Light-Truck Automatic Transmissions
Today's autotrannies last longer, but heat can still cripple them. Beat it by ordering the right equipment and caring for it.
Tom Berg
Equipment Editor
Heat is the enemy of the automatic transmission. That remains a fact, even with mechanical and electronic improvements that mean longer life and better performance than trannies of the early to mid-1990s.
Today's automatics in commercial light trucks should go 80,000 to 100,000 miles if the chassis is heavy enough for the job in the first place — and one or two simple options are chosen.
Service life of '90s-era automatics was short because the then-new electronically controlled transmissions were too weak. Operators were spoiled by the toughness of the tried-and-true three-speed "slush boxes" like Ford's C6, Chrysler's 727 and General Motors' Turbo 400 Hydra-matic. As a result, they were stunned when their electronic four-speed-overdrive replacements burned up in as little as 20,000 or 30,000 miles — and usually in 40,000 to 60,000.
Back then, fleet managers said they liked the better fuel economy delivered by the new overdrive automatics, but complained that they were highly susceptible to heat generated in stop-and-go operations common to commercial usage. Today's products have been improved with tougher bearings and other items, and have better lubrication systems. And software logic in their electronic controls better match clutch action to loads, easing strain on internal parts. However, heat is still a problem if it's not managed correctly.
RECOMMENDED PRACTICE
Problems with the early '90s transmissions caused members of the Technology & Maintenance Council of ATA to publish a list of guidelines on how to care for automatics. Recommended Practice 1410, as it's called, includes routine maintenance schedules, troubleshooting items, and admonitions to use correct fluids. Fluid types are usually unique to each transmission product, so shop people must know which tranny they're servicing and use the right fluid.
Technicians must also be trained to service and troubleshoot the latest products. For instance, erratic shifting may or may not be the fault of a transmission's electronic controls; a bad sensor or a short somewhere in the truck's wiring system may be to blame, and the technician must know how to trace down the problem. He can only do so with up-to-date knowledge and proper tools, which are available through the truck builder.
If you're a fleet buyer and manage much of your own maintenance, negotiate a deal that provides training and tools as well as new trucks. Don't let mechanics get into rebuilding modern autotrannies unless they're specially trained for it.
The RP also suggests installing an external in-line fluid filter, which tests show can greatly extend life. Most light-truck automatics come only with an internal strainer — a "rock catcher," in the words of Gary Andrews, director of fleet sales for Tecumseh Fleet Engineering/National Fleet Services and a former Ryder System executive.
However, an external filter with a magnetic element catches smaller particles, especially metal bits produced during the transmission's break-in period or just after a rebuild. An external filter is highly useful to a fleet because its element can be changed without dropping the pan. That step itself can lead to additional problems, like stripped bolts and incorrectly installed gaskets.
SPEC'ING IS LIMITED
Andrews and others agree that automatic transmissions in a light truck cannot be specified by type. The truck builder pairs the chosen engine with a transmission and you can take it or leave it. If you'd like a builder's toughest automatic, you have to buy a diesel, or spec the biggest gasoline engine.
The Big Three domestic builders — Ford, General Motors and the Dodge Division of DaimlerChrysler — all offer a standard four-speed automatic with their smaller gasoline V-8s, and a stronger automatic with their largest engines, including diesels. For example, in GM's Chevrolet and GMC light-duty models, a 4L60E or 4L80E four-speed comes with Vortec 4800, 5300 and 6000 gas engines, while Allison's 1000 is paired with the Vortec 8100 and the Duramax 6600 diesel. Many fleet users might like the Allison with a smaller gasoline engine, but they can't get it — and they probably wouldn't want to pay for it anyway.
What they can get — and this goes for buyers of Ford and Dodge trucks, too — is a tow package, which adds a transmission cooler, as well as a bigger radiator and a wiring harness for the trailer hookup, says Dave Williams, regional fleet manager for Verizon Communications in Valhalla, N.Y. Many commercial light trucks tow trailers, so this is not a bad thing to have. A factory installed trailer towing package costs only about $200, and is among the items he has ordered in the past on Dodge 2500 vans and now GM 2500 vans used by telephone repairmen.
COOLER IS VALUABLE
The transmission cooler is especially valuable to Verizon because the vans' engines drive auxiliary equipment such as hydraulically operated man buckets. As a result, they idle a great deal of the day. Idling creates a lot of heat, and heat can cook a transmission, Williams says. The air-to-oil cooler is mounted ahead of the radiator, and while it gets no ram-air effect while idling, the engine fan does move some air through the cooler and radiator. He estimates the cooler extends the life of his automatics by 25% to 35%.
Williams also installs an in-line fluid filter — the Magnefine sold by Tecumseh Fleet Engineering — and recommends it. Users must seek and install an external filter because most light-truck automatics do not have one and builders will not install them as options. Two exceptions are Ford's five-speed TorqShift, which comes with the Power Stroke diesel, and the Allison 1000, according to Andrews of Tecumseh.
Tecumseh rebuilds automatic transmissions and its technicians regularly find metal particles in the cooler circuit. Particles are pumped there from inside the transmission, but cannot be dealt with by the cooler. A filter with a magnetic element captures those particles and prevents them from reentering the transmission and creating havoc on seals and moving parts.
On a new truck, an in-line filter should be installed on the outlet side of the transmission, upstream of the cooler, Andrews says. On a truck that's already in service, the filter should go downstream of the cooler to snag metal particles and other contaminants that may be in the cooler and elsewhere in the plumbing.
SYNTHETIC FLUID
Synthetic automatic transmission fluid runs cooler than petroleum-based fluid, Williams says, and should be used in any autotranny whose builder allows it. Here, too, the shop people dealing with a mixed fleet have to be careful, because some transmissions require synthetics and others prohibit it.
Andrews is on the TMC task force that wrote RP 1410, and he says his group is talking about updating the document to discuss fluids more thoroughly.
In the meantime, "change fluids more often," Williams advises, "maybe twice as often as what you may be used to. If you're changing it every 30,000 miles, maybe do it every 15,000." Andrews notes that commercial light trucks usually fall in the category of "severe service" as outlined in the owner's manual. He urges users to read that manual and adopt the severe-service maintenance intervals, which are much shorter than for "normal" service.
Checking the fluid level is among the more basic maintenance functions, and should be done at least every 5,000 miles, RP 1410 says. At that time, also look and smell the fluid for evidence of burning — the burnt" smell and dark coloration are classic symptoms of serious internal problems. Also look for any fluid leaks anywhere on or near the tranny, check for proper operation of the PRNDL indent, the throttle position and the park pawl. Plug in a service tool and check for fault codes that may have been recorded in the ECM.
Fluid should be changed at no more than 30,000 miles, and probably sooner, according to the RP. This includes flushing and flow-testing the cooler. Retorquing of bolts, and servicing of electrical connectors and the slip yoke are also on this list. The manufacturer's recommendations should be consulted and followed. Failure to follow these not only endangers the transmission, but also the warranty.
And if and when the tranny burns out, you may also find a burning hole in your repair budget.
