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What I learned at the DTT transmission class 101 - Part 3
What I learned at the DTT transmission class 101 - Part 3
Part 2 is at: http://216.235.147.117/forums/showthread.php?s=&threadid=57831
Part 1 is at: http://216.235.147.117/forums/showthread.php?s=&threadid=57830
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.
OVERDRIVE
The Dodge 47RH and 47RE transmissions are infamous for OD reliability problems in the past. To the best of my recollection Dodge made the following improvements. About 1994 Dodge instituted a series of upgrades that increased the direct clutches from 8 to 10, changed the OD planetary gears from 5 straight cut in an aluminum carrier to 5 helical cut in a steel carrier, and improved lubrication to the OD section. My impression is the overdrive problems are past history, current production (since 1994?) is largely trouble free if you do not tow at less than 1800 rpm. (There are probably some errors in my recollection, I trust Bill will clear up any errors. )
This does not mean that the OD clutch is foolproof. The OD clutch has a torque capability of 1. 1 to 1. 4 time the forward clutch depending on hydraulic pressure (lockup or not, throttle cable position). The service manual lists pressures of 80 to 130 psi depending on conditions. The OD clutch also has a very large spring that the hydraulic clamping force has to overcome. This spring requires 830 lbs of the clamping pressure. The effect of the spring reduces the torque advantage of the OD clutch over the front clutch. At about 70 psi the OD clutch torque capability is about equal to the front clutch. Thus, if you are idleing down the road at 1200-1400 rpm in OD lockup (40-45 mph as the Dodge setup will let you), your pressures are under specification due to accumulated internal leakage (say 70 psi or less), and you or the cruise control roll onto the throttle. The mighty Cummins delivers maximum torque and you are likely to wipe out the new weakest link, the OD clutch. A potential method of maximizing OD clutch life is do not operate in OD at less than 1600 rpm or tow in OD at less than 1800 rpm.
INPUT SHAFT, HUB, AND OUTPUT SHAFT
Bill showed me examples of broken input shafts and hubs. The granular appearance in the fracture zone made the cast material readily apparent. Bill stated that individuals experiencing fracture of the cast parts appear to be "luck of the draw". If you have operated several years without fracture you probably will not fracture in the future. Apparently, some castings have small internal defects or cracks and that continued stress cycling results in the internal defect/crack growing until the part ultimately fractures. Cracking and fracture is accelerated by high stresses and more stress cycles. The higher stresses can be power braking or harsher (lock to lock) shifting. The DTT Smart controller might result in more or earlier input shaft and hub fracture, it is too soon to tell from experience to date. I have the impression that fracture of these parts is not a big problem with trailer towers. It appears to me that the drag racers have broke most of them with power braking.
MY CONCLUSION
During the day, I came to the conclusion that I needed to install the DTT Smart Controller to provide additional transmission protection. I had not intended to purchase the Smart Controller when I made the trip to DTT. My reasons for purchasing the controller and my initial impressions are posted in:
http://www.dieseltrans.com/phpBB/viewtopic.php?t=32
What I learned at the DTT transmission class 101 - Part 3
Part 2 is at: http://216.235.147.117/forums/showthread.php?s=&threadid=57831
Part 1 is at: http://216.235.147.117/forums/showthread.php?s=&threadid=57830
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.
OVERDRIVE
The Dodge 47RH and 47RE transmissions are infamous for OD reliability problems in the past. To the best of my recollection Dodge made the following improvements. About 1994 Dodge instituted a series of upgrades that increased the direct clutches from 8 to 10, changed the OD planetary gears from 5 straight cut in an aluminum carrier to 5 helical cut in a steel carrier, and improved lubrication to the OD section. My impression is the overdrive problems are past history, current production (since 1994?) is largely trouble free if you do not tow at less than 1800 rpm. (There are probably some errors in my recollection, I trust Bill will clear up any errors. )
This does not mean that the OD clutch is foolproof. The OD clutch has a torque capability of 1. 1 to 1. 4 time the forward clutch depending on hydraulic pressure (lockup or not, throttle cable position). The service manual lists pressures of 80 to 130 psi depending on conditions. The OD clutch also has a very large spring that the hydraulic clamping force has to overcome. This spring requires 830 lbs of the clamping pressure. The effect of the spring reduces the torque advantage of the OD clutch over the front clutch. At about 70 psi the OD clutch torque capability is about equal to the front clutch. Thus, if you are idleing down the road at 1200-1400 rpm in OD lockup (40-45 mph as the Dodge setup will let you), your pressures are under specification due to accumulated internal leakage (say 70 psi or less), and you or the cruise control roll onto the throttle. The mighty Cummins delivers maximum torque and you are likely to wipe out the new weakest link, the OD clutch. A potential method of maximizing OD clutch life is do not operate in OD at less than 1600 rpm or tow in OD at less than 1800 rpm.
INPUT SHAFT, HUB, AND OUTPUT SHAFT
Bill showed me examples of broken input shafts and hubs. The granular appearance in the fracture zone made the cast material readily apparent. Bill stated that individuals experiencing fracture of the cast parts appear to be "luck of the draw". If you have operated several years without fracture you probably will not fracture in the future. Apparently, some castings have small internal defects or cracks and that continued stress cycling results in the internal defect/crack growing until the part ultimately fractures. Cracking and fracture is accelerated by high stresses and more stress cycles. The higher stresses can be power braking or harsher (lock to lock) shifting. The DTT Smart controller might result in more or earlier input shaft and hub fracture, it is too soon to tell from experience to date. I have the impression that fracture of these parts is not a big problem with trailer towers. It appears to me that the drag racers have broke most of them with power braking.
MY CONCLUSION
During the day, I came to the conclusion that I needed to install the DTT Smart Controller to provide additional transmission protection. I had not intended to purchase the Smart Controller when I made the trip to DTT. My reasons for purchasing the controller and my initial impressions are posted in:
http://www.dieseltrans.com/phpBB/viewtopic.php?t=32
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