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
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In most post -1990 vehicles with automatic transmissions, the vacuum modulator has been replaced by an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
The engine speeds up when you step on the accelerator but your vehicle does n’t, or hesitates
before responding when you shift gears (or does n’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.