Am I imagining this? Or could there be a good reason?

[6716]

So the first transmission service was at 200K, flush, pan drop, filter.

Put in Dex VI.

Then I noticed -- definitely when cold -- that the shift from first to second was pretty hard.

So, then I had a problem, lost transmission fluid twice, but fixed the problem (the splice / patch on a cooler line).

At the moment, I have the ... whatever was the fluid before Dex VI, since it was all the gas station had on the shelf when I needed five quarts.

It seems like the shift is a lot smoother than with the Dex VI.

It also seems to run a little quieter, too.

Am I completely imagining this, or could there be a good reason?

 

[chief0299]

Being that it's the first service (flush AND filter) with 200,000 miles on the clock, I'm amazed that it hasn't started slipping!

 

[gmcman]

So the first transmission service was at 200K, flush, pan drop, filter.

That's a stretch...... I think you may experience some odd issues in the near future but hopefully nothing too drastic, basically it's a waiting game. With the fresh fluid introduced to old, untreated seals and bushings, there will be some re-softening of seals but not in any predictable order. Give the fluid time to keep working and you may need to change the fluid out sometime before 5-10K miles, just keep monitoring the color and condition of the fluid.

 

[The_Roadie]

I'm amazed that it hasn't started slipping!

I'm amazed it hasn't shuffled off this mortal coil in protest!

But then I don't know a thing about the ownership history...

 

[eutechnyx]

I personally would have never flushed it,just a filter change and refill whatever fluid was lost during that.

 

[Wooluf1952]

I did a pan drop, filter change, added a higher capacity pan (2 more quarts) and used seven quarts of the newer Dexron VI at 50k miles. The trans definitely shifted better IMHO. (Harder shifts, IIRC, cause less wear in the trans.)

 

[6716]

What a bunch of jokers!

Well, I'll tell you I'm going to stand by my impression that the transmission does better on the Dex III than the Dex VI. There's probably not going to be a good reason that I can find as to why it should be true, but there you have it.

I just did some reading on the difference between the two fluids .... they don't really seem to be super different.

Here's what one website said about the change from III to VI back in 2005:

GM introduced the Dexron-III(H) spec just two years ago, but decided it needed to upgrade again to accommodate the Hydra-Matic 6L80, its first six-speed automatic transmission. As far as the transmission fluid is concerned, the biggest change with the 6L80 is that it puts clutch interfaces in direct contact with each other, rather than using a buffer such as a freewheeler between them. Having direct contact improves the speed and efficiency of power handoffs between clutches, but it also requires greater precision to keep those interactions consistent.
LUBE REPORT: GM Rolls Out Dexron-VI

So for the 4L60 it might not even really matter.

Other than GM doesn't license Dex III any more, so where's the quality control might be the question, but there seems to be plenty of product out on the shelf.

 

[gmcman]

What a bunch of jokers!

Well, I'll tell you I'm going to stand by my impression that the transmission does better on the Dex III than the Dex VI.

So what do you have in now?

You said you went from Dex VI to Dex VI.

 

[6716]

So what do you have in now?

You said you went from Dex VI to Dex VI.

Here's what I think I hope I meant to convey.

The truck must have shipped with Dex III. I got it at 77K, from a non-GM dealer who bought it at auction as a lease return. So I don't know that there wasn't a transmission service, but my guess is there wasn't.

When I finally did what I imagine was the first service, I went with Dex VI. Seemed like the right thing to do, when I sought input here at the 'nation. When I did that service, I also chopped out a bad section of cooler line and did a poor job of patching it with fuel line.

Additionally, I noticed right away that the shift from first to second was pretty hard, especially when cold. And it seemed to make more noise.

Then my bad patch caused me to lose all the fluid (twice). I have ended up with Dex III in there now, because that's what was on the shelf at the gas station I barely made it into the second time my patch fell apart.

And now with Dex III back in there it shifts as smoothly as it used to from first to second, and there seems to be less noise.

Which seems strange if one has the perspective that Dex VI is "better". Perhaps it is merely different ... or the improvement that it delivers (I read that it is more fuel efficient, since with lower viscosity the transmission looses fewer hp in drag, which helps GM's CAFE stats) doesn't actually do squat for a 2005 Trailblazer getting serviced at 200K.

 

[gmcman]

The truck must have shipped with Dex III. I got it at 77K, from a non-GM dealer who bought it at auction as a lease return. So I don't know that there wasn't a transmission service, but my guess is there wasn't.

That's what I was thinking but wanted to be sure. Changing all the fluid at that interval could pose some issues and like I said it's a waiting game, but if you were not having issues before then I think it will be ok.

New fluid will release at of varnish and possibly caused the harsh shifts, now it's been somewhat flushed out again and could be the reason it's doing better.