Forcing Torque Converter Lockup - Defender Source
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  #1  
Old September 9th, 2007, 02:52 AM
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Trevor Tarr
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Trevor Tarr
1997 D-90 4.6 NAS ST
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Forcing Torque Converter Lockup

My '97 D-90's auto-box is running hot, especially while towing my trailer: consistently above 220 degrees on long uphills. I've replaced the stock transmission oil cooler with two parallel radiators, each with thermostat-controlled electric cooling fans, without a lot of benefit.

So, I'm wondering if reducing slippage-generated heat, by forcing the torque converter to lock up, might be a solution? As I understand it, the ZF 4HP22 transmission's torque converter only locks in fourth gear. But when I'm slowly pulling my heavy trailer up a long incline, I'm usually in second.

Are there any transmission gurus out there who could say whether there's a safe/practical way to get the torque converter to lock up in lower gears? Is it an electrical or mechanical actuation? From what I've read, the ZF 4HP22EH (electro-hydraulic) transmission used on the Discovery Series II does allows for torque converter lock-up in all four gears, but is there any way to do this with the 4HP22?

Thanks in advance,
Trevor
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  #2  
Old September 9th, 2007, 03:48 PM
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S. Smith
72 Series III 109 Diesel
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I have seen aftermarket torque converters for such applications for other makes. the housings look the same as the rover version, I am sure there is a common manufacturer for these that you could cross reference.

http://www.tciauto.com/Products/Maxi...converters.asp
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Old September 9th, 2007, 04:34 PM
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jim pendleton
89'd90
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Its in the valve body not the torque convertor. Difficult to do. Off road you can use the brake and the gas to do it.

I may have seen information about this, but cannot recall just now.

JP
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  #4  
Old September 10th, 2007, 10:29 AM
Michael
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Michael
Discovery 1998
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220 is not ideal, but not that bad for towing on long hills. If I remember correctly, the stock temperature switch on my Disco grounded at about 250 - or was it 220? - will check and verify.

Use amsoil?

Follow-up Post:

Lowering the stall speed in the converter should lower temps prior to lock-up. I am not sure how much the stall speed can be lowered without stalling the engine.
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  #5  
Old September 10th, 2007, 10:33 AM
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Charles Galpin
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Trevor, how are you measuring the tranny temps? A sensor on the cooler?
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  #6  
Old September 10th, 2007, 11:59 AM
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Trevor Tarr
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Trevor Tarr
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Quote:
Originally Posted by cgalpin
Trevor, how are you measuring the tranny temps? A sensor on the cooler?
A sensor on the sump. (Each cooler also has a sensor, but these only control the coolers' electric fans.)

Follow-up Post:

Michael, thanks for your suggestions.


Quote:
Originally Posted by Michael
220 is not ideal, but not that bad for towing on long hills.
I keep coming back to the "transmission life halved for every 20 degrees above 175 degrees" rubric. I'm always at least 220 towing uphill, and frequently higher. At 250, I'll pull over to cool down.


Quote:
Originally Posted by Michael
Use amsoil?
I'm using Mobile One ATF.


Quote:
Originally Posted by Michael
Lowering the stall speed in the converter should lower temps prior to lock-up. I am not sure how much the stall speed can be lowered without stalling the engine.
Is there a way to lower the stall speed?
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  #7  
Old September 10th, 2007, 12:35 PM
Michael
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Michael
Discovery 1998
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yes, stall speed can be lowered by professionals. Pendy recommended I do this for my diesel re-power. Call up your local transmission shop and ask where they send torque converters to be repaired/rebuilt. There is a place near me called Converter Technologies that does this. They quoted about 250-300 to do it. The million dollar question is how low can you go without reinstalling it and finding out it stalls the engine when you put it in "D". Maybe get a torque curve for your engine?
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