Home Transmission Flush?

I am in the process of switching my fluids to synthetics in my m1008. Is it possible to drop the pan, replace the filter, gasket, and fluid (through the dipstick). Then disconnect the fluid return line from the transmission cooler in the radiator, connect some sort of short hose where the return line was and run it into a bucket. Then start the truck and replace the fluid through the dipstick until clean fluid is being pumped into the bucket. Finishing up by reconnecting the return line and topping the fluid level off? Just a thought. Id like to have all synthetic fluid rather than a mix. Thanks.

Flushing transmissions is,what kills them just drain it the best you can and then put in the fluid you want.

Okay I'll bite how does flushing a transmission out kill it?

I've done the method you mention, drawing in fresh fluid from a container, then having other line hooked to catch bucket. But I wouldn't recommend switching to syn-fluid on a transmission that has already been run/broken in with regular fluid.

Transmissions weren't designed to be 'flushed', as the service that the quick oil change places offer. Ever. Drain the fluid, drop the pan, change the filter. Add fresh transmission fluid. Check fluid level per instructions in manual.

Drive & enjoy it.

The problem with 'flushing' a trans is that many companies make 'flush' kits and chemicals, or you can have it done at a shop, but the chemicals used often swell/kill seals, or damage the paper/fiber clutch plates. And don't Mickey Mouse with draining the fluid through the dipstick.

Follow procedures & fluid specs in TM. Keep with traditional non-synthetic fluid in the beast.

'Tanner'

Okay never have put anything but atf in mine but have flushed a few what's wrong with flushing one no chemicals?

With a new trans, probably nothing.

With an older trans, sometimes there is a varnish build-up that is actually filling in voids. When you flush it, you clean out the varnish, and now you have a rough surface where you once had a smooth surface. This accelerates wear.

At least, that's what a lot of mechanics say. I've never done it myself.

The Turbo 400 doesn't like synthetic fluids anyway. Any clean new DexIII compatible fluid is best, and also the cheapest. I've never talked to anyone that rebuilds old T350/T400s recommend synthetics.

We never recommended synthetic trans fluid be used in older transmissions when I was working in the industry as a technical sales rep. Flushing can break lose old bits of metal, disc materials, etc, that can wreak havoc in the small fluid passages in the valve body, and plug up passages or jam the springs & balls. Manufacturers don't recommend flushing.

Just because someone says "I've never had a problem with flushing a trans" doesn't mean that the next guy will be as lucky. Most people I know have had fluid drain & fills, along with filter replacement, done for years. The flush concept was really designed as a profit adding center for oil change places, not as a manufacturers requirement.

Oddly enough, most people attempt a flush when their transmissions starts showing signs of delayed/sloppy/missed/hesitant/etc. shifts - which is a sign in many cases of more serious issues that a flush won't fix.

'Tanner'

I searched online for a verification of my upcoming comment, but I can't find one.

I was told by a mechanic that GM put out a notice to dealerships to NOT flush transmissions. Flushes were just a money making scheme for shops, as a previous post stated. You are always better off dropping the pan, changing filter and fluid.

I am far from an expert on any of this, but im just wondering if the word "flush" is deceiving ? I can see how a sort of forced flush could loosen various things but im thinking more of an entire fluid change, no force, no pressure, no chemicals to loosen anything , just a simple drain and replace as you would do if you were doing just the pan. im just wondering if it more efficient to drain all of the fluid so you dont end up with 40 percent good fluid and 60 percent bad, or whatever percentage it would work out to be. ive had the m1008 for 5yrs and 25k miles. it now has 50k miles on it. i havent changed the fluid yet and who knows how long it went before i had it. if it helps, the tranny runs fine. just trying to do some preventative maintance. thanks for the help

Drain what fluid you can when you drop pan, check pan for debris, R&R filter & pan gasket, button pan back up, and add fluid. If it was such a major concern to get all of the fluid out, the automakers would have developed a method of doing so YEARS ago. Matter of fact, I haven't seen a torque converter with a drain plug for years.

You are correct, Sir, that some old fluid will still be in system, but 20 Quadzillion TH400's & other transmissions on the road over the years haven't gone bad from the traditional drain/filter/fill method used by mechanics for ages... in the end, it's YOUR truck, and YOUR decision. But you'll end up 'flushing' quite a bit of new synthetic or traditional fluid through the trans in order to (never) get all the old non-synthetic fluid out.

'Tanner'

I would reccomend changing the fluid & filter, and installing a drain plug into the pan while you are at it. From there on out you could change it two more times without soaking your head with hot, stale ATF

Okay I am with Magpul on this someone needs to define flush, to me it is just replacing all the fluid in the system at normal pressure and no chemicals. How would this damage anything?

I have wondered the same thing!

... Jesus Christ.... where's the Doghead button? Okay. One last time... (hopefully)

Davis & magpul:

'Flushing' - as used in the transmission industry terminology - GENERALLY involves hooking a heated transmission fluid exchange system inline with one of the transmission cooler lines so that the machine can run a batch of transmission fluid with/without chemical additives through the transmission/cooler/lines. The 'fluid exchange machine' has a pump (this is the part where the pressure comes into play,and the pumps often have a shock or agitation feature, okay?) The fluid pulses & creates a bit of turbulence/agitation, the concept being that it helps 'loosen' particulate matter, sludge, varnish, etc., from inside the transmission. Now, for those that THINK you can get ALL the old fluid/detritus/metal/paper bits/small squirrels/ Jimmy Hoffa's remains/etc., out of the transmission with a flush - IT SIMPLY ISN'T GOING TO HAPPEN, UNLESS you tear the trans down and clean everything meticulously clean internally. Period. End of Subject. And if you wish to attempt to swap in syn-fluid, you'll never get 100% of the non-syn fluid out of the trans w/o said same tear-down, ever? People think that there is a 'magic wall of separation' between the old & new fluid - there isn't, so don't fool yourself into thinking that there is.

Another person has given me a great analogy for a fluid exchange: To understand why you'll never 'flush'/exchange out all the old fluid, picture a swimming pool filled with dark blue water. Then imagine what would happen if you took a garden hose and began filling the pool with clear water. The clear water would start to displace and dilute the dark blue water. But it would take a LOT of clear water to replace all the blue water. Now - envision that you are going to 'exchange' the old fluid in your trans with new, clean synthetic fluid. Are you ready to pay the tab to flush 2x-plus the quantity of syn-fluid through your trans for this flush?

With fluid flush machines, Chemical additives/seal softeners/cleaners have been used in these machines, and run through transmissions, often leading to problems down the road. OEM's do not recommend using fluid exchange machines - oil change shops & dealership that are owned independently of the OEM's offer the services to the unsuspecting public as a profit center.

TSB 26-003-07

Next, DEPENDING on the style of transmission cooler that was installed in the radiator header tanks, you MAY have a tubular cooler with internal fins/mesh that will NEVER be cleaned without replacing it. SO - follow along here as I mention that the aforementioned 'debris' MAY be ejected from the cooler during use of a 'heated turbulent agitation fluid exchange machine'.

Moving along - If you wish to use the transmission pump to 'REPLACE' the fluid (which is the term that OP is referring to when he instead uses the term 'flush') - Yes, it can be done. There are many posts on the Interwebs regarding a method of fluid exchange where a vat of clean trans fluid is inserted and 'intravenously' spliced into the trans cooler hose circuit. But - for 99 44/100ths% of the 'transmission fluid exchanges' done - it simply isn't needed. Period. Drain the traditional trans fluid with pan drop, replace filter & gasket, and refill with new fluid. Again, it's been done this way since the dawn of automatic transmission time. And those same bazillion autoboxes have cruised down the road with a mix of clean/'dirty residual fluid', for years. With no issues, for the most part. (someone will ALWAYS chime in with the rare exception - it's human nature). BUT, go back with traditional fluid. And note that this method may require upwards of twice the amount of clean fluid to 'flush thru' the system, with ZERO guarantee that you got all the old fluid & debris out.

And DO NOT simply 'add a drain plug' to the transmission drain pan - future owners of the vehicle may opt to go cheap & simply drain the fluid & replace it w/o removing the pan to inspect for debris in pan & replace the filter. Leading to more potential problems down the road.

I would strongly NOT encourage nor recommend any exchange of synthetic transmission fluid in place of an originally filled & 'broken-in' traditional trans fluid filled slushbox. Trans shops/builders/remanufacturers that I worked for would also not recommend synthetic fluid use in older transmissions.

I'm really trying to give the most excellent, solid, industry-proven advice here, but realize that some will want to chart their own path. Fair enough.

But the transmission you kill by going your own way may be your own transmission.

Tired of writing - I hope I've cleared this up. But feel free to ask any further questions.

To the OP - if your bonin' to swap in syn-fluid, then rock on. And Good Luck!

'Tanner'

Well stated Tanner! Synthetics offer very little in protection for automatic transmissions. If your transmission has been overheated, then you may have problems that will not be solved by switching to synthetics.

Synthetic oils offer one benefit, temperature tolerance. They do not lubricate any better under normal conditions. So if your clutches are engaging correctly and not slipping, there isn't an issue..

It is far better to increase cooling than switch to synthetic automatic transmission fluid if you are towing large loads.

Tanner I dont understand your anger and indignation at Davis and Magpuls question, I think we all understand that you cant get 100% of the old oil out. Just how can it hurt if you try to get as much new fluid in as you can, minus the chemicals or the agitation.
I had a friend that sunk his truck, so we did the home flush. 16 quarts in and 16 or so out with some water to go with it. his truck runs with the stock tranny to this day and that has been may years ago I have never used synthetic trans fluid and I dont plan to in my CUCV but I have had no problems with a complete fluid change done at home.

Just something to add to my comments. In the case of my friends underwater adventure I think anything other than a change as much fluid and get the water out change would have been woefully inadequate. There are times when I think you need other options, and this was one of them. I would bet nothing was hurt by doing the full oil change and I would bet just dropping the pan and changing the minimum amount would have caused problems later considering the water that was "Flushed".

stop pushing peoples buttons Idaho...

Tanner said:

And DO NOT simply 'add a drain plug' to the transmission drain pan - future owners of the vehicle may opt to go cheap & simply drain the fluid & replace it w/o removing the pan to inspect for debris in pan & replace the filter. Leading to more potential problems down the road.

Click to expand...

The only thing I didn't agree with. It makes it so much easier to do it right, and who cares if the next owner chooses not to? For the time the current owner has it, it will be much easier to do the next time.