Can A Bad CV Joint Affect The Transmission?

In this guide, we will discuss one of the most frequently asked questions: can a bad CV joint affect the transmission? CV joints are important for a car or truck to run smoothly and efficiently. Without these joints, the transmission, driveshaft, or differential would be prone to failure. CV joints keep the wheel aligned, transfer engine power to the front suspension, absorb road bumps and allow the car to turn. A bad CV joint could be caused by a worn CV joint bearing or a worn rubber boot of a CV joint.

Although a CV joint has no link with the internal components of a transmission, a bad CV joint can affect transmission in some cases. A bad CV joint or bad CV axle. A damaged CV joint can cause vibrations (usually after 60mph) which can be heard when the vehicle is driven. A rattling, clicking, clunking or tapping sound on acceleration while turning does not necessarily come straight from the transmission. That sound might be an indication that something is wrong with the CV axle or CV joint. The constant wobbling of the CV axle causes uneven strains on the ball bearings of the CV joint. If the ball joint of the driver-side CV joint fails and you continue to drive with it, it can damage the seal on the transaxle where the CV joint plugs. This is will cause leakage of transmission fluid. The loss of transmission fluid will cause transmission slip and hard shifting of gears.

Usually, vehicle owners think that rough acceleration or vibration is due to transmission problems. But, engine misfire also causes your vehicle to vibrate or shudder when it is under throttle. You can read my guide on check engine light flashing and car shaking to get further details. Usually, it is due to bad spark plugs, ignition coils, or a bad EGR valve. You should also use this scan tool to make sure whether there are any trouble codes stored in your engine’s memory.

What Is A CV Joint?

CV joint, also called a Constant Velocity joint, is present in four-wheel drives and forward-wheel drives (FWD). It is a type of joint that allows the wheels to turn smoothly. The CV joint is responsible for the transmission of power from the transaxle to the wheels at various angles.

The inner CV joint is connected to the transaxle while the outer CV joint goes into the wheel hub assembly.

CV joint consists of:

  • Spherical Ball bearings
  • Casing in which bearing rotates
  • Rubber boot
CV joint bearing parts

As your vehicle goes over the potholes or bumps, the vehicle’s suspension moves in a respective direction. The CV joints respond to the suspension movement and keep the drive wheels moving at a constant velocity. A CV joint does this due to constantly changing its angle, thus keeping the rotational speed the same.

CV joints make sure that the tires remain perpendicular to the road and are easy to steer when a vehicle passes over a bump or a pothole in a road.

demonstration of a purpose of a CV joint

From a small animation below, you can see how the CV joint constantly changes the shaft angle to keep the speed the same:

All CV joints require a special type of grease packed inside the joint. The rubber boot seals the CV joint. It prevents the grease to leak and also absorbs the load exerting on the bearing of the CV joint.

If the rubber boot of the CV joint cracks, the CV joint will be contaminated with a buildup of dirt and debris, which can damage the surface of one of the balls of the bearing. This can cause the CV joint to slip or lock, which can make steering difficult.

Also Read: Steering wheel turning by itself

What Is CV Axle?

CV axle, also called a CV shaft and half shaft, connects CV joints, transaxle, and wheels to transfer power from the transmission to the wheels. The inner CV joints connect the CV axle to the transaxle.

A vehicle has a CV axle on the passenger and the driver side. The driver side’s CV axle is shorter in length compared to the CV axle on the passenger side.

CV axles

What Does A Transmission Consist Of?

An automatic transmission system consists of:

  • Torque converter
  • Drivetrain (differential)
  • Valve body
  • Solenoids
  • Clutches and bands

Most of the time, problems in transmission, such as missing shifts, and clutch slip, mostly occur due to a low level of transmission fluid inside a transmission. In my guide on transmission shifting hard, you can find the working of automatic transmission and different causes of failure in transmission.

Transmission fluid is responsible for transferring power from the crankshaft to the torque converter, lubricating the gears in the drivetrain, and applying pressure on clutches and bands by passing through solenoids and passages in the valve body to shift gears. 

The problem in transmission due to a bad CV joint only occurs if a seal of the transaxle is broken or the driver’s side CV axle isn’t seated properly after CV axle replacement, due to which transmission fluid starts leaking or the level of transmission fluid becomes lower than the optimum level in the transmission system.

Symptoms Of A Bad CV Joint or A Bad CV Axle

The easiest method to tell whether a CV joint is bad is to carefully listen to the clunking sounds and vibrations emanating from your vehicle when taking tight turns (either left or right).

Typical symptoms of a bad CV joint and bad CV axle include:

  • Clunking noise when reversing or accelerating above 25mph speed
  • Clicking noise when taking tight turns
  • Vehicle vibrates, bounces, shudders or feels jerky while accelerating
  • Rubber boot of the CV joint is cracked
  • Excessive grease stains below the tires and on the wheel well

Problems in a Bad CV Joint Interpreted As Problems In A Transmission

Most of the time, some car owners assume that wheels, tie rods, sway bar has any link with the transmission system, due to which they assume that any vibration, clunking, or popping noise coming out from the front of the vehicle when taking a turn or accelerating a vehicle is attributed to the bad transmission.

Actually, when a CV joint becomes bad, torque from the transmission is not being smoothly transferred to the wheels via CV joints, due to which your vehicle may vibrate or makes clunking when accelerating or even shifting from drive to reverse. So, the chances are that your transmission is fine, and all that jerk and clunking sound from your vehicle is only coming from the bad CV joint.

The easiest way to diagnose a bad outer CV joint is to turn your car right in a tight circle on a smooth road, such as a parking lot. If you hear a clicking noise from the left wheel, it means that the outer left CV joint is bad. Now, if you turn the vehicle left and hear a clicking noise from the right wheel, it means the right outer CV joint is bad. This is because the side to which a car takes a turn always tries to exert strain on the opposite side. So, if the CV joint is bad, it will emit clunking sound.

Inner CV Joint Failure Symptoms

A bad inner CV joint makes clunking noise and causes vibrations in the vehicle while accelerating over 30mph.

If your vehicle shudders or vibrates while accelerating, there is a doubt whether the vibration is due to backlash in gears in the drivetrain or it is due to the bad inner CV joint. The damaged bearing of the transaxle shaft can also cause vibrations in the vehicle when accelerating.

One easier way of determining a bad inner CV joint is to quickly accelerate and decelerate the vehicle in reverse. If the clunking noise becomes pronounced, it means one of the inner CV joints is bad.

Another best way to diagnose a bad inner joint is to raise the front of your car and set it on the jack stand. Make sure to put the transmission in park mode. Put one hand firmly on the inner CV joint hub and move the CV axle back and forth, and up and down as close as to the inner CV joint with the other hand. Make sure the CV joint hub is not moving. If the CV shaft feels excessively sloppy, it means the CV joint needs to be replaced. If the rubber boot of inner CV joint has cracked or ripped off, it is a clear indication of a bad CV joint.

Can A Bad CV Axle Cause Hard Shifting?

A bad CV axle can cause hard shifting problems. This is caused by the transmission being subjected to excessive vibration. The inner CV joint transmits power from the drivetrain of transmission to the wheel. If there is vibration in the CV axle due to a bad inner CV joint, the gears in the drivetrain will produce clunking sound and will cause hard shifting problems.

Due to a vibrating CV axle, transmission fluid can also leak from the transmission which also causes hard shifting issues in the transmission.

Final Thoughts

So, a bad CV joint or axle can damage transmission if it is causing leakage of transmission fluid from the transmission due to excessive vibration. The bad inner joint causes vibration in the vehicle when acceleration. However, you should also examine rubber motor mounts, tie rod ends, control arm bushings and transaxle if your vehicle is jerky or vibrating while accelerating.