You can tell when the transmission filter gets clogged. The transmission will start to slip in and out of gear as you begin to drive again after you stopped the vehicle, you'll have trouble shifting the vehicle into reverse, and sometimes you can't get the car into gear at all. There can be other reasons for this type of trouble, but if you own an old vehicle that you know, or strongly suspect, has never had the transmission filter changed, you should change the filter before you do anything else. This is a job a beginning mechanic who knows how to set the vehicle up on jacks and knows where the transmission is can do by themselves. Here is how to change the filter on a 5R55S transmission commonly found on Ford SUVs and trucks made in the mid- to late-1990s.
Remove Oil Pan
Slide under the vehicle until you get to the transmission. You'll notice the large-shaped pan connected to the bottom of the transmission that you'll have to remove. Be prepared, this is going to be a messy job. Set a catch basin underneath the transmission pan to catch the fluid that will come out once you unbolt the pan from the bottom of the transmission.
There are about 15 13mm bolts around the perimeter of the transmission pan. Remove all the bolts except for two in the backside of the pan and one bolt in the front. Once the other 12 bolts have been removed, loosen the back two bolts a little and take out the front bolt. As soon as these bolts get loosened, the fluid is going to start to drain out of the pan. Drop the front part of the pan so it angles down into the catch basin. Let as much fluid as possible drain into the catch basin.
Press the pan back up against the bottom of the transmission with a floor jack and remove the two bolts on the backside of the pan. Carefully lower the pan down and pour the rest of the fluid into the catch basin.
The filter is held to the bottom of the transmission with a single 8mm bolt located in the middle section of the filter. Remove the bolt, take off the filter, and discard it. Be prepared, again, as more fluid will drain out of the transmission when you remove the filter.
Install New Filter
Set the new filter into position and bolt it in place. Bolt the pan back onto the bottom of the transmission.
Add Transmission Fluid
You should discard the old transmission fluid instead of trying to reuse it. Add new fluid to the transmission – which will usually take 4-5 quarts.
Test the Transmission
Go for a drive to make sure the transmission is now running well. If problems persist after changing the filter, you should seek out a reputable transmission repair specialist to look at the transmission to figure out what's wrong.