Attention: TDR Forum Junkies 
What I learned at the DTT transmission class 101 (Part 1)
Part 2 is at:
http://216.235.147.117/forums/showthread.php?s=&threadid=57831
Part 3 is at:
http://216.235.147.117/forums/showthread.php?s=&threadid=57832
This was originally posted on the DTT site in one piece at:
http://www.dieseltrans.com/phpBB/viewtopic.php?t=33
If you have comments or questions that you would like Bill Kondolay to address, post on the DTT site.
The following discussion is the result of a one day visit at DTT and my resulting opinions on the workings or not workings of the 47RE transmission. The opinions are mine and the results of questions to Bill and his attempts to impart knowledge to me. I may have heard or interpreted some things incorrectly and/or I may have different engineering opinions than Bills opinions based on experience. We both respect the other parties right to different opinions.
While I was waiting and watching the repair of my transmission as a result of slipping and welding the front clutch, Bill handed me a Dodge service manual, some calipers, and the hydraulic pressure plates for the Torque Converter, Front, Direct, and Overdrive clutches. He then invited me to make some calculations on the clutch capabilities (he obviously knew the answers beforehand). As a method to kill some time and to understand the 47RE better, I agreed.
The torque capability of the transmission clutches are proportional to the clamping force (piston area and hydraulic pressure), number of clutch surfaces stacked up, and average radius of the clutch face. The clutch area itself (a single clutch surface) has a minimal impact on the torque capability as the slipping force is the friction coefficient times the clamping force. Multiple clutch surfaces in a stacked disc array will multiply the effective torque capability. A larger average diameter clutch surface will have a larger torque capability as the slipping force (lbs) is applied at a larger lever (ft in the ft-lb torque capability).
Cutting to the chase, after calculating the clutch piston area and nominal clutch radius and then looking up the stock pressures and number of clutch surfaces the relative capabilities of the clutch packs was calculated. The approximate relative torque capabilities are TC = 1. 7, Direct = 1. 5, OD = 1. 2, and Front = 1. This is with the DTT front clutch upgrade from 4 to 5 clutch discs.
Well, I obviously wiped out the weakest link, the upgraded front clutch. The question now was how and why. Other questions were how come the TC clutch and OD have or have had problems in the past. Other failure items have been the input shaft, hub, and output shaft. I provide my opinions of the failure modes for individual items below.
THE FRONT CLUTCH
The failure of the front clutch, the weakest clutch for torque capability, is a result of low pressure. Lower hydraulic pressure results in lower clamping force and ultimately the clutch slips and is burned out in seconds. One set of reasons for low hydraulic pressure, according to the service manual, is caused by worn pump, incorrect control pressure adjustments, valve body warpage or malfunction, sticking governor, leaking seal rings, clutch seals leaking, servo leaks, clogged filter or cooler lines. In other words, wear and internal leakage in the transmission ultimately reduces the available hydraulic clamping pressure and results in clutch failure. It is not a matter of if the transmission will fail but when it will fail.
Bill Kondolay has been a leader in identifying internal leakage problems with R&D (the infamous lip seal) and is continuing to identify solutions; seals, parts with tighter tolerances, higher pump capacity, etc. The thing the owner/operator can do to maximize transmission life is to minimize temperatures. You will never operate the thousands of hours at higher temperatures to significantly degrade the transmission fluid. The few hours you do operate at higher temperatures will degrade seals and accelerate their wear. The worn seals will increase leakage, reduce pressures and result in clutch failure. The burned smell and off color in transmission fluid is not degraded fluid leading to failure, it is a symptom of clutch slippage that has already occurred and that total failure is not far behind. Thus, to maximize transmission life, keep the temperatures low.
The other principal cause of low pressures is operation of the transmission at low rpm. The transmission hydraulic pump is a positive displacement pump and the transmission pressure governor/regulator attempts to keep the pressures at constant levels depending on the gear selected as the rpm changes. With a constant leakage, there is a minimum rpm and resulting pump rate that will overcome the transmission internal leakage and result in the minimum pressures. As the transmission and seals wear, the minimum rpm that will deliver the required pressure increases. Operation at low rpm with high transmission loadings will ultimately result in earlier transmission failure than operation at higher rpm. This low rpm problem is worst with the 12 valve engines because they typically have higher torque values as rpm decrease. The 24 valve engines have flat torque curves to protect both automatic and manual transmissions. I believe that my transmission failure was this mode with operation at 1500-1800 engine rpm, with less than 1200-1500 pump rpm, and 600+ ft-lb torque increased by the torque converter multiplication resulted in overwhelming the forward clutch. I had got away with this earlier before internal leakage increased or possibly higher average transmission temperatures (pan temperatures) resulted in lower pressures (lower pump capacity and higher leakage). Operation in 2nd gear would have increased the pump capacity and resulting pressures. Increased HP in our rigs allows us to pull a grade in a higher gear but it is not necessarily good for the transmission. Operation in 2nd gear without TC lockup is not always good as the temperatures rise and speeds are limited by TC slippage. The obvious solution to 2nd gear grade climbing is TC lockup, with a mystery switch or a more sophisticated controller.
Bill and DTT have increased the capability of the 47RE transmission over stock. DTT torque capability improvements are obtained by increasing the front clutches from 4 to 5, increasing the clamping force by increasing the pressures, and using clutch material with better friction properties. I would estimate that the front clutch torque capability is increased by 75 percent or more with the DTT combination of improvements. Increasing the clutch diameter or still more clutch discs is not feasible as this would require a new transmission case (eg effectively a new transmission design). There is hope that the future higher capacity 48RE pump can be retrofit on the 47RE transmission. This would help protect the transmission from internal leaks at low rpm.
Use of an exhaust brake has the same problem of maintaining adequate rpm for hydraulic oil volume and pressure. Just because the exhaust brake will provide braking below 1600 rpm does not mean you should. Some exhaust brakes can generate high braking HP and torque at low engine rpm that can exceed the torque capability of clutches with lower pressures at lower rpm. You should probably maintain over 1600 rpm while using exhaust brakes (with high braking effort on downgrades) to maintain adequate clamping pressure on transmission clutches.
Of course, if you have an electronic or mechanical problem that puts you into 3rd gear starts, then instant front clutch failure is the probable result of pouring to coals to the engine.
I believe that trailer pullers are more likely to fail the front clutch than drag racers. Trailer pullers are apt to pound on the front clutch for 10-15 minutes at maximum torque and minimum rpm while pulling a grade. Drag racers only use the front clutch for a few seconds after they shift into 3rd and OD and the rpm will be at a higher value than trailer pullers. In addition, drag racers have a torque limiter that fifth wheel pullers do not, rear wheels will probably slip for drag racers before the front clutches do.
Part 2 is at:
http://216.235.147.117/forums/showthread.php?s=&threadid=57831
Part 3 is at:
http://216.235.147.117/forums/showthread.php?s=&threadid=57832
This was originally posted on the DTT site in one piece at:
http://www.dieseltrans.com/phpBB/viewtopic.php?t=33
If you have comments or questions that you would like Bill Kondolay to address, post on the DTT site.
The following discussion is the result of a one day visit at DTT and my resulting opinions on the workings or not workings of the 47RE transmission. The opinions are mine and the results of questions to Bill and his attempts to impart knowledge to me. I may have heard or interpreted some things incorrectly and/or I may have different engineering opinions than Bills opinions based on experience. We both respect the other parties right to different opinions.
While I was waiting and watching the repair of my transmission as a result of slipping and welding the front clutch, Bill handed me a Dodge service manual, some calipers, and the hydraulic pressure plates for the Torque Converter, Front, Direct, and Overdrive clutches. He then invited me to make some calculations on the clutch capabilities (he obviously knew the answers beforehand). As a method to kill some time and to understand the 47RE better, I agreed.
The torque capability of the transmission clutches are proportional to the clamping force (piston area and hydraulic pressure), number of clutch surfaces stacked up, and average radius of the clutch face. The clutch area itself (a single clutch surface) has a minimal impact on the torque capability as the slipping force is the friction coefficient times the clamping force. Multiple clutch surfaces in a stacked disc array will multiply the effective torque capability. A larger average diameter clutch surface will have a larger torque capability as the slipping force (lbs) is applied at a larger lever (ft in the ft-lb torque capability).
Cutting to the chase, after calculating the clutch piston area and nominal clutch radius and then looking up the stock pressures and number of clutch surfaces the relative capabilities of the clutch packs was calculated. The approximate relative torque capabilities are TC = 1. 7, Direct = 1. 5, OD = 1. 2, and Front = 1. This is with the DTT front clutch upgrade from 4 to 5 clutch discs.
Well, I obviously wiped out the weakest link, the upgraded front clutch. The question now was how and why. Other questions were how come the TC clutch and OD have or have had problems in the past. Other failure items have been the input shaft, hub, and output shaft. I provide my opinions of the failure modes for individual items below.
THE FRONT CLUTCH
The failure of the front clutch, the weakest clutch for torque capability, is a result of low pressure. Lower hydraulic pressure results in lower clamping force and ultimately the clutch slips and is burned out in seconds. One set of reasons for low hydraulic pressure, according to the service manual, is caused by worn pump, incorrect control pressure adjustments, valve body warpage or malfunction, sticking governor, leaking seal rings, clutch seals leaking, servo leaks, clogged filter or cooler lines. In other words, wear and internal leakage in the transmission ultimately reduces the available hydraulic clamping pressure and results in clutch failure. It is not a matter of if the transmission will fail but when it will fail.
Bill Kondolay has been a leader in identifying internal leakage problems with R&D (the infamous lip seal) and is continuing to identify solutions; seals, parts with tighter tolerances, higher pump capacity, etc. The thing the owner/operator can do to maximize transmission life is to minimize temperatures. You will never operate the thousands of hours at higher temperatures to significantly degrade the transmission fluid. The few hours you do operate at higher temperatures will degrade seals and accelerate their wear. The worn seals will increase leakage, reduce pressures and result in clutch failure. The burned smell and off color in transmission fluid is not degraded fluid leading to failure, it is a symptom of clutch slippage that has already occurred and that total failure is not far behind. Thus, to maximize transmission life, keep the temperatures low.
The other principal cause of low pressures is operation of the transmission at low rpm. The transmission hydraulic pump is a positive displacement pump and the transmission pressure governor/regulator attempts to keep the pressures at constant levels depending on the gear selected as the rpm changes. With a constant leakage, there is a minimum rpm and resulting pump rate that will overcome the transmission internal leakage and result in the minimum pressures. As the transmission and seals wear, the minimum rpm that will deliver the required pressure increases. Operation at low rpm with high transmission loadings will ultimately result in earlier transmission failure than operation at higher rpm. This low rpm problem is worst with the 12 valve engines because they typically have higher torque values as rpm decrease. The 24 valve engines have flat torque curves to protect both automatic and manual transmissions. I believe that my transmission failure was this mode with operation at 1500-1800 engine rpm, with less than 1200-1500 pump rpm, and 600+ ft-lb torque increased by the torque converter multiplication resulted in overwhelming the forward clutch. I had got away with this earlier before internal leakage increased or possibly higher average transmission temperatures (pan temperatures) resulted in lower pressures (lower pump capacity and higher leakage). Operation in 2nd gear would have increased the pump capacity and resulting pressures. Increased HP in our rigs allows us to pull a grade in a higher gear but it is not necessarily good for the transmission. Operation in 2nd gear without TC lockup is not always good as the temperatures rise and speeds are limited by TC slippage. The obvious solution to 2nd gear grade climbing is TC lockup, with a mystery switch or a more sophisticated controller.
Bill and DTT have increased the capability of the 47RE transmission over stock. DTT torque capability improvements are obtained by increasing the front clutches from 4 to 5, increasing the clamping force by increasing the pressures, and using clutch material with better friction properties. I would estimate that the front clutch torque capability is increased by 75 percent or more with the DTT combination of improvements. Increasing the clutch diameter or still more clutch discs is not feasible as this would require a new transmission case (eg effectively a new transmission design). There is hope that the future higher capacity 48RE pump can be retrofit on the 47RE transmission. This would help protect the transmission from internal leaks at low rpm.
Use of an exhaust brake has the same problem of maintaining adequate rpm for hydraulic oil volume and pressure. Just because the exhaust brake will provide braking below 1600 rpm does not mean you should. Some exhaust brakes can generate high braking HP and torque at low engine rpm that can exceed the torque capability of clutches with lower pressures at lower rpm. You should probably maintain over 1600 rpm while using exhaust brakes (with high braking effort on downgrades) to maintain adequate clamping pressure on transmission clutches.
Of course, if you have an electronic or mechanical problem that puts you into 3rd gear starts, then instant front clutch failure is the probable result of pouring to coals to the engine.
I believe that trailer pullers are more likely to fail the front clutch than drag racers. Trailer pullers are apt to pound on the front clutch for 10-15 minutes at maximum torque and minimum rpm while pulling a grade. Drag racers only use the front clutch for a few seconds after they shift into 3rd and OD and the rpm will be at a higher value than trailer pullers. In addition, drag racers have a torque limiter that fifth wheel pullers do not, rear wheels will probably slip for drag racers before the front clutches do.
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