Is There a Better Way to Flush Your Transmission?

[TurboDiverArt]

Hi All,

I'd like to flush my transmission fluid and put in synthetic. I've already changed my fluid and filter for this season but that's only about 6 quarts of fresh synthetic fluid. From what I understand our 4L80E transmission with the big converter take about 13-14 quarts of fluid to fill. So I figure I've replaced about 1/3 with synthetic. I want to switch to synthetic because I tow a fair amount per year. My transmission has a shift kit, never gives me any trouble and the pan barely shows any sign of clutch material when I change the filter so I believe it’s in very good condition.

I've read about the method of draining, adding to pan, disconnecting the trans filter line, starting and letting it drain until you see fresh fluid but with the price of synthetic fluid I'd like to see of there is a better way. I assume you can't start and let it drain without adding any new fluid? Basically letting it dun dry, then adding in the 13-14 quarts that it needs.

I know my transmission gets pretty hot when towing and the converter is not coupled. My transmission gauge seems to run high by about 40 degrees and is plumbed in the transmission line prior to entering the coolers. It's going to be the hottest reading in the transmission. I have an auxiliary cooler I installed so it should have enough cooling capacity but still I see temp readings as high as 270. Again, I'm pretty sure my trans temp gauge is off. When initially started my gauge will read about 40 degrees higher than ambient temperature outside.

Can you blow compressed air into the cooler line and flush the fluid out? Maybe with the pan down and filter removed? Hoping there is a better way than wasting synthetic fluid.

Thanks,
Art.

[Robyn]

In short, there is no way to do a "pure swap" to synthetic.
As you add the stuff to the pan it mixes with the old fluid and becomes one slightly deluted volume.

Back in the old days (70's) the converters had a drain plug that one could remove and drain the converter.
At that point a refill did replace the fluid content of the tranny.

Compressed air cant be used.

The only way to do a complete drain it dry and refill with totally clean fluid is to remove the tranny, remove the converter and turn it upside down in a bucket and let it drain out, then with the tranny dry, do a refill.

This is one of the reasons I do not like the synthetic fluids, you never get the pure thing and you waste so much fluid to even get a somewhat clean fluid back in the box.

Actually with good old tranny red juice and keeping the tranny cool the box will run just as long as with any of the trick stuff.

Heat is the killer.
The fluid responds to excess heat by breaking down. The additives package goes south as does the frictional quality of the oil.

The fluid in an auto tranny does multiple things.
1- It provides the medium for the hydraulic drive.
2- It serves as a friction modifier/improver for the clutches/bands
Most of this stuff has a "Paper" lining that becomes soaked with oil. The particular type of fluid is matched to work well with the friction material used in the particular trans.
3- The fluid transfers the generated heat from the converter away to the coolers to be radiated off.
4- Last but not least, it lubricates everything in the gearbox.

I have used synth in a couple boxes in past years and never found any advantage that could really be seen.

Now I'm sure that under closely controled labratory conditions that the folks selling the product can find things that make it look good but I doubt that the average buyer is going to see any real improvement.

Your hard earned $$$$ could be better spent with a good full flush of the box with standard red juice and a refill.
A bigger oil/to air cooler and a nice little dash gauge would be good too.
Even a cast aluminum pan with a drain plug and a place for the gauge sender would be cool too.

Unfortunately you cant get a good clean refill with the synth product.
(Or any oil)
Its at best,with repeated additions and drains, it's going to be slightly dirty "bath water"

You will however be able to change the filter and remove most of the old oil and end up with fluid that has most of the needed properties in it.


Just not much more I can say.

The engineers and "bean counters" fouled us again.

We can't do a proper service and we end up wasting expensive oil trying to do a half assed diluted attempt.

My best solution is stay with factory spec oil, replace the in pan filter and add a small spin on filter in the return line from the cooler and change that little creature every oil change and add a pint or ??? to keep the level good.

The in pan filters are at best a "Clod sifter".

Auto trannies make loads of junk. This is normal. The fine black sooty stuff you see in the pan is a combination of metal from the converter and clutch and band material as well as bushing materials.

The common auto tranny uses bushings to support the shafts and such and not ball or tapered roller bearings like a stick shift.

You will sometimes find fan type needle thrust bearings and the planet gears do have needle bearings but all other stuff is bronze or babitt bushings.


Have fun, enjoy and let us know.

Robyn

[DmaxMaverick]

You can use the same method posted over and over in the late model drivetrain forum for the Alison tranny.

Drain the pan to start with. Replace, with new filter. This would be a good time to install a drain plug if you have a mind to (Allison trannies have a drain plug). Pull the cooler return line at the tranny and route to a large container. Add about 6 qts. to the tranny then idle until the flow starts to fluctuate (means it's sucking air). Stop the engine and fill again. Repeat.

I suggest an overlap of at least 2 qts of the total capacity during the flush, before a final top-off and check at operating temp. More overlap is better. If you are changing from old dino ATF to new synthetic, you should be able to see a difference in the fluid color as it comes out of the cooler line. This method will replace 90-95% of the fluid, including the converter. What remains of the old ATF is insignificant, and will become less and less concentrated with later services.

[rustyk]

Well, having been a lube engineer in a past life, I both agree and disagree with Robyn.

The threat to ATF is high temps, and mineral oil-based ATFs don't have the resistance to those like synthetics do; the additive package is pretty much neutral with respect to temperature.

The advantage of synthetics is that, due to their homogenous constituency, they have much greater resistance to higher temps.

Sadly, contemporary torque converters have no way to drain the fluid, but ideally, dumping all the prior fluid is the way to go. However, an 80%/20% mix of synthetic/mineral oil will be more stable than straight mineral oil.

That said, if one runs one's transmission at temps that would stress mineral oil ATF, then that's an issue that needs addressing. Keeping AT temps below 230°F is a Good Idea, regardless of what's in the can...keeping temps well below 200°F is better; occasional excursions to 230-240°F aren't problematic. Constant readings in that range are.

[Robyn]

All the hastle over a two bit 1/8" pipe plug.

Used to drop the oil in the converter while I was changing the filter and washing out the pan.
Get the pan bolted back on and add 5-6 quarts and idle the engine in drive and top off. run through the gears to purge any air and poof all done and minty fresh.

Now its a hastle to do what we used to do in about 30 minutes.

Took the old fluid out back of the shop and gave the blackberry bushes a treat and the job was all done. :D

Dust a little grease sweep across the floor to tidy up the work area and put the tools away.

Things ain't the way they used to be for sure.

I am still not sold on the synth oils.
Fuller was pushing the synth stuff for the 18 spds in the class 8 stuff.

$50 a gallon for that stuff and now they tell me the trannies are doing better with less troubles on good old Dino 50W.

Hmmmmm my first 18 speed in the Ghost went 490K under hellish use pulling around 105,500 Lb loads all the time. That session was with good old dyno 50w

We put the synth stuff in the rebuilt one that went in back in Aug 06.
It does run a tad cooler but the shop tells me we should dump the synth and go back to mineral oil.

Hell I dont know, thing shifts fine anyhow. I never use the bloody clutch after its rolling anyway.

Let the Kitty purrrrr and grab gears.

My old tranny never really did anything wierd, just one day it started sounding like a 5 alarm cat fight in top gear. :eek:

Best of luck with whatever you decide to do on the fluid change.

The drain and add, drain and add as Maverick mentioned is really the only way.

The additon of the return line filter is a good one though. That will catch a lot of crap that the regular filter wont even notice.

Later

Robyn

[JohnC]

If you're really anal about it, you could try this. Disclaimer: I accept no responsibility for anyone who follows this suggestion and screws it up. I have never done it to a 4L80E. In fact, I have only done it on Borg Warner transmissions. Presented for entertainment value only.

Get access to the bottom of the torque convertor. Drill a 5/32" hole in the low point, making sure you don't drill into anything important. Rotate the convertor 180 degrees and repeat. The fluid will drain out. Plug the holes with special 5/32" pop rivits designed for high pressure applications. (I forget the part number).

[rustyk]

$50 a gallon for that stuff and now they tell me the trannies are doing better with less troubles on good old Dino 50W.

I assume you're talking about a Road Ranger or modern equivalent; many of my customers, when I worked for Shell, used Rimula 50W in trannies; it was such a beast of MO, it could do just about anything asked of it.

That withstanding, there's little rational argument that a synthetic stands up better to abuse than a mineral oil. This isn't hype, it's just that mineral oils have constituents in them that don't do well with extreme heat. While that proportion is very small, it doesn't take much crud to foul an automatic tranny.