Overdrive On/Off Debate

[Beau]

just a little note, with the overdrive on the torque converter will lock up at 50mph but with it off it won't lock up until 60mph in third. So if you coming to a long hill and you think you won't make it all the way above 50 in overdrive then you need to be above 60 in third for it to lock up, once locked up with you foot down it will stay locked up 5mph less than those figures until it releases.
Only an issue if you gearbox is prone to getting hot!

Not trying to argue or anything, but I believe you're wrong. The torque converting locking up is dependable upon RPM, not speed. You can have the torque converter locked in 1st to 4th gear but I think you have to be doing about 1600-1800 rpm's. This is why manuals can be more economic as they have 100% power from standstill.

 

[Rich Sims]

Not in a landcruiser, its elerically controlled to save stress on the drive train, we are talking of prado 90 or 70 gearbox auto with a A343F gearbox which are 3 speed with overdrive, the newer 5 speed may be differant.
the A343F auto box doesnt lock up at all in 1st and 2nd and wont lock up at all in low range.

Older landrover and bourg warner are differant, they are rpm related and controlled from inside the converter.

just to put a spanner in the works I have fitted a manual lock up in my cruiser mainly for towing up mountain passes or around the rounds nearby where we dont reach lock up speed. But you shouldnt allow the gearbox to change gear whilst locked so I put it in a gear where i hope its not going to change out of.

Of coarse all this slipping and heat build up also adds to the overheating problems of the 1kzt engine as the oil cooler is in the bottom of the rad and can reach 180 degrees.

 

[Beau]

Not in a landcruiser, its elerically controlled to save stress on the drive train, we are talking of prado 90 or 70 gearbox auto with a A343F gearbox which are 3 speed with overdrive, the newer 5 speed may be differant.
the A343F auto box doesnt lock up at all in 1st and 2nd and wont lock up at all in low range.

Older landrover and bourg warner are differant, they are rpm related and controlled from inside the converter.

just to put a spanner in the works I have fitted a manual lock up in my cruiser mainly for towing up mountain passes or around the rounds nearby where we dont reach lock up speed. But you shouldnt allow the gearbox to change gear whilst locked so I put it in a gear where i hope its not going to change out of.

Of coarse all this slipping and heat build up also adds to the overheating problems of the 1kzt engine as the oil cooler is in the bottom of the rad and can reach 180 degrees.

Learn something new everyday here! Interesting to know how you got the manual lock up to work, I've read others do the same and it increases drive-ability and performance?

 

[Rich Sims]

its about £10 of parts and 15-20 mins work depending how much rubbish you have in you glove box!lol

I used a cross over with from mapping and some 3 core wire simple...

BUT.... although has loads on the plus side there are always some bad features; 1, if you forget its locked on and you have to stop quickly or come to a junction its will be like stopping in a manual without using the clutch(you'll crash in to stuff) 2, if when locked your gearbox needs to change gear the clutch packs will take all the force of taking up the drive again with they were never designed to do and won't last long and again it will be like changing a gear in a manual with no clutch! 3, only a minor issue but if you use it from cold your gearbox will never heat up to the proper working temperature (around 90 and above) which is designed to evaporate moisture.

So you need to have you whits about you when using it, I may put a light on the dash or something, or if there is a techy out the that can make a up a box that below a certain revs it disengages i.e put the power through a relay, that would be the ultimate solution.

 

[tim falce]

I think I'm being dense here or have just never heard of a torque converter locking. Are you saying there is a physical shaft that engages that joins the two halves together? If so that would mean that when you release the accelerator the engine revs wont drop, on mine the revs die down to virtually a tickover if you release the pedal when you are at most speeds, more so when you are going over 40ish.
Please explain more as I've never heard of this before.

 

[Rich Sims]

Tim, the converter has a clutch in it which lock the two halves together and on A343F gearboxes (3 speed with overdive boxes) and happens around 50mph when at running temperature in overdrive and around 60mph without overdrive when you reach the above speed you should see the revs drop down and as you say the rpm gauge will follow the mph.

Also as soon as you touch the brakes the converter unlocks and wont relock until you touch the throttle again.

 

[tim falce]

Thanks for the explanation, the revs do drop when the overdrive engages but my point is that does the clutch disengage the moment you release the throttle?

 

[induna]

My 2001 petrol Prado locks up the torque converter at a much lower speed that listed in OD -- about 60 kph. The manual I have for the A343F list the lock-up speed in OD as 57-61 kph, and lock-up off speed as 50-55 kph, and that is what I'm seeing. I have a European spec Prado -- it just says Land Cruiser on the back --and am living in Costa Rica.

 

[Rich Sims]

Tim, no it shouldn't once it has locked and should stay locked in unless speed drops to around 45mph or the brake is pressed.

 

[Rich Sims]

Induna, I guess thats because its a petrol, the diesel hasn't really enough power to lock it up any lower, at 50mph the revs drop down to 1750rpm, I guess your rpm will be higher.

 

[induna]

Yes, for the 1KZ-TE the manual says that lock-up occurs between 77-81 kph in Normal mode and between 90-94 kph with the PWR button engaged. At 50 mph I believe that my petrol engine is at about 2000 RPM.

 

[tim falce]

Tim, no it shouldn't once it has locked and should stay locked in unless speed drops to around 45mph or the brake is pressed.

It doesn't seem to work on mine, I gave it a good go this morning and there appears to be no lock up and at 60+mph the revs just drop to around 1100 when I release the accelerator.
Mine is a November 1999 UK delivered Colorado, it's the revamped model (post June 99) prior to the D4D coming out.

 

[Rich Sims]

gearbox temperature of around 45 degrees has to be reached before it starts working properly so at least 5 miles, also make sure power button isn't on..

 

[tim falce]

Ah, this was at 3.30am this morning, pretty cold weather and I doubt it'd be that warm as I'd only done about 3 miles.

 

[MuddyAF]

Great thread, I also leave mine on 90% of the time unless Im going up hill.