Auto box overdrive??

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lerk

lerk

New Member
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Location
Creswell, Derbyshire UK
Evenin all!

Does anyone know if it's possible to fool the auto box into locking up the torque converter at lower speeds than 52mph?

I'm thinking along the lines of adding an O/D button on the dash as in a 50mph limit the engine is working quite hard, I know from my previous 300 (manual) that there is plenty of torque available down to 40mph in top gear and locking TC earlier should improve economy...

Any auto box experts on here???

LERK
 
Thank you Lerk for asking the question I was going to ask. My problem is with heavy towing (horses, 2.5+ tonnes total trailer weight) I have to change back to 2nd & sometimes 1st in order to anything like engine braking, even then it's hard on the electric trailer brakes! A lower speed lockup (say 25 - 30 kph would be great.
 
Locking the converter clutch is a wheeze to be encouraged, BUT, be aware that doing it in LOW GEARS with heavy trailers on the back may strip all the little planetary gears in the insides of the box, and tear the brake bands and clutch packs to bits due to excess torque being applied of you hit your switch at a bad moment.

The converter slipping a bit on the over-run (engine braking) protects the gears from shock loads and overloads.

Take care, but it's a great idea for DRIVING, as opposed to BRAKING.

It must be possible. Probably only requires one on/off switch and a 2-core cable.

CharlesY
 
I dont know why Land Rover didnt do it in the first place! Most other auto 4x4's have an OD button
 
DiscoTDi said:
It's a nice idea, but I don't think this would be possible electrically as the gearbox is mechanical.

Cheers
Click to expand...

Indeed, but the mechanical operations nowadays tend to be controlled by electronics, and electric valves.

DO NOT CONFUSE "OVERDRIVE" with a "LOCK-UP TORQUE CONVERTER"..

These are not the same thing at all.

"OVERDRIVE" is a second TWO SPEED gearbox (direct 1:1 drive and 1:1.25 usually) sitting behind (after) the main gearbox. Almost invariably these are switched manually with a leccy switch somewhere. In AUTO boxes the system cuts in Overdrive at moderate speeds and light loads.

"LOCK-UP TORQUE CONVERTER" is a simple single plate clutch operated by hydraulic pressure that simply makes a torque converter into a solid drive. At engine speeds above about 2,000 rpm this stops the small amount of slip that is otherwise always going to happen in the converter. It makes it more efficient, and it stops the gerarbox oil from getting too hot on long runs at cruising speeds in hot weather.

ISUZU Trooper Autos had both. 3 speed auto box with overdive and lockup converter. These are a treat to drive. Discos and so on now use a auto box with more gears inside, so the overdrive is not neded, but they do now use the lockup converter.

Question now becomes, how do we manually select LOCKUP, and what happens when we do!

First one to do it wins a valuable prize.

CharlesY
 
The 3.5 RRC locks up at around 42mph and it's dreadfull, try accelerating around that speed or just trying to maintain a 50mph the gearbox will change down and then it decides to change up then back down again. So much better having the lock up at 52mph. It may be different for towing I don't know i don't tow but for 'press on' driving lock up at 42mph is brain damage.
 
so does that mean an override is do able?Does the ECU come into it,seeing as the auto is fly by wire?Please,humour me,I know sod all about the subject :brick:
 
shocker said:
so does that mean an override is do able?Does the ECU come into it,seeing as the auto is fly by wire?Please,humour me,I know sod all about the subject :brick:
Click to expand...
I'm not sure if a manual override is possible but it looks like you can change the automatic lockup speed: Land Rover conversions - M&D Engineering a page on converting to the 2.8 TGV (300TDi) engine suggests

"The 4th gear lock up speed should be 45 mph, this can be altered by changing the hysterisis spring in the valve block. "

Mind you I know sod all about it as well.:(
 
shocker said:
so does that mean an override is do able?Does the ECU come into it,seeing as the auto is fly by wire?Please,humour me,I know sod all about the subject :brick:
Click to expand...

In thoery, with the EH varient of the ZF box you could switch the TC lockup 'on and off'......not sure what the ECU would make of it tho as the TC lockup speed is 'hard coded'.

However, the OP started by asking about an auto box behind a 300Tdi....in which case the TC lockup can be adjusted by changing the spring in the valve body as mentioned in the link above.....so in that case, no the TC lockup cannot be turned on and off.

Does that makes sense? :)
 
Thanks CharlesY, but the problem I am faced with is not the usual amount of T/C slippage but the fact that the trans lets the engine drop back to (almost) idle whilst we are merrily going along, and accelerating. I am not talking high road speeds, say 25 to 60 kph, but with the engine idling there is no braking at all from under the bonnet! P.S., in Australia we do have some quite long downhill stretches - hence the current total reliance on Disco & trailer brakes.
 
Automatic gearboxes in general do not provide as direct engine braking as manuals, and when the speed drops and the box goes into low gear there may be NO engine braking at all as most auto-boxes have a one-way free-wheel clutch in operation in first gear UNLESS the driver manually selects LOW.

Check your Driver manual as that should tell you explicitly how to achieve engine braking on gradients. It isn't the same in all cars.

CharlesY
 
shocker said:
so does that mean an override is do able?Does the ECU come into it,seeing as the auto is fly by wire?Please,humour me,I know sod all about the subject :brick:
Click to expand...

If you have the ZF 4HP 22-24 gearbox then I think it IS do-able!

The lockup clutch in the torque converter is operated by an electrically powered (solenoid) hydraulic valve MV3. It is ON or OFF and nothing in between, which is very good news.

The EAT ECU (under the passenger seat?) connector pin details show that the solenoid is operated by the cable at Pin 32 which runs to the solenoid valve MV3. Pin 32 is the 4th from the left in the bottom row.

If it was me ... I would temporarily connect a single wire to the cable connected to pin 32 (not a Scotch-lok please) and pass that through a small 12volt bulb, the other side of which is earthed.

Then drive off, and see what happens.
EITHER
1. the bulb goes live all the time and goes OFF when the lockup clutch engages, or
2. the bulb is out when you drive away but lights up WHEN the lockup engages. I believe this is the way it works, which suits you fine.

Let me know which as the use of a two-a-penny diode may be needed in case 2. if you add a switch. The switch needs to be a simple ON/OFF switch, but we should try to source its 12v supply from somewhere suitable so that it will ONLY operate the lockup clutch when driving forwards. I think that won't be a big problem either. At the very worst we can pass it through a relay so that in P or R the Lockup BYPASS switch won't work.

I can tell you now, if my Disco was an Auto, I would be trying this TOMORROW for sure. My consultancy fee note will follow!

CharlesY
 
CharlesY said:
If you have the ZF 4HP 22-24 gearbox then I think it IS do-able!

The lockup clutch in the torque converter is operated by an electrically powered (solenoid) hydraulic valve MV3. It is ON or OFF and nothing in between, which is very good news.

The EAT ECU (under the passenger seat?) connector pin details show that the solenoid is operated by the cable at Pin 32 which runs to the solenoid valve MV3. Pin 32 is the 4th from the left in the bottom row.

If it was me ... I would temporarily connect a single wire to the cable connected to pin 32 (not a Scotch-lok please) and pass that through a small 12volt bulb, the other side of which is earthed.

Then drive off, and see what happens.
EITHER
1. the bulb goes live all the time and goes OFF when the lockup clutch engages, or
2. the bulb is out when you drive away but lights up WHEN the lockup engages. I believe this is the way it works, which suits you fine.

Let me know which as the use of a two-a-penny diode may be needed in case 2. if you add a switch. The switch needs to be a simple ON/OFF switch, but we should try to source its 12v supply from somewhere suitable so that it will ONLY operate the lockup clutch when driving forwards. I think that won't be a big problem either. At the very worst we can pass it through a relay so that in P or R the Lockup BYPASS switch won't work.

I can tell you now, if my Disco was an Auto, I would be trying this TOMORROW for sure. My consultancy fee note will follow!

CharlesY
Click to expand...

The auto box on the TDi300 is non-electrical. There is no ECU involved and no electrical connections etc. You can adjust the upshift points by mechanical adjustment of the kick down cable, but that's about it.

I'll see if I can get the exact ZF model of gearbox, but if I recall it's a modified for LR one based on an older established design.
 
CharlesY said:
If you have the ZF 4HP 22-24 gearbox then I think it IS do-able!

The lockup clutch in the torque converter is operated by an electrically powered (solenoid) hydraulic valve MV3. It is ON or OFF and nothing in between, which is very good news.

The EAT ECU (under the passenger seat?) connector pin details show that the solenoid is operated by the cable at Pin 32 which runs to the solenoid valve MV3. Pin 32 is the 4th from the left in the bottom row.

If it was me ... I would temporarily connect a single wire to the cable connected to pin 32 (not a Scotch-lok please) and pass that through a small 12volt bulb, the other side of which is earthed.

Then drive off, and see what happens.
EITHER
1. the bulb goes live all the time and goes OFF when the lockup clutch engages, or
2. the bulb is out when you drive away but lights up WHEN the lockup engages. I believe this is the way it works, which suits you fine.

Let me know which as the use of a two-a-penny diode may be needed in case 2. if you add a switch. The switch needs to be a simple ON/OFF switch, but we should try to source its 12v supply from somewhere suitable so that it will ONLY operate the lockup clutch when driving forwards. I think that won't be a big problem either. At the very worst we can pass it through a relay so that in P or R the Lockup BYPASS switch won't work.

I can tell you now, if my Disco was an Auto, I would be trying this TOMORROW for sure. My consultancy fee note will follow!

CharlesY
Click to expand...


Charles

It's the former. There is 14v on startup and when the TCC engages it drops to 0v. I have subsequently cut the wire - to simluate TCC engage only to find the M and S gearbox fault lights appear on the dash. The electrical diagram only shows TCC to solinod to earth. How could the TCU know about the cut? could it detect no current in the system?

Steve
 
chosenview said:
Charles

It's the former. There is 14v on startup and when the TCC engages it drops to 0v. I have subsequently cut the wire - to simluate TCC engage only to find the M and S gearbox fault lights appear on the dash. The electrical diagram only shows TCC to solinod to earth. How could the TCU know about the cut? could it detect no current in the system?

Steve
Click to expand...


Hmmmmm.... by CUTTING the wire I suspect you have accidentally simulated a fault the engine system knows about - Torque Converter problems, or engaging lock-up at too low a speed.

I suggest you get a length of two-core wire and join the two cores one to each end of your cut. Lead the wire up to somewhere handy on the dash, and join them to a simple ON-OFF switch or "push on / push off" button (that stays where you put it). With the switch ON contact is made and the system should be fine again. Electrically it is the same as before you snipped the wire.

In that ON condition, drive away, and at say 40mph flick your switch OFF. This should lock the converter, and with any luck NOT report a fault.

It may be simple Road Speed being too low when you drive away with that cut wire that makes the fault report. If so you will soon find out what your speed must be before locking up.

Let us know. And at least you know you are on the correct wire.

CharlesY
 
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