Auto Repair Articles

Question:

I have a 2000 mustang with the 3.8v6 and 5 speed trans. It is making a popping noise from the transmission while in reverse. It is a continueus popping not just a single pop. What could be the problem?

Answer:

If you are certain it is not the front U-Joint, then you definitely have internal damage in the transmission. You may have a damaged Idler gear or synchronizer.

Reverse gear is handled by a small idler gear (purple). At all times, the blue reverse gear in this diagram is turning in a direction opposite to all of the other blue gears. Therefore, it would be impossible to throw the transmission into reverse while the car is moving forward — the dog teeth would never engage. However, they will make a lot of noise!

Synchronizers
Manual transmissions in modern passenger cars use synchronizers to eliminate the need for double-clutching. A synchro’s purpose is to allow the collar and the gear to make frictional contact before the dog teeth make contact. This lets the collar and the gear synchronize their speeds before the teeth need to engage, like this: 

The cone on the blue gear fits into the cone-shaped area in the collar, and friction between the cone and the collar synchronize the collar and the gear. The outer portion of the collar then slides so that the dog teeth can engage the gear.

Every manufacturer implements transmissions and synchros in different ways, but this is the general idea.

Reference Link: http://auto.howstuffworks.com/transmission3.htm 
 

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