to Flush or not to Flush -- that's the question

[cam7002]

Hi, gang. So I am preparing to drop the tranny pans on my M1009s to change the fluid and the filters when a buddy and I start gabbing about "flushing" the tranny. The merits of flushing are, supposedly, that it removes "ALL" the fluid from the tranny, torque converter, transfer case, etcetera, to be replaced with virgin fluid. And so then the question is whether virginity is such a good thing since some say "yeah, that's the best", and others say, "nah, man, you don't want virgin fluid and all clean inside. You want some old residue left on the innards of that tranny."

My WORD! If you never had a virgin transmission except maybe the one new car you had in your lifetime, and all the other trannies have already had a range of fluids flow through them, you really don't know what the truth is.

So, seriously now, do I want to flush it out and put virgin fluid in it? Or do I just want to drain it, change the filter, not flush, and then close it back up and go? Your thoughts, experience and wisdom are appreciated.

 

[Hammer]

How bad is the oil?
And how much stuff is in it?
If the oil is fine, and there is very little gunk in it, then a flush would be fine.
If there is either bad oil, or lots of junk, a flush runs the risk of dislodging something else and blocking something very important inside one of the circuits, etc.

Quick/simple flush?
drop pan, clean, put new filter on, replace pan, fill with fluid.
Remove return line (where is attaches to the tranny) that goes to the trans cooler in the radiator. Put large bucket under this line, fire it up!
Put in neutral, and run AT IDLE until it runs out (usually pretty fast).
Re-attach the line, refill with new fluid, and have fun.

Find someone with a multifuel and give them some free fuel/atf (or use it for your own if you do that).

 

[AJMBLAZER]

If the fluid in your transmission has been changed recently (say 50k miles) and/or is red(-dish) then a pan drop and filter change should be fine. That's all I do.

Now if the fluid is a brownish color or just something not red and it's been 100,000+ miles since the last change then just leave it. The transmission is on borrowed time and the goo inside of it is probably what's holding it together.

I try to do a pan drop and fluid change with quality ATF fluid in all my vehicles every 50k or several years at the max.

Consider putting a drain plug in the stock pan or just buying a bigger pan with a drain plug already in t. Makes fluid changes SO much easier it's silly. Pull the plug, the fluid drains out, take the pan off, no splash of fluid all over the place, and keep going from there.

 

[JohnnyReb]

As AJMBLAZER said, changing the fluid could cause the tranny to start slipping. I have done it on several older trans (C6, C4) and had to do a ring (clutch) job on each of them soon after.

 

[wallew]

Mileage is definitely something to consider. But so many of the M1009's never went ANYWHERE and just sat. And sat. And sat. If they got lucky, some National Guard unit used them one weekend a month. If not, there they sat.

So, how OLD is your M1009? When was the last time the high pressure hoses were changed (into the radiator)?

Same holds true for your power steering pump. Aside from providing easy steering, it also provides easy stopping as well. All from that one power steering pump. When it's been twenty plus years for high pressure hoses that cannot be told when they were last changed? Perhaps it's time to change the hoses as well.

Just something to think about...

 

[HeadWizard]

Mileage is definitely something to consider. But so many of the M1009's never went ANYWHERE and just sat. And sat. And sat. If they got lucky, some National Guard unit used them one weekend a month. If not, there they sat.

So, how OLD is your M1009? When was the last time the high pressure hoses were changed (into the radiator)?

So, I own an auto repair shop and this question comes up often. How many miles are on the M1009 now? What is the fluid condition? Red & sweet smelling? Brown and burnt smelling? Black?

We flush hundreds of transmissions per year and I can't remember the last time one shifted worse after the flush that before. BUT, let me qualify that. If the vehicle has never had it's fluid changed and is black, we won't flush it or pan drop it.

ATF has a very high detergency factor and cleans things very well. Try and wash your dirty hands with ATF - it works well. If you pan drop a trans with black fluid, the new fluid will clean out all the gunk that's in the trans just like a flush.

If you do flush it, make sure to use a solvent pre-cleaner (such as BG) before you have the flush done. It cleans all the crud off the parts so they can be flushed out.

My

 

[tsmall07]

Whenever I've dropped the pan, changed the filter, and replaced the fluid I haven't had trouble. Every time I've heard someone got they're trans "flushed" at a shop has had it start slipping afterward.

 

[AJMBLAZER]

Depends how they do it.

A reputable shop flushes everything AND changes the filter so the system is totally clean. A BS shop just flushes the trans on a machine which often knocks a lot of stuff out of the filter and back into the trans. Some don't even do complete flushes.

 

[cam7002]

This is such an interesting subject, and I am glad so many people are responding.

As best I can tell, one has about 87k miles and the other about 99k miles. The fluid in both smells ok, and it is pink -- with some grimy black on the dipstick.

 

[cam7002]

I should also mention that someone else recommended the drain plug. I had queried about a reluctant transmission (not a slipping transmission), and it was recommended that I swap out the filter and fluid first and, while I am at it, put the plug in. Feller said that the HMWVVV pan works and has a plug. I thought I could just put a plug in myself by drilling and then adding the male and female ends with rubber gaskets on either end.

So someone tell me if there is a cheaper way to do this or if I am being just plain dumb to waste my time hunting down the male/female parts, drilling, installing when I could just do "x".

 

[maybefixit]

I've always been wary of the transmission flush services, partly out of concern that the machine might have too much of another transmission's type fluid left in it. There are some newer transmissions (Chryslers especially) that are Really sensitive to the fluid type and viscosity. Over at www.allpar.com they have several pages about making sure the transmission fluid is the factory type (yeah, nothing to do with MV's).

There's a lot of truth to the detergent factors - in aviation, if a engine has been using only mineral oil its whole life, you don't want to change it over to detergent oil. Similar bad things can happen (except for the initial break-in service). I wonder if some of the transmission slipping issues might be due to the newer fluid being a different formula than the older fluids (modern Dexron IV versus original Dexron III, for instance - even though they're supposed to be interchangeable).

Cam7002: was it your earlier thread where someone said they noted a 'glaze' forming on the filter assembly? I was glad to hear about that, might save me a rebuild someday in the future. Obviously a plugged filter would be a problem.

Personally, I'd like to have a drain plug on the trans, but I've had good luck in the past just loosening the bolts in a triangle fashion - starting at the lowest corner, and loosening bolts most of the way there, less so toward the opposite corner. All the bolts need loosened, but by 'working' them down, I have been able to keep the splashing to a minimum.

 

[stampy]

Have you checked your vaccumn lines going to the modulator? Mine were damaged causing late shift on the trans. This means you have unusally high rpm's before the trans shifts.

 

[HeadWizard]

Depends how they do it.

A reputable shop flushes everything AND changes the filter so the system is totally clean. A BS shop just flushes the trans on a machine which often knocks a lot of stuff out of the filter and back into the trans. Some don't even do complete flushes.

Agreed on the reputable shop thing.

As to the knocking stuff out of the filter, that would only happen if the shop were to REVERSE flush the fluid, and I don't know how that could be done?

Good transmission flush machines will empty all the fluid you put into them - meaning that if you must use different fluids for different transmissions the vehicle gets the right fluid each time.

Proper way to flush:
1- Pour solvent based transmission cleaner into the transmission.
2- Drive the vehicle 15-30 minutes to clean hard parts and put "dirt" into suspension in the fluid.
3- Immediately flush the old fluid out of the transmission with the vehicle running via the pressure line to the transmission cooler, while replacing the old fluid with new fluid from the flush machine through the transmission cooler and into the transmission. Make sure to shift the transmission through all gears while this happens.
4- Flush at least 25% more fluid through the transmission than the actual capacity to ensure as much of a 100% exchange as possible.

I've heard all the stories of transmissions not shifting correctly after a flush. If that's the case, the flush certainly did not cause the problem, the flush merely exposed a transmission that was crap to begin with.

I really do consider myself somewhat of an expert on the matter with the years of experience owning a shop and flushing transmissions - probably in excess of 5000. I also work with ASE writing standards for auto technicians and job tasks.

Everyone has different experiences and opinions and I respect them all.

 

[randyscycle]

One issue that was sort of brought up in a couple of the posts was about the high-detergent factor of new ATF.

When a very high mileage, and probably near-death transmission has never been serviced, a lot of old clutch friction material and thrust bearing material is suspended in the fluid and carried all around to settle in corners of the transmission case, and behind seals and inside the valve body. When you flush the transmission, then add new fluid, the detergent can wash loose this material and do a couple of things:

First, it can carry this loose material around in the valve body and deposit it in a critical spool valve rendering it inoperative.

Second, it can wash the goo out from behind lip seals designed to hold pressure inside clutch application pistons which can then leak and not firmly apply clutches, making a sloppy or slipping engagement of the clutch pack.

Like HeadWizard stated, I doubt that a working transmission would be hurt by flushing it, but if it is questionable in the first place it will most likely drive the final nail in the coffin for your transmission.

In my experience in the automotive world (20 years) I found that a transmission flush is a lot like a tune-up. The only time anyone ever asked for one is when they had a problem, didn't tell you, and they figured it was a cheap fix.

 

[AJMBLAZER]

I should also mention that someone else recommended the drain plug. I had queried about a reluctant transmission (not a slipping transmission), and it was recommended that I swap out the filter and fluid first and, while I am at it, put the plug in. Feller said that the HMWVVV pan works and has a plug. I thought I could just put a plug in myself by drilling and then adding the male and female ends with rubber gaskets on either end.

So someone tell me if there is a cheaper way to do this or if I am being just plain dumb to waste my time hunting down the male/female parts, drilling, installing when I could just do "x".

I looked for a HMMWV TH400 pan for a good long time before giving up. If you find more than one let me know please. Couldn't find them anywhere.

www.summitracing.com has drain plug kits. It's been a few years but the last one I bought was under $10. I want to say $8 and with shipping it was under $20. Locally the only places that had them wanted $20 + tax.
They also have deep and standard TH400 pans with drain plugs.