Top 10 Signs of Transmission Trouble

Believe it or not, there are 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. About 3 percent of cars sold in America today have a manual transmission [source: Fleming].

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 you're 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. Keep reading to find out how your olfactory sense factors into transmission diagnosis.

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 also 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.

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 still 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.

Losing control while driving is never a fun experience. Find out next how a bum transmission could have a car "slipping" toward disaster if not repaired in time.

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.

Our next trouble sign might seem like a real "drag" if it happens to your vehicle, but its fix is often not so complicated.

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 you push in the clutch pedal.

When you attempt to shift gears, you can't because the still-engaged clutch is still spinning along with the engine. You'll know right away because of the grinding noise that you'll hear when you try to shift gears.

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. Often, 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 visible even to the lay person — if they know what to look for. We'll talk about that next.

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 must 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. Keep reading to find out how.

Your car's 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 detect 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.

If your check engine light isn't on, you can still be on the lookout for transmission problems.

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 several different factors.

For automatic transmission problems, you'll most likely feel the car shimmy into each gear rather than the typical almost imperceptible 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. You should also be listening to your car, as well.

It's difficult to nail down exactly how your car may sound if there's transmission trouble, but one thing's pretty certain: 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: AutoChimps].

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.

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 that needs attention.

For more information about transmissions and other related topics, follow the links below.

Originally Published: Oct 5, 2009