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Transmission Fluid Leaks


Types of transmission fluid leaks

How to identify a transmission fluid leak

Common transmission fluid leaks

Finding the source of a transmission fluid leak

Transmission fluid leak; repair and cost

The two most common ways people become aware that their automatic transmission or transaxle is leaking fluid is either noticing red colored stains on their driveway or garage floor and when checking their fluid level and seeing that it is low.  Regardless of how you become aware that your car is leaking transmission fluid, the important thing is that you get it fixed before serious damage is done.  An automatic transmission that runs low on fluid will not survive long.
 According to ATRA (Automatic Transmission Rebuilders Association), roughly 90% of all transmission failures are fluid related.  SERVICE your transmission at regular intervals and keep the fluid level FULL to avoid being being the NEXT transmission failure statistic.
Types of Transmission Fluid Leaks   
Transmission fluid leaks can be classified as either pressure related or non-pressure related.  Both types are explained in more detail below.   
Pressure Related ATF Leaks occur when the engine is running and fluid pressure is built up inside the transmission.  Common pressure related fluid leaks include: 
 > leaking front pump or front pump seal
> leaking output shaft seal
> loose or damaged oil cooler line or line connection fitting
> damaged or deteriorated side cover gasket
 damaged sensor or leaking sensor O-ring
> torque converter
Non-Pressure Related ATF Leaks are not caused by fluid pressure and will leak anytime the fluid level is high enough (engine running or not).  Common non-pressure transmission fluid leaks include: 
  > damaged transmission oil "fluid" pan
> damaged, deteriorated or misaligned oil pan gasket
> oil pan bolts loose
> oil pan bolts overly tightened
> leaking fluid dipstick/fill tube O-ring
> damaged or deteriorated shifter lever/linkage seal
Note: A pressure related fluid leak may still leak at the same spot even when the engine is off and there is no pressure built up inside the transmission if the fluid level is high enough to reach the spot where it leaks when the vehicle is parked.
Transmission Fluid Leak COMMON FLUID LEAK POINTS Transmission Fluid Leak
Transmission Fluid Leak Points
How to Identify a Transmission Fluid Leak  
Automatic transmission fluid (ATF) is typically red in color and translucent.  When rubbing transmission fluid between your finger and thumb it feels oily and slick.  After the fluid has been in the vehicle for awhile it gets darker in color and loses some or all of its translucency.  Lastly, oxidized transmission fluid is very dark in color (nearly black), non translucent and has a burnt odor.  (See image below)

My Automatic Transmission

If you have trouble determining the color of the leaked fluid, place a white sheet of paper underneath your vehicle where the fluid leaks to the floor and let it sit overnight.  Seeing the fluid on white paper makes it easier to determine the color.

If you suspect your transmission is leaking fluid, the first thing you need to do is check the transmission fluid level.  If low, fill to proper level and continue to maintain the proper fluid level until the leak is repaired.  Do not drive the vehicle with low transmission fluid - doing so will cause the transmission to overheat.  Excessive heat will oxidize the fluid and cause major damage to the transmission.

How to properly check transmission fluid level  
Finding the Source "point of origin" of
a Transmission Fluid Leak
Some transmission fluid leaks are easy to locate and others are not so easy.  The not so easy to find leaks are normally hidden by other parts of the transmission, engine or the undercarriage.  Oftentimes the leaked fluid is splattered over a large area adding to the difficulty of finding the source. 

If you have difficulty locating the exact point where a transmission leak originates, try one of the following methods:
1. RECOMMENDED: The easiest and fastest way to locate a transmission fluid leak is using leak detection dye.  You simply poor a small amount of the dye into the transmission and start the engine.  Using a UV light that comes with the leak detection dye kit the leaking fluid will appear in a florescent yellow/green color.  It's pretty amazing stuff!

2. If you do not use leak detection dye, use a degreaser or brake cleaner to clean the underside of both the engine and transmission, as well as the undercarriage.  Then wipe everything dry.  Once everything is clean and dry, start the engine and start looking for the source of the leak.  A good "bright" flashlight will help.

If after cleaning the transmission and undercarriage you still cannot locate the source of the leak then you may have to use the leak detection dye.
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