Clutch Packs: CRC's Calkins says that proper assembly is key. Most name-brand "heavy-duty" kits (e.g., Raybestos) work fine for serious towing.
Shift Kits: CRC uses TransGo and other well-known kits, generally following their instructions for towing. CRC also does custom valving for unique needs.
The incline roller clutch is another upgradeable area. The OE unit typically has nine roll
Aftermarket shift kits regulate fluid flow through the valve body to tune shifting charact
Pan: Heat is the trans-killer. So, a larger pan with increased oil capacity is optimal. Later TH400s offered deeper pans; retrofitting requires also using the later-style pickup adapter. Aftermarket cast-aluminum pans offer extra capacity and improved heat-dissipation, but they can be pricey. Calkins advises avoiding cheap overseas pans, which tend to have sealing problems.
Torque Converter: Big and low are the way to go. Calkins builds Turbo 400s that tow with an aftermarket 13-inch Allison-application converter, having a 1,100- to 1,200-stall speed for better take-off when towing. (Higher stall speeds are recommended for extreme towing.) These converters feature reinforced hub areas.
Cooling: Calkins says that Turbo 400 cooling issues often originate in the radiator. After you verify that the trans-cooling lines are actually routed there, then fixing the existing radiator or, ideally, upgrading to a larger one can solve the problem. Coming out of the radiator, the ATF should go through the largest auxiliary cooler that'll fit in the vehicle. If the auxiliary cooler doesn't get good airflow, consider using an aftermarket unit that has its own electric fan.
Swaps: Depending on all the other variables, a properly set up, conservatively driven Turbo 400 can survive 400-500 hp engine power, 4.56 axle gears, and 37s while towing 12,000-13,000 pounds. Chevy/GMC owners who tax these limits regularly should consider upgrading to a more modern automatic. The 4L80E offers comparable strength and an overdrive Fourth gear (although Calkins cautions that towing heavy loads often requires higher revs than overdrive offers). Advance Adapters is one company that offers a controller to retrofit the computerized 4L80E into older vehicles.
An even stouter option is swapping in an Allison automatic rated at 620 lb-ft. DeStroked makes a standalone controller and adapters to swap the Allison into many nonstock applications. If towing requires an Allison, though, it might be cheaper and faster to trade in the old truck for a diesel rig. (Jim Bigley of The Diesel Page, www.thedieselpage.com, sells a swap manual that details how to retrofit a Duramax/Allison combo into older trucks.)
So, each totally-built-to-tow Turbo 400 prescription varies by vehicle and use. Good transmission shops should be able to recommend the best combination for the towing task at hand.
Most Turbo 400s have four-gear planetaries (left). More desirable is the five-gear setup f
An aftermarket heavy-capacity Allison-application torque converter (right) is the hot towi
|"HEAVY" LIGHT-DUTY GM AUTOMATIC TRANSMISSION GEAR RATIOS |
|Model ||1st ||2nd ||3rd ||4th ||5th ||6th ||Rev. |
|TH400 ||2.48 ||1.48 ||1.00 ||- ||- ||- ||2.07 |
|4L80E ||2.48 ||1.48 ||1.00 ||0.75 ||- ||- ||2.07 |
|Allison 1000 ||3.10 ||1.81 ||1.41 ||1.00 ||0.71 ||0.61 ||4.49 |
|Allison 2000 ||3.51 ||1.90 ||1.44 ||1.00 ||0.74 ||- ||5.09 |
Turbo 400 Trivia
Most four-wheelers respect the TH400 for its strength. Its only knocks are the long housing (which is still shorter than the newer OD automatics) and the lack of a fourth (Overdrive) gear.
This beloved automatic made its first mass-production appearance in '64 Cadillacs and Buicks as the Super Turbine 400. It eventually handled gear reduction in large GM passenger cars, 3/4- and 1-ton trucks, medium-duty trucks, cab/chassis vehicles (including many motorhome coaches), step vans, and buses. Many higher-end British cars and even Ferraris have had the Turbo 400.
In 1987 GM's Turbo-Hydramatic division dumped the cable-operated speedometer for an electric one and renamed the transmission the 3L80 (trucks received the 3L80HD designation to indicate the stronger case and deeper pan); all other Turbo 400 components remained the same. By 1992 the Turbo 400 had been replaced in all passenger and light-duty-truck applications with four-speed overdrive automatics. However, the Turbo 400 continued to be produced for military Humvees.
Not all OE pans are created equal: Truck applications' are deeper. Upgrading a shallow pan
Inexpensive pans (top) often don't have as much metal between the bolt holes and inner lip
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