Torque Converter slippage + kickdown cable - Fuelly Forums

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Old 07-23-2007, 09:24 AM   #1
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Torque Converter slippage + kickdown cable

I loosened my kickdown cable a few nut-turns to activate the kickdown less often. For better FE I want to stay in higher gears longer and not downshift as much.

Am I inviting more slippage in the torque converter or any other part of the hydraulic system by doing this? I don't expect to damage the tranny, but I'm wondering if the adjustment affects the fluid pressures in a way that would allow more slippage.

My '89 auto trans does not have a lockup torque converter. Swappping one in is not an option right now and I do expect this one to last the life of the car; the AW70 series tranny is extremely durable.
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Old 07-23-2007, 10:18 AM   #2
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From my understanding of torque converters, they are highly rpm dependent. Actual load makes little difference in their maximum stall speed.

Another way around this if you were inclined to do some wrenching would be to install a torque converter with a lower than stock stall rpm.

In a nutshell, I believe it works like this:

Higher stall speed produces greater heat generation, energy loss, and torque multiplication. Lower stall speed is the opposite.
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Old 07-23-2007, 10:47 AM   #3
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Snax, I think you're right in what you say, based on
http://www.bankspower.com/Tech_understandstallspeed.cfm
which has a link to a good page on torque converters, if anybody here would like to read up on those.

However I still don't have enough background to understand whether the kickdown cable tension & length are going to affect t/c slippage. And how to minimize the slippage.

Anybody?
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Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 07-23-2007, 10:58 AM   #4
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I would think it would increase slippage, as you will be running in higher gears = lower RPM. The only possible negative that I can see is more heat in the tranny fluid.....
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Old 07-23-2007, 12:28 PM   #5
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Shop Manual

The Integra shop manual says that its kickdown cable regulates fluid pressure (and determines the firmness of the shift). Together with the Transmission Control Module (and its various inputs), it determines when to shift (except for the TC, which depends on: coolant temp, speed, (fuzzy logic for the hill ascent/descent), and ultimately the cable position.

About 6-months ago, I discovered that the cable wasn't tight enough to engage the TC regularly. It turns out that it was too loose (slipped off of the mount). I tightened it beyond factory specs and TC lockup is quicker, hangs-on longer, and shifts are firmer. During the year or 2 it was loose, shifts were semi-firm, and TC lockup was only partial.

Through experimentation, pulling the cable to a very loose position resulted in added slippage and delayed shifting. For example, getting on the highway, it tached up to 5000 before it would shift, and took 4 seconds to slip up to the next gear.

If your adjustment is outside of spec, it should suffer the symptoms of less fluid pressure: additional slippage between gears (with added heat). If it's noticable, probably accelerated damage is possible. Otherwise, it may survive with the pressure it has, and not act so quickly to downshift. I tightened mine since the TC is very temperamental. The Control Module decides when to downshift on mine. I fear of increased wear due to harsher shifts, but the bulk of my driving is in full-lockup, which I need as soon as possible. The TCM still gets confused with EOC. Full control over the transmission would be great, but too costly.

RH77
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Old 07-23-2007, 04:19 PM   #6
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If I understand auto trannys correctly, each gearset has it's own internal dry clutch band, and any slippage at all is going to accelerate wear. Thus it is important to assure that there is adequate line pressure to keep the friction surfaces firmly engaged. The waste energy through the torque converter is relatively unaffected, providing the same difference in rpm stall point regardless of gear.

In much fewer words, stall ok, slip bad.

This is the reason many manufacturers recommend against towing in overdrive, as it overloads and more quickly wears the high gear friction band as the converter locks up. With the addition of more frequent kick-downs, wear is accelerated even further. Similarly, due to the lack of lockup while towing, the transmission fluid will be continuously heated by the torque converter, illustrating the need for a better fluid cooler.
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