The transmission, as we all must be aware, is one of the key components of your car. Transmission mounts are responsible for holding this key component in place. This makes the transmission mounts as important as the transmission itself. Therefore, understanding what it does and how it can go wrong is essential for any car user.
The transmission mounts are generally very simple in their construction, but they do an exceedingly important job. Failure of transmission mounts is not very common, but it can happen in your vehicle at some point in its life. In this story, we will see how to prepare for such a situation, if it happens.
It is also important to know what it takes to detect bad transmission mounts. To add to it, we can see how transmission mounts are replaced. You know, for the DIY folks among us.
What Is A Transmission Mount?
In simple words, mounts for your transmission. It does get any simpler than that. The transmission mounts attach the transmission to the vehicle. This helps in integrating the heavy transmission with the weight of the vehicle. This can aid in improving comfort and handling.
Transmission mounts are mainly responsible for two functions. Keeping the transmission in place is the most obvious one. Most vehicles will at least have two transmission mounts to hold the transmission and connect it to the frame of the vehicle.
This firmly fastens the transmission to the frame, ensuring that it does not shift during the drive. This is especially important as the internals of the transmission are closely placed. A wrong misalignment can cause the transmission to shift, and create problems during the drive.
The second function of transmission mounts is to reduce vibrations that seep into the vehicle. Just like the engine mounts that dampen the vibrations from the engine. The transmission mounts are also expected to do the same function, but this time, with the vibrations associated with shifting gears. The transmission mounts utilize rubber bushings, or special fluids to dampen these vibrations.
This function of the transmission mounts is responsible for ironing out a majority of the vibrations seeping into the cabin. Engine mounts do their part in killing off vibrations from the motor as well.
It is also a good thing to know that the construction and basic working of the transmission mounts are exactly the same as that of the engine mounts. Both of them are made with the same materials, same construction, and they are employed to do the same tasks. The only difference between them is the part they help to mount. Engine and transmission, for reference.
Types Of Transmission Mounts
Just like any car part, transmission mounts come in different types. Manufacturers choose different kinds of transmission mounts based on a lot of factors. Before we delve into these, let us see what are the options available in different vehicles
1. Rubber Transmission Mounts
This is the simplest kind of transmission mounts. It is basically a metal container stuffed with a strong rubber material. The metal part of rubber transmission mounts is a strong mount bracket that gives the part strength. This metal structure is strong enough to hold the transmission in place and handle its weight while the vehicle is on the move.
On uneven roads, it is hard for transmission mounts to handle the weight of the transmission. With strong mount brackets, the fasteners can tighten up the grip of the transmission and gel it with the frame of the vehicle.
Inside the metallic mount bracket, rubber transmission mounts use an elastic rubber material to damper vibrations. The moving parts inside the transmission can send vibrations through the mounts to the cabin. If the transmission mounts are not designed to absorb these vibrations, these can seep in through the seats and increase the noise and vibration levels. Comfort reduces when this happens.
As a cost-effective way to stop these vibrations from making their way into the cabin, rubber transmission mounts are used. The elastic rubber material inside the metal bracket holds the connecting arm of the transmission. The arm will not touch any metal part like this, keeping vibrations to a minimum. The rubber part absorbs the vibrations that do not make it to the mount.
This helps dampen these vibrations to a minimum. But just like most cost-effective technologies, rubber transmission mounts have their own drawbacks. Though vibrations are dampened out, some of them do make it to the cabin. For economy vehicles where cost is the primary concern, this is not an issue. But for luxury cars, this is not acceptable. They need better tech to improve the comfort.
2. Fluid Filled Hydraulic Transmission Mounts
To improve on the benefits of the rubber transmission mounts, some premium cars use hydraulic mounts. Rubber mounts can only kill so many vibrations. So, for these cars which need optimum comfort, this level of damping may not cut it. As cost is not a stringent constraint in these market segments, manufacturers can experiment with different kinds of transmission mounts, and hence this is offered.
The hydraulic transmission mounts work in the same way as hydraulic engine mounts. They both use a liquid or gel inside the mounts to absorb the vibrations. This is far more efficient than a rubber mount as these fluids possess superior damping capabilities.
Their superior damping capability makes them the favorite choices where comfort is paramount. But this type of transmission mounts has its own drawbacks as well. Just like any advanced technology, the cost is the main issue. With their complex construction, specialized fluid, and the seals require, these kinds of mounts are more expensive than simple rubber units.
The added costs limit their usage to premium cars, the market of which is not too sensitive to the cost. On top of this, hydraulic mounts are not as durable as rubber mounts. The rubber mounts with their solid and simple construction can last you for many years. They do need replacement some time but they certainly will outlive hydraulic transmission mounts. The hydraulic mounts also bring in an issue that is common for any fluid in the car, leaks.
Therefore, hydraulic mounts are only good when you prefer comfort over cost and durability. Though it finds fewer applications than rubber mounts, the comfort it brings to the table is second to none.
3. Active Mounts
As this story focuses on transmission mounts, active mounts may not look like a perfect fit here as this technology is mostly used in engine mounts. But as the engine mounts have the same construction and basically the same function as the transmission mounts, it is beneficial to know the latest trends in the field.
After rubber and hydraulic mounts, active hydraulic mounts are the most cutting-edge option available on the market. This tech is mostly used for motor mounts as they must dampen even higher vibrations than transmission mounts.
Active mounts are basically what their name days. They actively change the stiffness of the mount to adapt to the situations. In idle situations, the engine shakes more. The mounts loosen up to actively take in these vibrations. When the engine speed rises, the mounts can stiffen up, stopping the engine from making unwanted motions.
There are different kinds of active mounts. Here are a few of them:
A) Vacuum Actuated Active Mounts
In this kind of active mounts, there will be a hollow chamber inside them. This hollow chamber allows applying vacuum as needed, changing the stiffness of the mount.
When the engine is idling, the mounts are supposed to be more absorbent allowing to eat up the vibrations. In the case of vacuum-actuated active mounts, this is done by applying a vacuum to the mount. As the engine speed increases, this is slowly released to increase the stiffness of the mount.
This change in stiffness is done via a Vacuum Switching Valve (VSV) that is controlled by the Powertrain Control Module (PCM). The problem with these kinds of valves includes leakage of vacuum that may happen after some years of usage.
This being a mechanical system, leaves more room for improvement. And as always, electronics jump into the scene to improve it.
B) Electronically Actuated Active Mounts
Instead of utilizing vacuum tubes and valves, these valves get an electronic system that changes the stiffness of the mount. The electronic actuation is governed by the powertrain control module itself.
At engine idle, the hydraulic mount is electronically relaxed to enhance leeway hence it absorbs the harsher vibes. At higher engine speeds, the mount stiffens up to restrict the motion of the motor. Or, in the case of transmission mounts, they restrict the transmission’s movement.
C) Magneto-Rheological Mounts
Another complex, yet effective twist on the field of mounts is Magneto-Rheological Mounts. Delphy recently came up with this tech and it is similar to some active suspension technologies available right now.
The Magneto-Rheological Mount is a type of hydraulic mount. The fluid in these mounts contains small iron particles suspended in it. Depending on the load, an electric current or magnetic field is applied to the mount. When this happens, the iron particles line up, increasing the viscosity of the fluid they are in.
This controllable change in viscosity can easily be utilized to control the character of the mount. As the engine speed and load change, the Magneto-Rheological mount can change the viscosity of the fluid as needed, stiffening or loosening up the mount.
A microprocessor controls the action of a Magneto-Rheological mount and feeds off the data supplied to the powertrain control module. There is a fluid pressure sensor inside the mount that sends feedback to the processor to make adjustments on the go.
Of course, like any complex technology, diagnosis, repair or replacement are all expensive. Garages with special scanning tools can only detect an issue with these mounts. You can also expect a pretty decent-sized repair bill if and when one of these goes wrong.
D) Vibration Cancelling Mounts
No technology is perfect. Everything leaves room for someone to improve it. In 2009, Lexus debuted a vibration canceling mount for its ES sedan. This technology took inspiration from noise-cancellation headphones to reduce engine vibrations.
Instead of dampening these vibrations, these mounts have an active motor. This motor generates counter vibrations that cancel out the existing vibrations, effectively killing them off.
These mounts come with a separate computer for themselves, called the Active Control Engine Mount ECU. To feed this ECU, an accelerometer attached to the front reads the amount of engine shake and relays the data. The ECU also picks up inputs from a myriad of other sources. These include transmission gear position, vehicle speed, engine load ratio, and more.
The motor makes calculations as per the inputs. It then produces counter vibrations relative to the input to effectively smoothen everything out.
Detect A Bad Transmission Mount
We have discussed what transmission mounts are. We have also seen what flavors they come in. It is a seemingly simple technology that engineering pushed in pursuit of more refinement. The modern transmission mounts are prone to failure due to their complex hydraulic and electronic setup.
This does not mean that the regular rubber transmission mounts are immune to failure. Yes, they are more durable than modern hydraulic units. But sooner or later, they too may give up. Especially if your car is driven a lot, and is getting quite old.
With the possible failure of a transmission mount that can have an unpleasant outcome, it is beneficial to know what happens when it does let go. With this, we must have a look at the symptoms your car will throw at you when its transmission mounts are letting go. These are quite easy to spot as they can alter the refinement of your vehicle completely. But in the case of more complex mounts, only a proper diagnosis with a fitting scanning tool can precisely spot the failure.
So, in bad transmission mounts 101, the first lesson is how to detect the issue. Here are a few symptoms that you can look out for.
1. High Noise, Vibrations, And Harshness
As we know, the transmission mounts are employed to reduce the vibration seeping into the cabin. So the very first symptom of failed transmission mounts is an increased level of vibrations.
The vibrations are the most evident when the engine is idling. This is when the vibrations are at their peak and obviously that is when you will feel them the most. When the vehicle starts first, if you feel there is a lurching motion, forwards or backward, that can be a sign of a bad transmission mount. This can happen mostly in front-wheel drive vehicles.
In rear-wheel-drive vehicles, it can be a rocking motion from side to side. The vibrations may slightly reduce after the engine picks up speed but the idling is when they are the most pronounced.
The same surging motion can also be experienced when the engine is finally turned off. If this happens, you can be certain that your transmission mounts have let go.
2. Higher Noise
What happens when vibrations increase? Noise increases along with it. When transmission mounts give up, you can hear quite scary noises from under the hood. These can range in intensity from small banging sounds to loud noises that make you feel that the engine is going to fall off. These sounds arise from metal hitting metal, as transmission mounts do not secure these parts anymore.
The transmission will not fall off the car, despite the fact that the situation can sound like that. But it is not safe to drive around with these noises as the loose transmission can hit other parts, effectively damaging them.
Like most noises in a car, these noises also get amplified when you hit a pothole. The transmission can shift when the car hits a pothole. It can rise and fall in its position, generating a scary thump.
3. Issues With Cornering
As transmission mounts hold the transmission firmly in place, a failure in their operation can allow the transmission to move around. When the car moves around, the transmission can shift and cause issues.
This can be especially dangerous while cornering. The G forces acting on the car can make the transmission move as well. Meanwhile, the inertia of the heavy transmission may counter this movement. With this tug-of-war going on and nothing to hold it in place, the weight of transmission can shift violently.
This can be an inconvenience while you are taking a corner or it can be a complete disaster, depending on how fast you are going. If the cornering forces are high, the transmission can shift further, upsetting the balance of the vehicle.
4. Chassis Flex
More than a symptom, this is a catastrophic aftereffect. Transmission is a heavy part under the hood of the vehicle. When such a heavy part connected to the chassis is moving around, it is not a surprise that the chassis gets damaged.
Especially when you drive over a bump or a pothole, or when you take a fast corner, the weight can shift around too much. This sudden movement can flex or bend the chassis of the vehicle. In severe cases, it will completely go off shape.
Checking Transmission Mounts
If you experience some or all of the aforementioned symptoms, it is likely that your transmission mounts have given up. To confirm this, you will have to check for a few signs. This can give you a clear idea about what has gone wrong and what can be done to correct it.
1. Listen For Abnormal Sounds
In the symptoms of bad transmission mounts, knocking, banging sounds are very important ones. You can listen to sounds like this from your engine. Especially when the engine is idle or while it is turned on/off. Similar sounds emanate when the load on the engine changes.
2. Inspect The Underside Of The Vehicle
Lift your vehicle and look under it to spot any irregularities. If the transmission mounts have gone bad to a severe extent, you can see the transmission sagging a little. Else, you can inspect the transmission mounts directly to spot any loose brackets or bolts.
3. Inspect The Transmission Mounts
While your vehicle is on the lift, look at the rubber of the transmission mounts. If the rubber has rotten or cracked, you may have to replace the mounts. Rotten rubber is impossible to repair. Replacement is the only fix.
How To Replace Transmission Mount?
The best bet for you to replace your transmission mounts is to take your vehicle to a garage. But for the DIY freaks among us, here is a guide to walk you through the process of replacing transmission mounts.
1. Loosen The Bad Transmission Mounts
Once you spot the bad transmission mounts, you should park your vehicle on a flat surface and choke the wheels. Spray the bolts on the mount with penetrating fluid and allow it to seep into them.
Use a breaker bar or two wrenches connected to each other to loosen the bolt on the mount. Using these longer arms can help to give more torque and reach.
2. Lift The Car
Lift the car using a jack or a hydraulic lift, if you have access to one. Use another jack to support the transmission. Make sure that you place the jack properly under the transmission on a solid surface. Use some wooden blocks to support the transmission and jack up the vehicle a bit more. This can relieve the pressure from the bolts. Now you can easily remove the transmission mounts.
3. Replace The Transmission Mounts
After removing the bolts from the mounts, remove the mounts from their position. Make sure that you always buy genuine transmission mounts for replacement. Slide the new mount into place using a hammer and screwdriver. The new mount may be taller than the existing one as the rubber is not compressed yet. So, it may take a bit of fiddling around to squeeze it in.
After fitting the new mount in the space and bolt it up tightly. Use Threadlocker fluid to make sure that it will not loosen over time. You can jack up the vehicle a bit more to make sure that the fitment is easy. After this, lower the vehicle and use a torque wrench to torque the bolts completely.
Transmission Mounts: Final Words
Some metal and rubber may not look like a complex combination. But this small part can cause a lot of damage if left ignored. It is imperative that you inspect and confirm that the vehicle’s transmission mounts are always in their best condition.