Transmission flush out or just changer oil/filter

I have a 06 Av Z71, that just got cheap with 235,000 km.  It subject to a small delayed shifting to second but wasn't really in bad way, just different from 2000 Sliverado.  I was going do myself and change the the filter/oil in transmission but I was thinking now to wait and pay up for a complete transmission flushed out at the dealership.  I know they did help my other truck with issues.....so what do you think?  Or it could of been just the fact they changed the filter/oil.

Regarding the tranny flush. I've heard on multiple occasions that the flush may actually do more harm than good when not having been done prior. The reason being that the pressure may force loose particles into various spaces in the tranny thus causing future issues. I do recommend an annual fluid replacement, so I'd start by dropping the pan and then a flush next year.

On the shifting from first to second, welcome to the club. I finally saw this on my 2006 at about 160K miles. I drove with it for several months then went in for a transmission rebuild. I would have upgraded to a 4L65e but am not putting more than 4K miles on the truck annually these days.  You might need a new transmission or a rebuild.

Take a look at this, it's pretty accurate.

https://www.transmissionrepaircostguide.com/what-is-a-transmission-flush/

Good link, yes I know about the 1-2 issue and mine s not really noticeable right now, so hoping for the best.....perhaps i shouldnt bother with the flush and save money for a rebuild at one point. I hate to have to put almost more money for the new transmission than what I bought it for.

If you don't know the mileage on the fluid I'd just drop the pan and change the filter.

If the fluid smells burnt you may have a problem.

As a hydraulic guy.... I would not flush if they use anything other than tranny fluid...

And if they flush they need to go the same direction normal fluid flows....

But I would not flush... as what are we trying to do?  If you have stuff inside the tranny you are trying to clean out the filter should have caught it... or it is suspended in the fluid and will come out when you change the fluid.

Yes lots of fluid remains inside the torq convertor and other passages inside tranny but once you crank her up and she starts pumping this old oil mixes with the new oil and the dirt is not as concentrated suspended in the oil and hopefully the new filter will catch it.

Most issues with tranny in my experience are not due to dirty oil etc but something mechanical

Broken gear, burnt clutch, solenoid valve issue....

so If you do not know history.... drop pan, change filter spray underside with brake cleaner to get as much stuff as you can see out.... button back up and re-fill.

Cylce tranny to refill passage ways...

Drive a bit...
Better?
Drive 10K or so and change again...

But that is me..... and I know what a microscopic piece of dirt can due to hydraulics.

PS Flushing OIL COOLERS is OK and a good thing as long as they are flushed separately...

Oil coolers are very dirty by nature since they have small passages that can hold dirt... so flushing those are good a thing.

Thanks for the responses, I know its been dealt with before on here and old subject.  Really good information and makes sense.....I guess because fixed my other truck 4l60 doesn't nessarly mean that it's a cure all.

I wouldn't do a flush.  Drop the pan, change the filter and the 1-2 and 2-3 solenoids.  The solenoids can easily be changed with the pan off, and you can get them for under $20 each online.  They are identical and interchangeable.  If you are still having issues you may have a slight tear in a servo o-ring and you may want to look into doing a servo upgrade, which will come with new O-rings.  Can do the servo upgrade without having to drop the pan.

Thanks got the solenoids ordered, it's worth a shot.  Seems like the transmission works normally otherwise.

FWIW I am ordering a fluid extractor to service a variety of things - including the Avalanche.  It allows you to extract fluid at home in the garage without making a mess.  They can be had for like $100.  Use that and avoid the whole flush.  Just get new fluid in there.

Fluid transfer pump less than 10 bucks

Yes I have a fluid extractor, mostly use for brake bleeding, however used it for other fluids. Does anyone know if it would it extract the oil from trans 100%, if I connected to one of oil cooling line and which line would you use or maybe just not recommended to do.

A fluid extractor like this one has a very small hardened plastic line that you push down the dipstick in to the drain pan.  It will suck the thing dry.  The only issue is a lot of fluid is not in the pan.  It is in the lines, the cooler, and the torque converter.  That's okay though... just do it twice if you are really concerned.



The only way to empty it completely is to do a flush (which is not recommended by most). Call me a skeptic but I doubt that fluid is the reason for your delayed shift.  However its good maintenance anyways, and you can at least eliminate that as a cause.

If you just disconnected a cooling line and ran it into a pail while the truck is running......  I think that would work but I have no idea what that would do to the pump or the torque converter.  A good question to ask someone who knows more than me.

I don't think running the vehicle dry transmisson would be a good idea even on idle.  We will see if the solenoid change out will help, it's my main focus right now.

Allot of people have reported problems after a trans flush at the dealer. A "Trans Flush"  at the dealer uses high pressure and some believe it dislodges dirt and grime damaging the trans.. That article explains it pretty good.

If you want to change your trans fluid 100 percent then find a shop or oil change only shop that uses a "Fluid Exchange" machine which only recovers the old fluid and puts in new at the same pressure, same direction. This is how I've changed the fluid in all the automatics I've had over the years and have never had a problem or heard of any problems doing this way.

You get almost 100 percent new fluid in the trans and torque converter which to me what is needed especially if you tow and/or the fluid is black or burned.. It cost around a hundred bucks, more if you bring your oil like I do (they usually don't give you a discount using your oil). Then after that's done drop the pan and change the filter, top it off and your go to go for the next ?00,000 miles.

By the way the manual says (on a 2002 anyway) 50,000 miles for fluid and filter, it also says you can go 100,000 if you don't tow, drive in city traffic over 90 deg., drive hilly or mountainous terrain or uses as found in taxi, police or delivery service.


My 2500 has 249,000 miles, I've changed the trans fluid and filter about every 50,000 miles and have not had any problems... Knock, Knock on wood..

But with that vacuum hand pump thingyyy....
you still need to drop the pan to change the filter...

No sense changing oil without changing the filter....