Engine Drivetrain 1st Gen Cooper S The Automatic Transmission Rebuild Thread

This thread provides some valuable info on what to do about a dead / dying / misbehaving Aisin TF-60SN automatic transmission, found in 1st-3rd generation MINIs of many flavors. While my experience is limited to the 1st gen MCS, much of this will be directly applicable to other models.

Disclaimer:
I am not a professional mechanic or transmission repair expert. I do not do this for a living. Information provided here is provided as-is, in the hope that it may help someone with "issues". Do NOT PM me asking for my phone number, do not expect to have a 6 hour phone conversation (or 1000 message text conversation) about your specific issue. I wish you great success, but I don't have time to diagnose everyone's transmission issues. I will NOT rebuild your transmission for you, unless that is my punishment once I get to Hell. Don't ask. :devil:

Background:
Blimey, my 2006 MCSA convertible, was my daily driver for about 7 years. This included lots of highway miles, but also lots of aggressively driven twisty miles (14 trips to the Dragon so far, and counting). After about 60k miles, I started having some delayed shifting and general misbehaving. I was among the first batch of owners to ignore the "lifetime fluid" BS and start the fluid refresh regimen pioneered by fishbone and described here. Partial changes every 20k miles or so served me well until several weeks ago, at about 151k, when my transmission started going south in a big way.

My symptoms:
While returning home after a rousing day at Carolina Motorsports Park, the car started exhibiting weird shifting behavior, and would eventually go into "neutral" with no propulsion. Switching the car off and back on would set things right for somewhere between 30 seconds and 30 minutes, then the behavior would recur. I limped home like this over a 3 hour drive. The nature of the symptoms, and the ability to temporarily resolve it with a power cycle, led me to believe it was a valve body failure of some kind.

What I did:
I first attempted a valve body replacement. Purchased a remanufactured valve body form RevMax and installed it using instructions found here. I noted a lot of magnetic residue on the fluid pan magnets... not a good sign. But these hadn't been cleaned in 150k miles, so some amount of magnetics is expected.



After buttoning this up and testing, I still had some issues. Used the BMW scan tool to read codes off the transmission control unit, the errors pointed to a faulty solenoid. Talked with the folks at RevMax and they sent out a replacement solenoid to test. I installed this and it resolved that issue, but on testing I found that I still had significant shifting issues from 3-4 and above after the transmission heated up. Checked the fresh fluid and it had tons of black particulates in it. Some clutch was toast, probably the K-2.

Time for a rebuild.

I've heard of people spending $3000-$5000 for this. I'm pretty handy, and figured I'd tackle it myself. It's not my daily driver, and I could deal with the car being down for a month or more if that's what it took. I also have enough garage space, a good workshop space, and lots of tools. Don't attempt it otherwise.

Many shops won't touch these, apparently. And, when they do, it's crazy expensive. There's really nothing special about the transmission itself. There are no "hard parts" available (nor do they typically need any), but service kits are readily available. The biggest deal is that the engine must be pulled to get to the transmission. If you're not up to doing the transmission rebuild yourself, and you have problems finding a transmission shop that will work on MINIs, you may find a shop that will do the actual rebuild, if you or a friend or a MINI-capable mechanic can do the engine work and just bring the shop the transmission, off the car. Investigate this option if you think it may fit your situation. Some shops may do that, some may not.

The rebuild:
Luckily, the MINI automatic transmission isn't the mystery that it was a few years ago.

All automatic MINIs except 1st gen CVTs use the Aisin TF-60SN transmission. This same transmission, with some minor variations, is used in a number of VW and Audi models. Rebuild parts kits and service manuals are available from transmission supply houses.

Here's the transmission service manual.


An online copy is here.
It's extremely detailed, with all schematics, electrical and hydraulic testing parameters, and step-by-step tear down, inspection, rebuild and reassembly instructions. This one is 124 pages long. You'd be a fool to attempt this without a hardcopy of the manual handy where you can get it greasy (about $30).

Here's a good exploded view of the transmission: http://www.makcotransmissionparts.com/mm5/graphics/Catalog-pdf/AWTF60SN.pdf

Valve body failures are common, and most early failures can be cured (if caught in time) with a valve body replacement. This can be done without removing the transmission from the car. Frank at RevMax is a valve body guru and can talk through the symptoms you're having and determine if a valve body may fix resolve them, before you spend the money on one.

Beyond the valve body, a common problem (that I thought I had, but didn't) is that the K-2 clutch sleeve spins on the mount in the case. This restricts fluid flow and causes clutch failure. A replacement is made by Sonnax, and is recommended for ALL rebuilds to prevent future problems: K-2 Clutch Seal Ring Sleeve Kit - 15759-01K - Sonnax
Installation requires a 0.062" drill bit, I bought a couple from DigiKey for a few bucks.

Here's a supplier for the transmission parts (there are others):
VW 09M, 09G, Aisin TF60SN Transmission Parts Volkswagon / Audi
The best actual rebuild kits are made by TransTec and resold by Macko and others. Some folks may sell less extensive kits, hold out for the TransTec kit if you can, this definitely has all the parts that the manual calls for.

I opted to buy the basic "overhaul" kit, and add all friction plates, and also replace a couple of sets of worn steels (the K-2 and B-1, I think) based on what I found in the tear-down. They offer some kits that claim to include all the friction plates also, but the manual says that numbers of plates vary by transmission variant, and I didn't want to risk getting the wrong number of plates. The overhaul kit actually contains all the seals and filters for the valve body also, which I didn't need. But there's no practical way to get all the things I DID need without buying the full kit. I spent about $500 on parts, but could have saved about $100 if I hadn't bought the Sonnax K-2 clutch sleeve (which, ultimately, I didn't need).

I also found a low-mileage torque converter on eBay and decided to swap that out while I have it apart. There are rebuilt torque converters available for the VW\Audi, but those have the starter gear welded to the converter shell; I don't know if they're interchangeable with the MINI OEM one. The used TC was $350. That, plus the $750 or so I spent on the valve body, and fluid, and the total job will cost me about $1700. Not cheap, but better than a $3500 used transmission with no warranty, or $3000-$5000 for a shop to do the full job. You can save some money by doing the valve body rebuild yourself; you'll need a rebuild kit that includes bonded pistons.

Unfortunately, all this requires removal of the engine, which is a big reason this is a pretty expensive job that many transmission shops won't even attempt. Bentley manual has the info you need to pull the engine.

This was the first time I had ever pulled the engine out of the car. Took a full weekend, including a trip to Harbor Freight to buy a shop crane. Next time I'll be faster.

After pulling the engine, you remove six nuts holding the flywheel to the torque converter, and several bolts connecting the transmission bell housing to the engine. Then you can separate the transmission. The Bentley manual gets you through this point.


You don't need the special BMW tools to remove the torque converter. Just wrap your fingers around the sides, use both hands, and pull. Careful, it's heavy and full of fluid.

The transmission is pretty heavy, I'd guess well over 100 pounds. I used the crane to move it to my workmate beside my workbench, then slid and rolled it onto the bench top.

The ATSG service manual provides all the info you need to actually do the tear-down and rebuild. Make sure you have a large, heavy-duty workbench, with either a metal top or a sacrificial surface you don't mind destroying with fluid and dragging a heavy transmission around on it (I had an extra piece of heavy MDF that I put on my bench). Also have a large table to lay out the parts as you do the disassembly, this will help you not get things mixed up later.

So after pulling off the pan, valve body, gear selector switch and heat exchanger, it's time to remove 21 bolts and crack open the case. Here's what you'll see:


The book makes tear-down easy. Really no big deal. I'm not going to repeat the step-by-step tear-down and reassembly, because that's all in the book. Even though the book has great instructions and schematics, I took LOTS of pictures as I went, of every step, so I could figure out things later if any questions arose. I was glad I did, at a few points. I recommend you do the same.

There was one snap ring identified in the instructions, that wasn't present in my version of the transmission. And a couple of parts had been "revised" compared to the original TF-60SN (the book noted improved aftermarket parts, but my parts were like the "improved" ones). Otherwise the ATSG manual was dead-on.

After a couple of hours, you end up with a table that looks like this:


I took GREAT CARE to follow the directions in sequence, and lay out the parts in the sequence removed to aid in both identification and reassembly.

All the hard parts (gears, bearings, etc.) looked perfect. My suspicion was that one or more clutches were toast. Especially the K-2 clutch, which is pretty much what always fails. I took apart all the clutch and brake assemblies and inspected them thoroughly, as well as counted the number of friction and steel plates in each one for my parts order.
They all looked pretty much like new, except for this one (the K-2):


The first clue was the discoloration of the steel pressure plate on the top of the stack. That should be clean and shiny... not looking like it's been on fire...

Disassembled:


And, sure enough, most of the friction plates showed obvious wear, with some surfaces completely lacking any friction material... looks like it had been running metal-on-metal for a while. Here's the worst friction plate surface (should be a textured black surface... NOT shiny...):


And a typical steel plate looked like this:


So that's a good reason why my transmission pan magnets were coated with material. Lots of metal dust being created...

One common reason why this happens, is that a press-fit sleeve that the whole assembly rides on can spin on the case, and block some fluid ports, making the whole thing FUBAR.
I suspected this was my problem, but upon checking the sleeve position, it was correct; it hadn't spun. I decided instead of pulling it and replacing it with the Sonnax sleeve, I would just drill it and install the roll pin that came with my Sonnax sleeve, preventing any rotation in the future.



Since my sleeve hadn't spun, I'm suspecting that my K-2 just plain wore out from too much heat (maybe exacerbated by valve body issues)... the 3-4 shift is my "money" shift on the track and on the twisties, and I have shifted it hard many, many times.

If you want to get an idea of how it goes back together, here's a video (it doesn't show the details of the sub-assemblies, but the book does):
[ame="https://www.youtube.com/watch?v=33rYBqa9zD4"]09G / TF60SN Transmission Re-Assembly - Transmission Repair - YouTube[/ame]

Rebuild took about a day's work. The only part that was problematic for me, was the splines of the oil pump shaft wouldn't slide into the sun gear properly. Something had gotten dinged up a bit and made a burr that kept these close-fitting parts from going together. I had to disassemble to get the sun gear out, and persuade them together and apart several times (hammer and pliers at first, then eventually by hand) to get things fitting properly, then reassembled.

Finally everything went back together as it should. No left over parts!!!


Here's all the stuff I replaced: all frictions, some steel plates, and every seal and o-ring in the unit.


Another thing I did while on the bench, that isn't explicitly called out in the manual, is to remove all the T-55 and 10mm hex plugs in the case and bell housing, and replace the o-rings on these. The appropriate o-rings are in the kit.

Having this all apart, I learned a good bit about what all the various bolts and plugs are in the case. The port on top, that many of us use for fluid fill, actually connects to the cooling and lube circuit with lots of restrictions. That's why it takes so long to fill that way.

The REAL fill port is at the 11 o'clock position on the differential portion of the bell housing. This one has no internal restrictions, just dumps straight into the differential case. Unfortunately, it's a bear to access when on the car. Supposedly you can get to it somehow...


I also scoped out positioning for a couple of oil pan nipples to allow an auxiliary oil cooling circuit to be setup. I have a plan for this, will get a new pan and have a couple of nipples welded on, but needed to figure out where they would work. Here:


Now just waiting to get my replacement torque converter, and I can put it back on the engine and get it all back together. Will be a few more weeks before that happens.

 

No limited slip diff that I'm aware of will work. Quite different from the manual.

 

I'm thinking about trying to come up with some kind of metal fill tube assembly that would screw into the fill port, and hold pressure... Or at least come us with a hose with a screw-in fitting for that port that could be fitted for filling from the top...

 

That's what I had in mind

 

Symptoms?