No matter how well you look after your car in terms of regular maintenance and servicing, it is almost certain that you will encounter transmission related problems during the life of your car. Modern transmissions are extremely complex, and there are many things that can go wrong, but how do you know when it the problem is serious enough to warrant immediate attention?
The short answer is that any transmission problem is potentially serious (and expensive to repair), so if you recognise any of the symptoms below, have the issue investigated immediately to avoid adding to the repair bill.
There should be no hesitation at all when you try to move off from a standstill. Hesitation can be caused by low transmission fluid levels, excessive mechanical wear, and by fluid that is dirty, contaminated, or degraded as the result of overheating.
Hesitation is also dangerous from a safety perspective, since you could be hit by other cars from behind when they assume you are going to move, or, by drivers that don’t know your car is hesitating, especially when you plan to turn into, or across oncoming traffic from a side road.
Check Engine Light
On some cars the engine is controlled by the transmission, in the sense that the engine will not accelerate or respond to throttle inputs if there is something wrong with the transmission. In these cases, the CHECK ENGINE LIGHT will illuminate, even if the driver is not yet aware that a problem is developing.
CHECK ENGINE warning lights should never be ignored, and especially if the transmission is fitted with several “modes” of operation. The only reliable way to determine whether the engine or transmission is at fault is to have a comprehensive diagnostic check performed by qualified and certified technicians. If the transmission or transmission control module is defective, the transmission can fail completely and unexpectedly- even if the driver does not yet realize that there is an incipient problem present.
All transmissions, regardless of whether they are manual or automatic, should operate without noises of any kind. Any clunking, grinding, whining, knocking, or thudding sounds are abnormal, and a sure sign that there is something seriously wrong with a transmission.
The most common cause of noisy transmissions is lack of lubrication, or the use of unsuitable lubricants and fluids, which from the perspective of a transmission, amounts to the same thing. Therefore it is vitally important to maintain the correct levels of only the lubricants that are specified for your vehicle.
Transmission Noise in Neutral
Transmissions may be noisy in neutral, but silent when gears are selected, which is a sure sign of worn parts, or fluid issues. In manual transmissions, this problem is almost always related to the condition of input shaft bearings, but in automatics, the problem could be any one, or all of a great many causes, such as worn or damaged clutch packs and planetary gears, among others.
However, resist the temptation to have the transmission flushed, even if a mechanic recommends it, on the grounds that the fluid might be dirty or degraded. Many, if not most mechanics cannot diagnose the cause(s) of noise(s) in automatic transmissions just by listening it, which is why you should only consult knowledgeable technicians on this particular issue.
Some transmissions are known to develop secondary problems after a flushing procedure, which why some manufacturers, such as Honda, prohibit the flushing of their transmissions. Other manufacturers might not ban the practice outright, but very few approve of the practice, so talk to your dealer before you flush your transmission.
Difficult, Harsh, or Erratic Shifting
There are dozens of possible causes for all, or any of these problems. Moreover, some symptoms can be the result of one or more problems, which is why it is very important to have any of these problems investigated and resolved as soon as they appear, because continued use of the transmission can lead to total failure.
Some of the more notable problems include the following:
- Refusal to engage any gear.
- Gear shifts are accompanied by mechanical noises, or harshness.
- Vehicle does not accelerate as before.
- Shifts happen unpredictably, or in some cases, erratically.
- Hesitation in moving off from a standstill.
- Vehicle has to be held stationary with the brakes while in “P”
- Transmission “misses” some gears, for instance; it might shift into 3rd straight from 1st, or it might downshift from 4th gear into 1st, without going through the range as it should.
While there are many possible causes of surging, one possible cause is occasional, or intermittent blockages of some fluid passages in the valve body of the transmission. The controlling mechanism of the transmission depends on sustained fluid pressure at different points at different times, which means that if a fluid passage is blocked intermittently, the clutch packs that transmit power in the transmission could slip, and engage on an intermittent basis.
Again, resist the temptation to have the transmission flushed, because the object that causes the intermittent blockage could become permanently lodged in a position where it could conceivably plug, and thus disable pressure circuits in the transmission.
When it comes to transmission problems, it is sometimes more cost effective to replace a transmission, as opposed to attempting repairs. Some failures and defects cannot be repaired economically, especially if the fluid had overheated.
Overheated transmission fluid forms several kinds of waxes and varnishes that can “weld” small parts together permanently, so when this happens to you, you might be better served by simply replacing the transmission, but be sure to have the cause of the overheating resolved as well to prevent a recurrence of the problem.