Modern Day Tranny: Shifting Gears
By: Grant W. RepsherYour transmission: What it does
Service (flush) vs. rebuild
What to watch out for
Continuously Variable Transmission (CVT)
Performance-minded transmissionsMost people realize that essentially every vehicle, from the smallest electric moped to the largest Semi-tractor, employs some sort of transmission. Aside from knowing to label it either "manual" or "automatic," however, this automotive system is often misunderstood. Actually, with today's Tiptronics, Manu-matics, Direct Shift Gearboxes (DSG), Sequential Manual Gearbox (SMG), and F1 transmissions, it has become even more difficult to get that far.
Regardless of whether the car has a clutch pedal, shift paddles, steering wheel mounted rockers, or "+" and "-" labeled gear shift lever, all transmissions function on the same principles. Before listing the symptoms to watch out for and where to seek repairs, it makes sense to define this component of your car's power train and describe its responsibility.
A transmission -- whether manual, automatic, continuously variable (CVT), twin clutch or otherwise -- is used to transmit (or regulate) the speed of a vehicle's engine to that of the car's wheels, specifically the front wheels (front-wheel drive), rear wheels (rear-wheel drive), or all four (all-wheel drive). Even when a car is stationary, such as at a stop light, the engine spins a shaft that connects to the clutch and transmission. It's the job of the transmission to convert that fast-spinning shaft into controllable acceleration.
In other words, the transmission bears the responsibility of taking the wheels from zero miles per hour through to highway speeds, countless times each day.
To get technical for a moment, the transmission utilizes a complex gear set -- a hydraulic system of bands and internal clutches to engage/disengage the different gears from the engine flywheel to the drive shaft (which spins the wheels), and a pump to keep the transmission lubricating fluid circulating.
The whole component is neatly packaged and appears as a single unit, yet it can be made up of hundreds of individual parts. And while operating an auto transmission may seem quite different from a manual, they are otherwise analogous in operation. (Automatic transmissions replace the clutch found in manuals with something called a torque converter).
As you can imagine, something so complex with so many individual parts must be susceptible to wear and expensive breakdown. From a repair and maintenance standpoint, the issue with transmission work is that "neat packaging."
Transmissions are built to last for many miles (if not the life of a vehicle), with only minor servicing for this very reason. Because this component is sandwiched between your vehicle's engine and driveshaft, access is severely limited. Therefore, service is often limited to minor adjustments and or replacing the fluid (flushing).
If the transmission requires further attention, it will need to be removed from the vehicle, which can almost always be qualified as "major" procedure. Additionally, because you have gone to the lengths of "dropping" (removing) the transmission, it is often suggested -- and worthwhile -- to do everything possible to bring it as close to new operation as feasible.
You will hear the word "rebuild" thrown around quite liberally at this point, as this is the most common and logical next step. A rebuild includes the disassembly and cleaning of all the parts, checking for wear, and replacing all seals, gaskets and fluid. Unless the unit is completely shot (requiring the whole thing to be replaced), the majority of service cost associated with this service will be labor-related. Fortunately, transmissions are often included in a manufacturer's extended (powertrain) warranty, typically 10 years or 100,000 miles.
Before jumping into a rebuild, though, a reputable shop will exhaust (no pun intended) all other potential causes or problems. The clutch, for example, is closely related to the "transmission" of power and is really the only other line of defense between a very fast spinning shaft and all those delicate gears. Also, an improperly tuned engine, especially with the increased complexity of newer automatics/CVTs with electronic control of the transmission, can sometimes mimic the symptoms of poorly functioning gearbox.
Some things that do signal the need for transmission work include:
The transmission seems to hesitate when you're "selecting" a gear (for example, if when you put the car into drive it takes a few seconds for the wheels to engage).
The transmission "slips" or does not stay in-gear during normal operation.
Unusual noise or grinding accompanies gear selection or acceleration.
The car's clutch does not seem to be operating properly (this is specifically for manual vehicles).
Because transmission preventative maintenance is fairly basic and inexpensive, it is helpful to make sure you complete the one or two major service procedures that include replacing (flushing) your transmission fluid. Check your owner's manual to determine when this should be done, but it's usually around 100,000 miles.
Almost all repair facilities and dealerships, whether large small, independent or chain, will offer at least the basic transmission service including flush and fluid replacement. As a matter of fact, if a store you come across doesn't, it may be a sign of concern. If you aren't there as part of a scheduled service, the cost of this is usually anywhere from $89 to $150, however be certain to consult your owner's manual prior to having it done at non-dealer stores as there are some brands out there that not only don't recommend flushing the transmission, but will void your warranty if you do.
A Word about Continuously Variable Transmissions (CVT)
Several manufacturers have recently re-introduced this century-old transmission technology in their mainstream vehicles, as improvements in CVT design and materials have made them appropriate for today's automotive applications. You may have one in your car, which could be a good thing as they are designed to be somewhat more durable.
The system itself is much simpler than a conventional gearbox and contains merely a hydraulically operated pulley (driving), a mechanically operated torque pulley, a special rubber belt to link the two, and a host of electronics and sensors to control it.
Each pulley is cone shaped (one is ridged), allowing the belt to move to different positions based on pre-set driving 'maps' or requirements of the driving conditions. This means the gearbox is not limited to the 4, 5, 6, or 7 forward set gear ratios found in a traditional transmission.
The main benefits of the design is the theoretic durability from fewer moving parts, increased fuel economy and decreased emissions by allowing the engine to always operate within its optimal power band and smoother delivery of power.
Drawbacks include size, weight and bulkiness of the CVT as well as the limits in application horsepower due to limits in the belt specifications. The most common criticism however, comes from drivers who are not used to driving what feels like a single speed vehicle (acting mechanically much like a large golf cart). Because there are no "steps" in power and the engine sound doesn't change pitch, there is a learning curve to living with one.
When it comes to servicing a CVT, you can expect the same service intervals as with a traditional transmission. But because it has far fewer moving parts, it should theoretically be much easier to repair.
Performance-minded transmissions
The semi-automatic transmission, also known by many as Porsche's "Tiptronic" trade name is essentially an automatic transmission with the added feature of allowing the driver to manually select gears via the gear shift lever or shift buttons without having to employ a foot-operated clutch. Where the CVT transmissions are reserved for passenger vehicles with somewhat limited horsepower ratings, these transmissions are more "geared" toward performance.Many, of not most manufacturers have either developed or outsourced similar technologies, but recently the most serious sports manufacturers have taken the development to new lengths. SMG (BMW), DSG (Audi/VW), and F1 (Ferrari/Maserati) are a few examples of how the original tiptronic idea has evolved. Based on transmissions found in racing cars, these gearbox are electronically controlled and are seamless wired to the engine and its fuel management system. Sometimes it is even connected to (and acts in accordance with) suspension components.
Typically these systems have a fully automatic mode, similar in function to a traditional automatic, as well as a manual mode, where the operator shifts manually (though without a manually operated clutch) via a gear lever or shift paddles located on or behind the steering wheel. One side shifts up and the opposite side, down.
Because of their complexity, these systems only take the usual principles of transmissions and complicate them by adding even further electronic control and responsibility. That in turn makes them a whole lot of fun to drive, but even harder and more expensive to repair.
Grant W. Repsher is the founder of Servassist Online. He is a writer with Automotive News, the auto industry's premier trade publication, and a former contributing editor with the AIADA (American International Automobile Dealers Association). To contact Grant about this article or to suggest future topics, please click here.
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