Torque Converter\Overdrive

[Bob Ellithorpe]

I guess it's time someone enlightened this old man,because I'm confused to say the least!!

When you guys are talking about locking out the TC,do you mean pushing in the manual OD switch on the dash??? My comprehension of the Dodge transmission\Torque Converter is that it's in OD when the torque converter locks up at approx. 47mph.

Why would locking out the TC make the transmission build up so much heat??

I thought I also read that a stock 94 3500 CTD with 4:10's was rated to pull 18,000 GCWT.

I guess something else I don't understand is why if you're pulling a hill and you have to put it in D2 0r "2" why this builds up the heat you're talking about?

I guess there's alot about all this that I don't understand!!!

After reading some of the posts on this subject,I'm almost afraid to drive my truck up even the slightest hill!!

 

[Howard Durand]

Bob,



There are guys here that know a lot more about the auto transmission and the torque converter than I do but I'll tell you what I know or believe.



The 47rh transmission torque converter has a built in clutch that is electrically engaged under certain conditions to provide a solid, direct drive through the transmission much the same as a standard transmission. This is called torque convertor lock up.

The power train control module controls this function.

Normally, lockup does not occur until the transmission has shifted into OD unless OD is manually disabled. Then it will lock up in 3rd.

It's primary function is to provide direct drive through the transmission to gain fuel economy at highway speed.



Some of us have installed a switch in the circuit from the PCM that controls the TC lockup solenoid. This allows us to manually lock the TC clutch when we choose. The switch can also be wired to allow one to manually unlock the TC.

Use of this switch is controversial as are most of the "improvements" that we make to these trucks and must be applied with caution. It should not be used for locking and unlocking under load unless the transmission and TC have been upgraded for towing.

My main purpose for the TC lockup switch is to allow me to keep the TC locked when I am using the exhaust brake.



The GCWR of your truck is as you stated, approximately 18. 000 lb. (That means total weight of truck and trailer).

I pull a 7,000 lb trailer with my rig which is just about what it is rated for.



The torque converter clutch will not lock in 1st or 2nd gear, consequently, when you are pulling hard in either of these gears you are depending on fluid coupling in the TC for transfer of power and that is what generates heat.



Hope this helps some. I am sure others will add to this.

 

[BK]

I wasnt sure what was going on with the OD switch and lockup and OD. .

OD is a 4th gear,,, lockup is the locking up the two halfs of the viscous drives halves in the TC.



The switch is supposed to lock out the OD gear. . nothing ever is said about what happens to Lockup. So I myself and mechanic friend were interested.



The Ace mechanic friend of mine brought over his SnapOn scan tool with the correct module for my truck. We weren't sure what data we could get with the Dodge module...



We went for a ride and played. . Tons and Tons of data from the SnapOn tool. It would tell use what the computer was telling the transmission todo. We would see the command being sent and feel it happen. It was too cool.



When OD is switched off, the transmission will still go into lockup of the TC. . But never go into OD.

If you are driving with OD switched off, and are in 3rd and lockedup and than switch it on, the transmission will come out of Lockup, wait for the the correct speed and such and the transmission will go into OD, than lockup.



With OD switch off, meaning you are allowing the transmission to go into OverDrive, If your crusing along in OD and Lockup, and are coming to a hill, and decide you do not want OD... and then switch it off, the transmission 1st goes out of Lockup, than out of OD and into 3rd. At the right time the transmission will lock up again.



We did this without a load, and tried it with a light and heavy foot on the pedal.



The heat build up comes from the slipping clutches in the transmission, the fluid is used to cool, operate and lubricate all in the transmission.

Your supposed to be able to tow in OD and Lockup. But the constant shifting of the gears is a real killer. So keeping it in one gear is the best. When the transmission hunts in and out of OD and lockup, thats when you want to atleast press the OD button and kill the 4th gear. Than if needed back off of the throttle... than if needed go into 2nd.

Since the CTD produce sooo much torque at low rpm (unlike gassers), during shifting and accelerating, at low rpms the transmission is not at it's best since internal pressures are low. Hence why allowing the transmission to hunt through the gears isn't nice.



But if you can increase the efficiency of the TC, (reduce slipping) and the clutches, you reduce the heat. Thats what the Valve Body and special TC from DTT are designed to do.

DC designed the transmission and TD to make the yuppies that dont like driving a tuck happy,... soften the shift and such. . but that increases the losses and heat...



When I have the bucks and after warrenty, I plan on getting the DTT VB and TC.

In the mean time, get a transmission temp gauge, it will let the transmission talk to you and let you know when your pushing it too much.

 

[Joe G.]

Bob,



The TCC and OD are separate things. Our transmissions are really TorqueFlite three speeds. "Fourth" gear is the OD unit. This thing is in the tailshaft part of the transmission. We can prevent the shift to OD with the OD lockout button on the dash. For a stock transmission setup there is no control over the torque converter clutch lockup. If we have the OD locked out and are running in 3rd gear it will lockup the TCC if conditions are right. If OD is not locked out it won't do this until the transmission shifts to OD. The TCC has clutch facing similar to a manual transmission clutch. Nothing viscous about it, it's really a mechanical gadget. It's not nearly as heavy as the one used with a manual trans and that's the main reason we can't pull hard with it locked. The lockup is caused by hydraulic pressure when the TCC lockup solenoid is activated. If the hydraulic pressures are not right the TCC will not lockup even if the solenoid is activated. Slipping the TCC very much will destroy it. If heat build up in your transmission is caused by any slipping of any of the clutches it won't last long. Most excessive heat is caused by fluid shear in the TC. The so called mystery switch (manual TCC lockup switch) allows us some control over this situation. It also prevents automatic unlocking (kick down) of the TCC so we can kill the TCC by forceing a lockup under heavy load (racing or towing). Another problem is that the stock setup will keep the TCC locked when we have more power than stock and that will kill it too. I have my manual lockup switch wired so that I can force lockup or force unlock. Bill K. has a smart controller that will take care of controlling the TCC lockup and help prevent it's destruction.



If I have any of this wrong maybe Bill K. will chime in an set us straight.

 

[BK]

Joe...



"The TCC has clutch facing similar to a manual transmission clutch. Nothing viscous about it, it's really a mechanical gadget. "



I didn't mean that TC Lockup happens though viscous pressure, but that the two parts (the stator and housing (rotor?)) that are normally driven through viscous coupling are locked up mechanically through the TCC.



I didn't know and wasnt sure till we put the SnapOn scan tool on and got the real time data when and how the lockup occured. But the one thing that was clear, before anything changes in the transmission the 1st thing that happens is that it unlocks if it's locked up and when cruising it eventually will... and that last thing is does is lock up. It was very interesting

 

[Joe G.]

The way I understand it is that the term viscous refers to the thickness of the fluid as in oil viscosity. The viscous coupling in our radiator cooling fans depends on the fluid inside the clutch getting thicker when it heats up. This does not happen in our transmissions. If anything, the fluid gets thinner. The TC is really a hydraulic turbine where the impeller (turns with flywheel) blows oil thru the stator (turns with trans input shaft).

 

[Bob Ellithorpe]

Joe,

Is the smart controller that Bill K. has, a seperate item or part of the valve body??



Bob

 

[Joe G.]

The smart controller and TC saver are electronic boxes. Check will Bill about the details and which boxes fit which trucks.

 

[BK]

Joe,

I would say by your definition, I've used the word "viscous" incorrectly. And again based on that definition, I know that "that" doesn't happen in our transmission's.



But bypassing the "fluid drive" between the housing and stator is what happens via the TCC ("lock up") . . which is the point I was trying to get across.



With all of this back and forth, it should become more clear for Bob E.

 

[BK]

Bob E,

incase your look'n for it , here's Bill url...



http://www.dieseltrans.com/DTTech/index.sht