Troubleshooting Your Vehicle's Drive Train - dummies

Troubleshooting Your Vehicle’s Drive Train

By Deanna Sclar

If weird things start happening on the road, how can you tell whether your vehicle’s transmission or one of the other parts of the drive train is in trouble? If this is the case, continuing to drive may make the situation worse.

However, a low transmission fluid level or a malfunctioning, inexpensive engine part may cause the same symptoms as a faulty transmission. Who knows how many unsuspecting customers have paid big bucks to rebuild or replace transmissions when they could have corrected the problems themselves with very little money or effort! Here are ways your vehicle tries to tip you off:

  • Light grey smoke is coming out of the tailpipe: This can mean you’re low on transmission fluid and the engine could be burning.

    In some pre-1990 vehicles, the smoke may also be due to a faulty vacuum modulator that’s siphoning the fluid out of the transmission and into cylinders of the hot engine. Consult a service manual for your make, model, and year to see if Old Faithful has a vacuum modulator; if it’s easy to reach, try unscrewing it and replacing it before you consider more costly remedies.

    In most post-1990 vehicles with automatic transmissions, the vacuum modulator has been replaced by an electronic solenoid. It does the same job but is controlled by the electronic control unit (ECU) rather than engine vacuum, so there’s no siphoning problem.

  • Thick, black or tan, oily liquid is coming from under the vehicle: Gear oil may be leaking from a manual transmission, the differential, an axle, or the steering gears. Any of these leaks needs immediate attention.

  • The engine speeds up when you step on the accelerator but your vehicle doesn’t, or hesitates before responding when you shift gears (or doesn’t respond at all), or shifting becomes awkward or noisy: The cause depends on whether you have an automatic or manual transmission. If you have an automatic transmission, you may just be low on transmission fluid, have a disconnected hose or plugged filter, or your transmission controller may be out of whack. If you have a manual transmission, the trouble could be in the clutch or another component. In any case, it’s a job for the car doctor.

  • You hear a clunking sound: This can mean transmission trouble or just a low fluid level. If a loud clunking suddenly comes from under the hood, it could be just a broken accessory belt. In either case, pull to the side of the road and call for a tow.