The modern automatic transmission is by far, the most complicated mechanical component in today's automobile. Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony which goes virtually unnoticed until there is a problem. The Information below will help you understand the concepts behind what goes on inside these technological marvels and what goes into repairing them when they fail.
10 Signs of Transmission Trouble
1: Lack of Response
Transmissions are designed to go into the correct gear every time, so when they hesitate or refuse to go, it's a sure sign there's something wrong. With manual transmission problems, you may notice after shifting into a gear that the car's engine will rev up, but the car won't be moving as quickly as the engine is running. In this case, a worn-out clutch or more serious transmission problem may be occurring [source: AAMCO].
Automatic transmissions have the same lack-of-response problem, but will usually manifest the issue while engaging the "Park" or "Drive" selection. The car should shift quickly into either of these modes, but if your transmission hesitates to go into either one, then it's likely there's an issue with the transmission.
2: Whining, Clunking and Humming
It's difficult to nail down exactly how your car may sound if there's transmission trouble, but one thing's pretty certain, you'll probably get a that-doesn't-sound-right feeling when you hear it. Every car is built differently, so the sounds they produce can vary greatly, but if you have an automatic transmission, there's a good chance you may hear a whining, humming or even a slight buzzing sound [source: Lee Myles Transmissions and Auto Care].
With manual transmissions, the sounds will usually come across as a bit more abrupt and mechanical sounding. If you shift gears and hear a clunking sound, then you definitely need to have it checked out by a professional [source: AAMCO]. But a clunking sound from underneath your vehicle may not always point to a transmission problem. Your constant velocity joints (CV joints), or even your differential may be the culprit [source: AAMCO].
The sounds you hear may happen from time to time at first, but if you neglect the noises, they'll occur more frequently as time goes on.
3: Grinding or Shaking
Depending on whether you have a manual or automatic transmission, your car may respond differently when your transmission isn't working correctly. As noted in a previous section, with a manual transmission, a common sign of trouble is a grinding sound or feeling when you shift into a new gear. If you fully engage the clutch, shift and then hear a grinding sound, you may have a worn clutch or you may just need to have it adjusted [source: AAMCO]. Or perhaps one or more of your transmission's gear synchronizers, or synchros, is worn out or damaged. Grinding gears can be caused by a number of different factors.
For automatic transmissions problems, you'll most likely feel the car shimmy into each gear rather than the typical almost unnoticeable shifts, or the transmission will make a jarring transition into the next gear. Both are signs that your transmission needs attention. If you notice anything other than a smooth transition between gears, then you might need to have your automatic transmission looked at for adjustments or repair.
But feeling transmission problems aren't the only way to use your senses.There are also sounds you should be listening for as well.
4: Check Engine Light
The check engine light can be a great early indicator that something is starting to go wrong with your transmission. The check engine light can come on for any number of reasons not related to your transmission as well, but don't overlook this clear warning sign.
In newer cars there are sensors throughout the engine that pick up irregularities in the engine and notify the computer that there's something wrong in a particular area. In the case of transmissions, these sensors can pick up vibrations and early problems that you may not even be able to feel or see. If you want to know if your check engine light is telling you about a transmission problem, you can purchase a diagnostic scan tool that you plug into your car underneath the driver's side of the instrument panel. The scan tool will display a code that corresponds to the area of the vehicle causing the fault. If the code tells you there's a transmission problem, well, that's a good time to see your mechanic.
But even if your check engine light isn't on, you can still be on the lookout for transmission problems.
5: Leaking Fluid
Leaking transmission fluid is probably one of the easiest ways to identify that your transmission needs attention. Automatic transmission fluid is vital to your car's shifting capabilities, so a little fluid on your driveway can quickly turn into a major problem. Automatic transmission fluid is bright red, clear and a little sweet-smelling when everything's working correctly [source: AAMCO]. When you check your automatic transmission fluid, make sure it's not a dark color and that it doesn't have a burnt smell. If it is, you'll need to take it to a mechanic and have it replaced. Unlike your car's motor oil, the transmission doesn't really consume or burn up any fluid during use, so if you notice you're running low on fluid, then it's definitely leaking out somewhere.
If you have a manual transmission, checking the fluid levels may not be as easy as simply lifting the hood and reading a dipstick. Manual transmission fluid has to be checked right at the transmission case -- usually through the fill plug. Again, if you suspect your transmission is losing fluid, have a mechanic locate the leak and have it fixed.
If your fluid level is good, there's another easy way to know if there's something wrong with the transmission:
6: Dragging Clutch
Here's another transmission trouble sign that haunts manual transmission vehicle owners: the dreaded dragging clutch. A dragging clutch is one that fails to disengage the clutch disk from the flywheel when the driver pushes in the clutch pedal.
When the driver attempts to shift gears, he or she can't because the still-engaged clutch is still spinning along with the engine. The driver is abruptly made aware of this by the grinding noise that then ensues with each attempt to shift.
Fortunately, the most common cause for this problem is not that severe or costly to fix -- at least not compared to some other transmission issues. More often than not, the problem is too much slack in the clutch pedal. With too much free play, the cable or linkage between the pedal and the clutch disk doesn't have enough leverage to disengage the clutch disk from the flywheel (or pressure plate).
Some transmission trouble signs are plainly visible even to the lay person -- if that person knows what to look for.
7: Gears Slipping
In a normally functioning transmission, the car stays in the gear you designate, or that the computer designates for a given RPM range, until you or the computer initiate a gear shift.
But on a transmission in which the gears slip, the car can spontaneously pop out of the gear it's in while driving and (in a manual) force the stick back into neutral [source: Procarcare.com].
This is unnerving at best and potentially dangerous at worst: when you mash the gas pedal to avoid an out-of-control vehicle, the last thing you want is a transmission that doesn't get power to the wheels. No need to scratch your head over whether this is trouble or not: if it happens, you know it's time to have your transmission examined.
8: Transmission Noisy in Neutral
It seems intuitive that if you hear weird noises when the car should be shifting, that the transmission is acting up. But would you suspect it if things were going "bump" in neutral? Yes, it could be the transmission.
Such sounds could have a simple and inexpensive solution -- as with many of the problems on our list, adding or replacing the transmission fluid sometimes does the trick. Bear in mind that as is the case with engine oil, different vehicles do best with the specific formulation called for in the owner's manual.
Alternatively, lots of noises from the transmission while it's in neutral could signal something more serious, like mechanical wear that will need the replacement of parts. In this case, common culprits are a worn reverse idler gear or worn bearings, possibly coupled with worn gear teeth [source: Procarcare.com].
Losing control while driving is never a fun experience. Find out on the next page how a bum transmission could have a car "slipping" toward disaster if not repaired in time.
9: Burning Smell
If you get a whiff of burning transmission fluid, be advised it is definitely not the sweet smell of success. That's because it may indicate your transmission is overheating. Transmission fluid not only keeps the transmission's many moving parts properly lubricated, but it prevents the unit from burning itself up, by providing much-needed cooling.
In some vehicles, the transmission even has its own mini-radiator (an oil cooler) that circulates fluid to transport heat away from the transmission unit itself.
Common causes include low or inadequate transmission fluid, which can in turn indicate a leak or dirty fluid that needs changing.
If you thought your transmission was safe from wear at least while it was in neutral, the truth might surprise you.
10: Refuses to Go Into Gear
Believe it or not, there are still quite a few people out there who practice the fading art of shifting manually, with a foot pedal and a "stick" gearshift, and who do so willingly.
Despite their somewhat simpler operation, manual transmissions nonetheless have their share of things that can go wrong. One potential problem is that the transmission refuses to budge when you depress the clutch pedal and attempt to move the stick shifter.
It may happen when trying to get into first gear from a stop, or at any point up and down the assorted gears. Common causes include low transmission fluid, wrong viscosity (thickness) of fluid, or required adjusting of the shift cables or clutch linkage.
The nose knows when it comes to things being not quite right with your vehicle.
Understanding Automatic Transmission Modes
Conventionally, in order to select the transmission operating mode, the driver moves a selection lever located either on the steering column or on the floor (as with a manual on the floor, except that most automatic selectors on the floor don't move in the same type of pattern as a manual lever; most automatic levers only move vertically). In order to select modes, or to manually select specific gear ratios, the driver must push a button in (called the shift lock button) or pull the handle (only on column mounted shifters) out. Some vehicles position selector buttons for each mode on the cockpit instead, freeing up space on the central console. Vehicles conforming to US Government standards must have the modes ordered P-R-N-D-L (left to right, top to bottom, or clockwise). Prior to this, quadrant-selected automatic transmissions often used a P-N-D-L-R layout, or similar. Such a pattern led to a number of deaths and injuries owing to driver error causing unintentional gear selection, as well as the danger of having a selector (when worn) jump into Reverse from Low gear during engine braking maneuvers.
Automatic transmissions have various modes depending on the model and make of the transmission. Some of the common modes include
Park (P)
This selection mechanically locks the output shaft of transmission, restricting the vehicle from moving in any direction. A parking pawl prevents the transmission from rotating, and therefore the vehicle from moving, although the vehicle's non-driven roadwheels may still rotate freely. For this reason, it is recommended to use the hand brake (or parking brake) because this actually locks (in most cases) the rear wheels and prevents them from moving. This also increases the life of the transmission and the park pin mechanism, because parking on an incline with the transmission in park without the parking brake engaged will cause undue stress on the parking pin. An efficiently adjusted hand brake should also prevent the car from moving if a worn selector accidentally drops into reverse gear during early morning fast-idle engine warm-ups[citation needed]. It should be noted that locking the transmission output shaft does not positively lock the driving wheels. If one driving wheel slips while the transmission is in park, the other will roll freely as the slipping wheel rotates in the opposite direction. Only a (properly adjusted) parking brake can be relied upon to positively lock both of the parking-braked wheels. (This is not the case with certain 1950's Chrysler products that carried their parking brake on the transmission tailshaft, a defect compounded by the provision of a bumper jack). It is typical of front-wheel-drive vehicles for the parking brake to be on the rear (non-driving) wheels, so use of both the parking brake and the transmission park lock provides the greatest security against unintended movement on slopes.
A car should be allowed to come to a complete stop before setting the transmission into park to prevent damage. Usually, Park (P) is one of only two selections in which the car's engine can be started, the other being Neutral (N). In many modern cars and trucks, the driver must have the foot brake applied before the transmission can be taken out of park. The Park position is omitted on buses/coaches with automatic transmission (on which a parking pawl is not practical), which must be placed in neutral with the parking brakes set. Advice is given in some owner's manuals (example: 1997 Oldsmobile Cutlass Supreme owner's manual) that if the vehicle is parked on a steep slope using the park lock only, it may not be possible to release the park lock (move the selector lever out of "P"). Another vehicle may be required to push the stuck vehicle uphill slightly to remove the loading on the park lock pawl.
Most automobiles require P or N to be set on the selector lever before the internal combustion engine can be started. This is typically achieved via a normally open inhibitor switch, which is wired in series with the starter motor engagement circuit, and is only closed when P or N is selected, thus completing the circuit (when the key is turned to the start position)
Reverse (R)
This engages reverse gear within the transmission, giving the ability for the vehicle to drive backwards. In order for the driver to select reverse in modern transmissions, they must come to a complete stop, push the shift lock button in (or pull the shift lever forward in the case of a column shifter) and select reverse. Not coming to a complete stop can cause severe damage to the transmission[citation needed]. Many modern automatic transmissions have a safety mechanism in place, which does to some extent prevent (but does not completely avoid) inadvertently putting the car in reverse when the vehicle is moving forwards. This mechanism usually consists of a solenoid-controlled physical barrier on either side of the Reverse position, which is electronically engaged by a switch on the brake pedal. Therefore, the brake pedal needs to be depressed in order to allow the selection of reverse. Some electronic transmissions prevent or delay engagement of reverse gear altogether while the car is moving.
Some shifters with a shift button allow the driver to freely move the shifter from R to N or D, or simply moving the shifter to N or D without actually depressing the button. However, the driver cannot put back the shifter to R without depressing the shift button to prevent accidental shifting, especially at high speeds, which could damage the transmission.
Neutral/No gear (N)
This disengages all gear trains within the transmission, effectively disconnecting the transmission from the driven roadwheels, so the vehicle is able to move freely under its own weight and gain momentum without the motive force from the engine (engine braking). This is the only other selection in which the vehicle's engine can be started.
Drive (D)
This position allows the transmission to engage the full range of available forward gear trains, and therefore allows the vehicle to move forward and accelerate through its range of gears. The number of gear ratios a transmission has depends on the model, but they initially ranged from three (predominant before the 1990s), to four and five speeds (losing popularity to six-speed autos, though still favored by Chrysler and Honda/Acura)[citation needed]. Six-speed automatic transmissions are probably the most common offering in cars from 2010 in cars like Toyota Camry V6 models, the newer GM cars and trucks, Ford Falcon BF 2005-2007 and Falcon FG 2008 - current in Australia with 6 speed ZF, and most newer model Ford/Lincoln/Mercury vehicles). However, seven-speed autos are becoming available in some cars (found in Mercedes 7G gearbox, Infiniti), as are eight-speed autos in models from 2006 introduced by Aisin Seiki Co. in Lexus, ZF and Hyundai Motor Company.
Overdrive (D, OD, or a boxed [D])
This mode is used in some transmissions to allow early computer-controlled transmissions to engage the automatic overdrive. In these transmissions, Drive (D) locks the automatic overdrive off, but is identical otherwise. OD (Overdrive) in these cars is engaged under steady speeds or low acceleration at approximately 35–45 mph (56–72 km/h). Under hard acceleration or below 35–45 mph (56–72 km/h), the transmission will automatically downshift. Vehicles with this option should be driven in this mode unless circumstances require a lower gear.
Third (3)
This mode limits the transmission to the first three gear ratios, or sometimes locks the transmission in third gear. This can be used to climb or going down hill. Some vehicles will automatically shift up out of third gear in this mode if a certain RPM range is reached in order to prevent engine damage. This gear is also recommended while towing a caravan.
Second (2 or S)
This mode limits the transmission to the first two gear ratios, or locks the transmission in second gear on Ford, Kia, and Honda models. This can be used to drive in adverse conditions such as snow and ice, as well as climbing or going down hills in the winter time. It is usually recommended to use second gear for starting on snow and ice, and use of this position enables this with an automatic transmission. Some vehicles will automatically shift up out of second gear in this mode if a certain RPM range is reached in order to prevent engine damage.
Although traditionally considered second gear, there are other names used. Chrysler models with a three-speed automatic since the late 1980s have called this gear 3 while using the traditional names for Drive and Low. Oldsmobile has called second gear as the 'Super' range - which was first used on their 4-speed Hydramatic transmissions although the use of the term continued until the early 1980s when GM's Turbo Hydramatic automatic transmissions were standardized by all of their divisions years after the 4-speed Hydramatic was discontinued.
First (1 or L [Low])
This mode locks the transmission in first gear only. In older vehicles, it will not change to any other gear range. Some vehicles will automatically shift up out of first gear in this mode if a certain RPM range is reached in order to prevent engine damage. This, like second, can be used during the winter season, for towing, or for downhill driving to increase the engine braking effect.
As well as the above modes there are also other modes, dependent on the manufacturer and model. Some examples include:
D5
In Hondas and Acuras equipped with five-speed automatic transmissions, this mode is used commonly for highway use (as stated in the manual), and uses all five forward gears.
D4
This mode is also found in Honda and Acura four or five-speed automatics, and only uses the first four gear ratios. According to the manual, it is used for stop-and-go traffic, such as city driving.
D3 or 3
This mode is found in Honda, Acura, Volkswagen and Pontiac four-speed automatics and only uses the first three gear ratios. According to the manual, it is used for stop-and-go traffic, such as city driving.
D2 and D1
These modes are found on older Ford transmissions (C6, etc.). In D1, all three gears are used, whereas in D2 the car starts in second gear and upshifts to third.
S or Sport
This is commonly described as Sport mode. It operates in an identical manner as "D" mode, except that the upshifts change much higher up the engine's rev range. This has the effect on maximising all the available engine output, and therefore enhances the performance of the vehicle, particularly during acceleration. This mode will also downchange much higher up the rev range compared to "D" mode, maximising the effects of engine braking. This mode will have a detrimental effect on fuel economy. Hyundai has a Norm/Power switch next to the gearshift for this purpose on the Tiburon.
Some early GMs equipped with HYDRA-MATIC transmissions used (S) to indicate Second gear, being the same as the 2 position on a Chrysler, shifting between only first and second gears. This would have been recommended for use on steep grades, or slippery roads like dirt, or ice, and limited to speeds under 40 mph. (L) was used in some early GMs to indicate (L)ow gear, being the same as the 2 position on a Chrysler, locking the transmission into first gear. This would have been recommended for use on steep grades, or slippery roads like dirt, or ice, and limited to speeds under 15 mph.
This would have been recommended for use on steep grades, or slippery roads like dirt, or ice, and limited to speeds under 40 mph.
(L) was used in some early GMs to indicate (L)ow gear, being the same as the 2 position on a Chrysler, locking the transmission into first gear. This would have been recommended for use on steep grades, or slippery roads like dirt, or ice, and limited to speeds under 15 mph.
+ −, and M
This is for the Manual mode selection of gears in certain automatics, such as Porsche's Tiptronic. The M feature can also be found in Chrysler and General Motors products such as the Dodge Magnum, Journey, and Pontiac G6, as well as Toyota's Camry, Corolla, Fortuner, Previa and Innova. Mitsubishi and some Audi models (Audi TT), meanwhile do not have the M, and instead have the + and -, which is separated from the rest of the shift modes; the same is true for some Peugeot products like Peugeot 206. Meanwhile, the driver can shift up and down at will by toggling the (console mounted) shift lever like a semi-automatic transmission. This mode may be engaged either through a selector/position or by actually changing the gears (e.g., tipping the gear-down paddles mounted near the driver's fingers on the steering wheel).
Winter (W)
In some Volvo, Mercedes-Benz, BMW and General Motors Europe models, a winter mode can be engaged so that second gear is selected instead of first when pulling away from stationary, to reduce the likelihood of loss of traction due to wheelspin on snow or ice. On GM cars, this was D2 in the 1950s, and is Second Gear Start after 1990. On Ford, Kia, and Honda automatics, this feature can be accessed by moving the gear selector to 2 to start, then taking your foot off the accelerator while selecting D once the car is moving.
Brake (B)
A mode selectable on some Toyota models. In non-hybrid cars, this mode lets the engine do compression braking, also known as engine braking, typically when encountering a steep downhill. Instead of engaging the brakes, the engine in a non-hybrid car switches to a lower gear and slows down the spinning tires. The engine holds the car back, instead of the brakes slowing it down. GM called this "HR" ("hill retarder") and "GR" ("grade retarder") in the 1950s. For hybrid cars, this mode converts the electric motor into a generator for the battery (Regenerative Braking). It is not the same as downshifting in a non-hybrid car, but it has the same effect in slowing the car without using the brakes.
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Sources
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