Truck Transmissions and You!
Pickup truck transmissions have come a long way since the 80's. With the invention of the lock up torque converter in automatic transmissions, the better-made transmissions today can stand up to the torque put out by diesel engines and help slow you down. Practically all of the buses and more medium duty big trucks are going to automatic transmissions. Folks who drive mostly in the mountains like the engine braking they get with manual transmissions and the extra gears. Manufactures generally will give you around 3000 pounds more towing warranty on the automatic tranny on ½ ton pickups, SUV's and mini-trucks . This is because of the automatic transmission lock up torque converter, which locks up mechanically like a clutch and pressure plate, the absence of asbestos, (heat resistant,) from clutch discs, the torque converter doubling the torque coming from the engine flywheel, and the manufacture having more faith in the computer knowing when to shift verses us human types.
Diesels are generally harder to shift with a manual transmission than are gas-powered trucks. Because of the power and compression of a diesel, (usually twice the compression of a gas engine,) this compression, when you let off the gas pedal and engage the clutch pedal, causes the truck to decelerate quicker than the same process in a gas powered truck. So you have to shift a diesel quicker to avoid the jerk between gears. An automatic transmission on the other hand requires no such skill. I work in the city, with all of those stop signs and traffic lights; you know I drive an automatic. If I pulled a heavy trailer, (at the limits of the trucks capacity,) in the mountains, I would opt for a manual transmission. That compression in the diesel mentioned earlier helps slow you down on level ground. It doesn't quite work the same way, slowing you down on a steep grade. Diesels don t have a throttle plate like a gas engine so engine braking a diesel under load won t hold you as well as a gas engine. An actual engine brake or exhaust brake can be very effective with a diesel, but it s a gray area with manufacture warranties presently. I m hoping they will see the light. They keep giving us more power but the only thing they have given us lately for stopping is 4-wheel disc brakes. Each gear you shift with a manual tranny, will hold you there. And I like all the gears I can find, when I m going down a mountain with a heavy trailer chasing me! Especially in the Dodge with the in-line 6 cylinder Cummins diesel that has basically 1000rpm s less in the power band than a V-8 diesel found in Ford and GM. The extra gears will give you more top speed and staying power. Dodge also increases the torque by 45 pounds and the horsepower by 10 in the 6-speed manual transmission over their automatic transmission or their 5-speed manual.
In the newer trucks, all three makes use the same 6-speed manual tranny. With Ford and GM, they rate the auto and manual transmission close or the same depending on which month or year they were built. The Ford 4R100 automatic transmission in the F250 and above diesel or gas engine, will lockup its torque converter in third gear. Which is where you would want the transmission to lockup when pulling a load most of the time. The new Allison 1000 automatic transmission behind GM s new Duramax diesel or the new 8.1L gas engine will lock up the torque converter in each gear. This would be an advantage for the novice driver coming down the mountain loaded. Even an experienced driver can get a little nervous if they miss a gear on a manual using the fast side of the mountain. The Allison also has a downshifting feature just like the medium duty two-ton trucks that downshifts a gear when you let off the gas pedal and tap the brake pedal when in tow-mode.
But again in the mountains the more gears the better and you can leave it each gear longer when you are down shifting a manual transmission. The rest of the time diesels are a pain to shift all day if you are using it as a car. If you are only going to pull a 10,000 #' gooseneck or fifth wheel trailer, a 3/4-ton, (F250, C-K 20, 2500) will do. If you were in the future planning on hauling larger loads, then the 1-ton, (F350, C-K 30, 3500) or larger would be better. Generally the factory dually or cab and chassis dually have larger brakes and axles. The brakes on the newer Ford, Dodge, Chevy and GMC will be 4 wheel disc brakes, which are great at getting rid of the extra heat generated braking hard and cost less to replace.
Warning about overdrive in automatic transmissions. And overhead cam engines.
Automatic transmissions overdrive saves you fuel. And on fairly flat roads with the right engine combinations you can use overdrive with a load. Generally overdrive has no engine braking ability even on level ground. I m near the mountains and here you don t use the overdrive on an auto tranny when you are loaded. Coming down the mountain loaded in overdrive can be freewheeling life threatening experience. Overdrive as I said earlier is designed to save fuel not slow you down. The transmissions will also generally run cooler under a heavy load if you shift down one gear out of overdrive. This allows the pumps in the tranny to increase line pressure and provide better cooling. Synthetic oil can also help auto and manual transmissions run cooler. If you pull heavy loads, having synthetic oil in the differentials can add life to them. Synthetic oil doesn't tend to thin out in the cold as much as mineral based oil. Synthetic oil will build oil pressure in the engine sooner also. This is a big advantage in overhead engines. The newer Ford Triton engines, ( 4.6L, 5.4L, and the 6.8L V-10,) are aluminum head overhead cam design. If you've ever driven a smaller car with an overhead engine, they tend to clatter a little when you first start them. The oil has to build up pressure and lubricate more components in the head. With a quality synthetic oil the pressure is instant and quiet. I m glad to see the improvements that have come to pickup truck automatics and diesels, the only problem is this means they can pull bigger trailers, oh my look out below.
Till next time, Good Truck'n.
Kent Sundling (MrTruck)
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