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TD5 Auto Torque converter lock up


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I have a 2001 TD5 Auto Disco and I am trying to understand the function of the Torque Converter lock up.

I am trying to do this as a thought engaging the lock up would aid in engine breaking, but now I’m not so sure.

I have a volt meter on the orange and white cable (Pin 33) coming out from the Auto ECU which goes to the Lock up solenoid. All it seams to do is energise at 3rd gear and de energise at near standstill.

The RAVE cd suggests that it plays a part in Low Range, but I can’t get it to do anything other than engage at 3rd gear.

I’m a bit of novice at driving autos so have been practicing left foot braking on descents but if the lock up is not engaged then this seams a waste of time

Have I misunderstood the purpose of the lock up?

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The main purpose of lockup is at high road speeds to prevent overheating of the oil in 3rd and 4th and AFAIK it only works in those gears - older hydraulic boxes only had a lockup on 4th. Basically if the TC is slipping all the time on something like a long motorway journey where it may be transmitting near full engine power for a continual period of time then it will cook the oil and this isn't good for the gearbox.

Yes it would aid in engine braking and yes it does up to a point but it isn't as effective as it might be if you could lock it in 1st and 2nd for engine braking in those gears as well. I don't know if it practical to modify this to lock in 1st and 2nd, or if there is a reason for not doing it, or even whether the newer more sophisticated boxes such as in the Discovery 3 may have lockups in lower gears as well.

Dave Ashcroft is a member of LR4x4 so if we are lucky he might offer some insight into this question as it is an interesting one :)

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Sounds odd, doesn't it. But the Volt metre shows the circuit to the lock solinoid energised when I select reverse.

Makes we wonder if I have the right circuit. But it also energises as soon as the car hit's 3rd gear and it's the right colour and place as per the RAVE CD

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I have a lockup override button on the dash, this will lockup the TC in any gear and at any speed providing that the speed is above a pre set wheel speed inside the gearbox ecu, this is about 15k/h in high range and about 1.5 in low box, it is very usefully sometimes but you will actually find that in most circumstances, as long as you are off of the throttle in "over run" situations, the TC is locked by the computer anyway.

JE Engineering did mine at my request several years ago. ("Julian's Tomb Raider" if you want to inquire, they will remember)


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