What is the reason for slight shaking when stepping on the brake in D gear?

[MacKennedy]

Possible reasons include: aging of engine or transmission mounts, gear engagement impact in the transmission, or improper engine air-fuel mixture matching. Below is an analysis of the causes of car shaking: 1. Engine or transmission mounts, commonly known as engine mounts, may be affected by aging or improper installation. Further inspection is needed to confirm whether replacement is required; 2. Gear engagement impact in the transmission, caused by impurities or dirt in the transmission fluid, leading to poor performance of the transmission hydraulic system. Further inspection of the transmission fluid and transmission components is necessary; 3. Improper engine air-fuel mixture matching, such as poor engine performance, issues with spark plugs, fuel injectors, etc., requires further inspection to confirm the cause of the fault.

[VonKarter]

I've been driving a manual transmission car for many years, and recently when I put it in D gear and stepped on the brake, the car shook slightly, which really annoyed me. The most common cause of this situation is unstable engine idle speed, possibly due to old spark plugs or too much carbon buildup, leading to RPM fluctuations. Another reason could be aging engine mounts, especially in older models—if the rubber in the mounts cracks and can't absorb vibrations, the car will shake when parked. Don't overlook the transmission either; the torque converter doesn't fully disengage in D gear, and stepping on the brake adds extra strain, which becomes more noticeable if the fluid temperature is high or the fluid level is low. Later, I replaced the mounts and cleaned the carbon deposits, and the problem was resolved. I recommend not delaying repairs until it becomes a bigger issue—just get it checked at a repair shop for peace of mind.

[DiEdward]

This kind of shaking is really annoying. I've discussed it in the car owners' group, and the main reason is the engine's unstable operation at idle. When the car is stopped in D gear, the engine still tries to drive the wheels while the brakes hold them back, causing imbalance and vibration. Common causes include weak spark plug ignition or a clogged engine air filter affecting air intake, leading to fluctuating idle speeds. Another possibility is uneven brake discs or pads, which can combine with engine vibrations to cause minor shaking. From my experience, regular checks on the brake system's cleanliness and engine maintenance, such as replacing spark plugs, can improve the situation. Additionally, expired transmission fluid might worsen the problem, and letting this issue persist is bad for the car.

[DiJayla]

I've been driving for decades and have seen plenty of shaking issues, which are usually common in older vehicles. When the engine mount rubber cracks, it can't absorb the shocks, causing the car to shake when braking at a red light. Problems with spark plugs or ignition coils are also common, leading to unstable engine RPM. Don't overlook the transmission either—a worn torque converter can cause shaking under load in Drive (D). I'd recommend checking the mounts and spark plugs first, and regularly cleaning carbon deposits to maintain engine health. These fixes are straightforward and cost-effective.