| Auto Transmission - Lock Up -
Posted on 24-07-2008 15:06 |
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Has anyone tried the system described at:
http://www.automatictransmission.com.au/release.asp?NewsId=12101
Sounds like a cheaper solution to lack of auto engine braking than a Mark's Adaptors gear set. Any problems with it?
Thanks,
Brian
Edited by Hammer on 25-07-2008 09:09 |
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| RE: Auto trans lock up -
Posted on 25-07-2008 20:41 |
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While I have not tried these lock up controllers myself, I believe they are a good idea, giving engine braking equal to a manual, though not as good as reduction gears.
All late model auto transmissions that I know of come standard with a lock up torque converter, usually they are programmed to lock up in the higher gears in cruise mode (some are now programmed to lock in all gears), but all disengage at low speed or high load.
Essentially, what these lock up controllers do is hook into the wire that runs from the transmission computer to the lock up solenoid (the solenoid controls oil flow to the lock up clutch in the converter), and put in a seperate power feed through a driver controlled switch. This gives the driver a manual control over the lock up torque converter, much like an air locker/ pro locker. With the switch in the off position, the converter returns to normal computer controlled operation.
Note though, they do not give you full control like the clutch in a manual. Lock up converters are hydraullicaly operated, relying on hydraulic pressure generated by a pump inside the transmission. When the engine stops, pressure is lost and the converter unlocks. so don't expect to be able to push start the car, or do a manual style stall start recovery.
The only two problems I can see with these controllers, would be if you were to continually stall the engine by stopping the vehicle with the converter locked, this puts on torque loading on the lock up clutch in the converter that they were never designed for, and damage could occur. Which leads to the second problem. This modification will void your vehicle warranty.
Automatic transmissions work very well in 4wd's, (compared to manuals) giving you the abillity to feed power in smoothly when climbing over rocks etc, and on the soft sand they can change down gears without getting off the power, their one downfall has always been the lack of engine braking (compared to a manual), fitting one of these controllers will give you the best of both worlds.
If I had an auto, I would fit one.
Tony
Edited by on 25-07-2008 20:55 |
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| RE: Auto Transmission - Lock Up -
Posted on 26-07-2008 04:58 |
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Blocker
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Tony,
What a great reply!
I had never heard of these things till Brians post and I was actually wondering if you
could tow-start or push-start an Auto with one of these mods fitted.
I now know you can't but agree with you, they sound like a good mod for an automatic.
I can go to the Training Ground now with a bit more knowledge to pass on!
Thanks
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| RE: Auto Transmission - Lock Up -
Posted on 26-07-2008 13:20 |
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Wow, and wow again!! I agree with Blocker. What a great reply. Thanks, Tony. I hope you don't mind a few more questions as information on these devices is not readily available.
Are there any restrictions when the converter can be locked up and unlocked?
Can you manually lock it in "drive" or only when 1st or 2nd is selected?
Does it have to be unlocked in low 4wd to go from 1st to 2nd?
In our automatic 2004 GU, it seems that 1st in low range 4wd has a lot of retardation compared to 2nd gear. Problem for some conditions is that 1st low range 4wd is a bit too slow, and 2nd is too fast. When a lot of engine braking is required low range 1st and 2nd are, of course, nowhere near slow enough. Being a 2004 model, it is out of warranty as we did not purchase the extended warranty option. I have a suspicion that being locked up in 2nd could save a lot of disk pad wear.
As an extra benefit, I have seen a post elsewhere claiming a reduction in fuel consumption for these devices in locked up state when towing vans etc at speeds below that at which ecu activated lockup would normally occur. I would expect this as the ecu lock up function seems to hunt (switch on and off) a lot under certain conditions. Sounds like eliminating some torque converter slip could save $$.
I have to get some new tyres first, but could be tempted with one of these devices later on.
Thanks again.
Brian
Edited by on 26-07-2008 13:24 |
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| RE: Auto trans lock up -
Posted on 26-07-2008 21:49 |
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Aw shucks, thanks guys.
As I said in my first reply, I have never actually used one of these lock up controllers so my advice is based on theory mainly, combined with what I've learnt in 16 years as a mechanic.
The controllers give you the abillity to lock the converter at ANY time, however knowing when not to lock it could save you a lot of money in repairs to the transmission and converter.
You dont ever want to have the converter locked when the transmission is changing gears (up or down), as this would be like changing gears in a manual without using the clutch. Best bet is to let the transmission get into the gear that suits the situation and then lock the converter. Always be mindful of when the transmission is likely to change gear and be ready to unlock.
The only restriction with unlocking would be the loss of engine braking if you were to unlock it during a descent. Driveline damage is most unlikely as you are simply reverting back to standard operation.
1st gear too slow, 2nd gear too fast, can't do much about that, it's a product of the gear ratio's. Standard Patrol gearing means 1st low is the only ratio lower than 1st high.
When you need maxium engine braking, being able to lock the converter will definately help, but only to the same extent as the engine braking in a manual. If that is not enough then only reduction gears will help. Only experience will show if there is a reduction in brake pad wear.
A reduction in fuel consumption is likely, as you say by eliminating converter slip (slip between the engine and gearbox, think of a slipping clutch). Again, only experience will tell.
As a side note, when you are descending really rough or slippery tracks, manual diff locks can be a great help. Just as they help when you lift a wheel going uphill, when you are going down hill and you lift a wheel, the wheel off the ground can spin backwards allowing the opposing wheel still with traction to freewheel, leaving the back wheels to do all the engine braking. Engaging the diff lock can give you a lot more control.
In this situation I don't think an automatic diff lock (Detroit, lokka etc) would work, as they rely on torque from a wheel being driven faster than the differential to unlock the diff. So in theory while the wheel off the ground would stay locked to differential speed, the wheel still on the ground would unlock and freewheel. This is based on my understanding of how automatic lockers work, feel free to correct me if I'm wrong.
Tony |
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| RE: Auto Transmission - Lock Up -
Posted on 27-07-2008 08:51 |
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Once again, thanks Tony.
Very interesting about the different behaviour of air lockers and auto lockers (Detroit and its cousins) when going down hill.
Brian
Edited by on 27-07-2008 09:26 |
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| RE: Auto Transmission - Lock Up -
Posted on 29-07-2008 13:26 |
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Reading all of the above, it reminds me of my old GQ which had a similar control switch fitted.
The reason for fitting the over-ride switch was because the torque converter didn't work in that wagon. (Due to the engine and transmission changeover it had earlier, namely starting of as a 1990 RB 30 wagon, and ending up with a 1992 4.2 EFI auto wagon!)
I think it was because the computerised parts weren't completely matched, that it didn't function properly.
Anyway once the over-ride switch was fitted, it worked well, you just had to remember when and when not to use it !
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| RE: Auto Transmission - Lock Up -
Posted on 30-07-2008 11:28 |
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Thanks to all contributors. Seems like the only issue is remembering to disengage the auxillary lock before changing gears, whether done by the driver or the auto function.
While the differential and transfer case ratios seem to be the same for the auto and manual models, first gear ratio seems to be lower for the manual gear box.
The URL makes the claim:
"Eliminates all convertor slippage and convertor runaway on steep down hill descents allowing full 100% engine braking. "
So while you get some improvement, perhaps the end result is not quite as good as a manual low range 1st gear.
What is convertor runaway? I think I know and have experienced it but could not find a definition anwhere with Google.
Have not tried the new search engine that is taking aim at Google yet.
http://www.cuil.com
Thanks,
Brian
Edited by Hammer on 30-07-2008 12:16 |
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| RE: Auto trans lock up -
Posted on 30-07-2008 13:29 |
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I think converter slippage and converter runaway are basicly the same thing.
A torque converter is a fluid coupling, imagine two fans very close together facing each other and immersed in oil. One fan (turbine) is connected directly to the engine, while the other (impeller) is connected to the input shaft of the transmission. At idle the turbine spins but the impeller does not as it is being held stationary by the driveline after it which is also stationary.
When you begin to accelerate more oil is pushed from the turbine to the impeller causing the impeller to begin turning, and the vehicle starts moving. Although there is drive, there is never direct drive, the turbine always spins faster than the impeller, this is converter slip and the reason lock up clutches are now fitted.
Now imagine your driving down one of those gut wrenchingly steep hills that we love, the weight of the vehicle going down that hill is trying to accelerate the vehicle, this transfers up the driveline until it reaches the converter. This time the impeller is spun faster than the turbine and the vehicle "runs away" (converter runaway), as there is no direct drive.
This is where the lock up controllers come in. The Nissan factory fitted a perfectly good lock up clutch in your torque converter, but programmed it to only work on the highway. Fit a seperate controller and eliminate this runaway down hills.
In between the turbine and impeller is a set of vanes called a stator, these direct the oil onto the impeller in such a way as to cause a torque multiplying effect, and is the reason autos can often get away with having a taller first gear than manuals in the same model vehicle.
Tony
Edited by on 30-07-2008 13:38 |
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