benefit in your driving situation, but if there is a risk of damage leave it off.
Of course, if you have any questions you can contact us here.
Happy travels,
Marshall