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drivetrain Bliss - torque Converter - Photo 30828257

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  • A torque converter provides a fluid coupling between the engine and the internal automatic transmission gearing. This photo shows a disassembled converter. You can see the internal vanes, or blades, of a converter that are used to provide the fluid coupling. The converter also serves as a torque multiplier (by a factor of 2 or more) as you accelerate from a standstill.
A torque converter provides a fluid coupling between the engine and the internal automatic transmission gearing. This photo shows a disassembled converter. You can see the internal vanes, or blades, of a converter that are used to provide the fluid coupling. The converter also serves as a torque multiplier (by a factor of 2 or more) as you accelerate from a standstill.
1106 4wd 17+drivetrain bliss+transfer case Bigger tires mean better ground clearance and the ability to roll over bigger obstacles, but adding larger tires means the rotational speed of the engine drops for a given road speed. Going from a stock-ish 28-inch tire up to a 35-inch tire is an increase in size of 25 percent over stock. This means that an engine turning a comfortable 2,000 rpm at 65 mph drops to a more lugging 1,600 rpm with the bigger meats. This knocks the engine out of its efficient powerband, spoiling fuel economy, acceleration, and the ability to hold good speed on hills. To help compensate for the larger tire diameter and restore a good bit of the engine efficiency, the gearing in both axles can be changed. A simple calculation can be done to determine the new axle ratio needed to restore the original cruising rpm while running the new tires. It’s also not uncommon to slightly over-compensate on the gearing as the heavier tires rob a bit more power and can benefit from a little more drop in gearing (high numerically) in the axles. Using the proper ratio axle gears in regards to tire size helps maintain decent fuel economy, good acceleration off the line, better highway passing performance, and greater torque and smoother application of power to the tires. Whenever power is transmitted through a manual gearbox, the output rotation speed differs from the input speed by the gear ratio of the selected gear. This will affect the available torque. For instance, in first gear, the output spins slower than the input and the output torque is proportionately higher than that at the input. If we have a 4:1 first-gear ratio, output torque would be four times as great as the input torque. A torque converter provides a fluid coupling between the engine and the internal automatic transmission gearing. This photo shows a disassembled converter. You can see the internal vanes, or blades, of a converter that are used to provide the fluid coupling. The converter also serves as a torque multiplier (by a factor of 2 or more) as you accelerate from a standstill. 1106 4wd 07+drivetrain bliss+transfer case Here’s an example of the dual case setup from Offroad Design (ORD) that’s suitable for a wide range of full-size applications. They offer a conversion kit that mates the reduction portion of an NP203 to the venerable NP205 case. You can use their kit along with a couple of salvaged T-cases to build a doubler setup. ORD can also provide a two- or three-stick shifter mechanism to control both cases. Stepping up in performance, you can choose one of several complete aftermarket transfer cases on the market, such as the Atlas II. With this, you have the option of choosing transfer case low range gearing. You can go high or low ratio here and combine the choice with axle gearing to give you a good low range crawl ratio. However, you’ll need to make sure that when in 1:1 high range the axle gearing is appropriate for whatever high speed needs you have.
When very low gearing is used behind an automatic transmission, downhill compression braking can be substantial and highly beneficial, allowing you to keep your foot off the brakes and reduce heating them up. One word of caution is in order when it comes to the use of low-low doublers mated to a manual transmission. If you have a 10:1 low-low-range, you’re geared four to five times lower than a stock T-case. Should you be coming down a hill in deep low-range and gain too much speed with the clutch pushed in, it’s possible to quickly exceed the maximum rpm rating of the clutch disc. In such a case, you can literally spin one apart and destroy it under these circumstances. Another way to get lower T-case gearing is through the installation of an aftermarket gear set such as this 3:1 low-range set from JB Conversions for the NP205 transfer case. A stock NP205 has a 2:1 low-range. JB produces a new ductile iron casting to house the lower ratio gears, gaining you both a lower ratio and increased strength over the stock setup. When putting together a drivetrain for a project vehicle, you often have choices of components. Consider this example, which illustrates how power is transmitted through a 4WD drivetrain. We can see that if we start with a given output torque number from the engine, the torque progressively increases as it is transferred through gear reductions. Transfer case swaps are common and with a little ingenuity can often be done to upgrade to beefier hardware. Sometimes the conversions can be done using salvaged factory parts. Other times, companies like Advance Adapters or Novak can be called upon to provide the method to mate mismatched components. This kit helps mate a Toyota truck reduction box to a Dana 300 or Advance Adapters Atlas T-case. Advance Adapters came up with the Rubicrawler Kit to add a 2.72:1 planetary set to the 4:1 Rock-Trac transfer case to provide two more gear range options. Advance was able to cunningly stuff the six-pinion planetary in the area taken by a dead-space transmission housing on the tail of the 42RLE automatic transmission in ’03-to-’10 Wranglers. This allows installation of a doubler kit without the need for driveshaft or crossmember modifications. Slick! Here you can see a complete Marlin Crawler T-case stack. To the right is a standard Toyota T-case, fed by a Marlin adapter assembly (middle), preceded by an added Toyota reduction box on the left. The reduction box is the forward half of a stock gear model T-case and houses a 2.28:1 reduction gear set. Using a stock donor reduction yields a T-case with 2.28:1 or 5.2:1 low-range gearing. With the installation of aftermarket 4.7:1 low-range gears, the result is a low-low-range of about 11:1. In both cases, assume we have 400 lb-ft of torque at the output of the transmission and you can see both cases deliver similar output torque to the axle shafts and tire assemblies. However, look at the difference in torque at the output of the transfer cases. The one with the 4:1 transfer case ratio puts twice the torque to the driveshaft as the 2:1 transfer case. This means the pinion gear sees twice the torque load with the lower geared T-case. While these are opposite extremes, it serves to illustrate our point about where the greater torque load occurs. (400 lb-ft) T-CASE 4:1 low range (1600 lb-ft) AXLE GEARS 2.73:1 ratio (2184 lb-ft per 2WD tire) (1092 lb-ft per 4WD tire) On a portal axle, there is a gear reduction box that slows the axle shaft speed a second time. This means that the final output stub axle must be very strong to withstand the increased torque due to the gearing at the portal. However, the torque present at the differential and its axle shafts is effectively less when compared to a standard non-portal design.
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