The transmission system transfers power from the engine to the wheels, allowing you to move the car forward or backward. However, one frustrating issue is when a car pops out of gear unexpectedly. This is inconvenient and dangerous, especially as it always happens while happily driving along. In this article, we will answer the question “why does my car pop out of gear” and what you can do if it does happen.
What causes a car to pop out of gear?
There are multiple reasons why your car may pop out of gear, and there is no guaranteed one reason. Diagnosing each potential problem is hands-on and may require getting under the vehicle to check different components for movement. Some faults require physically removing the transmission and inspecting its internals. You may need to consult a mechanic for their knowledge on knowing if the fault is inside the gearbox. Regardless, here are the most common causes of a car popping out of gear.
Low transmission fluid
Transmission fluid lubricates the gears, bearings, and other moving parts, reducing friction (heat) and preventing excessive wear and tear.
No lubrication is provided when the transmission fluid level is low, causing the transmission temperatures to exceed normal operating levels. Overheating increases the wear rate of each gear; they can even break, which will cause the transmission gears to grind or pop out of gear.
Another problem with a low transmission fluid level is the drop in hydraulic pressure within the transmission system. Specific to an automatic gearbox, hydraulic pressure is necessary to engage and disengage the gears smoothly. When the pressure drops due to a lack of fluid, the gears may not engage fully or pop out when driving.
Shifter linkage issue
When you move the gear shifter, the linkages connect your movement to the transmission forcing it to change gears. There are a few different types of shifter linkages, but they all do the same job. It may be a series of rods with tiny ball joints or cables with ball joints. Shifter linkage and transmission mount problems are the two most common causes of a car popping out of gear. The common faults found with them are:
- Misaligned linkage – With a misaligned linkage, the gear may not fully engage. Misalignment can occur due to damage, wear and tear, or improper routing of cable-type linkages.
- Loose or worn linkage – If the linkage is loose or the ball joints are worn, it can cause the linkage to move around excessively, preventing the gears from staying engaged.
- Damaged or broken linkage – The most obvious but any damage to the gear linkage, which runs from the gear stick in the cabin to the gearbox, you will either not be able to put the car into or keep the vehicle in any gear.
- Improper cable adjustment – Usually, cables have a lock nut that takes the slack and makes any adjustments; if a cable shifter linkage is not adjusted correctly(under or over-adjusted), it can cause problems with the engagement of the gears.
The clutch connects the engine to the transmission, allowing you to engage and disengage the engine’s power from the transmission while changing gears. There are two different types of systems, a hydraulic and a mechanical clutch which can fail in various ways; all can lead to the car jumping out of gear. You will probably hear someone saying a clutch is slipping, which usually means the clutch has worn out. Typical common clutch problems(not all of them), regardless of the system type, are:
- Worn friction plate
- Broken clutch release fork
- Damaged or improperly fitted throw-out bearing
- Contaminated clutch disc surface
- Broken or worn diaphragm plate springs
A hydraulic clutch uses the brake fluid(hydraulic fluid) to operate the clutch. Sometimes brake and clutch issues can come hand in hand if there is a problem with the fluid level. Issues that are specific to hydraulic clutches are:
- Leaking hydraulic line
- Low brake fluid level
- Slave/master cylinder problem
Mechanical clutches use cables and rods to engage/disengage the clutch. The issues that can occur with mechanical clutches are:
- Improper adjustment of the cable
- Broken cable internals
- Damaged linkages
Transmission mounts worn
A transmission/gearbox mount attaches the transmission to the vehicle chassis. The mounts are primarily made of rubber inside a metal casing which absorbs vibrations, and small amounts of movement are created when changing gears. However, a worn transmission mount allows the whole gearbox unit to move around, under acceleration, starting a car, switching it off and braking, causing the transmission to move excessively, putting extra pressure on gear linkages, and forcing the gear to disengage or pop out.
Worn or damaged gear synchros
Damage to the input shaft can cause increased wear on the transmission synchronizer, which keeps the gears in sync. If the synchronizer is worn or damaged due to input shaft problems, it can cause the gears to pop out of gear even more frequently. This item is only diagnosable by removing the transmission and inspecting its internals.
Damaged input shaft
The input shaft connects the clutch disc to the transmission gears, keeping them in place and transmitting the engine’s power to the wheels. If the input shaft is damaged or worn, it can cause the transmission to select or slip into the wrong gear. The input shaft doesn’t usually force the car to pop completely out of gear unless it snaps, which can and does happen, but it isn’t particularly common. This type of issue only really occurs if the car is being thrashed or the engine is modified, and the standard transmission can keep up with the extra power.
Wrong transmission for the engine
This isn’t something that happens very often, but it can occur when an engine or transmission has been changed, and a new unit is reinstalled. Usually, by mistake, some very slight variations between the old and unit may not be noticeable at the time but will be evident in problems like the car popping out of gear.
How to stop a car from jumping out of gear?
There are some basic things you can do to stop the car from jumping out of gear:
- Used as a safety precaution to get you out of trouble while driving, you can hold the gear/shifter stick while in gear. Depending on the cause of the problem, this can keep the transmission in gear, but as a downside, it will cause further damage to other components if you continue driving for long periods. Drive slowly and carefully; accelerating carefully will help reduce stress on whatever is causing the problem.
- Check the fluid levels. Basic checks on the transmission and brake/clutch fluid levels may be to blame and can be easily topped up, possibly illuminating the problem.
- Check and replace the components causing the problem. Not so straightforward and doesn’t help you in an emergency, but if the car continues to jump out of gear while driving. You must stop and get the vehicle recovered to a mechanic who will inspect and replace any problems. Unfortunately, most transmission-related faults involve removing the gearbox and supporting components, which is labor-intensive and costly.
A car popping out of gear is a serious fault that must be rectified immediately. Delaying the repair can cause further damage. If you drive and the vehicle keeps popping out of gear, try holding the shifter in place. If you find yourself under the car inspecting the problem, either a worn transmission mount or shifter linkages worn are the two most common problems. If neither of these is to blame and the fluid levels are correct, consider taking your car to a mechanic to inspect, as the repair is probably a bit more complex.