Attention: TDR Forum Junkies What I learned at the DTT transmission class 101 - Part 2
Part 1 is at:
http://216.235.147.117/forums/showthread.php?s=&threadid=57830
Part 3 is at:
http://216.235.147.117/forums/showthread.php?s=&postid=517425#post517425
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.
TORQUE CONVERTER CLUTCH
With a torque converter clutch capacity about 1. 7 times that of the forward clutch, why do torque converter clutches fail? In my opinion it wears out and much faster than the other clutches. It also has another failure mode that the other clutches do not have.
Clutches wear during engagement and disengagement. As the speeds of the clutch elements change during engagement/disengagement, the clutch faces slip and rub and wear. If clutches engage faster, there is less total rubbing of faces (less time, fewer revolutions during the slip; if you run a belt sander for 1 second instead of 3 seconds, there will be less material removed). The other clutch packs have grooved clutch discs to aid in fluid removal between clutch elements and speed engagement. Faster engagement reduces clutch wear but also increases the shift firmness (called severe or harsh by some, the general public). The TC clutch is smooth because the clutch facing also serves as the seal for the piston providing TC clutch clamping force. The TC clutch also has a much larger volume of fluid to bleed through the clutch surface. I would guess that the TC clutch engagement time is the largest in the transmission.
The TC clutch is also exposed to the highest temperatures in the transmission. The other clutches are exposed to the pan temperature, the TC clutch is exposed to the pan temperature further heated by the TC when the TC clutch is unlocked. The TC clutch material will routinely see temperatures 100-150 degrees hotter than the other clutches. These higher temperatures may accelerate aging and wear of the clutch material.
In addition, 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 mystery switch with an open position that prevents any TC clutch engagement (city driving) or 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.
The other failure mode unique to the TC clutch is related to the fact that the clutch facing also provides the hydraulic seal to engage the clutch and provide clamping force. If a small area wears, fails, or has a piece of debris caught on the sealing face, this produces an internal hydraulic leak with resulting reduction in clamping force. If the leak past the clutch face is high enough, the TC clutch will slip and burn. Thus the clutch material and facing have performance requirements that other clutches do not have.
Thus the TC clutch has the severest duty and highest requirements of all the transmission clutches and might be expected to wear out sooner.
Some, including Ford Motor Company, have proposed multiple or stacked clutches in the TC as an improvement. Since the single clutch surface has a torque capability 1. 7 times the front clutch, the additional torque capability up to 5 times the front clutch with 3 clutch surfaces is not needed. The three individual clutch surfaces each wear at the same rate (or more) than a single clutch surface as the total revolutions to engagement is probably the same. The failure mode by clutch sealing failure is probably sooner as now there is three times the seal area subject to defects and accelerated wear. In addition, some of the multiple clutch elements are anchored to the outer perimeter with tabs into slots. The dynamics of the diesel produce impulses in the output to the drive train that can be destructive to the gear train. This is typically attenuated with damper plates or damper plates to absorb the vibrations and must be tuned to the engine and power levels (one size might not fit all power levels and injection timing). In any event you should expect some vibration and impulse wear between the tabs and slots of the clutch elements. If any chips are produced, these chips might be expelled from the TC, through the TC clutch/seal. This additional foreign material might get embedded in the clutch material and result in scoring the clutch/seal face or holding the seal faces apart with the result of TC clutch failure. I would be wary of accepting claims of increased TC life with multiple clutch plates. Increased toque capability is not needed and I personally would expect a shorter life due to increased sealing problems. Bill and DTT apparently have similar conclusions as DTT is marketing a single clutch TC to replace the problematic Ford multiple clutch TC that was introduced in 1999.
I am now skeptical to claims that more, stronger, bigger, etc is better as I admit to being seduced in the past by glowing marketing claims and deception in advertising (telling truths, just not telling all of the truths). The TC business is rife with claims and the consumer should proceed with caution. My opinions on stators, lock to lock shifts, and billet covers are presented below.
Milled Stators - I was guilty of buying a milled stator in the past based on the claim that it was more efficient by reducing the stall speed. On the first grade I came to while pulling the trailer I discovered that the milled stator also reduced torque multiplication and reduced the speed I was able to climb the grade from the stock stator. It became apparent to me why people were installing mystery switches, it was to compensate for the mistake in buying a milled stator TC. The milled stator cuts the rear third off the stator. The stock stator has hydrodynamic/aerodynamic shape similar to an airfoil for efficient operation. Milling off the rear third of the stator reduces the efficiency and resulting stall speed by generating more stirring, friction, and heat. In the process it also destroys torque multiplication needed by trailer towers. Would you fly in an airplane that someone claimed was better by chopping off the rear third of the wings?
Lock to Lock Shifts - Reportedly there have been claims that locked shifting has no clutch slipping. This is bunk, there may be no TC clutch slipping during shifts 2-3-OD-3-2, but there is definitely slippage of the front, rear, direct, and OD clutches during engagement. If there were an instantaneous change in rpm during shifting with no slippage, the shafts would disintegrate.
TC Billet Covers - The claim for billet covers is that they prevent ballooning of the cover and infer this will thus prevent TC clutch failure. The TC pressure is about 130 psi during lockup. The V10 uses the same TC as the Cummins diesel. The V10 at 5,000 rpm develops 370 psi hydrostatic head for a total of 500 psi. The Cummins at 2600 rpm develops 100 psi hydrostatic head for a total of 230 psi. If the V10 does not have a ballooning problem with nearly 300 psi increase, how can ballooning be a problem with the diesel? However, the billet cover does introduce another problem. The TC is supported by bolting to the flex plate on the front and by a bearing/bushing in the transmission on the back. The billet cover results in a significantly heavier TC. I asked Bill why the billet cover TCs resulted in bushing wear in the transmission if the billet weight was supported by the flex plate. His answer should have been obvious, "Flex plates flex". The flex plate would have been engineered for the loads specific to the stock converter. Increasing the mass of the TC would result in different flexing and harmonics with predictable greater deflections resulting at the transmission and early bushing/bearing failure. A heavier billet cover (that is not needed to eliminate nonexistent ballooning) requires a custom redesigned flex plate to match the billet cover TC characteristics. I doubt that the vendors of billet cover TCs will spend the money for engineering and the thousands of hours of testing that Dodge no doubt has in their combination. I asked Bill about the claim that the stock cover would bend at the steel mounting tabs welded on the cover for bolting to the flex plate. Bill stated that he has never seen a TC come in with bent mounting tabs. It appears that the TC cover is not broken so we should not try to fix it and introduce other problems. But, the marketing looks good. Isn't bigger always better?
Part 1 is at:
http://216.235.147.117/forums/showthread.php?s=&threadid=57830
Part 3 is at:
http://216.235.147.117/forums/showthread.php?s=&postid=517425#post517425
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.
TORQUE CONVERTER CLUTCH
With a torque converter clutch capacity about 1. 7 times that of the forward clutch, why do torque converter clutches fail? In my opinion it wears out and much faster than the other clutches. It also has another failure mode that the other clutches do not have.
Clutches wear during engagement and disengagement. As the speeds of the clutch elements change during engagement/disengagement, the clutch faces slip and rub and wear. If clutches engage faster, there is less total rubbing of faces (less time, fewer revolutions during the slip; if you run a belt sander for 1 second instead of 3 seconds, there will be less material removed). The other clutch packs have grooved clutch discs to aid in fluid removal between clutch elements and speed engagement. Faster engagement reduces clutch wear but also increases the shift firmness (called severe or harsh by some, the general public). The TC clutch is smooth because the clutch facing also serves as the seal for the piston providing TC clutch clamping force. The TC clutch also has a much larger volume of fluid to bleed through the clutch surface. I would guess that the TC clutch engagement time is the largest in the transmission.
The TC clutch is also exposed to the highest temperatures in the transmission. The other clutches are exposed to the pan temperature, the TC clutch is exposed to the pan temperature further heated by the TC when the TC clutch is unlocked. The TC clutch material will routinely see temperatures 100-150 degrees hotter than the other clutches. These higher temperatures may accelerate aging and wear of the clutch material.
In addition, 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 mystery switch with an open position that prevents any TC clutch engagement (city driving) or 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.
The other failure mode unique to the TC clutch is related to the fact that the clutch facing also provides the hydraulic seal to engage the clutch and provide clamping force. If a small area wears, fails, or has a piece of debris caught on the sealing face, this produces an internal hydraulic leak with resulting reduction in clamping force. If the leak past the clutch face is high enough, the TC clutch will slip and burn. Thus the clutch material and facing have performance requirements that other clutches do not have.
Thus the TC clutch has the severest duty and highest requirements of all the transmission clutches and might be expected to wear out sooner.
Some, including Ford Motor Company, have proposed multiple or stacked clutches in the TC as an improvement. Since the single clutch surface has a torque capability 1. 7 times the front clutch, the additional torque capability up to 5 times the front clutch with 3 clutch surfaces is not needed. The three individual clutch surfaces each wear at the same rate (or more) than a single clutch surface as the total revolutions to engagement is probably the same. The failure mode by clutch sealing failure is probably sooner as now there is three times the seal area subject to defects and accelerated wear. In addition, some of the multiple clutch elements are anchored to the outer perimeter with tabs into slots. The dynamics of the diesel produce impulses in the output to the drive train that can be destructive to the gear train. This is typically attenuated with damper plates or damper plates to absorb the vibrations and must be tuned to the engine and power levels (one size might not fit all power levels and injection timing). In any event you should expect some vibration and impulse wear between the tabs and slots of the clutch elements. If any chips are produced, these chips might be expelled from the TC, through the TC clutch/seal. This additional foreign material might get embedded in the clutch material and result in scoring the clutch/seal face or holding the seal faces apart with the result of TC clutch failure. I would be wary of accepting claims of increased TC life with multiple clutch plates. Increased toque capability is not needed and I personally would expect a shorter life due to increased sealing problems. Bill and DTT apparently have similar conclusions as DTT is marketing a single clutch TC to replace the problematic Ford multiple clutch TC that was introduced in 1999.
I am now skeptical to claims that more, stronger, bigger, etc is better as I admit to being seduced in the past by glowing marketing claims and deception in advertising (telling truths, just not telling all of the truths). The TC business is rife with claims and the consumer should proceed with caution. My opinions on stators, lock to lock shifts, and billet covers are presented below.
Milled Stators - I was guilty of buying a milled stator in the past based on the claim that it was more efficient by reducing the stall speed. On the first grade I came to while pulling the trailer I discovered that the milled stator also reduced torque multiplication and reduced the speed I was able to climb the grade from the stock stator. It became apparent to me why people were installing mystery switches, it was to compensate for the mistake in buying a milled stator TC. The milled stator cuts the rear third off the stator. The stock stator has hydrodynamic/aerodynamic shape similar to an airfoil for efficient operation. Milling off the rear third of the stator reduces the efficiency and resulting stall speed by generating more stirring, friction, and heat. In the process it also destroys torque multiplication needed by trailer towers. Would you fly in an airplane that someone claimed was better by chopping off the rear third of the wings?
Lock to Lock Shifts - Reportedly there have been claims that locked shifting has no clutch slipping. This is bunk, there may be no TC clutch slipping during shifts 2-3-OD-3-2, but there is definitely slippage of the front, rear, direct, and OD clutches during engagement. If there were an instantaneous change in rpm during shifting with no slippage, the shafts would disintegrate.
TC Billet Covers - The claim for billet covers is that they prevent ballooning of the cover and infer this will thus prevent TC clutch failure. The TC pressure is about 130 psi during lockup. The V10 uses the same TC as the Cummins diesel. The V10 at 5,000 rpm develops 370 psi hydrostatic head for a total of 500 psi. The Cummins at 2600 rpm develops 100 psi hydrostatic head for a total of 230 psi. If the V10 does not have a ballooning problem with nearly 300 psi increase, how can ballooning be a problem with the diesel? However, the billet cover does introduce another problem. The TC is supported by bolting to the flex plate on the front and by a bearing/bushing in the transmission on the back. The billet cover results in a significantly heavier TC. I asked Bill why the billet cover TCs resulted in bushing wear in the transmission if the billet weight was supported by the flex plate. His answer should have been obvious, "Flex plates flex". The flex plate would have been engineered for the loads specific to the stock converter. Increasing the mass of the TC would result in different flexing and harmonics with predictable greater deflections resulting at the transmission and early bushing/bearing failure. A heavier billet cover (that is not needed to eliminate nonexistent ballooning) requires a custom redesigned flex plate to match the billet cover TC characteristics. I doubt that the vendors of billet cover TCs will spend the money for engineering and the thousands of hours of testing that Dodge no doubt has in their combination. I asked Bill about the claim that the stock cover would bend at the steel mounting tabs welded on the cover for bolting to the flex plate. Bill stated that he has never seen a TC come in with bent mounting tabs. It appears that the TC cover is not broken so we should not try to fix it and introduce other problems. But, the marketing looks good. Isn't bigger always better?
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