Information
From: Robert Patton
I have had occasion to discuss this subject with TDR writer, John Holmes. John and Polly own a 2003 truck with the 48RE transmission, and he is close to doing an exhaust brake installation on their truck.
As most of you know, John works at Caron Dodge in Carson City, NV. Their dealership has several excellent transmission technicians.
With this motivation to do an exhaust brake installation and the connections to get answers, I asked John to do some research. His comment, "Yea, I've got to dot the "i's" and cross the "t's" 'cause it looks like I'm going to be my own warranty station if I install an exhaust brake on our '03 truck. "
John confirms that R. McCulloch is on the right track as he suspects that "the controlling software is the problem and that the combination isn't working in the manner that they want it to; it is not a seamless automatic interface. "
Further details on the controlling software: with the '03 trucks with the 47RE and '03. 5 trucks with the 48RE transmission, the transmission is controlled using Chrysler's powertrain control module (PCM). The '04 trucks will use the Cummins' engine control module (ECM) to control the transmission. As there will be changes to the engine to meet 1/1/04 emissions standards, Dodge and Cummins have targeted this date as the release of approval for exhaust brakes with automatic transmissions.
Effectively, this leaves '03/47RE, '03. 5/48RE and '04/48RE customers in limbo as to warranty approval. Speculation has it that the early '04/48RE customer (these trucks are equipped with the Cummins ECM) will be approved for exhaust brake usage, but it will require a reflash of the engine's ECM.
As stated, the '03/47RE and '03. 5/48RE are controlled with Chrysler's PCM. Countless hours were spent trying to make the PCM compatible with an exhaust brake in all driving conditions. Key words in the preceding sentence, "countless hours" and "all driving conditions. " As you read, these ’03 vehicles will not be approved for exhaust brake usage.
Those that have followed the use of exhaust brakes with automatic transmissions know that in order for an exhaust brake to be effective, the transmission has to be locked-up in the gear selected. Lock-up mode insures that there is a direct couple between the engine and the drive wheels, thus the engine rpm remains high and the brake is effective. More importantly, there is no internal slippage inside the torque converter. It is internal slippage (the shearing of the transmission fluid between the torque converter's impeller and turbine blades) that causes internal heat and ultimately damage to a torque converter.
With the understanding that there must be torque converter lock-up, owners with an '03/47RE or '03. 5/48RE transmission can see and feel the lock-up as the transmission shifts through the gears and goes into overdrive. As you reach approximately 50 – 55 miles per hour, watch the tachometer for the 150 - 200 rpm drop and the seat-of-the-pants acceleration as the transmission locks up in overdrive.
Overdrive lock-up is easy to identify. Third gear lock-up is much more subtle. Yet, each time you accelerate the transmission actually shifts five times: one, two, three, three-lock, overdrive, overdrive-lock. To feel the three to three-lock transition, one should hit the overdrive "off" button and take the truck slowly through the gears. See and feel the third gear lock up as you watch the tachometer for a subtle 50 - 100 rpm drop as third lock-up kicks in.
Now that you are familiar with lock-up, it is easy to watch the tachometer for transmission (third or overdrive) unlock. Unlock will occur at lower rpm engine goes to idle and there is no braking effect. This "remain in lock-up, then drop out of lock-up at a lower rpm" is a new feature that the '03/47RE and '03. 5/48RE customers have. Previously, owners that used exhaust brakes (albeit in unauthorized and warranty jeopardizing applications) had to manually lock-up the torque converter with the overly simplistic "mystery switch" or with some combination of aftermarket switches and hydraulic line pressure devices. Lock-up they did, and many have enjoyed their modified toys.
So, '03/47RE and '03. 5/48RE customers can enjoy automatic lock-up, in third and overdrive as the truck decelerates, but no authorization for exhaust brake usage - what gives?
To answer, "what gives?" readers should look back to R. McCulloch's comment, "My speculation is that the combination simply isn't working in the manner that they (Dodge and Cummins engineering) what it to: it isn't a seamless automatic interface. " A seamless interface would have the customer select "brake" mode and the transmission shift from overdrive (with the brake on) then shift to third (with brake on) and, possibly, shift to second (with brake on). Unfortunately, the engineers could not program the PCM to make the seamless downshifts combine with positive, without-a-doubt, torque converter lock-up. Hence, non-approval of the ‘03/47RE and, ‘04/48RE transmission applications.
Currently with my ‘03/47RE transmission and with Dodge's powertrain control, overdrive lock-up will slow the vehicle from 90+ mph down to 45 mph (1200 rpm), at which time the torque converter unlocks. If I leave the truck in third gear lock-up, the effective braking zone is from 83 mph (3400 rpm) to 23 mph (900 rpm). That is all I can do with my '03/47RE transmission.
John Holmes reports that his '03. 5/48RE transmission acts a little differently. It does not hold overdrive to 1200 rpm or third down to 900 rpm, but rather it kicks out of lock-up (in overdrive or third) at 1500 rpm. The 1500 rpm kick out leaves the vehicle at too high of a speed. Anticipation of a downhill situation is in order as one would want to have selected third (and feel the lock-up) and then turn on the brake as you crest and then decent the hill. Third will also unlock at 1500 rpm, so selection of second (and feel lock-up) is required in those tight, twisty applications.
What is a 2003 owner to do? Is an unauthorized, non-approved, "I am my own warranty station" installation something you feel comfortable doing?
Referencing my Issue 41 article, my answer is "yes. " The same answer holds true for John and his 2003. 5 truck. With knowledge of why the brake is not approved and the logic to work around the problem, I'll make my truck perform to suit my needs. The simple answer is to manually select a lower gear, make sure you feel lock-up, then apply the exhaust brake. If you have trouble feeling the subtle transition to lock-up or if the truck will not stay locked up, there are aftermarket products (line lock) that will increase the line pressure to insure torque converter clutch engagement.
That's all for now. I have the opportunity to drive a Chevy Duramax/Allison with a BD Exhaust Brake. It will make an interesting comparison to my 47RE and Pacbrake. I'll report the test drive later.
Attention: TDR Forum Junkies 
