Category Archives: Transmission

6 Signs That Your Car Needs Transmission Repairs

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6 Signs That Your Car Needs Transmission Repairs

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.

Hesitation

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

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.

Mechanical Noises

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.

Vehicle Surges

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.

When to Change Your Car’s Transmission Fluid?

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When to Change Your Car’s Transmission Fluid?

You may have heard or read somewhere that you only need to replace your transmission fluid every 100 000 miles or so, but the fact is that by doing so, you could damage your transmission simply because you do not remove contaminants regularly enough. Your transmission depends on clean, filtered, and uncontaminated fluid to work properly. Something else you may not know is that most automatic transmission failures occur because dirty, degraded, and contaminated transmission fluid prevents the smooth operation of a myriad small, but critically important moving parts.

Automatic transmissions briefly explained

Without getting too technical, it is fair to say that instead of using a lot of different gears that need to be locked together on a manual transmission to achieve a power output, an automatic transmission only uses a few gears that can be locked together in different ways to achieve a similar power output.

Nonetheless, the way in which an automatic transmission uses the same gears to arrive at different speeds is controlled by a hugely complicated hydraulic system that is in turn controlled by a complicated electronic control module. The whole system is supplied with pressurized fluid by a powerful pump that also serves to circulate the fluid around the transmission for lubrication purposes, and this is where the quality, as opposed to the quantity, of the fluid in the transmission plays a critical role to prevent problems with harsh or erratic shifting.

While it is true that the actual gear set can function with relatively dirty fluid, the same cannot be said for the hydraulic control system. This system is mostly located in a part of the transmission called the “valve body”, and it consists of an intricate system of small-diameter valves, check valves, and pressure regulators that are all interconnected via small-diameter passages that supply each part with pressurised fluid.
One more critical component of an automatic transmission to consider is the set of clutches that locks different parts of the gear set together in different ways to achieve gear ratios. In most transmissions, the clutches are controlled by hydraulic actuators that are in turn controlled by an electronic control module, and the quality of the transmission fluid plays a crucial role in how well, or reliably these clutches perform to prevent slipping, or hesitation when taking off.

How does it all work?

In full automatic mode, a transmission will not shift up or down unless at least half a dozen sensors and control circuits agree that a shift is required, which is when a signal, or impulse is generated by the transmission/engine management system(s) that tells the transmission what to do.

When the transmission receives the impulse, one or more valves in the valve body is instructed to divert pressure to a different part of the assembly. This causes the clutches to re-arrange the way the gear set is interlocked, and the transmission is said to have executed a gear shift. In this manner, the transmission will shift gears in accordance with instructions generated by the control system(s) without any input required by the driver.

However, when one or more valve shuttles sticks in position because of the presence of contaminants in the fluid the transmission cannot execute the shift, but if it does manage to shift, the operation may cause harsh, or jerky shifts- or it may “miss” a shift, and shift to the next higher or lower gear.

Similarly, if the transmission selector is moved from “P” or “N”, the valve body may not be able to divert pressure from the by-pass circuit to an active circuit, which means that the transmission is unable to engage the desired gear because the affected valve shuttle(s) cannot move due to the presence of dirt, or other contaminants in the fluid.

So what is automatic transmission fluid?  

Apart from its excellent flow properties, transmission fluid is similar to other lubricating oils in the sense that it also contains additives that clean, lubricate, and prevent the formation of corrosion inside the transmission.

However, transmission fluids are not created equal, and some formulations work better in specific applications, which is why it is critically important never to use a generic formulation. Moreover, some transmissions, such as those on pick-up trucks require a specific formulation because it may run at higher temperatures than say, a transmission in a normal family sedan, which is why you should only ever use the formulation recommended, or specified by your manufacturer.

Moreover, the ability of a specific formulation to withstand the effects of heat is just as important as that formulation’s ability to resist oxidation, which is aggravated by higher than normal operating temperatures. Oxidation is the single biggest factor in the degradation of automatic transmission fluid, and when that is coupled to the effect of heat, some of the additives start to form various gums, varnishes, and sludge that can literally “weld” moving parts together. Once this has happened, the transmission must be replaced since there is no known way to free the seized parts without ruining the transmission.

Below is a table that illustrates the life expectancy of transmission when the fluid exceeds acceptable operating temperatures. Note how small differences in temperature bring about a drastic reduction in the life expectancy of a transmission.

Transmission Fluid Temperature Chart

From the above it will be seen that overheating of the fluid must be avoided at all costs, and since most cars use the same radiator to cool the transmission fluid that cools the engine, any engine overheating will affect the life expectancy of the transmission as well, which is why the transmission fluid MUST be replaced if the engine has overheated.

One more thing to remember is that transmission fluid is translucent and bright red in color when it is fresh.  Fluid that is not translucent, dark in color, or has a “burnt” smell, is degraded to the point where it could start to affect the performance of the transmission, and it must be replaced, regardless of the distance traveled.

Many car manufacturers recommend fluid replacement at 30 000 miles or so, but factors such as towing, carrying heavy loads, or engine overheating can dramatically reduce this mileage, so whenever this has occurred, have the fluid checked and replaced if necessary.

Some symptoms of degraded transmission fluid

It is not always easy to diagnose automatic transmission problems because many electronic issues could mimic the symptoms of dirty or degraded fluid. However, whenever your car develops transmission related problems, always check the fluid level and condition first, since in some cases, the problem can be resolved merely by replacing the fluid.

Bear in mind though that a fluid replacement may be too little too late in many cases, especially where the transmission has become noisy at any speed, or in any gear. Nevertheless, below are listed some of the most common issues that could be directly related to dirty, contaminated, or degraded transmission fluid.

Noisy transmission:

Dirty fluid can mimic the symptoms of low fluid levels that can cause some transmissions to be noisy.  So whenever your transmission becomes noisy in any way, first check the fluid level to confirm that the transmission is not running dry. If the fluid is at the correct level, but appears dark, “tarry”, or has a “burnt” smell, the cause of the noise is likely to be related to an inadequate flow rate. If however, the fluid is at the correct level and appears clean, fresh, and translucent, the cause is more likely to be a purely mechanical malfunction.

Harsh, or erratic shifting:

In almost all cases, this is caused either by a low fluid level, or dirty/contaminated fluid. In some cases, the issue can be resolved by replacing the fluid, but do not bank on this- in some cases, the harsh or erratic shifting may damage internal parts that can only be repaired or resolved by professional servicing and repairs.

Slipping in gear, or hesitation on take-off:

This is almost always caused by insufficient fluid pressure, which in turn, can have many possible causes. However, if the fluid appears dark, “tarry”, or has a “burnt” smell but is at the correct level, it would be safe to assume that one or more internal fluid passages is partially, or even completely blocked by dirt, varnish, or sludge. In these cases, a fluid replacement is seldom the answer, and the issue must be seen to by professional personnel.

Unexplained surging:

In transmissions that have not had their fluid replaced at recommended intervals, it is possible for dirt and sludge to cause intermittent blockages. However, a simple fluid replacement may, or may not resolve the issue, and in these cases, it is recommended that the transmission be flushed by suitable equipment, and by personnel that are trained to operate such equipment.
Incorrect flushing procedures can cause permanent blockages that cannot be cleared by any means, but it is also important to remember that some manufacturers, and Honda in particular, strongly advise against any form of flushing on their transmissions, so before you decide to have your transmission flushed, contact the manufacturer or dealer for information.

There are off course other causes of transmission problems that have nothing whatever to do with the condition of the fluid. Defective, or flat batteries, malfunctioning electronics, or extreme temperatures can cause most, if not all of the problems associated with degraded transmission fluid, so before you replace the transmission just because a mechanic says you must, have the electrical system of your car checked out with suitable diagnostic equipment.

It could save you a ton of money!