Basic How-To to Change your Auto-Transmission Fluid

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Basic How-To to Change your Auto-Transmission Fluid

Post by Shipkiller » Sun Feb 24, 2008 1:35 am

Changing your Automatic Transmission fluid is not hard, just messy...

It was raining hard here so this was a good project for the day.... Yea, the car needs a bath....

I write this because there is NO DIY I have found for our Z4 5-speed Steptronic Transmissions. Model A5S325Z

I started to take photos but got caught up in the process and I had some problems too... More on that later...

Tools on hand:
1. Fluid Pump. You WILL need this...
2. No. 27 Torx Bit. (Pan Bolts)
3. Metric Allen set. (Drain and Fill Plugs)
4. Large pan to catch all the fluid.
5. Small piece of wood and soft metal bristle brush.
6. Lots of rags.

Supplies needed:
1. Seven quarts of BMW or equivalent ATF. (The Spec. is ESSO LT71141)
2. New Transmission Filter (24 34 1 423 376) and Pan Gasket (24 10 1 423 380).

Lift or jack your car up. I will not get into this. If you can't figure this out, you should not be doing this.....


Now find your fill hole first. It is on the rear, left side of the transmission. If you cannot find the fill hole, then stop....


A better picture.


Now just loosen the Fill Plug using a 6mm Allen wrench, a tiny amount. I always do this FIRST. If you can't get it loose, then DO NOT drain the transmission.

(Tech tip: Sometimes a Bolt or Nut will not loosen. Sometimes you have to TIGHTEN it first then it will loosen up..)

Now find the Drain Plug. Bottom of the transmission pan.


Get what ever you are going to use to catch all the fluid and place it under the the drain plug. A large Trash Can lid works well...
Make SURE your transmission is not HOT or you will burn yourself in the next step.

Remove the drain plug and let the fluid drain....

Now with the fluid drained, take your no.27 torx bit and loosen all 22 pan bolts, then remove.


Notice the green gasket and filter.


The transmission will drip with the pan off. Drip alot.... That's just the bad fluid leaving the body.... Image

Now attempt to remove the gasket material. Any parts still attached, you can use the piece of wood to assist in removal. I use wood so as not to damage the gasket seating surface.

Then take the soft metal brush (bronze or soft steel) and lightly scrub the seating surface to remove an debris left. Run your finger around it to make sure there is no more debris on the seating surface.

Now clean the pan and look for any large metal particles indicating a potential problem. Also check your catch pan where you drained the fluid for any large particles.

Inside the pan are eight rectangular magnets. Take them out and clean them. Look for those same large metal particles. The small, very fine, metal particulate (like a paste) on the magnets is normal wear. Put them back....


Run your finger around the pan's seating surface looking for the bad stuff.

Now loosen the two Allen key bolts holding the filter in place. Remove filter. Replacement is the reverse. Tighten to 4ft/lbs or 6Nm. The filter mounts are PLASTIC. Don't over torque..

Now put your NEW gasket on the pan. The gasket only goes on one way, but it is not marked which end is supposed to go UP. Think of it like a jig-saw puzzle. :rofl: :rofl:

Hold the pan up to the transmission and start putting the torx bolts back in. Just put them in a couple of threads and then on to the next bolts. Be careful that you do not pinch the gasket...

One all bolts are in the pan, snug them all up, then tighten to 7ft/lbs or 10Nm. Do this sequentially, NOT diagonally, according to the BMW service manual.

Put the drain plug back in and tighten to 25ft/lbs or 35Nm.

Now is where the fluid pump is used. Start pumping..... I pumped little less than one gallon of ATF into the fill hole before it started to run out of the hole. Put the fill plug back in and make it snug....NOT TIGHT.

The pan looks like it cannot hold six quarts of fluid. It can't. There is a reason for this (I think) stated at the end of the DIY.

Start the car at IDLE speed. Do NOT rev. the engine.

Allow the transmission temperature to build up to normal operating temps. This took about 10 mins. or so for me.

Operate the transmission through all gears, leaving it in each gear for at least 10 seconds.

Once the transmission is up to operating temps, with engine running, remove the fill plug and start filling again. I pumped about two more quarts into the tranny at this time.
When it starts to overflow, I gave it another squirt and put the fill plug back in....and tighten to 22ft/lbs or 30Nm.

You are now done.

Thoughts on this.

I had ONE pan bolt that would not loosen. They are NOT real tight but this one would not come out. The torx slot was already half stripped then became completely stripped so I had use a grinder to cut a groove to get a large screwdriver on the bolt to turn it and break it free. What we found it that there was a 'thread locking compound' on the threads. This was the only one with this crap. I was able to put the bolt back in and get some torque on it so it would not leak, but I am going to have to go to the dealer and order a new torx bolt.

Before I drained the pan, I removed the fill plug, engine OFF. I wanted to just check the fluid level... BAD Choice... About two quarts of fluid came out. Now I am thinking, What the hell do I do now.... How do I get that two quarts of ATF back in..... I just trudged on thinking that a solution will present itself... then the solution came to me...

What I think is going on is that the BMW torque converter drains when the engine is not running. This behaver is not like an American Automatic, where you have to drain the torque converter separately. (I did this yesterday on my F-150, all 11 quarts of ATF from the torque converter) This is why you must run the car then finish the filling process.

I have never seen the BMW ATF for these cars, the fluid that came out was a Dark Grey and very THIN....Not like normal ATF. Even used ATF is thicker than this.... Way too thin for my tastes...

The fluid I used was Amzoil Universal ATF. It is BMW spec. ESSO LT71141. At $7.50 a quart, it is $10.00 a quart less than the BMW stuff. I have been using it for 15 years on my vehicles without a problem. My F-150 has 175000 miles on it and is still going strong...

Amzoil, Redline, Royal Purple are all good stuff.. What ever you use make SURE it is the ESSO LT71141 Spec...

The reason I say this is that when I was driving home, the transmission shifted MUCH smoother and the engine ran at a lower RPM for each gear I was in. About 400 RPM less. Better torque through out the power band.

Based on these findings on MY car, I would change my ATF fluid every 30K miles. Especially if you drive it hard like I do.....
Last edited by Shipkiller on Sun Feb 24, 2008 3:05 am, edited 1 time in total.
Drives 2008 Z4MC (His) & 2003 Z4 Roadster (Her's)

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Re: Basic How-To to Change your Auto-Transmission Fluid

Post by ovrkll » Sun Feb 24, 2008 2:33 am

Great write-up!!! :thumbsup:
'06 Interlagos Blue Z4M

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Re: Basic How-To to Change your Auto-Transmission Fluid

Post by Guiseley » Fri Jun 11, 2010 12:19 pm

Digging up a seriously old thread - Anyone had experience of leaks from the back of the auto box? Left mine standing for 2 weeks, and noticed an egg-cup full on the garage floor, and tell tale stains on the pan. :(
Hopefully covered by the main dealer used car warranty, as I'm still counting ownership in terms of weeks, and it's booked in next week, but might have to do a diy / indy job if they decline. (p.s. Car is 4 years old with 26k on the clock) Any thoughts?
Blue Z4C now long gone, as is it's replacement, and the Red Zed's gone too.. now piloting a rather tasty Carmine flat6

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Re: Basic How-To to Change your Auto-Transmission Fluid

Post by james078 » Sat Feb 20, 2016 10:40 pm

Wanted to say a huge thanks to shipkiller for this article...I changed my tranny fluid/filter today on my 04' Z4 3.0...It has 191K miles, and only had a few flushes done, never a filter replaced... this DIY worked great, no issues...couple of additional bits of data of note - the filler plug takes a larger allen head wrench, I used a 5/16 that fit very filter bolts were torx heads (T40) , not allen heads...and lastly as tip, used a super thin coat of Mystik wheel bearing grease to hold the gasket in place on the pan when re-installing, worked great...for fluid, I used the Royal Purple Max ATF, it is bright red in color...I got similar results to shipkiller, smoother shifts, more torque, less RPM demand...

Thx again!!!


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Basic How-To to Change your Auto-Transmission Fluid

Post by bilchuck » Sat Jun 16, 2018 5:19 pm

Great writing, thanks for the information!

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Basic How-To to Change your Auto-Transmission Fluid

Post by cmaza » Thu Jul 19, 2018 12:30 pm

Has anyone got the pictures for this guide archived? Or is anyone in contact with Shipkiller? He has some fantastic how-to guides which i was hoping to get the in PDF form...

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Basic How-To to Change your Auto-Transmission Fluid

Post by rudey » Sat Sep 28, 2019 11:05 am

Is there any information on how much fluid is needed ? Also when the pan was removed were you able to see torque converter ?

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