I understand how the torque converter works, essentially a fan based system moving hydraulics to transmit power to the wheels. But I would like to understand better when and when not to have the torque converter lock up engaged. Yes , I do have a switch that will manually lock up the TC (only in 3rd and 4th).
I understand that when the TC is locked up its gear to gear with practically 100% power to the wheels. And that when it is not its relying upon the fluids to transmit power and therefore will transfer less (between 10 to 30 percent)--the rest being lost to heat, etc.
It seems logical that you would want the TC locked up whenever possible to maximize power and fuel efficiencies. Since, after all, when it's not you're losing upwards of 30% power.
However, I've been hearing that you actually want to DISENGAGE the lock up when you ARE pulling a heavy load, especially uphill. This is crazy, because it seems that this is exactly when you want that full power. The reason I've been given is that the lock up is being held in by hydraulic pressure and that under heavier loads it doesn't have enough holding power and the gears will begin to slip--and in doing so, start ripping things apart and spitting your TC out in itty bity little metal pieces.
If this is the case then it's pretty unfortunate to be losing that power when you need it the most.
So, consider my setup (12V cummins and stock rebuilt auto tranny from 96 -- no upgraded TC or tranny--we're talking pretty much stock here). Should I disengage that TC lock up when pulling a heavier load (especially when up a hill)? Or is that exactly when I want it on?
Also, I've heard that torque converters actually multiply torque, at the cost of fuel efficiencies. Is there truth to that?
I'm just one guy making sense of all this. Hoping to keep the truck running strong for the years to come.
Thanks to any one in advance for tackling this one.
You would benefit much more with an upgraded converter like mine. Billet low stall singles are a worlds difference especially when combined with a good valve body. I used to use the lockup switch with my stock converter allot. At times I think I was asking to snap a shaft by doing that. It would lockup in 2nd gear if I put it in drive then shift through the ranges up to overdrive. I would lockout overdrive till higher speed. After I installed the revmax stage 3, I hardly use it. Mostly I use it on the highway or for some engine braking. On the highway I use it so the clutch doesnt engage and disengage every time I hit the pedal.
The biggest issue with a lockup switch is that if your rpms are too low your transmission clutches could slip because there wont be enough pressure build up to hold them together.
Stock converter is about 65% efficient. My aftermarket revmax is about 90% :thumbsup:
Dodge automatics leave alot to be desired and from the factory are just plain junk. However, they are the easiest and probably the cheapest to upgrade and once you upgrade it goes from one extreme to the other just like that.
There is a reason why there is a conversion kit out there to bolt up 47/48re's to a Duramax.
I hear ya bootstrap. I am looking forward to upscaling the drive train and that will include a beefier converter and possibly new tranny. But considering I'm more of a broke B these days that'll be a couple years down the road. So, getting lifespan out of my truck as is is pretty important to me right now. I'm just wondering if I need to be leery of that switch -- only using it on flat ground or moderate weight uphills, or if I'm worrying about the wrong thing.
Hi BootStrap just wondering if you could give me the Revmax part number you went with for Low stall and the Revmax Perf/towing VB. Do you tow alot and how much weight just wanted to know if it shifted hard when you are pulling say 10,000 or so from First to Overdrive and what is the higest RPM does the truck rev to. How does the converter handle cold starts also. Thanks
My tc locks up at 47 mph and unlocks at 45 mph. I can lockup manually at about 42 or 43 mph and feel ok. Basically you have maybe 2-4 mph before the factory locks up the tc that you can use manually. When towing you may decide to let the computer take over. The big advantage of a tc lockup switch is that extra 2 mph before you start going up a hill unlocked and also going downhill locked up so you do not gain so much speed without any engine braking.
You will know when the engine lugs. That is a bad thing. If the motor starts to work harder than you think it should or lugs and vibrates take the tc switch off.
Just think of that tc l/u switch as the next lower gear. When you feel like the truck should not be in the high gear any longer unlock the tc and allow the computer to take over. You may decide that going uphill in 3rd gear (o/d off) is a better idea than trying it in overdrive.
I think I understand what you're saying... that it really comes down to keeping the motor in the right RPM range. Are you saying that its not an issue to be in TC lock up as long as you're not lugging out or otherwise stressing your truck out at those higher speeds?
IF you go to the revmax converters website it kinda explains itself. I have a revmax stage 3 with the low stall option. IF its not self explanatory, then just give them a call and their number is on the website as well. You can get a lower stall than the low stall which is supposedly around 300rpm less than stock. There isnt an actual designated stall speed as its different from truck to truck depending on mods.
I tow 12000 or so. I can hit the defueling rpm of 2250 or so but it pulls way harder now with this converter.
quoting what you said:
The biggest issue with a lockup switch is that if your rpms are too low your transmission clutches could slip because there wont be enough pressure build up to hold them together.
That makes sense. So, would you say that as long as I keep the RPMs up around 1800 to 2300 I should be OK in keeping that lock up engaged? Considering my 96 truck is pretty much stock all the way through (from the engine to the tranny to the TC). And that I'm pulling around 10 grand.
On bigger hills I'll be dropping out of OD down to third. Would it be a good idea to lock the TC back up in third in these cases?
From what I experienced I would agree that around 1,300 rpm is the lowest speed being locked up makes sense. Below that it lugs. Perhaps it is 1,325 or 1,275 but it is right around that rpm.
The problem is that the factory tc slips so much you have to learn what mph relates to that rpm once you lock up the tc.
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