I've got a 1996 C1500 5.0L with the 4L60E transmission. In 2009, at 100,000 miles, I had the transmission filter and fluid changed. I kinda did it as panicked preventative maintenance after my 2003 Yukon transmission had to be rebuilt at 130K miles.

Anyway, it is now 2024, and the 1996 C1500 has recently rolled over 200,000 miles, currently sitting at 201750. I am ordering new spark plugs and wires from Rockauto, and I am pondering the wisdom of flushing the transmission again. I've read more online in recent years about transmission failures caused by changing out the fluid, as the detergents in the new fluid supposedly break free deposits that can cause the transmission to then fail. Knowing what I know today, I probably should have been thinking about transmission fluid much more often than 100K miles, but its a pain to do yourself when there is no drain plug, and you have part of the frame blocking dropping the pan...

Any thoughts or wisdom from you guys (and gals) here as to what needs to happen here? Should I drop the pan, change the fluid and filter, flush it, or leave it alone at that age and mileage? My son in law had a 2004 Silverado with 260,000 miles on it and a transmission shop refused to flush it, as they claimed it would cause a failure - but he was on the original fluid. I changed it once, 100,000 miles ago on this truck.

Thanks!

 

At 200k w/o a rebuild you have done better than most. Unfortunately, 100k since last service not so good for your tranny's future. A full flush and fluid change now may do more harm than good. Drop the pan and fluid & filter probably ok, but at 200K it has had a full life. Years ago we had our 93 Sub 4L60E full flush at 200k; fluid/filter had been changed two times previously. 20k miles later it was dead. Coincidence?

 

For this cowboy is . Never flush anything but a toilet. Change the fluid and filter and at 200k keep your fingers crossed.

 

I guess I should have been clear. I am NOT talking about a flush like they do at the quick change oil places. I really just meant, in my garage here at home, dropping the pan, replacing the pan gasket and filter, and adding however many quarts the pan holds if new ATF fluid. I'm for sure have no intent of flushing the torque converter or anything like that. From what I read, the flushing can dislodge stuff that causes a lot of problems.

The real question is, will changing the amount of fluid in the pan while replacing the filter and gasket (5 quarts?) be enough to screw the transmission up.

 

You are not flushing.You are simply changing the Trans fluid and filters which is what 90% of us do regularly which is what maintenance requires.. Removing all the fluid in a transmission and replacing all of it at once is still not flushing. Its just changing all of the fluid a transmission can hold.
This is a lose definition of what flushing a trans entails.. If you do it manually, you’ll need to release the old fluid first then add new fluid and swap out the filter. Using a trans cleaner can help clean your transmission and prepare it for new transmission fluid. Close everything up, drive the car for a while, then repeat the process at least two more times.

 

I call this a drain & fill. "Flushing" usually involves hooking up some sort of contraption to the cooler lines.


You've already exceeded the expected lifetime of the 4L60E. I don't expect it to last much longer no matter what you do.
The benefits from changing the fluid at this point will be minimal, and you risk finishing it off prematurely.
Up to you.


Cut that in half. you should be doing every 50-60k. Less if you tow.

 

Good to know. I'll take this under consideration (and budget for a replacement transmission or a rebuild) as I continue working on restoring this truck. And lasting longer is relative. I don't expect to put more than about 2000 miles a year on this truck, so it could last another 10 years. Right now, it still shifts and behaves the same as it did when I bought the truck used in 2000 with 54,000 miles on it.

I just started down the road of working on the truck recently after a delivery guy who rang my doorbell and saw it in the driveway asked if I wanted to sell it, and offered me $1500. I had been thinking of fixing it up for years, as I like the step side body style better than the fleetside on my newer 2006 Silverado. Maybe I should have taken his offer, haha...

 

You would be surprised. I recently had a reman trans put in, and it was like a whole different truck. The wear that happens is so gradual that you don't notice how bad it gets.