How often to flush transmission

[BZieg]

How often should I flush my transmission? The truck is an 2004. 5 5. 9L 48re 4x4, should I change transfer case as well? The truck only has 21k miles but it is an '04. 5. Thanks

 

[JHardwick]

How often should I flush my transmission? The truck is an 2004. 5 5. 9L 48re 4x4, should I change transfer case as well? The truck only has 21k miles but it is an '04. 5. Thanks

I do the transmission, X-sfer and both diffs every 3rd oil change ... ... ... ..... or roughly 50,000 miles.

 

[BZieg]

Thanks. I think that's what I'll do as well, 21k miles seems a bit overkill to change it now.

 

[DeezelDood]

It depends on how you use your truck. First thing I installed on my truck is a transmission temp gage, which is standard equipment on Chevy's and maybe Fords.

Should be standard on Dodge heavy duty trucks as as well. There are quite few posts on a search of "transmission temp". At 175 degrees the ATF+4 synthetic fluid is good for 100,000 miles. At 240 its toast after a few thousand miles. The light-duty interval in the manual is 100,000 miles. The heavy duty interval is, I believe, 60,000 miles. Some people change/flush at 30,000 miles. Others dump and refill (no flush). As long as my oil stays below 180 or so I'll flush and fill at 60,000 miles. I do recommend a transmission temp gage if you have not already installed one. I change the ATF+4 in the xfer case when I change my diffs at 20-30,000 miles (dependent on how much towing I'm doing) . It's not necessary, but it's easy.

 

[BZieg]

Thanks, very helpful, I just bought the truck and plan to install pyrometer, boost, and trans temp. guages.

 

[John - K5AWO]

My brother used to run a Chevy 3+3 1 ton dually pulling a race car trailer that grossed at 37,000# with spare engines, fuel, cars, parts, etc... .

He would drive that thing at 90+ regardless of where he was going, east coast, west coast, new race every weekend.

The transmission temps behind that 454 engine got way up under that kind of stress. He changed transmission oil and filter before leaving the shop on every race weekend.
transmission lasted 336,000 miles without any repairs ever being needed and then the truck was sold. It did consume a lot of oil changes though

I like to change my transmission fluid every 25-30k. If the oil temp ever goes over 240 though, I change it "just because". I also have an external 1 quart capacity oil filter in the oil cooler return line.