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Discussion Starter · #1 ·
Hi all,

I'm going through my new to me 08 Envoy with 160,000 miles on it.

Recently I dropped the transmission pan, cleaned it up, and replaced the filter. The old fluid didn't seem especially bad. it was red, maybe a little dark red. Certainly not brown or black.

I didn't think anything was wrong with my transmission when I bought the car, but I noticed a huge improvement after doing that service.

Before dropping the pan, if I was sitting in traffic in Drive the car didn't pull forward at all. I had to give it some gas before there was any forward movement. Now it wants to pull forward while in Drive at idle, and it accelerates with much more authority when I give it some gas.

So, I have 2 questions. First, what would cause the change ? I'm assuming that the old filter was so clogged that there wasn't enough pressure (or maybe flow) for the torque converter to work at full efficiency, but that is just a guess.

Second, things seem to be working perfectly now, but in light of what happened, should I be doing more maintenance to prevent future problems ? Should I drop the pan again and replace the filter again assuming that the new filter might be clogging with old crud that the old filter was too full to trap ?

I've seen some YouTubes where people flush the tranny by pulling the cooler hose. I could do that, but it looks like a real mess, and I don't have a helper readily available. But, I could do it if really necessary.

Thanks for any advice !!
 

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Never flush.
Never flush.
Never flush. (3 times for emphasis.)

You did it right - and that's what GM wants you to do - on a regular schedule.

It reenergizes the aromatics so they keep seals supple and the various additives can work their chemical magic.

IF the filter were to somehow clog - it's not the convertor charging that you need to worry about.

The filter is only going to find things in the pan and if the pan was clean-ish, the filter should be too. If you REALLY had a clogged filter, you'd be buying a rebuild - so thinking that way is pandering to old wives' tales.

Don't be an old wife.
 

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Discussion Starter · #3 ·
Thanks. I think I'll drive it as is (which seems perfect) and maybe drop the pan and change the filter next summer.
 

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Discussion Starter · #5 ·
Hmm, that in now !! I have a oil extractor pump, I may suck out the pan oil through the dipstick since I only dropped the pan 3 months ago.

Sound reasonable ?
 

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That's a good plan - but you only get to do this once! Next time, you drop it --- hear?
 

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2004 chevy trailblazer_lt
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Mr. Peabody, listen to our resident transmission expert, Ravalli Surfer. He is a great asset to this forum. He is the one I go to when I have transmission questions.

Pan drops are good. I installed an aftermarket transmission oil pan a few years back to make fluid and fluid & filter changes much easier. I'll drain several quarts out of the transmission ever year or so, replenish with fresh Dexron VI fluid (I do not use universal AT fluids that are good for "all makes and models") and then after the third draining of the fluid, I remove the pan (less messy) install a new filter, put the pan back on, add fresh Dexron VI and then start the cycle again.

OK on having an oil extraction pump. Almost as good as a pan draining in my book.

Good Luck and thanks to Ravalli for jumping in!
 

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When it's me, I drop the cooler tube so it squirts into a drain pan, run the engine just long enough to nearly-empty the pan. That way there's no spillage when I remove the pan to change the filter, and I don't have to cry about the trans pan not having a drain plug. Once the new filter and cleaned pan are back in place, I add 5-ish quarts of fluid, open eight or ten more quarts, start the engine and start dumping fluid down the dipstick tube. When the fluid squirting out of the cooler tube looks virgin-fresh I stop the engine, connect the cooler tube, restart the engine, and adjust fluid level as needed. I change (almost) all the fluid, not just what's in the pan.

It's helpful to have someone to start and stop the engine, but since I don't, I do the job alone.

I have no idea why folks are allergic to a properly-done fluid flush. Who changes half the engine oil and pretends to have done a proper service?
 

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When it's me, I drop the cooler tube so it squirts into a drain pan, run the engine just long enough to nearly-empty the pan. That way there's no spillage when I remove the pan to change the filter, and I don't have to cry about the trans pan not having a drain plug. Once the new filter and cleaned pan are back in place, I add 5-ish quarts of fluid, open eight or ten more quarts, start the engine and start dumping fluid down the dipstick tube. When the fluid squirting out of the cooler tube looks virgin-fresh I stop the engine, connect the cooler tube, restart the engine, and adjust fluid level as needed. I change (almost) all the fluid, not just what's in the pan.

It's helpful to have someone to start and stop the engine, but since I don't, I do the job alone.

I have no idea why folks are allergic to a properly-done fluid flush. Who changes half the engine oil and pretends to have done a proper service?
......... because that's a tried and true way to do it.

Flushes are not inherently dangerous, but if there's a "something" that's lurking in a passageway and you are slugging it loose with a change like you suggest ---well ----

I've seen vehicles not able to drive out of shops that perform this "valuable" service.
 

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If there's "something" lurking in a passageway, the trans is already wounded. Then there's no "safe" amount of fresh fluid, one quart is "safer" then five quarts, which is safer than ten quarts, which is safer than fifteen quarts...but even one quart presents a certain amount of risk...IF (big IF) you're of the impression that clean trans fluid is somehow more dangerous than worn-out, depleted trans fluid.

I'll pass on that, thanks. I'll take the clean, fresh fluid, please.
 
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I've rebuilt a few transmissions in my lifetime, starting with a 4 speed Hydramatic in '63.
Do yourself a favor, drop the pan and change the filter.
As far as flushes, never have it done at a "shop" or do it at home.

As far as a "flush" you have no idea of how a trans is built or works if you think you are changing all the fluid.
You are not changing the fluid in the clutch packs, torque converter or valve body.
A "flush" doesn't do it either
The average trans has a total capacity of about 12 qts. (700R4 -4L60e)
A pan drop/refill takes about 5-6 qts. the remaining fluid is in the torque converter, valve body and clutch drums/ packs and internal passages and remains unchanged.
Dropping the pan gives you a real indication of the trans condition, just like a blood sample does from a human body.
After a drain/filter and refill, drive for a few months or so, and then either drain/refill again (if you installed a drain plug pan) or suck it out and refill.
That way you are getting as best as can be "oil change" without removing the trans and rebuilding it.
 

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As I described my procedure, of course I'm changing the fluid in the torque converter.

You're right about the clutch packs and most of the valve body, along with whatever's loitering in the lubrication, governor and accumulator circuits. Likely one quart, MAYBE two--but I don't think there's that much of the old fluid left inside.

It's enormously better than just a pan drop. And nowhere near as inefficient as multi-stage drain/fill/drive/drain/fill/drive
 

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Obviously you have no clue as to the lubrication system in the transmission or you would not say "your changing the fluid in the torque converter" ---- Governor? are you talking a 4l60e?
Some vehicles, older thunderbirds comes to mind, did have a drain plug in the torque converter.
But you proceed as you wish, sorry I tried to be helpful.
I do wish you luck.
 

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As I described my procedure, of course I'm changing the fluid in the torque converter.

You're right about the clutch packs and most of the valve body, along with whatever's loitering in the lubrication, governor and accumulator circuits. Likely one quart, MAYBE two--but I don't think there's that much of the old fluid left inside.

It's enormously better than just a pan drop. And nowhere near as inefficient as multi-stage drain/fill/drive/drain/fill/drive
I'll give you 50% because there's so little captive fluid in the clutch packs and valve body as to be minimal so you're right there.

The convertor, though, is not going to hold on to the debris in its periphery so easily.

The convertor acts as a huge psychrometer in that it captures a lot of debris in the periphery and that's something you don't want to have let go and begin hitch-hiking on the new fluid.

Don't start kicking - I've truly seen units not make it to the end of the parking lot after coming out of the service bay after a flush.

It's also a known that there have been some occasional machining matter (chips) hung up in a passageway from time to time and I've taken what looked like mechanic's fingernail clipping out of more than one governor - so, yes - they do exist.
 

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Obviously you have no clue as to the lubrication system in the transmission or you would not say "your changing the fluid in the torque converter" ---- Governor? are you talking a 4l60e?
Some vehicles, older thunderbirds comes to mind, did have a drain plug in the torque converter.
But you proceed as you wish, sorry I tried to be helpful.
I do wish you luck.
You got it right, George. Many C3, C4, FMX and Green Dot Cruise-o's had 1/4" NPT plugs in the convertor to drain them --- but they totally needed it since on most of those units they used Madagascar cork for the friction material.
 

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Obviously you have no clue as to the lubrication system in the transmission or you would not say "your changing the fluid in the torque converter" ---- Governor? are you talking a 4l60e?
Some vehicles, older thunderbirds comes to mind, did have a drain plug in the torque converter.
But you proceed as you wish, sorry I tried to be helpful.
I do wish you luck.
When it's me, I drop the cooler tube so it squirts into a drain pan, run the engine just long enough to nearly-empty the pan. That way there's no spillage when I remove the pan to change the filter, and I don't have to cry about the trans pan not having a drain plug. Once the new filter and cleaned pan are back in place, I add 5-ish quarts of fluid, open eight or ten more quarts, start the engine and start dumping fluid down the dipstick tube. When the fluid squirting out of the cooler tube looks virgin-fresh I stop the engine, connect the cooler tube, restart the engine, and adjust fluid level as needed. I change (almost) all the fluid, not just what's in the pan.
As I described my procedure, of course I'm changing the fluid in the torque converter.
I guess I'm just stupid.

The converter fluid outlet is the fluid going to the cooler--because the converter is the biggest single heat source in the transmission until the lockup clutch engages. The trans pump picks up fluid in the pan, sucks it through a filter, and pressurizes the entire system based on manual valve position (Park or Neutral) and zero road speed. Which would include pumping fluid into the torque converter, and then on to the cooler.

If I drop the pan, change the filter, and put five fresh quarts in the pan, run the engine, and let the cooler tube spray into a bucket while I add another eight or ten quarts...How am I NOT changing the fluid in the converter? I'm clearly pumping fresh fluid into it; and you can't argue with the bucket of old, discolored fluid that's no longer in the transmission.

You need to explain--in GREAT DETAIL how I'm not changing the fluid in the torque converter; 'cause I can't figure it out.
 

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Do you mean "centrifuge"? I'm reasonably certain you're not using the torque converter to measure humidity.
I was after the theatrics - unlike you ... and there's a joke there, since it's all relative! Get it?

Pardon me - but results is still results.

I've seen (that's a past-tense verb) vehicles not be able to get to the driveway apron after a flush unless it was all downhill.

I have never - ever performed a flush and every one of my services drove away, happy that they didn't get roped into a transmission overhaul because of a jerk service manager looking for his monthly bonus.

It's a bogus process designed to grab all the dollars a shop can generate for a service that's at best, questionable, non-ethical and also non-indicated by every manufacturer --------->TTBOMK.
 
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