#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.
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 0r 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.
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 . 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.
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 Shacking
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. 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.
#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.
#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. 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.
#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).
#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.
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.
#9 Burning Smell
Ahhh…. The sweet smell of success! Unless that smell is coming from your car. If your transmission is overheating, the first sign is usually transmission fluid burning. The fluid not only helps lubricate all the moving parts inside your transmission but also helps dissipate and radiate heat. If your transmission fluid is burning, you could have a leak, your fluid levels could be low or your fluid may be dirty and require cleaning.
#10 Refuses to go into gear
While manual transmissions are becoming less common, many people still drive them and some even prefer it. When shifting into first from a stop, or anywhere else along the shifting column, if it doesn’t want to go into gear, that’s a sign your having problems. Some symptoms are low fluid, or even the wrong viscosity of fluid (wrong thickness). It could also be a readjustment of your shift cable or clutch linkage.