Why the Car Shakes In Reverse? 7 Causes And Solutions To Fix It!

car shakes in reverse
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People often experience the issue of car vibrations while in drive or reverse mode at some point in time, especially if the car has already crossed a few thousand miles (say 75000 miles plus).

But what if you observe that the car shakes in reverse only and not in drive mode, then the problem is altogether different.

If the car shakes in reverse, then you need to diagnose any issue with the engine and transmission mounts, leaky or dirty transmission fluids, bad torque converter, or any issue associated with one of the engine systems like the fuel delivery, air intake, or ignition system for the possible root cause.

Is your car shake in reverse? Then you are in right place! Here, we will discuss all parameters that you need to look to troubleshoot the problem.

Believe, you are not alone in this journey! Many people experience this issue and looking for ways to fix it. Stay tuned!

Why The Car Shakes In Reverse? 7 Causes And Solutions To Fix It!

In an ideal scenario, the reverse gear should not vibrate more than any other gear selection but there is a distinct transmission whine on most cars while engaged in reverse, since the reverse gears are usually spur gears (straight gears) and not helical gears.

The reason behind the usage of straight gears is to avoid the axial thrust load which comes on the transmission bearing which is typically exerted by the helical gears owing to its angular teeth cut on the gear face.

But the helical gears run smoothly due to the larger bearing surface it offers over a spur gear that creates a typical whining noise when engaged.

Since the axial thrust exerted by the helical gear is difficult to deal with, the OEMs perhaps may have considered having the whining noise as a sensible trade-off.

Since the reverse is engaged once in a while that too at the time of parking or removing the car, maybe it is not worthwhile for OEMs to aim at costlier transmission bearing mounting solution to go for smoother helical gears.

Following are the few reasons for the problem of the car shaking in reverse and solutions to fix it.

Damaged engine mount

The engine is usually braced by a couple of engine mounts to prevent its movement while running. The engine mount usually consists of a steel or die-cast bracket and rubber or hydraulic damper.

The combustion process that takes place in the engine cylinder during the firing creates an excitation force that would get transmitted directly to the car chassis frame unless it is damped through the engine mount components.

These excitation forces are more predominant in the engine idle frequency range since it is the lowest frequency that one would target to isolate from the natural frequency of the engine mount system.

Otherwise, it would result in resonance between the engine excitation frequency and the natural frequency of the engine mounting system. We are getting too technical here!

The steel bracket plays an important role in firmly fixing the engine to the car frame and taking up all the loads coming onto it.

The rubber or hydraulic damper is involved in absorbing the vibrations that are coming from the engine and transmitting only a fraction of vibrations to the car frame and so the occupant in the car feel comfortable.

These rubber mounts are designed neither too hard nor too soft to withstand load and to absorb vibration at the same time. But the rubber mount has got some durability life.

Over some period of usage, it is possible that the rubber softens and gets torn-off or cracked, thereby transmits the engine vibration directly to the car frame and you would notice that the car shakes in reverse gear because it is when the engine works hard.

Inspect the engine mount and if you notice that the engine mount is damaged and the engine is rocking violently, then it is time to replace the engine mounts with a new one.                      

Torn-out transmission mount

The general idea behind diagnosing the engine or transmission mount is that when you put the car into reverse gear, the torque offered by the engine is more than any other gear mode so the forces coming on the mounts are maximum in this case.

In the event of a broken or torn-off transmission mount, the engine vibrations will be directly transferred to the chassis without it being absorbed in the mounts and because of this fact, the car shakes in reverse. 

The issue will persist unless the torn-out transmission mount is replaced with a new one.

But How To Diagnose The Mounts?

It is often reported that the car shakes in reverse when there is a huge load on the car and that too the issue can be simulated more easily on a non-hard surface like gravel than on concrete or asphalt surface.

The reason is, more load on the car, makes the engine work hard and the gravel surface offers a good amount of load on the transmission.

It is easy to identify the damage in one of the mounts by following the below method.

Put the left foot hard on the brake and with the gear shifted to drive mode, accelerate the gas pedal with your right foot. The engine RPM shall go above 2000 or more.

Put the gear in reverse mode and repeat the above operation. The drive mode would torque the engine and exert the forces on one side. The reverse mode would strain the mount on the other side.

A slight rocking of the engine is normal, but the excessive movement is a sign of a bad mount and you need to replace the concerned mount with a new one.

The reason why we ask to check in both drive and reverse mode is to check all mounts i.e. both engine and transmission mounts.

Also, the reason behind accelerating the gas pedal during the activity while the brake is applied is because, even if the mounts are damaged, if you don’t press the gas pedal the engine won’t be producing sufficient torque to rock the engine and you may miss the issue of damaged mounts.

By applying brakes, you are putting more load on the engine. In case of low load condition, maybe the car won’t shake in reverse.

Hence it is necessary to give gas to the engine and apply the brake while diagnosing the issue to simulate the failure in front of maybe a dealer technician.

For this activity, you would need someone to monitor the mounts for excessive movement to confirm that the engine is lifting to a greater extent while you do the pedalling work inside the car.

Nowadays, the mounts getting damaged is a rare case, thanks to the robust design of OEMs, but if it is an old vehicle, then the chances of mounts getting torn-off can’t be ruled out.

Low and dirty transmission fluid

In the case of an automatic transmission, the transmission fluid plays an important role in engaging and disengaging the transmission to the engine.

Do you remember when you have changed the transmission fluid? If it is not replaced for a long time, then it is time to check the levels.

If the amount of transmission fluid goes well below what the vehicle manufacturer suggests then the tranny output RPM reduces drastically and makes your car shake when in reverse since the engine has to work hard in reverse gear.

In a few cases, a leaky seal inside the transmission would reduce the pressure build-up when shifting to reverse.

If the transmission is losing pressure, then it would not work properly and would make the transmission shake which in turn would make the car shake or shudder in reverse.

You may check the transmission fluid pressure at the idle, stall, and reverse conditions at the test port to get an idea of what is going on inside.

It is recommended to inspect the tranny fluid and replenish it to OEM recommended level to rule out it as the possible cause for this problem and to avoid possible costlier transmission repairs.

If the question is about partial refill by dropping the pan or complete flushing of the transmission? Then our answer would be, if partial change doesn’t solve the problem, then you may try complete flushing of the tranny fluid to check whether it solves the car shaking issue in reverse mode.

Clogged transmission oil filter

If the oil filter which cleans the transmission oil gets clogged, then it will reduce the fluid pressure inside the tranny and affects the fluid coupling properties. 

Due to reduced oil pressure, it may not be effectively transfer the torque from the engine drive to transmission that results in car shaking problem.

It is advisable to drop the pan and replace the transmission oil filter whenever you refill or replace the tranny oil.

Bad torque convertor

The transmission fluid and torque convertor play a similar role as what a clutch does to a manual transmission.

If the car shakes in reverse only when the engine is revved below 2000 RPM and the car shuddering goes away when revved to 3000 RPMs or more, then you have all the reason to diagnose the torque convertor.

If the engine mounts are the problem, then the car vibrating issue in reverse shall be there even when the engine RPM is about 3000 RPM. Since it is not the case, then you can rule out mounts and start focusing on the torque convertor or other parts for possible damage and replace the torque converter with a new one, if found faulty.

Faulty EPC solenoid

The EPC solenoid (Electronic pressure control solenoid) ensures the pressure in the automatic transmission by getting feedback from the vehicle ECM (Electronic control module).

If the EPC solenoid goes bad, then it would not be maintaining the desired pressure inside the tranny and this affects the transmission performance and may induce vibration in transmission depending upon the scenario, which is why you experience that the car shakes in reverse.

Hence it is recommended to replace the bad EPC solenoid with a new one.

Malfunctioning Engine Systems

Typically, the gear ratio for the reverse gear is the max. one. The reverse gear usually has the largest diameter to provide max. torque for the car.

This would mean the engine has to comparatively work hard with greater RPM to drive the reverse gear than any other gear.

If the engine RPM gets low, or the gas pedal is pressed lightly, the engine won’t be able to drive the reverse gear properly which results in shuddering or shaking of the transmission.

If the car shakes both in reverse and drive mode, then it would be apparent that there is some issue in the primary engine systems which keep the engine ticking.

The reason could be a fault in either the air intake, fuel delivery, or ignition system involved in the powertrain functioning.

Below are the possible sources for the car shuddering problem and the solutions to fix it!

1. Faulty throttle body sensors

There are many sensors mounted on the throttle body that play an important role in ensuring the air-fuel mixture ratio for proper and complete combustion of the fuel inside the piston-cylinder arrangement.

The failure of even one of the sensors would affect the air-fuel stoichiometric ratio that may cause engine misfire resulting in a drastic drop in engine RPM.

Whenever the engine RPM drops below the normal idling range, the engine excitation frequency reduces to an extent that it matches with the natural frequency of the engine on its rubber mounts which leads to the resonance of the systems.

The resonance causes the engine to vibrate with a high amplitude of vibrations and you will start noticing that the car shakes in reverse.

The engine misfiring also creates imbalanced forces in the piston-cylinder arrangement and the engine cylinder block starts shuddering which also adds to the car shaking problem especially when you take reverse.

Below are the sensors used in the throttle body to facilitate ECM operation to control the air-fuel ratio. The malfunctioning of these sensors affects the engine’s functioning.

Article you may like to read “Car Stalls in reverse? 9 Reasons and solutions to fix it!

If the Manifold Absolute Pressure (MAP) sensor goes bad, it will not sense the vacuum present in the intake manifold which is proportional to the load coming onto the engine and it would start sending random or abnormal signals to the vehicle ECM (Electronic Control Module).

This affects the air-fuel ratio during the combustion process and eventually drops the engine idle RPM and you would start experiencing that the car shakes in reverse.

Similar to the MAP, if other sensors like the MAF, IACV, or TPS sensor go faulty, then it would end up sending wrong information to the ECM and the result is that the car shakes while backing up in reverse.

Hence it is worthwhile to inspect all these sensors and replace them with a new one if found faulty.

2. Unclean throttle Body

The count of idle is typically monitored by the vehicle ECM and this information helps ECM in increasing the idle RPM in steps to compensate for the accumulation of the dust and carbon particles inside the throttle body around the throttle plate.

when the car runs idle without any gas pedal input, the accumulation of carbon particles at the throttle body reduces the airflow path between the throttle plate and the throttle body’s inner surface.

The reduced airflow causes the engine to run very leanly at idle in reverse and reduces the idle RPM significantly, hence the car shakes in reverse.

It is therefore essential that the ECM need to get the idle count right to gradually increase the idle RPM.

But when we disconnect the battery for some reason, the engine power is lost and the counts of idle go to zero in ECM and the compensation goes off causing the reduction of the idle RPM.

This RPM reduction causes the car to shake in reverse. Hence if your vehicle is shaking in reverse, you may try cleaning the throttle plate with a seafoam cleaner to ensure proper airflow and air-fuel ratio and thereby the combustion of the mixture.

3. Poor fuel pressure

Similar to the air intake requirement, the engine also needs a precise supply of fuel to control the air-fuel ratio to ensure smooth engine operation.

But if one of the fuel system parts malfunctions, then it will not ensure a stoichiometric air-fuel ratio and would cause engine misfiring issues and the associated imbalance forces result in car shuddering issues in reverse, which is when the engine has to work hard.

Below are the probable root causes that may make you experience that the car shakes in reverse. It is essential to replace the faulty part with a new one to get rid of the car shuddering problem.

Article you may like to read “Ford F150 Sputtering When Accelerating? 12 Causes and Solutions To Fix it!”

4. Bad ignition system

Even if the air intake and fuel delivery system performs good, if the fault lies with the ignition system, then also there will be chances of an engine misfire that would lead to an imbalance in the engine forces and finally, the issue gets manifest as car shake while backing up in reverse.

The typical fault area includes,

  • Faulty spark plugs
  • Bad ignition coil pack
  • Damaged ignition coil plug wires

The carbon typically gets deposited between the spark plugs electrodes which may lead to engine misfire and car shuddering issues.

The problem area also may be a faulty ignition pack that is not supplying high voltage energy to the spark plugs for a powerful ignition to take place.

In a few cases, damaged ignition coil plug wires expose the wire and cause jumping of arc to the nearest metallic objects and prevent high energy voltage to the spark plug that results in improper ignition of the air-fuel mixture.

This leads to engine misfire and introduces a shaking or shuddering experience to the occupants of the car.

Therefore, if you notice any of the ignition system components are going bad, then it is essential to inspect and replace them if found faulty.

Final Thoughts

When the car shakes in reverse, you need to primarily look into the condition of engine and transmission mounts first. This is because often they are the prime contributor to vibration-related problems.

It could be essentially a damaged mount that doesn’t perform its operation of vibration isolation and thereby allows the transmission of engine forces to the car frame which causes the car to shudder in reverse.

It is easy to check whether the mount has got damaged or not, just by holding the brake pedal while gradually pressing the gas pedal to make the engine apply torque on the mounts. If during this activity, the car shakes in reverse, then it would mean that one of the mounts is the culprit.

If the engine and transmission mounts are ok, then the next step is to check the quantity and quality of the transmission fluid. Either refill the tranny fluid if your car is running out of fluid or flush the entire fluid if the fluid quality already shows some deterioration.

If the car shakes in reverse only when the engine runs below a certain RPM and the shuddering goes away when the engine is revved to a higher RPMs, then you need to diagnose the torque convertor in case of auto transmission.

If the car shakes both in reverse and drive mode, then the issue may be related to one of the powertrain systems like air intake, fuel, and ignition system.

You need to troubleshoot one system after the other to get to the root cause of the problem.

If your vehicle is not very old, then the troubleshooting becomes simple, you may simply connect the diagnostic scanner tool to OBD ports on your vehicle and you will get a series of codes related to the problem area.

We have tried to collate all possible reasons that you need to look at when your car shakes in reverse. I hope, with this information in hand you will be fully armed to fix the issue.

Happy Motoring!

 

References

https://www.quora.com/Why-does-a-car-vibrate-in-reverse-gear

https://maxima.org/forums/3rd-generation-maxima-1989-1994/370229-car-vibrates-when-reverse-drive-gears.html

https://forums.redflagdeals.com/car-rumbling-vibrating-reverse-gear-1299637/

https://www.2carpros.com/questions/car-shakes-in-reverse

https://www.bimmerforums.com/forum/showthread.php?1970443-Car-shakes-in-reverse-ideas

 

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