Transmission (Gearbox)

What is a Gearbox, how to maintain and known problems

It is advisable to read this article in conjunction with the article written about the clutch system.

In this article, we will continue to acquaint our readers with vehicle component knowledge. You will learn more about the transmission (gearbox), how to look after it and any known problems that a transmission (gearbox) may present you with.

A clarification of the differences in understanding between the term transmission and gearbox will suffice before we continue. What YOU may understand under the term “transmission” may not be what someone else understands. In British English, the term “transmission” refers to the entire drivetrain (clutch, gearbox, prop shaft, differential, and drive shafts) but in American English, the term “transmission” refers simply to the gearbox alone. I am willing to make a tiny wager that not many of you knew this little fact. During the course of this article, I will stick to the term transmission, but with the American English understanding of “gearbox” in mind.

What is the basic function of the transmission then?

The transmission usually consist of a cast iron or aluminium case that house multiple gears with the ability to switch between these gears. Most commonly, the transmission connects to the crankshaft of the engine via a flywheel or clutch or fluid coupling. The output of the transmission takes place via the driveshaft to one or more differentials, which drives the wheels. Switching between gears can be done manually or automatically (or both) in order to bring about forward and reverse (or even sideways) control. The transmission therefore makes use of gears and gear trains in order to provide speed and torque conversions from a rotating power source to another device. Simply put, the job of a vehicle’s transmission is to make sure that the right amount of power goes to your wheels to enable you to drive at a given speed.

Transmission types falls into four categories: Manual, Automatic, Semi-Automatic and Continuously Variable. A quick overview of each follows for the sake of a better understanding.

Manual Transmission

Two types of the Manual transmissions exist:
• A simple yet rugged sliding-mesh system, where straight-cut spur gear sets spin freely and must be synchronized by the operator matching engine revs to road speed in order to avoid noisy and damaging clashing of the gears. This type was standard in many vintage cars.
• The universal constant-mesh gearboxes are now the modern standard for on- and off-road, manual and semi-automatic transmissions. In these, typically diagonal cut helical (or sometimes straight-cut or double-helical) gear sets are constantly “meshed” together. The changing of gears happens by way of a dog clutch (two rotating components that couples by interference and not by friction).

Manual Transmission

Automatic Transmission

An automatic transmission primarily uses hydraulics to select gears, depending on the pressure exerted by a fluid within the transmission assembly. Rather than using a clutch to engage the transmission, a torque converter or fluid flywheel, placed in-between the engine and the transmission, makes it possible for the driver to control the number of gears in use or select reverse, though precise control of which gear is in use, may or may not be possible.

Automatic Transmission

Semi-Automatic Transmission

Who says you cannot have your bread buttered on both sides? Not solely into manual? Not solely into automatic? The semi-automatic may then be more to your liking. This is a hybrid form of transmission where an integrated control system handles the manipulation of the clutch automatically but the driver can still take manual control of gear selection.

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Semi-Automatic Transmission

Continuously Variable Transmission (CVT)

This type of transmission offers a similar driving experience to an automatic, but operates using a completely different mechanism. It does not have gears; it uses a system of belts and pulleys to produce an infinite range of ratios. Your vehicle’s computer controls the adjustment of the pulleys to create the optimal ratio for the particular driving situation. This makes the CVT exceptionally fuel-efficient.

This, in short, explains the differences in transmission types.

CVT Transmission

How should I look after my transmission?

Your vehicle’s transmission contributes 50% to your vehicle’s ability to move, the other 50% being the engine. If either of these malfunction, then you will have no movement. Okay, let us not get technical. If someone or something pushes the vehicle, there will surely be movement, and when the wheels fall off, there will surely be no movement. This is not what I refer to when I say that movement or the lack thereof relies 50-50 on the transmission and the engine. What I refer to here is what I said in the beginning: the job of a vehicle’s transmission is to make sure that the right amount of power goes to your wheels to enable you to drive at a given speed. No transmission, no engine torque directed to the wheels, no driving ability.

To ensure that your vehicle’s transmission is always in a good working condition, you have to practice proper maintenance procedures on that transmission. Proper maintenance procedures will significantly reduce the risk of costly servicing and component replacements. An ill-kept transmission may also contribute to a loss in fuel economy, but more so, to a loss in functionality, and that will leave you stranded and hurt your pocket dearly. Preventative maintenance on you vehicle’s transmission will not take you as long as reading Moby Dick or The Iliad. Such maintenance starts at checking the lifeblood of your transmission, namely the transmission fluid.

Transmission fluid has different purposes when it comes to manual and automatic transmissions. In the former, the transmission fluid keeps the gears lubricated (prevent grinding) and in the latter, it creates hydraulic pressure that powers movement within the transmission. Transmission fluid does not last forever, and from the above it should be clear to understand why checking the transmission fluid is so important.

Before you check the fluid, make sure whether your vehicle should be running while performing this task, or not (this may usually be found inside your vehicle’s manual). There is a reason why this should or should not be the case, so stick to it. Locate the vehicle’s transmission fluid dipstick (not the one for the oil) and pull it out. It should be covered with fluid and the fluid should be at the required indicator on the dipstick. Wipe the dipstick clean with a decently clean rag and repeat the process. If the fluid is below the required indicator, then fill it up slowly. If you add too much transmission fluid, it can be as bad for your transmission as when you have too little in the transmission.

When you inspect the level of fluid, also check the condition of the fluid. Transmission fluid is supposed to be pink or red; the reason for this is mainly to enable easy visibility. Ensure that your transmission fluid is clean enough to see through (it should be translucent). If the fluid is visibly a darker colour, then that may be signs of degraded transmission fluid or transmission problems. Also, take a moment and smell the liquid. If it smells burnt, then that may be grounds for concern. If you feel uncomfortable about the transmission fluid condition, then do consider having a mechanic flush your transmission system and replace all of the fluid instead of just topping it up. Doing this may cost you far less than an entire transmission replacement.

Apart from checking the transmission fluid dipstick, also take some time (if you can) and inspect the vehicle for any transmission fluid leakages. The most common places to inspect are the seals, transmission lines, loose pans or faulty gaskets. If you notice any leaks, have it repaired as soon as possible.

I am not going to give you distance-driven-estimates at which you should check your transmission fluid. If you do a lot of driving that involves a lot of stop-and-go gear changing, then you should consider checking the fluid more frequently than someone who do not drive under these conditions. You will learn in the following section about the problems that faulty and low transmission fluids can bring about, and you will then see why keeping the transmission fluid in check, is so extremely important.

Which known issues may a transmission present?

A defective transmission is a nightmare; not only is it expensive to repair, but such reparation can be a time consuming affair. If you practice preventative maintenance, have some knowledge of common signs of transmission problems, and address them before they become unmanageable, then you might just save yourself from a lot of unnecessary stress.

The following are the most common symptoms that you may encounter from an unwell transmission:

Transmission noisy in neutral

If the transmission, in its neutral position, is a bit noisy and goes “bump”, then it is likely that the transmission fluid is low; you should therefore check the level. Do not convince yourself that it cannot be the fluid because you checked it last week – leakages happens. Check it! If the level is fine then there might be something else wrong, such as worn out bearings, gear teeth or a reverse idler gear, in which case you should have it checked and fixed by a professional.

Transmission slipping or jumping during gear shift.

This symptom is one to that you must not take lightly. What if the transmission slips or jumps out the moment you need to gear down and accelerate in order to prevent a serious incident? You will experience a slipping transmission when the following happens: You are driving in a gear and then it changes to another gear for no apparent reason. Your vehicle may also feel like it is struggling to get along, especially when you step on the gas but find there is no true acceleration and the engine simply pics up revs. If your vehicle’s transmission acts in such a way, the possibility exist that the link holding the gears is worn or broken; it may also be due to a defective solenoid or a burnt clutch disc, more about the solenoids later. You need to get your vehicle to a qualified mechanic immediately due to it being a huge safety risk.

Grinding or shaking gear change.

If your manual transmission makes a grinding noise or feeling when you shift into a gear, then it is highly likely that that gear’s teeth or synchronizer is worn or damaged. Take note that the clutch might also present this symptom. If the grinding occurs after engaging the clutch, then the clutch may need replacement or adjustment. Your vehicle’s automatic transmissions may act otherwise. It will not make the grinding noise but instead you might feel a lack of smooth gear transitions. As the problem worsen, the transitions become jarring, accompanied by shaking. The best thing to do is have it checked and repaired.

A burnt smell.

Any burning smell is a cause for concern. With regard to our discussion of the transmission, our focus of the burning smell will therefore be directed to the transmission. When the transmission fluid overheats, it will cause a burning smell. Generally, transmission fluid has a slightly sweet odour but when you get that burning smell, then it is time to investigate. Why would it overheat? What happens is that the fluid breaks down due to debris and sludge and when this happens, the system runs too hot. Always ensure that the fluid level is to its required mark, and use the correct brand/type of fluid in your vehicle. Dirty fluid will not efficiently keep your transmission parts cooled and lubricated, it will only contribute to more serious component damage.

Fluid leaking from the vehicle

A fluid leak is one of the most common causes of a transmission breakdown. Transmissions are generally sealed units that should never leak fluid, but if you experience a leakage, then it is highly likely that its origin may be found at the torque converter, the transmission pan, the fluid lines, the pan gasket or even at one of the seals. Have them fixed. A leakage reduce transmission fluid, which reduce friction and/or hydraulic pressure, all of which will render your vehicle’s transmission inadequate for its task.

Engine light.

The check engine light on your vehicle’s dashboard is there for a reason; do not ignore it. The sensors present in your vehicle’s transmission can notice the slightest spasms and vibrations that you are not able to see or feel. If the light goes on, do the self-maintenance explained earlier in this article. If the fluid level is fine, the texture is in order and you cannot detected any visible leeks, then there is only one way – to a professional to have it inspected.

Transmission solenoid problems (Automatic transmissions)

An automatic transmission makes use of solenoids for its smooth functioning, such as the transmission shift solenoid, the lock-up solenoid, or transmission control solenoid and even the torque converter clutch solenoid. A solenoid may be the cause of many automatic transmission problems. Electronic malfunctions or inadequate fluid levels can damage the solenoid. Why is this? Because the transmission fluid is directed through the valve body by way of these solenoids. They open and close hydraulic valves in order to regulate the flow. A faulty solenoid may allow too much fluid pressure (you may then experience rough shifting) or too little pressure (in which case the clutch plates can overheat). If there is a delay in shifting, no downshifting or not shifting into the correct gear, then it is likely that a solenoid problem exist. Have it inspected and fixed.

Transmission fluid on dipstick is cloudy, thick or foul smelling.

We touched on this, and the best and only thing to do is to have the transmission fluid system flushed and replaced with new fluid. Do not take a gamble because you will regret it.

Failed needle roller bearings (automatic transmission)

Needle bearings are small, lightweight roller bearings that help prevent gears in the automatic transmission’s torque converter from grinding. If the transmission’s needle bearings become worn or sluggish, you may hear grinding or brushing noises coming from your vehicle while the car is in motion. This sound can mean your transmission gears are moving inefficiently and prematurely worn down. Have it checked and fix the issue.

Your vehicle’s transmission is a complex mechanical system that experience more wear and tear over time than most other parts in your vehicle. Issues are bound to arise if you fail to maintain your vehicle’s transmission; issues will also worsen if a professional does not check symptoms soon after they developed. If you notice something unusual and you are not able to rectify the problem, then you should have your vehicle immediately inspected by a specialist. At Steves Auto Clinic, we have the expertise, the machinery and the friendly service to assist you with any transmission related matter.

As a final thought, before authorizing any transmission repairs, always ask and ensure that the workshop you utilise will use new parts to replace the replacing parts and ask where those new parts will come from. Also, ensure (whenever they rebuild/replace the existing transmission) that there is a warranty in place.