Servicing auto tranny, should I drain torque converter?

About a year or so ago I realized the tranny fluid was getting a bit smelly, though I'm usually good about changing it. So, drain, refill. Six month later, repeat. Still a bit smelly, time to drain and refill.

Question - should I drain the torque converter, or can that even be done? My thinking is maybe by doing so I can get rid of more of the old fluid? My certifications are in brakes, engine repair, tune up, and electrical systems, and they date back to the late 1970s. I never did anything with auto transmissions.

1994 Subaru Legacy, 2wd, auto transmission, 180,000 miles on car.

the trans holds about 10.3 qts.

FWD may be a little less, idk.

a drain will net you less than a gal, about 3.5 qts.

do 3 drain and fills, with driving in between each,

and it will replace about 80 % of the old fluid.

then do it once or twice a year to keep it fresh.

you cannot drain the TC with the trans in the car.

I struggled with this on my '04 Forester. I bit the bullet and took it to Oilcan Henry's. They use the (engine) running AT's pump to pump out ALL the old ATF while pumping in new ATF - a complete flush/fill. This method does not stress the AT's hydraulic system since it utilizes the transmission pump to do the work (which it does all the time anyway). It was expensive up front, but well worth it (and I noticed an immediate improvement).

Do the math - it is virtually impossible to get 100% replacement using the drain/fill/drive/drain/fill/drive cycle - no matter how many times you do this. When all said and done, you will have spent hours and gone through several gallons of ATF before getting something close to a good flush/fill. It's not worth it.

Oh, and I should mention the environmental headache of having to dispose of those several gallons of used/diluted ATF and the economic impact by demanding more production of the oil companies for all that wasted ATF.

My son's LGT is next.

a couple of warnings using this method,

the fluid pumps out faster than it will gravity feed in.

so stops and starts are recommended.

do not let the oil pump run dry.

lack of fluid will damage the trans.

less of a problem with the car sitting still in park,

but still be careful.

ATF is one of the few fluids that it is ok to use the drain and fill method.

it ''replenishes'' the fluid and keeps it fresh.

it is not like engine oil where oil becomes compromised and does not work as well.

besides, the change interval for the ATF is inspect every 30k, replace every 60k.

this is dramatically different than engine oil.

so if you do 3 drain and fills and replace 80%,

just reduce the the change interval by 25%, to 48k,

and you'll be back to where you started.

If the fluid smells burnt or feels gritty then it might be best to leave the fluid. Replacing that bad of fluid can cause the trans to develop issues because the grittiness was helping the trans perform the way it was.

Also if you don't keep up on fluid changes but the fluid isn't too bad the best way to get all of the fluid out would be to take it into a shop and have a full fluid exchange done. This will ensure all of the fluid gets pulled out and fresh stuff gets in. Usually costs about $100 at a shop and spending a hundred is far better than spending thousands later when the trans goes. Now I can get away with just drain and fills because I change my trans fluid often, like 15-20k max. Going longer than that usually you'll have to replace all of the fluid.

I remember many years ago these old timers coming in from the fields, telling me the oil in their equipment is feeling gritty and needs changing. This is the point at which I roll my eyes, because if their oil was actually gritty, the engine would have long since stopped running.

Can transmission fluid actually get to the point where you can feel particulates in the fluid?

trans fluid gets dirty in a different manner than engine oil.

engine oil has gas, and exhaust carbon to deal with,

as well as metal wear particles.

the trans only has the metal and friction? wear particles.

of course both have to deal with the ''oil breakdown''.

but the engine has much higher temps and much more severe pressures.

all auto trans have metal ''flakes'' in the bottom of the pan. (not chunks)

the internal parts of the trans are wear items,

and as they wear, the flakes flow to the pan.

often a trans shop will use this fact / image to convince an unlearned owner to spring for a rebuild.

any lubricating fluid that is gritty is going to cause problems.

but gritty is much different than normal aging and wear.

especially if you refresh the fluid on a regular basis.

The transmission on my car probably hasn't had the fluid changed in well over 100k. At this point I'm too terrified to touch it.

a ''flush'' by a shop will replace all of your fluid, for $125.?

but folks are always talking about problems if you do a flush.

that is why the drain and fill method is recommended.

if you do not change your fluid you will be lucky to get to 175k miles.

do a drain and fill every time you change toe oil.

you will already have all of the tools, tubs, and rags out.

and it will only add $15 to the price.

to make it easy, measure how much you drain out ,

and add that same amount back.

this eliminates the ''hard to read'' dipstick part of the job.

I remember many years ago these old timers coming in from the fields, telling me the oil in their equipment is feeling gritty and needs changing. This is the point at which I roll my eyes, because if their oil was actually gritty, the engine would have long since stopped running.

 

Can transmission fluid actually get to the point where you can feel particulates in the fluid?

Yes it will feel gritty if you don't change your fluid when it should be changed. This happens when the internal parts start to break down and can cause major issues. For one it will clog the passages within the valve body causing shifting issues. The main thing or parts to break down are the transmissions clutch friction plates and the transfer plates for AWD trannys.

Transmission failures usually start like this. You don't change the fluid and the parts said above start to break down and over time they will actually break down faster because the particles that are now in the fluid act like an abrasives wearing everything out. Then say you don't change your fluid for 100k plus and once you do there's now fresh and as I would say "slippery" fluid and the worn plates now don't have that particle infested fluid to help keep things working. Basically causing the trans to start slipping. At my shop when we get people that want a trans service and notice the trans fluid is burnt smelling and feels gritty we will warn the customer that doing a fluid exchange can cause trans problems. So just keep up on your maintenance and you shouldn't have any problems.