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Single versus multi disk torque converters. and lockup for towing/exhaust brake...


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Guys, school me on these please. I need to upgrade my current (stock replacement) converter and valvebody. On the 47RE how do I up my line pressure so I can lockup the converter safely when going downhill?

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Im really not sure I think the line pressure has nothing to do with it ......... I think its just a switch to engage the lockup clutch ............. like 2nd gear lockup etc .......... all I do know is that using the TC lockup for braking is really hard on input shafts .....obviously with an exhuast brake -- not sure how much your using the TC lockup ........ so again not sure - and just subscribing instead :think:W&F will know

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Im really not sure I think the line pressure has nothing to do with it ......... I think its just a switch to engage the lockup clutch ............. like 2nd gear lockup etc .......... all I do know is that using the TC lockup for braking is really hard on input shafts ..... obviously with an exhuast brake -- not sure how much your using the TC lockup ........ so again not sure - and just subscribing instead :think: W&F will know

I have a lockup switch. So I can be locked down hills. My thinking is that since line pressure is based somewhat off accellerator pedal position, the low line pressure of idle as I go down a hill in lockup will not allow the clutch to hold any real torque... and possibly burning it up. Hopefully someone can clue us in.
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I have a lockup switch. So I can be locked down hills. My thinking is that since line pressure is based somewhat off accellerator pedal position, the low line pressure of idle as I go down a hill in lockup will not allow the clutch to hold any real torque... and possibly burning it up. Hopefully someone can clue us in.

hmm ....but the line pressure is for the internal gear clutch packs right - nothing to do with the TC ..... thats just the TC pump.
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hmm ....but the line pressure is for the internal gear clutch packs right - nothing to do with the TC ..... thats just the TC pump.

Then perhaps the packs slipping are the concern, not the clutch.
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Exhaust braking on a automatic is no more than accelerating at 50-55 PSI of boost. Same amount of force should be applied as a braking force. I know ol' CajFlynn has a lockup controller on his 01 Dodge and had (past tense) exhaust brake on it till it wore out. So it would be a good idea to upgrad the input shaft before using exhaust brake.

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Exhaust braking on a automatic is no more than accelerating at 50-55 PSI of boost. Same amount of force should be applied as a braking force. I know ol' CajFlynn has a lockup controller on his 01 Dodge and had (past tense) exhaust brake on it till it wore out. So it would be a good idea to upgrad the input shaft before using exhaust brake.

Wow. I didn't realize that it put that much load on it... but it makes sense. I should IM CajFlynn.
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When in lock up your TC is being fed line pressure, it should be about 80 psi in Neutral. Now when in lock up you will notice you have pressure coming out of your transmission this output line going to the cooler is the output line from the TC.When you use a lock up switch your commanding the solenoid to feed line pressure to the TC to allow for it to lock up.You also need higher line pressures to keep your clutch packs happy, especially 4th the O/D is a weak setup on its own.Now as for towing, light weight towing a single is fine, but if your towing heavier loads a 3x TC is what you need. A triple allows you to add more surface area, the stock single disk is only about 33 square inches of lining between your pressure plate and the front of the TC. Now a triple disk is closer to 130 Square inches. this extra lining allows for better grip in lock up, but it allows for better lock up at the same line pressures.Its hard to explain but for example, If your TC is running 100PSI of line pressure at 55Mph and your accelerating, it will slip, but you could have the same 100psi and same set up, except a triple disk, it will not slip because of the increased surface area of lock up.the same can be used for engine braking. When braking you need to keep your line pressures up, which is indeed controlled VIA the throttle position. However built automatics usually run higher then stock line pressures off the bat so they don't need to worry as much. As practice, i usually keep my pedal off idle so as to keep the pressures up a bit. But its best to Keep your engine rpm's above 1200 rpm's for the sake of the TC and the TC springs inside.I agree, a billet input shaft is most warranted, because if you break a input shaft, usually you trash your pump, and sometimes the 2nd gear band area.I also recommend either a strengthened SFI flex plate, or a Billeted one, but a stocker should be replaced if you plan to use the trans as a Eugine brake, mainly because the torque reversals going back and fourth can cause the center to tear out/ or cause the plate to become out of round..

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Thanks for the great way of explaining it. Be nice if this information could be a sticky. I know nothing about the automatic trans but I'll be due for a proper build in a few years. :spend:

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When in lock up your TC is being fed line pressure, it should be about 80 psi in Neutral. Now when in lock up you will notice you have pressure coming out of your transmission this output line going to the cooler is the output line from the TC. When you use a lock up switch your commanding the solenoid to feed line pressure to the TC to allow for it to lock up. You also need higher line pressures to keep your clutch packs happy, especially 4th the O/D is a weak setup on its own. Now as for towing, light weight towing a single is fine, but if your towing heavier loads a 3x TC is what you need. A triple allows you to add more surface area, the stock single disk is only about 33 square inches of lining between your pressure plate and the front of the TC. Now a triple disk is closer to 130 Square inches. this extra lining allows for better grip in lock up, but it allows for better lock up at the same line pressures. Its hard to explain but for example, If your TC is running 100PSI of line pressure at 55Mph and your accelerating, it will slip, but you could have the same 100psi and same set up, except a triple disk, it will not slip because of the increased surface area of lock up. the same can be used for engine braking. When braking you need to keep your line pressures up, which is indeed controlled VIA the throttle position. However built automatics usually run higher then stock line pressures off the bat so they don't need to worry as much. As practice, i usually keep my pedal off idle so as to keep the pressures up a bit. But its best to Keep your engine rpm's above 1200 rpm's for the sake of the TC and the TC springs inside. I agree, a billet input shaft is most warranted, because if you break a input shaft, usually you trash your pump, and sometimes the 2nd gear band area. I also recommend either a strengthened SFI flex plate, or a Billeted one, but a stocker should be replaced if you plan to use the trans as a Eugine brake, mainly because the torque reversals going back and fourth can cause the center to tear out/ or cause the plate to become out of round..

Good description :thumb1: How does the line pressure in the tranny feed the TC - thought it went through the pump - but maybe the flows the other way around. Also - doesn't the lockup solenoid engage the TC lockup clutches via a mixture of the TPS/line pressure values ?? What I mean is I didnt think it had anything to do with pressure in the TC - just simply the TPS as well as a certain line pressure on your VB will then engage the lockup switch for the TC ........
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Thanks everybody! I am going to go talk to a trans shop or two when I get home. Until then I am going to drive nice and keep the comp fueled down to a 1. Thankfully, I am not doing much towing at the moment, though there is always the chance I may need to rescue There is a Goerend affiliated shop about an hour away, and a local place with a good reputation about 5min from my house. Its looking like the best option would be a triple disk, billet input, and a pretty healthy amount of line pressure. Hopefully I can sell the CVC stock replacement converter and "hardened" input shaft and recoup some of the $$$.

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Thanks for the great way of explaining it. Be nice if this information could be a sticky. I know nothing about the automatic trans but I'll be due for a proper build in a few years. :spend:

DO like the rest of us, and do it right when yo do go for it.

Good description :thumb1: How does the line pressure in the tranny feed the TC - thought it went through the pump - but maybe the flows the other way around. Also - doesn't the lockup solenoid engage the TC lockup clutches via a mixture of the TPS/line pressure values ?? What I mean is I didnt think it had anything to do with pressure in the TC - just simply the TPS as well as a certain line pressure on your VB will then engage the lockup switch for the TC ........

your transmissions output line pressures should be there at idle, unless its not in lock up. Once in lock up you should see with a pressure gauge the value go up with rpm. No, the Lock up solenoid is in the VB, it increases line pressure flow to overcome the springs inside, that then pushes your pressure plate against the clutches and the front of the TC. This increased line pressure will cause the output line to rise as well. the truck will lock up based on speed, and throttle load, if you increase your throttle to fast it will unlock, if the o/D is off it will lock 3rd automatically. The PCM is programmed to lock the truck in 3rd automatically and stay locked regardless if the the trucks O/D is off, i believe (could be wrong)
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