Geoff said:
Well, Bill, I'm finally going to argue about this one. I've seen this
solution bandied about here and there for some time now, and as a
recommendation to a newbie tech, I think it's really fraught with the
possibility for disaster. My recommendation would be: a standard pan drop,
filter change and refill ought to be good enough. If you're concerned about
a mess when dropping the pan, pump as much of the old fluid out as possible
through the dipstick tube.
I think my main concern with this flush idea is the possibility that the
trans will pump itself dry. I realize that you make the point to 'add fresh
makeup fluid' as necessary, but I know from experience in trying new things
like this, that the process often becomes much more chaotic than originally
planned. I don't know about yourself, but to me, the idea that the trans
pump would run dry is a little scary. Perhaps my concern is needless? Or
is there the chance that the pump will suck air for awhile, and cause all
sorts of resulting bad secondary effects? Has anyone considered this? I'd
like to know.
My second concern with this is that it wastes fluid! This ATF+4 stuff is
expensive, and even though you might make the claim that the net cost is
lower than replacing/rebuilding the transmission, I question how much more
effective this method is than just dropping the pan and replacing what fluid
comes out at regular intervals. Pissing away expensive fluid for a
maintenance process seems like overkill to me, not to mention a waste of
resources. Certainly there will be some older fluid still in the
transmission if you forego the flush, but if you're maintaining a regular
maintenance interval, how much does it really matter? I think little. If
there's a study that indicates that the benefits of throwing away good fluid
in a flush are really high, I'd like to see it.
Thirdly, I think that this is a potentially dangerous process. Engaging a
vehicle's transmission with the engine running while it's being worked on is
inherently dangerous. Not to mention that typically it will be supported on
jack stands during the process; I'm always particularly concerned about
entering a vehicle that's supported on jack stands, as would be necessary to
operate the shift lever. It seems to me that you're creating an additional
opportunity to knock the thing off the stands; perhaps not a real easy thing
to do, but to be honest, claustrophobic as I sometimes get when lying under
a vehicle, I don't like taking chances.
So I'm interested in seeing a debate on this topic. I'll freely admit that
I'm going to be tough to convince that this flush idea is a good one, but
I'll try to keep an open mind. Whatcha got?
I appreciate an honest debate.
I can't back up anything that I said with anything other than gut feel
and a little (more than none, less than a lot) experience in doing the
procedure I described.
You are right - for me, it did initially become more chaotic than I had
anticipated. However, within less than a minute of starting it, my
over-optimism became obvious, and I stopped and had my wife come out to
assist. She sat in the driver's seat to periodically start the engine,
move the shifter, stop the engine, etc. at my command. With a helper it
was very manageable. It will be easy going the next time I do it. I
even spliced the line for easy disconnect and re-connect for future
flushes.
Once I got my bearings, it was very simple to periodically check the
fluid - it wasn't like it was going to empty iteslf out in a minute or
less - there was a comforable amount of time to check fluid during the
process, and when it started getting low, stop the engine and add more
fluid, then proceed. Never came close to sucking air.
Re: the wasted fluid, my reasoning is this: If one believes that the
fluid deteriorates at a certain rate (due to temperature and shearing),
then over the life of the vehicle, one would need to put (approximately)
the same amount of fresh fluid thru the vehicle whether in a
partial-change fashion, or thru sudden 100% changes - the former being
closer to your one pan-full at a time, the latter being closer to my
90+% transfusion at a time. Since any time any procedure is done, there
is a certain fixed amount of overhead involved (in getting tools, out,
cleaning up, etc.), I figure I will do my 90+% procedure less often than
you would have to do your less-than-50% change to get the same benefits
(in tranny life and performance), and due to the "overhead effect", will
save time overall. But yes - I probably do waste more fluid. But for
less total money than if I paid a shop to do it, I get a *lot* more
fluid to do with what I want, and get the benefit of a more thorough
change.
As far as the danger, I would not be under the vehicle during any of
this - I make the rubber hose long enough to do it all standing up
(except for the initial hookup).
That's it for me. We each look at the facts at hand and make our
decisions, and get the results good or bad. I am not saying your
philosophy is wrong. I'm just saying what feels right for me as one who
is arguably an obsessive-compulsive (as in "Hmmm - in the above post,
did I spell "shearing" right? Is it "procede" and "preceed", or is it
"proceed" and "precede", but I know it's "procedure"), but getting less
so as I get older.
Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")
