For those of you with some expertise with the AISIN 6 speed Automatic GA6F21WA,

Im putting a new motor in my 2008 Cooper S R56 which has 153,000 miles on it because I lost compression in two cylinders. (note that the Mini R3 wholesale-price engine replacement program ends June 31 2018).

This car never had the transmission serviced so its had the same tranny oil all 153,000 miles. It actually shifts fine 99% of the time. Once in a while I get a hard downshift.

When I pull the axles to pull the engine I expect to lose most of the old fluid. I could collect the old fluid and reuse it or do a flush but I'm terrified of putting new fluid into this old tranny. Common knowledge says do not flush an old transmission or risk failure.

Should I collect and reuse the old oil or just drain and put in new filter and fluid?

 

I would never ever reuse old fluid - and not at 153,000 for sure. I think some have the idea that changing it as preventive maintenance is not advised. But not me. Change all fluids on some regular schedule. But you need to do other work that would cause some of the ATF to come out, correct? So in that case - change it.

 

Who's "common knowledge"? Any research to back this up?

 

Hey Timski,

Well I wasnt responsible for the car before this and I sure didnt want to touch that tranny at 153k miles. There is a giant sticker which says DO NOT CHANGE FLUID with a "!". AISIN knows better than I do, how to maintain their own product. I would have flushed it regularly had it been my choice.

Yes Im changing the motor and have no choice but to pull axles and drain the fluid.

I think its gonna fail once I flush it...frankly. But I dont think I have much choice.

 

Most mechanics Ive spoken to over the years.

 

Lex,
No need to worked up. I'm on your side I think most people on here are as well. The idea that new fluid alone will make the trans fail is crazy.
Isn't the fluid new at the factory? That sticker may have other implications such as debris is introduced while changing or the seals may now leak (change the axle seals) or something of that nature. Other people on here have changed the ATF before. I'm more likely to believe the 153,000 miles without changing is the reason it fails and it's a coincidence it fails a few thousand miles later.

 

Fingers crossed!

The aisin unit is the only thing that hasnt leaked on this vehicle.

I have the 3 seals, the axle and input seal.

http://www.realoem.com/bmw/enUS/show...diagId=24_1063

 

According to Fishbone, in his PDF instructions https://www.northamericanmotoring.co...ml#post3502021 (thanks Fishbone, you're awesome), this is perhaps why AISIN doesnt want the tranny serviced:

The transmission cannot be flushed like a traditional automatic because it has no front external cooler; it uses a heat exchanger. This is one of the main reasons most shops will refuse to service it.

There is no dipstick to measure the ATF or fill through it either. There is NO transmission filter to be replaced, there is just an internal strainer which is not accessible unless you drop the pan, which you should have no reason to do so.

 

MINI and other manufacturers considered the fluid to be lifetime, probably because it would last past the warranty and also for lower maintenance and costs to the buyer. I don't remember if MINI ever sent out a TSB, but VW has changed the service interval from lifetime to 40K.

I think the belief of not touching the fluid on neglected auto's is there's a lot of crud/metal in the old fluid that adds friction. When you replace it with clean fluid, the transmission parts start to slip because of the larger tolerances due to wear that the crud is no longer filling.

People usually do three changes with short driving intervals between each when replacing fluid through the drain plug. That's because you only get about 2 quarts of fluid out with each drain as most of the fluid is stuck in the torque converter. 3 drain/refills should get you about 85% new fluid. The fluid level is on an Aisin is checked when overflowing from the drain within a certain temperature range because the volume of fluid changes with temp. Since you have a 2nd gen MINI, you can read the trans temp with a diagnostic tool or program to make sure the fluid is in the correct range when setting the fluid level. I don't think you can get this reading on a 1st gen.

Here are some links with info on servicing similar Aisin transmission.

https://www.sonnax.com/tech_resource...n-fwd-6-speeds

 

"I think the belief of not touching the fluid on neglected auto's is there's a lot of crud/metal in the old fluid that adds friction. When you replace it with clean fluid, the transmission parts start to slip because of the larger tolerances due to wear that the crud is no longer filling."

That's more or less what I've heard and what I'm afraid of. Is it a wive's tale? I don't know. Its probably more relevant to trannys that are nearly dead (burnt fluid, floating metal bits). I may just try and save the old fluid and pour it back in. I dont know if I want to add a transmission flush to an engine swap. I have limited time to get this done. If I can get the engine out and all the new parts back in fast enough maybe Ill mess with a flush.

I can tell you that the tranny outlasted the engine despite no transmission service. Its the first car Ive ever heard of that had it's tranny outlast it's engine.

 

Here is an letter to that effect in the Chicago Tribune.

http://articles.chicagotribune.com/2...-atf-oxidation

And When Not To Flush

http://mdhmotors.com/transmission-fl...-transmission/