Transmission Flush Opinions

[Beamie]

We're do for our (first) scheduled 100,000 mile transmission fluid change on our '08 4 speed automatic trans and our regular servicing shop says they have a machine the flushes the trans and replaced "all" 12 quarts of fluid. One of the remarks that throws me is hearing that the filter gets flushed.

I really don't know the details of the procedure as I didn't know what to ask.

I have read opinions on both sides of the fence but don't know the basis of the opinions, irregardless of which side of the fence they are on.

I would appreciate hearing from anyone with first hand experiences with that so I can make an informed decision.

[Sharpz]

I would suggest not getting a flush persay but do the slow drain method, using the cooler line.  This method does replace all the tranny fluid with new, and also doing this method the filter would be changed, not flushed.

 

 

Here is a write up/how to from one of the site members.   https://www.truckmodcentral.com/threads/how-to-flush-your-transmission-on-a-gmt800-gm-truck.4699/

 

[Beamie]

5 hours ago, Sharpz said:

I would suggest not getting a flush persay but do the slow drain method, using the cooler line.  This method does replace all the tranny fluid with new, and also doing this method the filter would be changed, not flushed.

 

 

Here is a write up/how to from one of the site members.   https://www.truckmodcentral.com/threads/how-to-flush-your-transmission-on-a-gmt800-gm-truck.4699/

 

 

If only I had a pan with a drain bolt. What was Chevy thinking eliminating the drain plug?

Does the fill tube go directly into the pan? If so, maybe the pan could be pumped out before dropping it.

Edited September 4, 2021 by Beamie

[Sharpz]

8 hours ago, Beamie said:

 

If only I had a pan with a drain bolt. What was Chevy thinking eliminating the drain plug?

Does the fill tube go directly into the pan? If so, maybe the pan could be pumped out before dropping it.

even with out the drain hole, you just unbolt the pan (evenly and slowly) if you do it right you can prevent a huge mess, but its not perfect.  You can also purchase a new pan relatively cheap (last I looked) with a drain screw.  

 

https://www.amazon.com/Transmission-Chevrolet-Silverado-Suburban-Workhorse/dp/B07GJF6WYN/ref=sr_1_2?_encoding=UTF8&dchild=1&qid=1630754314&s=automotive&sr=1-2&vehicle=2004-48-548-296-29-77-6-8-7910--9--145--2&vehicleName=2004+GMC+Sierra+1500

 

you will have to verify that you have the 4l80e trans.  Gasket and filter sold separately.  There are also plenty of you tube videos on "how to"  if you didnt find what you needed in the video I suggested to you.

[Beamie]

1 hour ago, Sharpz said:

even with out the drain hole, you just unbolt the pan (evenly and slowly) if you do it right you can prevent a huge mess, but its not perfect.  You can also purchase a new pan relatively cheap (last I looked) with a drain screw.  

 

https://www.amazon.com/Transmission-Chevrolet-Silverado-Suburban-Workhorse/dp/B07GJF6WYN/ref=sr_1_2?_encoding=UTF8&dchild=1&qid=1630754314&s=automotive&sr=1-2&vehicle=2004-48-548-296-29-77-6-8-7910--9--145--2&vehicleName=2004+GMC+Sierra+1500

 

you will have to verify that you have the 4l80e trans.  Gasket and filter sold separately.  There are also plenty of you tube videos on "how to"  if you didnt find what you needed in the video I suggested to you.

Thanks. That pan may not be compatible as my pan is stepped but maybe there is something else in the alternates list there..

I've seen the videos and that's what makes me think twice about the potential mess removing the full pan. No lift here so it would be in close quarters, on the back, in the driveway for the pan removal and I don't want an oil spill. The exhaust crossover will run interference making the "careful" removal all that much more iffy. If the pan were mostly empty it would make the removal procedure less of a potential problem.

 

[Jworks]

I had the same question a while back.  I have '11 GMC Sierra 4x4 with 134k miles I bought used from a dealer 18 mos ago.  I felt the dealership might have changed the fluid when I bought because it was bright red.  Even though the fluid was stil a good color at 129k it was slightly less red than when I bought it.  So,,,, do I flush, or just change fluid?  The dealership and two trans shops said don't change it at all...leave it alone.... because a change not done at 100k miles like the manual says do I might get a trans failure.  But, knowing shops "might" have a built in bias, and after getting opinions from others on here (and mostly from Ray Voy) I decided to do the change, not flush.  I knew I was running a risk (at least according to shop and dealership advice), but I did it.  After 4k miles after the change I have No problems.  However, in your case, you are right on 100k miles.  So....in your case....I would go with whatever the owner manual says. If says flush, I'd flush.  If it says change, I'd change.  I'd go with the owner manual.  In my case, though I was well over the 100k mark by 29k miles. 

[diyer2]

Beamie,

I used this to remove as much fluid as I could before trans pan removal. Worked great.

https://www.amazon.com/gp/product/B0002AJR8E/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

 

 

[Beamie]

5 hours ago, Jworks said:

I had the same question a while back.  I have '11 GMC Sierra 4x4 with 134k miles I bought used from a dealer 18 mos ago.  I felt the dealership might have changed the fluid when I bought because it was bright red.  Even though the fluid was stil a good color at 129k it was slightly less red than when I bought it.  So,,,, do I flush, or just change fluid?  The dealership and two trans shops said don't change it at all...leave it alone.... because a change not done at 100k miles like the manual says do I might get a trans failure.  But, knowing shops "might" have a built in bias, and after getting opinions from others on here (and mostly from Ray Voy) I decided to do the change, not flush.  I knew I was running a risk (at least according to shop and dealership advice), but I did it.  After 4k miles after the change I have No problems.  However, in your case, you are right on 100k miles.  So....in your case....I would go with whatever the owner manual says. If says flush, I'd flush.  If it says change, I'd change.  I'd go with the owner manual.  In my case, though I was well over the 100k mark by 29k miles. 

Thanks for that.

As far as I can see the manual just has a table with a dot in the "change fluid and filter" without getting into the details.

 

For yours, were they implying that merely swapping out 5 or so quarts of new for old fluid was a risk?

I don't understand how dropping the pan, draining and cleaning the pan is anything but good. 

 

Edited September 4, 2021 by Beamie

[Beamie]

5 hours ago, diyer2 said:

Beamie,

I used this to remove as much fluid as I could before trans pan removal. Worked great.

https://www.amazon.com/gp/product/B0002AJR8E/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

 

 

Thanks for that idea. It got quite a lot of negative feedback. Is yours an older generation perhaps?

[Black02Silverado]

At that mileage, I would change the filter out. 

 

That being said,  the procedure at the dealer doesn't do anything but a fluid exchange.  They hook up a tank with two bladders.  One on top of the other.  They fill the bottom bladder with new fluid, hook up to the cooler lines and start the vehicle.  As the vehicle runs it puts the old fluid into the top bladder which pushes down on the bottom bladder and pushes the new fluid into the system.  They use more than what the total capacity of the transmission uses so that they get a complete exchange of fluid.

 

The transmission does all the work.  No force or anything like that.  When they are done and the bottom bladder is empty, they disconnect everything and hook back up to the vehicle and then top off as needed.

 

If you did this and didn't change the filter then you have a dirty filter.  The new fluid doesn't do anything to it.  That is why it is better to change out the filter and then do the fluid exchange.

 

I had the dealer do my 2002 Silverado at around 10k miles from new and installed AMSOIL. I then dropped the pan and changed out the filter at around 70k miles.  Here is my write-up on it.

 

I have done the same thing now on our 2016 suburban.

 

I've changed out several GM truck transmission with over 100k miles with no issues.

[Beamie]

2 hours ago, Black02Silverado said:

At that mileage, I would change the filter out. 

 

That being said,  the procedure at the dealer doesn't do anything but a fluid exchange.  They hook up a tank with two bladders.  One on top of the other.  They fill the bottom bladder with new fluid, hook up to the cooler lines and start the vehicle.  As the vehicle runs it puts the old fluid into the top bladder which pushes down on the bottom bladder and pushes the new fluid into the system.  They use more than what the total capacity of the transmission uses so that they get a complete exchange of fluid.

 

The transmission does all the work.  No force or anything like that.  When they are done and the bottom bladder is empty, they disconnect everything and hook back up to the vehicle and then top off as needed.

 

If you did this and didn't change the filter then you have a dirty filter.  The new fluid doesn't do anything to it.  That is why it is better to change out the filter and then do the fluid exchange.

 

I had the dealer do my 2002 Silverado at around 10k miles from new and installed AMSOIL. I then dropped the pan and changed out the filter at around 70k miles.  Here is my write-up on it.

 

I have done the same thing now on our 2016 suburban.

 

I've changed out several GM truck transmission with over 100k miles with no issues.

 

The shop claims they "flush" the filter and that caused concern. Sitting on the fence but thinking I won't have them do it, just in case. Maybe I'll try to reduce the fluid in the pan through the dipstick tube and a vacuum pump and then try to drop the pan and access the filter. The crossover pipe is a potential hurdle.

Is there any harm to be done with a conventional pan drop/filter change with just changing the pan fluid?

I recall a former Tahoe with that done and tranny burning smell a short while later.

Edited September 4, 2021 by Beamie

[Black02Silverado]

 

 

The shop claims they "flush" the filter and that caused concern. Sitting on the fence but thinking I won't have them do it, just in case. Maybe I'll try to reduce the fluid in the pan through the dipstick tube and a vacuum pump and then try to drop the pan and access the filter. The crossover pipe is a potential hurdle.

Is there any harm to be done with a conventional pan drop/filter change with just changing the pan fluid?

I recall a former Tahoe with that done and tranny burning smell a short while later.

I don't know their procedure, but to me you don't want to "flush" the filter and have all that debris flowing through your transmission.   Dropping the pan with the cross over exhaust pipe can be a challenge.  Some can get the pan off some can't.  I had to drop my exhaust down some to get mine off.  Nothing else that I could do,  ie jack up the transmission tail shaft after loosening the cross-member bolts and pull down on the exhaust didn't work for me.  After that mess I put a drain plug in my transmission pan.

[Beamie]

1 hour ago, Black02Silverado said:

I don't know their procedure, but to me you don't want to "flush" the filter and have all that debris flowing through your transmission.   Dropping the pan with the cross over exhaust pipe can be a challenge.  Some can get the pan off some can't.  I had to drop my exhaust down some to get mine off.  Nothing else that I could do,  ie jack up the transmission tail shaft after loosening the cross-member bolts and pull down on the exhaust didn't work for me.  After that mess I put a drain plug in my transmission pan.

 

Searching for more clarity, would the transmissions be circulating all the debris all the time when they run?

[Beamie]

Would GM have been using synthetic fluid in 2008?

[Black02Silverado]

 

 

Searching for more clarity, would the transmissions be circulating all the debris all the time when they run?

No, that is why there is a filter.  But if they are saying they flush the filter then that makes me believe that it pushed what the filter caught out into the fluid and you don't want that.  Drop the pan, remove the filter that is dirty, replace with new and go from there.

 

Dexron VI has been out since 2006 so it is a better fluid then the old dexron III but GM's isn't a full synthetic