Automatic Transmission

Making the Automatic Transmission Live 

Automatic Transmissions have gotten a bad rap by some. The main causes for automatic transmission failure are excessive heat, and slippage of the internal friction elements. And of course, if your trans suffers catastrophic breakage. 

Heat

The worst enemy of an automatic transmission is heat . Run a big enough tranny cooler,  do NOT run the tranny fluid through the radiator, and DO use a tranny temp gauge. That simple. 

How hot is too HOT?

An automatic tranny is happiest at 190 degrees or less most of the time. They really do not mind getting up as high as 240 on occasion, but you definitely don’t want them there for a long time.  A tranny that hits 260 is in imminent danger of having a catastrophic failure and blowing tranny fluid all over the trail, not to mention the rig won’t drive well after that. Also, unlike an engine, it really does the no harm to run them overly cool. Engines get fuel diluting the oil (a little sneaks past the piston rings during compression). If you run the engine warm enough, this fuel evaporates and then gets sucked back into the engine to be burned through the PCV system.  Tranny fluid is thinner and works fine at temperatures much lower than it is wise to run your engine at.

Tranny Cooler:

The answer is simple: Use a huge tranny cooler, like an aftermarket unit designed for a 25,000lb towing application. We then prefer to NOT route the tranny fluid through the radiator. The engine is often hotter than the tranny (and when the tranny DOES make heat, like on a long hard climb, it does not add as much of it’s heat to the tranny.

We commonly use B&M PN 70264 as a replacement cooler (mounted in front of the radiator) in 1/2T vehicles, and do not run tranny fluid through the radiator. B&M also makes a couple models of coolers which have their own electric fan. It is thermostatically controlled, and kicks in when the tranny fluid gets over 180 degrees (B&M PN 70297 or 70298). This can be used by locating it where it does not interfere with the airflow to the radiator, it can get a easy flow of cool air through it, and is out of harms way (from rocks, etc). In a towing application, we might be inclined to use BOTH. Bottom line: Your tranny temp gauge will tell you if you have enough cooling or not.

Tranny Temp Gauge

We recommend one highly. Without it you haven’t a clue how hot your tranny is running. It is scary sometimes how hot they can get! If you have an automatic tranny, have a tranny temp gauge. It will certainly help you make your tranny live longer, and could prevent a catastrophic failure.

Lock-up Torque Converters

In overdrive automatics, the torque converter slippage without a lock up can be quite significant. This adds up to lots of extra heat, and wasted fuel. Use a lock up converter on the highway.

article: Lock up Torque Converters

Slippage - losing fluid pressure

An automatic transmission uses fluid pressure to hydraulically hold clutches together and apply bands. These bands and clutches are how it selects what gear it is in. If this pressure drops too low, the clutches or bands can slip causing rapid transmission failure. 

Non electronic transmissions control fluid pressure by valves and springs in the valve body, and a cable r linkage to the throttle, or sometimes are vacuum controlled

Electronic control trans - Stock trans electronic control often programs for a soft mushy shift. That means it is already designed to slip some. Makes for a smooth shift, but it is bad for the trans and also makes extra heat. Add more power than the program was originally designed for and you really slip In an electronic trans, part of this is physical, mechanical in the trans, and part is in the software. Your reprogrammer must have the capability to re program the ecm for firmer shifts and properly control converter lockup, (or when installing an electronic trans in a vehicle that has no trans ecm,  you can use an aftermarket programmable ecm such as a Baumanator (for Ford apps) or PCS ecm

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Use a transmission that was built for your application, (We optimize some things differently for rock crawling, mud bogging, towing or general highway). Use the correct fluid, and make sure it is full to the correct level. And run a transmission line pressure gauge to tell you if there is a problem before the tranny fails. 

At the bottom of the tranny is a pan, like the oil pan on the motor. A supply of oil is kept in this pan, with a pickup and filter dipping down into the oil.  In four wheeling, vehicles are often operated at crazy angles. If the angel causes the oil in the pan to uncover the pickup, the tranny’s pump will suck air, hydro pressure will drop and…

Tranny builders that know how to build rock crawling trannies (Race cars and desert race trucks don’t have these same angle problems) know-how to deal with these problems in various transmissions.

Water

Water in an auto trans. Sealing one up is mostly observation and common sense, however here are some observations:

The dip-stick/filler tube. Use RTV sealant when installing this so it cant leak where it goes into the trans

The vent: Yes, you must rig the vent (In some cases you can simply RTV a hose onto the vent tube) so that a hose can go onto it, and run this up the filler tube and tie wrap near the top. If the water gets that deep, you're in trouble anyway!

In some cases water can get in where the kickdown cable enters ther trans. This must be sealed up.

look it over in detail, see if anything else must be sealed. the selector shaft will already have a seal on it to keep oil IN.

Catastrophic Breakage

You're slamming on the throttle, something goes whang, scrunch whirrrrr,  and forward movement stops. This is bad. If this happens, it is time to call Houston. The best answer to this is do the above preventative actions regarding heat and pressure, and BUILD THE RIGHT TRANSMISSION IN THE FIRST PLACE.  If we know the intended application (read "abuse"), we can specify and use the right parts that will be strong enough. No need to spend money on expensive trick stuff you won't need, but much cheaper to get trick stuff where it is needed. We can assist you selecting both the best transmission for the application, as well as what degree and type of build-up is indicated.