Transmission shifting rough


Automatic transmissions are a mystery to most.  Many mechanics will quickly tackle a timing belt job or a head gasket replacement, but when it comes to transmission even the most seasoned mechanics often shy away.  When they work correctly, we usually don’t think about them because they are automatic.  When they don’t work correctly, it usually goes past annoying and leaves you stranded.

Hard Shifting Transmission
Automatic transmissions use a planetary gear system to transfer power and to create different gear ratios and a reverse option.  A planetary gear set has a single center gear, a large ring gear around that with internal teeth, and multiple small gears in between the center and ring gears.  In an automobile transmission, there usually are two sets of these gear systems.  This arrangement allows for a variety of gear ratios that can be shifted very easily, but if one part of the system fails, it often renders the whole system inoperable.

Like many problems that arise in your car, there are usually early warning signs to let you know that one of these systems is about to fail.  Luckily, the automatic transmission in your vehicle has some early warning signs of its own.

Automatic Transmission Failure Early Warning Signs:

• Low fluid level on the dipstick
• Dark or discolored fluid
• Whining or grinding noises
• Loose shifting or over revving
• Hard or jerky shifting

The best way you can keep tabs on your transmission and make sure it last as long as possible is to make sure it always has enough clean transmission fluid.  Most passenger vehicles today have a dip stick in the engine bay for the automatic transmission.  Check your manual for the location of the dip stick and the recommended procedure for checking the level.  On most vehicles the transmission level should be checked with the engine operating and there will be a “cold” and “hot” range.  It is easiest to check the fluid level in the morning after your car has sat all night and is cold.  In this case use the “cold” range.  If you’ve been driving and want to check your fluid level, try operating your vehicle in the lower gear to ensure the transmission fluid is sufficiently hot and use the “hot” range on the dip stick.

Leaking Transmission
While checking the fluid level, check the fluid for discoloration, particles or a burnt smell.  If any of these are evident, it may be time to change your transmission fluid.  You should always change your transmission fluid at the factory recommended interval using the recommended fluid for your vehicle.  If you use your vehicle for towing, drive in the city or in stop-and-go traffic, or live in a significantly warm or cold place, you may need to change your fluid 10% to 25% more often.

Another way to diagnose an impending transmission problem is if it starts making whining or grinding noises.  This would single out a large problem and the vehicle should be taken to a transmission repair shop immediately.

A change in the way the transmission shifts compared to normal is another telltale sign that something is off with your automatic transmission.  An automatic transmission shifts gears by changing which of the planetary gears are moving, held stationary, or coupled to the input or output shafts.  These changes are made by a series of clutches and bands, and are activated by pressure changes of the transmission fluid.  As these clutches and bands wear out it can cause your shifts to feel sloppy, take longer or even have the engine over rev.  The wear of these clutches and bands is accelerated by having dirty transmission fluid circulating cause excessive wear and premature failure.  In this case, a transmission rebuild is the only thing that can solve the problem.

If you are experiencing hard transmission shifts, it is possible that the only problem is a low transmission fluid level.  Low transmission fluid level can change the operating pressures of the transmission as well as reduce the amount of lubricant present between the clutches and bands and raise transmission temperatures.  All these things can cause hard or jerky shifting.  You need to identify why the transmission has a low fluid level and refill it as soon as possible.

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