This was originally posted on the DTT site at:
http://www.dieseltrans.com/phpBB/viewtopic.php?t=32
If you have comments or questions that you would like Bill Kondolay to address, post on the DTT site.
Why I installed a DTT Smart Controller and my initial impressions.
On Oct 10 I was at DTT getting my transmission repaired. (A description of how I broke a DTT transmission is posted at:
http://www.dieseltrans.com/phpBB/vie....php?p=103#103
During the day I got an introductory course in the care, feeding, and failures of transmissions. Discussions with Bill, the opportunity to examine transmission parts, make some measurements, and do some simplified engineering calculations led me to a decision. I requested they install a DTT Smart Controller that I had not intended on buying prior to the trip. My reasoning and initial impressions, without towing experience, are discussed below. (A discussion of what I learned and how not to abuse a transmission is the subject of a separate posting:
http://www.dieseltrans.com/phpBB/vie....php?p=102#102
TRANSMISSION RELIABILITY
My primary reason for installing the DTT Smart Controller was to increase the transmission reliability (I do not want my Dodge to visit Bills shop again).
The transmission reliability is increased by the ability to pull steep or slow (hairpin curves) grades in 2nd locked with the Smart Controller. This eliminates the weakest link direct clutch problem in 3rd with lower speeds (pump rpm). This reduces the torque on other clutches and provides additional hydraulic fluid flow. This function does require using the DTT valve body (enables manual 2nd lockup of the TC clutch) with the Smart Controller.
The second transmission reliability increase is less wear on the TC lockup clutch. The TC clutch is the busiest clutch in the transmission. In the interest of fuel economy, Chrysler chose to disengage the TC clutch every time you let off on the accelerator. Of course the TC clutch re-engages when you touch the accelerator again. I would guess that the TC clutch cycles 10 to 100 times more than the front clutch depending on individual driving conditions. This busy TC clutch cycling can be eliminated or minimized by installing a controller such at the DTT Smart Controller. The Smart Controller latches the TC engagement signal once you go over the adjustable set point (usually about 30 mph) and keeps the TC clutch engaged until your speed drops below the set point value.
INCREASED ENGINE BRAKING CAPABILITY
This is my secondary reason for installing the DTT Smart Controller. (If you are towing at 20,000 lbs GCWR, Gross Combined Weight Recorded, or more or if you do not understand the reasons for downshifting on grades with lower GCWR, this should be your primary reason for installing the DTT Smart Controller in conjunction with installing an exhaust brake.) I do not use an exhaust brake and down shift to 2nd or 1st, as required, for engine braking. (Do as I say, do not do as I do.)
Unfortunately, an automatic transmission provides engine braking at only one speed/rpm. At 2800-3000 engine rpm the TC is tight enough to provide some engine braking (approximately 75 HP). With a 3.54 rear end, this is about 55 mph in 2nd or 35 mph in 1st. Slower speeds/rpm result in ineffective engine braking with greater TC slip and low engine rpm. The Smart Controller and DTT valve body will result more effective engine braking (even without an exhaust brake) with the TC lockup over all speeds (down to approximately 30 mph in 3rd and 20 mph in 2nd) and reduced transmission temperatures that improve transmission reliability.
Note: If you use an exhaust brake without a mystery switch or TC controller, you are assured of future transmission failure. (Dodge paid for removal of Dodge and Cummins installed exhaust brakes when they figured out that exhaust brakes on automatic transmissions without TC lockup resulted in transmission failure. Dodge did not market a TC lockup controller.)
OTHER FEATURES
The speeds that the transmission shifts from 3rd to OD or OD to 3rd, the shift in and out of 3rd lockup, and the shift in and out of manual 2nd lockup are individually adjustable. Some other controllers have a single adjustment and require fiddling if you want to change for differing driving conditions.
The sensitivity of the unlock kick down is separately adjustable corresponding to accelerator position. You can adjust the unlock accelerator position for driveability and not lug the engine, floor the accelerator, tap the brake pedal, or double punch the OD switch to momentarily unlock the TC clutch.
The Smart Controller effectively provides an automatic OD inverter circuit or automatically switching the OD to off when you start up. Setting the OD to come on at 50-55 mph eliminates the annoying and transmission wearing OD operation at low speeds/rpm.
AN IRRITATING FEATURE
No product report is complete without the irritating features. Once the Smart Controller latches the TC lockup at a nominal 30 mph (20 mph in manual 2nd), it stays in lockup during shifting until the speed is below the speed setting again. Thus the transmission shifts TC locked in the 3-OD and OD-3 shifts. The 3-OD, OD-3, 2-3, and 3-2 locked shifts have been described by some as harsh. Bill is aware of this and stated that he has asked his electrical design people if they can provide a second or so TC unlock during transmission shifts.
SUMMARY
The Smart Controller, when used with the DTT valve body for manual 2nd locked operation, provides most of the functionality of the GM/Allison transmission with the Tow/Haul Mode. It does not automatically increase the 1-2 and 2-3 shift points nor does it automatically downshift the transmission when you tap the brakes. You have to provide the computer function and muscles for engine braking downshifts. The net result of using the Smart Controller will be longer transmission life, longer brake pad/shoe life, and safer operation during braking.
Linear Mode
