Automatic Transmission (AT) flush procedure

General information about the first-generation Nissan Maxima in the US. What was the Datsun 810 became the luxury leader Maxima in the US in 1981.

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asavage
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Automatic Transmission (AT) flush procedure

#1

Post by asavage » 11 years ago

Changing (all) the fluids on your vehicle is one of the most-overlooked and most important ways you can extend the life of the fluid-using systems. One of the more daunting fluids to replace is the automatic transmission (AT) fluid, because most of the oil in the AT is not in the pan, where you can get at it. Most of the oil in the AT is in the torque converter, and torque converters for passenger vehicles haven't had a drain plug in decades (they did, however, used to have one, and some heavy duty equipment/trucks still do). The usual maintenance interval for AT fluid change is 60k miles, same as for the IP belt. For most, this works out to about every four years. Most older ATs will have visibly degraded AT fluid (ATF) after 60k miles, though actual fluid degradation varies widely; some folks can get 90k from fluid before it smells bad and has a distinct brownish tinge to it, others may be ready for a fluid change after only 2.5-3 years.

There is expensive equipment that is designed to flush the old fluid from the transmission, including the torque converter. There's also fairly inexpensive equipment that does a somewhat less thorough job. We used to get $125-175 for this service. But in any case, you are entrusting your vehicle to someone who may or may not have much interest in performing professional work, and usually are concerned with how much time it takes. This latter factor leads to not using enough flush fluid -- not flushing enough fluid through. However, you can do a very good job of flushing your AT yourself, without (much) expensive equipment, if you're willing to allocate enough time, and round up some items beforehand.

The general idea is to have all of the fluid in the AT replaced. In practice, this isn't possible, but you can fairly easily get to about 80-90% replaced by following the procedure below. The process involves disconnecting one of the flexible transmission cooler lines from the radiator, and letting the transmission's internal pump move the old fluid out into a catch jug. Because the transmission pulls oil from the transmission pan, pumps it through the torque converter, then out to be cooled, by adding fresh oil to the pan and catching old oil at the radiator end, you can do you own flush!

There are several variations on this procedure, and everyone likes to add their own embellishments; I detail what I consider the "least hassle" method below. There are really only two major decisions about the process: to remove the AT pan, or not.

There is virtually no filtering of the ATF in Nissan ATs as installed in the Gen1 Maxima. If you are really lazy, and don't mind using a lot of flushing oil, you do are not required to remove the AT pan. This is the method most "Jiffy Lube" type quick oil change outfits use, because it requires much less time, and time is profit for those types of outfits. It is faster. But most transmissions have some accumulation of solids at the bottom of the pan -- normal -- that could be removed during a "pan drop", and which will tend to re-contaminate any new fluid you install.

For transmissions that have a "real" filter, the filter should be changed as well. This is not an issue with our transmissions, but I mention it for completeness.

Having just performed this service on Carimbo's '82 Sedan diesel last night, I thought I'd attempt to formalize the steps.

Note for those who wish to perform their own transmission flush: the transmission outlet line is the line that connects to the passenger side of the radiator, so connect your drain hose from the driver's side radiator nipple to your drain jug.

Consumables needed:
  • Automatic Transmission Fluid (ATF): If you begin with reasonable-color used oil in the trans, and an empty torque converter (ie you had the trans out and drained the converter), this can be as little as six or eight quarts. A typical trans with a converter full of old oil can require sixteen or more quarts to obtain a sufficient clarity of return oil. Not removing the pan and cleaning? Add at least eight more quarts. Always buy extra -- you can usually return the excess later, and it's a bummer to be a quart or three short! Generally, any ATF that says "Dexron II/III" is going to work fine. Many have preferences on brand or type: let's discuss those preferences in a different thread, OK?
  • Transmission cooler hose. It looks just like fuel line, but isn't. They're both about a foot long at the radiator connection, so you'll need maybe 30". The most readily available stuff is 5/16", but in most cases the OD will be just enough smaller than the thick OEM lines that you will be forced to replace the . . .
  • Hose clamps. I like Fuel Injection line band clamps over the typical worm-drive style. NAPA 705-1226 are 5/16":
    Image
  • Trans pan gasket. It's easy to get the "filter kit", but the AT "filter" is a brass mesh screen, so there's really no need to remove it, it will not have anything to clean. So save some money and special order the pan gasket only.
Tools/Supplies needed:
  • For pan bolts: 10mm socket, extension, ratchet. I recommend 1/4" drive.
  • For black plastic splash shield under the radiator: No. 3 Phillips screwdriver. For you Right Coasters, or corrosion areas, be prepared to have to drill the heads off the screws if they're very bad.
  • Cooler hoses at radiator: No. 2 Phillips screwdriver. If the hose clamps are very rusty, forget the screwdriver and use a Dremel, hacksaw, or other destructive device (even Vise-Grips) to get the four OEM clamps off. If you're using replacement line other than OEM, chances are you'll have to replace the clamps anyway, because they won't fit.
  • Funnel system for filling. Filling requires either a special funnel (std trans funnel will not fit into the fill tube) or an alternative method. I've used a bit of 3/8" steel tubing with some 3/8" fuel line or equivalent hose-clamped to it, then adapted to a std funnel or an electric fuel pump that I use to transfer ATF from the jugs to the fill tube. Be certain that you clamp the steel tube to the hose; you do not want it coming off and falling down into the fill tube!.
  • Jugs. Translucent gallon water/milk jugs work very well, because they can't overfill without you being aware of incipient spillage: you can see the level rising easily. But coolant jugs or anything that has a small opening can be used. I do not recommend using a catch pan, as the stuff will splash as it comes out of the line.
  • Rags, paper towels, cleaning tools (for AT pan cleaning, splash pan cleaning, etc.)
  • Aerosol cleaner. I use cheap carburetor cleaner, but brake cleaner will do as well. Whatever is on sale is OK. You will be using it primarily to spray up at deposits/coating on the parts of the transmission that that pan covers.
  • Optional: vacuum device. Handy for sucking oil from the pan before removing it, sucking old oil from the cooler return line. I like the larger Mity-Vac:
    Image

Flush procedure:
  • You have to remove the AT pan, so if you have a vacuum device (I use the 1.5 gallon Mity-Vac, but Kassim came up with an ingenious method using intake manifold vacuum and a jug; other methods also apply), suck two quarts out of the AT pan via the dipstick tube. My Mity-Vac comes with several lengths of semi-rigid nylon tubing @ 4' each, which can be coupled together and which make this very easy and less messy.
  • Jack the car up level, high enough so you can get the front splash shield off/on and service the AT pan. Use jack stands or really good blocking, and never, ever use cinder blocks or bricks.
  • Remove AT pan and clean the pan to "very clean". If you wipe a white paper towel on the inside, it should not show any grey.
  • Use your aerosol carb cleaner (or brake cleaner) and spray off the exposed parts of the transmission that the pan covered. The objective is to remove the common visible coating of gray crud on the filter and exposed valve body. This is not a critical step.
  • Got a vacuum device? Skip to next step. No vacuum? Skip down several steps, and find a way to blow air into the driver's side cooler hardline at the radiator, blowing old oil back to the pan area, then come back here. This step is not critical.
  • Reinstall AT pan with new gasket. Make certain that the gasket surfaces are both clean and oil-free! Careful tightening the 6mm bolts (10mm heads), as they are not particularly high-strength items. Also, the gasket can creep out of place, so make certain that you start all the little bolts before tightening any of them.
  • Remove the black plastic front splash pan under the radiator (six No. 3 Phillips head screws). Clean it off if you wish, it generally collects a lot of crud.
  • Remove both 8mm AT cooler hoses between the hardlines and the radiator nipples. Oil will drip, but not a whole lot. Two drain pans are usually needed to collect oil from all four connections. The OEM double-wire clamps are sometimes so rusty that they cannot be re-used, or even removed without a Dremel or equivalent. I have had to use a utility knife (razor blade) and cut the lines off the radiator nipples on a couple of cars; tugging on them threatened the radiator's integrity, that's how much force would have been required.
  • Cut new lines, using only hose rated for transmission cooler duty.
  • Got a vacuum device? Suck the fluid out of the driver's side hardline, which is the return line to the trans. Not critical.
  • Fully install the passenger side line. It is not unusual to have the hose clamps "tight" but still be able to twist/wiggle the line on nipple or hardline: don't worry about it, it won't leak. Install the driver's side line only on the hardline, and let the other end dangle.
  • Install a temporary length of 5/16" line (any kind) on the driver's side radiator cooler nipple, long enough to direct out to a catch jug.
  • Refill the trans' pan with two quarts of ATF.
  • You can add as much as three quarts and not have it come immediately out the trans' vent line (at least, on the L3N71B) but two quarts is the normal full level.
  • Is the car level? Is the line from the driver's side radiator nipple in the catch jug? If you helper holding it in the jug?
  • Glow and start the engine. As soon as practical, shift into every gear selector position, pausing for a few seconds in each range. Including Park (make sure the brakes are applied when you shift to Park, or the Park pawl can be damaged). If you have an OD trans, try to get it to upshift to OD (ie run it fast enough to shift to OD) Your helper will yell when fluid stops flowing strongly into the jug, at which point you should turn off the engine. You do not need to shift to Park to shut off the engine.
  • Add two more quarts of ATF via the fill tube.
  • Lather, rinse, repeat. You are aiming for the same color of oil leaving the drain hose as goes in the fill tube.
  • Remove the temporary drain line on driver's side radiator nipple, connect and clamp new driver's side hose.
  • Reinstall black plastic splash shield.
  • If you didn't refill the AT after the last run, do so now. Two quarts is very close to warm/Full for the L3N71b.
  • Lower car, clean up. No job is complete until the work area is clean and the tools wiped down and put away.
Another note:
If your fluid was especially bad, it is not unusual for the ATF to become several shades darker fairly quickly -- sometimes by the next oil change. The reason isn't because you didn't get sufficient fluid removed, rather it's because the torque converter is a big centrifugal filter that spins solids to its inner surface. The new fluid is loosening up and suspending those old solids. This is especially true with certain vintage Toyota ATs. If you flush often, the interval that it requires for the ATF to darken will increase.


L3N71b "filter" (click on image for larger):
Image Image
Last edited by asavage 11 years ago, edited 3 times in total.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

HowlerMonkey
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#2

Post by HowlerMonkey » 11 years ago

One thing to do is make sure you use the same additive nissan dealerships use when flushing a 3n71 or 4n71 tranny.

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asavage
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#3

Post by asavage » 11 years ago

Oh? Can you tell us more? I had no idea there was a xN71x trans additive. Because most of us have this trans, I'm keen to know more. I don't suppose you have an empty bottle of it kicking around with the Nissan part No. on it?

Do you know what it does? Is it a flush aid, or an oil modifier for the refill?

rlaggren
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#4

Post by rlaggren » 11 years ago

Why not run it "dry" first thing to clear the pan before dropping it?

Rufus
82 Maxima wagon

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kassim503
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#5

Post by kassim503 » 11 years ago

Ooops, I didnt know there is a trans addictive for the N71 transmissions either. Are you running it? If so, does it tighten up the 1-2 plush shift?
'83 maxima sedan, l24e, a/t, black

227K SOLD 6/7/2012

davehoos
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#6

Post by davehoos » 11 years ago

Why not run it "dry" first thing to clear the pan before dropping it?
this is how we do it.
when i started work most trans had oil drain plugs and steel pipes.we used a large raised drain tray you removed bolts at one end and worked back towards yourself until it dropped.

we now run the gearbox allmost dry through the oil cooler pipes,so the hot oil is less likely to burn your self.you replace the hoses at most services.
clean the pan and inspect to see if its worth while bothering with.refit the pan and add oil.start the engine and flush the oil through till new oil comes out the oil cooler pipes.refit pipes.

the pan must be removed as there is an adjustment inside.this effects the 1-2 shift.to loose is is a slugish upshift.
some trans have a soft shift dampened servo.these are adjusted with shims.remove and relace with a better servo.

the jatco trans here have a internal filter this may have been dealer fitted as i have seen wire mech filters on imports.the filter material type has a tin cover with a suction hole.it was a common problem with the GM trans to block up with clutch linings,the dealer sold replacement filter had a strainer the size of the pan.

Ooops, I didnt know there is a trans addictive for the N71 transmissions either. Are you running it? If so, does it tighten up the 1-2 plush shift?
NO.

nissan recomend dextron for early trans and dextron 2 for later types..when these cars where new had dextron-dextron type F or Dextron type D.
type D gets confused for nissan matic D witch might be type F,what i cant remember is F or D is recomended for BW35 an XN71X trans.
the other dextrons work well.the jatco-borg warner dont use additives-they dont like friction reducers.the jatco trans works well on this basic oil.

aditives to soften oil seals is a diferent matter with older trans-if the oil is changed regular this is should not be a problem.

servicing
-recently the ford agents additive dealer came to our workshop to make a hose to conect the flush machine to the new 6 speed ZF trans.these have the sqeeze and pull plugs.so it was easy to flush.cant see that it needed it but its a good money spinner.

i looked it up there is no recomended oil trans replacment milage.
working for a dealer we changed it on the big 2 yearly service.
i think it was a oil company recomendation and we did it on the GM products.
the warranty in those days was 2 years and people traded the cars at 80 000KM or 4-5 years.
WCJR31 Skyline.3.0 manual.wagon
R31 SKYLINE/Passage GT/PINTARA
LPG Ford Falcon 99-06 93 Disco
Local Shire Southern Zone Mechanic.

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asavage
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#7

Post by asavage » 11 years ago

Because I've had access to a flushing machine in the past, which has a large rectangular funnel-like affair on a telescoping drain rig on a stand which fits under the trans when the car is up on a rack, it was always fastest to remove the pan with the oil still in it, and because that particular flush rig does not require opening the cooler lines, using the trans to pump out the initial load of oil wasn't efficient.

However, you have a good point, for home flushing: that may be a better way of removing the initial load of oil, if one doesn't have a large Mity-Vac.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

rlaggren
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Location: San Francisco

#8

Post by rlaggren » 11 years ago

Because I've had access to a flushing machine in the past, which has a large rectangular funnel-like affair on a telescoping drain rig on a stand which fits under the trans when the car is up on a rack, it was always fastest to remove the pan with the oil still in it,
Ah, different environment, makes sense. "Appropriate" is a real important concept.

Rufus
82 Maxima wagon

HowlerMonkey
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#9

Post by HowlerMonkey » 11 years ago

Very early versions of that jatco used type F tranny fluid.

I worked at the nissan dealerships during the 90s when flushing first came into voque and trannies were dropping like flies after being flushed.

Much of it had to do with deposits loosening up and getting trapped such as they limit the flow for the cooler circuit which heats the tranny to death.

Removing the pan (and the particles in it) and then doing the flush after is best.

I mentioned additives because of the trouble we had at nissan flushing a tranny with high mileage and that you could easily end up with TCC shudder and slow shifts now that the new fluid has a lower coefficient of friction meaning things don't "grab" as well with the new fluid.

Some nissan dealerships used an additive on older trannies when they should have just denied the service based on tranny condition.

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asavage
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#10

Post by asavage » 11 years ago

HowlerMonkey wrote:Very early versions of that jatco used type F tranny fluid.
Checking my 1981 FSM, Dexron is specified, so at least we don't have to worry about trying to find the old Type F ATF for our Maximas.

If Dexron is used in place of Type F for a trans that requires F, the trans will slip.
Removing the pan (and the particles in it) and then doing the flush after is best.
Agreed. Unfortunately, that's not how most quick lubes do it, because it takes too much time (and, really, too much smarts).
Some nissan dealerships used an additive on older trannies when they should have just denied the service based on tranny condition.
Yup. We turned away trans service work for that reason. Fortunately, all my "regulars" got the trans service sermon every oil change, and I sold a lot of flushes. It's nice when you work in a small enough shop that you can actually remember some of the vehicles and customers over the years.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

davehoos
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Location: Karuah Valley,NSW Australia
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#11

Post by davehoos » 11 years ago

TYPE F is recomended by for the best performance,dextron is OK for normal use,as it standard the oil needs with powersteer etc.

most workshops here now use type IIIE

type F is easy to get here,there is also dextron for older cars,this is not dextron but oil for older transmissions.

same deal with engine oil-there is a listing of pre 1989 and pre unleded.
WCJR31 Skyline.3.0 manual.wagon
R31 SKYLINE/Passage GT/PINTARA
LPG Ford Falcon 99-06 93 Disco
Local Shire Southern Zone Mechanic.

goglio704
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#12

Post by goglio704 » 11 years ago

Has anybody here ever bought from tooldesk? The mitivac link from upthread is to their site. I'm thinking about getting one...

Image
Matt B.

83 Maxima Sedan, LD28, 5 speed, white, 130k miles. My original Maxima.
83 Maxima Sedan converted from gasser, LD28, 5 speed, 2 tone blue, 230k miles
82 Maxima Sedan, LD28, 3 speed auto, 2 tone Gray/Silver, 140k miles
81 810 Sedan, LD28, 3 speed auto, rust, rust, and more rust!

2005 Jeep Liberty CRD

Carimbo
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#13

Post by Carimbo » 11 years ago

Sorry, no experience w/ Tooldesk but for flushing the AT fluid the mityvac only gets you so far-- it cannot remove the not-insignificant amount of fluid from inside the torque converter. For this it is better to remove the AT cooler lines and keep the intake hose in the bottle(s) of fresh fluid, and the outflow in a large waste jug. While running the engine. Don't let the intake run dry. Be sure you reconnect the cooler hoses before testing the results of your flushing procedure! (Don't ask...)

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asavage
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#14

Post by asavage » 11 years ago

Matt, I've got one of those and I love it. It's great for so many things: draining the PS fluid, the brake fluid reservoir, the coolant reservoir. Overfilled the trans? No problem, suck out that extra 1/2 quart.

For AT service though, one should remove the pan and clean it, reinstall it and do the cooler line disconnect, as Carimbo notes. That's the only way to get 2/3rd of the old fluid out.

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#15

Post by kamakazidreamer » 8 years ago

so i followed all these steps as best as i could, went to drive the car and it shifted fine, after a few turns it started to rev real high and then act like it was not getting power, then shifted. and now its dripping AT fluid again. Any ideas on what i did wrong?...

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