Should I Flush Transmission? - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Transmission Mods Performance Transmission Modifications

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  #1  
Old 04-13-2019, 02:18 PM
Videot Videot is offline
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2002 Chevy TrailBlazer LT EXT
Pewter Metallic 4.2L I6 2WD
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Should I Flush Transmission?

Hello All,
This might be a stupid question, but I have a reason for asking it.

We have a 2002 Trailblazer with the I6 engine and 238K miles. It's been a while, perhaps over 100K miles, since we've had the transmission fluid changed. The fluid is a dull pink. I should add that we are not currently experiencing any shifting problems.

The obvious answer is Yes. And I'm sure that some might put several exclamation points behind that answer! However, I have read that you shouldn't change the transmission fluid if it is way overdue because the friction material that was once on disks in the clutch packs is in the old fluid. When the old fluid is removed, so is the friction material.

I poked around in the forum, and I didn't really see this particular topic addressed relevant to Trailblazers.

Is this a myth or is there something to this? Anybody here changed your fluid after it hadn't been done a while? What was your experience?

Here's a pic:

Thanks, Videot
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  #2  
Old 04-13-2019, 03:14 PM
06denaliman 06denaliman is offline
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2006 GMC TrailBlazer LS
Cranberry Red Metallic 5.3L V8 4X4
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Im in the same boat. Mine has 145k and i bought used and not sure if i should do it. My gathering show as long as you do not use a flush machine that forces it in you should be fine. What i plan on doing is using the diy way of undoing the transmission line and using the pump to pump out old fluid. Ive read that doesnt hurt anything because ur using the transmissions internal pump to push out old fluid and not a machine using bunch of pressure to do it.


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  #3  
Old 04-14-2019, 07:00 PM
John in RI's Avatar
John in RI John in RI is offline
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2005 BowTie TrailBlazer LT
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Quote:
is this a myth or is there something to this?
Honestly; 238K on a factory installed tranny is real good and the tranny will only last so long before it will require a rebuild. My first TB tranny (04) failed a 180K and the second TB I bought (05) had a dead tranny @ 165K.

Yes; There is something to it. Transmissions contain 'wear' parts and those parts leave pieces in the fluid when they break down over time. When those 'wear' parts are worn out,... the friction caused by all that crap in the fluid CAN help retain engagement of those worn-out 'wear' parts. The fluid in that pics looks pretty good for 100K old, I would have no problem using 06denaliman method to remove all the fluid when I replaced the filter.

IMO you should already be saving up for tranny work; so if you don't want to 'risk it' than just drop the pan and change the filter. (Again; that fluid looked pretty good so just a filter and fill-up is probably going to be all that's needed till it's time to replace/rebuild anyway.)

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  #4  
Old 04-15-2019, 05:00 AM
miketexas miketexas is offline
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2003 Chevy TrailBlazer LS
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Quote:
Originally Posted by Videot View Post
Hello All,
This might be a stupid question, but I have a reason for asking it.

We have a 2002 Trailblazer with the I6 engine and 238K miles. It's been a while, perhaps over 100K miles, since we've had the transmission fluid changed. The fluid is a dull pink. I should add that we are not currently experiencing any shifting problems.

The obvious answer is Yes. And I'm sure that some might put several exclamation points behind that answer! However, I have read that you shouldn't change the transmission fluid if it is way overdue because the friction material that was once on disks in the clutch packs is in the old fluid. When the old fluid is removed, so is the friction material.

I poked around in the forum, and I didn't really see this particular topic addressed relevant to Trailblazers.

Is this a myth or is there something to this? Anybody here changed your fluid after it hadn't been done a while? What was your experience?

Here's a pic:

Thanks, Videot
Changing the fluid or flushing it never gets all the old fluid out. The color looks good on the paper towel so flush it. The flush machine doesn't use high pressure to flush, they use whatever pressure the pump in the trans produces to do it.
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  #5  
Old 04-17-2019, 08:10 PM
Jekkals7 Jekkals7 is offline
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So a differing and agreeing opinion. I worked at a transmission shop as a diagstician and had this conversation time and time again. If it hasn’t been changed and is overdue with that amount of mileage, don’t do a Complete change. Varnish like coating and stuff builds up on the parts inside, the new fluid is so strong and has a lot of detergents that will strip away all that stuff and with it can be clutch material and the varnish. That stuff can get into the valve body and in between other moving parts and solenoids etc. Thus causing a problem that was not there before. Just my two cents.
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  #6  
Old 04-17-2019, 08:40 PM
miketexas miketexas is offline
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Originally Posted by Jekkals7 View Post
So a differing and agreeing opinion. I worked at a transmission shop as a diagstician and had this conversation time and time again. If it hasnít been changed and is overdue with that amount of mileage, donít do a Complete change. Varnish like coating and stuff builds up on the parts inside, the new fluid is so strong and has a lot of detergents that will strip away all that stuff and with it can be clutch material and the varnish. That stuff can get into the valve body and in between other moving parts and solenoids etc. Thus causing a problem that was not there before. Just my two cents.
Nonsense. The 60's and 70's are gone. You sound like you are practicing voodoo!
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  #7  
Old 04-17-2019, 09:22 PM
Videot Videot is offline
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2002 Chevy TrailBlazer LT EXT
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Quote:
Originally Posted by Jekkals7 View Post
So a differing and agreeing opinion. I worked at a transmission shop as a diagstician and had this conversation time and time again. If it hasnít been changed and is overdue with that amount of mileage, donít do a Complete change. Varnish like coating and stuff builds up on the parts inside, the new fluid is so strong and has a lot of detergents that will strip away all that stuff and with it can be clutch material and the varnish. That stuff can get into the valve body and in between other moving parts and solenoids etc. Thus causing a problem that was not there before. Just my two cents.
OP here: So it's sounding to me like you are recommending a basic drain and refill, which would get some, but not all out? Right?

Or are you saying to not do it at all?
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  #8  
Old 04-17-2019, 10:45 PM
dmtaurus dmtaurus is offline
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2006 Chevy TrailBlazer LS
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From what several ASE master mechanics, that talked about this very subject, have said, the oil itself does not wear out. It is the additive package that is in the oil that eventually breaks down and goes away. So what they recommend is not a flush to the transmission, as one said earlier, but rather a fluid drain by removing the pan and letting the fluid drain out so that the transmission doesn't get a chemical shock. With a full flush and refill after so many miles of use, there is a chance that the detergents in new fluid will quickly scrub clean any build-up on the valve pistons and passages and cause blockages to those same passages and, therefore, cause shifting problems. A drain and refill, in their words, performs a gentle cleaning to spool valves and passages. Based on that logic, I bought a Dorman replacement pan with the built-in drain plug that fits my short wheel base 2006 LS and installed a new filter when I put the Dorman pan on. Every 3 or 4 months all I do is remove the drain plug, let it drain into a graduated plastic bucket that I bought at Walmart, replace the plug, and just put in what showed on the drain bucket. It has worked out well.
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  #9  
Old 04-18-2019, 04:06 AM
samlab1 samlab1 is offline
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2002 Chevy TrailBlazer LT
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Yikes I'm actually an agreement with the gentleman above that used to work at a transmission shop sorry. He's actually correct. I change my transmission oil every 45000 miles and I've never had a problem. I perform a Bg flush and then add in the OEM gear fluid this gets all the carbon deposits out so it does not screw up the solenoid pack I've never had a problem with my transmission. Now watch it go kaput after I send this to the board hahaha. This part about losing clutch lubricant, sorry is weird as hell I have no idea what that got started. Basically what you're losing pouring it out is what you get pouring it back in.
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