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Swapping A-604 Automatic Transmissions from Chrysler to Chrysler

by Jeremy Schrag

The early Chrysler A-604. Rarely has such an innocuous looking collection of letters and numbers provoked such a shudder of trepidation; but this transmission was a nightmare in its early days. Introduced at the tail end of the 1980s, the 41TE, as it's now known, was groundbreaking in its day. It was electronically controlled, and used clutches for shifting gears, not bands.

Unfortunately, it was rushed out the door far too quickly, and used on more cars and minivans than was wise. For four years, these transmissions underwent a staggering number of part upgrades and redesigns as Chris Theodore led a team of engineers in fixing numerous small issues that together had led to big problems. They failed left and right in those days, sometimes in the middle. Countless owners were left stranded by them.

Someone had decided that the transmissions could use Dexron fluid, and that someone turned out to be wrong, but not before Dexron made it into scores of owners' manuals and shop literature (Chrysler was also lax in removing references to using Dexron "when ATF+3 is not available.") Even today, there are still some people out there who have no idea how picky these units are, and some of them work at transmission shops. [See Chris Theodore on fixing the A-604 UltradriveSee our four-speed automatic repairs page]

Long story short, things didn't get really reliable for the good old A604 until the year 2000, when ATF+4 was introduced. Earlier units could be made reliable, but the key was to change the fluid frequently and use only ATF+3 or ATF+4.

I fell victim to the reliability issues plaguing the early A-604 when I bought the car in the above picture, a silver 1992 Imperial. It had been moderately well cared for mechanically, as the previous owner was the daughter of a mechanic. Even so, the car inherited several issues from the original owner, who bought it new. The mechanic's daughter didn't have it long enough for the mechanic to address all these. Indeed, he didn't even know about some of the issues I discovered.

The transmission first gave me some hints of what I would be in for when I drove it back from Vancouver. I had already planned for a full ATF+4 flush and new filter once I got home, but it became clear to me once I got into the mountains that perhaps I'd gotten to this car too late for this to save the transmission. It began to harshly kick into and out of torque converter lockup. Shifting became rougher. I knew the flush would smooth things out , as the fluid was dirty and way past needing a change, but as long as I could put off the major expense of transmission surgery for a couple of years, I'd be ahead. The car was only a thousand bucks to buy and so rare in my province you're lucky to see one for sale in a year.

I got the car home, then did the flush using the method found on Allpar, using 12 liters of ATF+4 and a new filter. Then, in warm weather, it shifted almost perfectly. 1-2 had a small delay, but the rest of the shifts were smooth and fast. But the huge amount of metal I'd also found on the oil pan magnet did little to make me think things were over.

Sure enough, once winter came, I found some more issues. The car would stop at stop signs with the engine cold, and slip out of gear. That first 1-2 shift became longer and more noticeable. It was okay again once the car warmed up, but it still worried me.

I tried to nurse the transmission through another year of service. I changed the fluid more often than even the severe duty schedule calls for, cleaning a pile of debris off the magnet each time. I cleaned the speed sensors. I upgraded the TCM to the flashable one with current firmware. I tried Lucas Transmission Fix. I even rebuilt the solenoid pack, which gave the most improvement, not counting that initial ATF+4 flush. But the transmission still had trouble at stop signs when cold.

Then, one day, I became convinced the car was running a liter low on transmission fluid. I was always adjusting fluid levels back then, trying to find that magic level where the unit would work best. Being the cautious type, I added half a liter, intending to add more once I checked the fluid again. It didn't take long for the transmission to scold me for that one. Within ten minutes, it began to slip and buck. I came to a stop, let the transmission cool, and went back home at a slower speed to keep the fluid from getting any worse. I corrected the fluid level. But it was too late - the torque converter started slamming into and out of lockup, as it had in the mountains of BC. I changed the fluid again. No good. Then, reverse gear turned intermittent, and I realized it was all over for the Imperial's original transmission. I'd nursed it through four years and 23,000 kilometers, and that's all I was going to get from it. This car needed a new transmission.

That's where this sad looking car comes in. A 1991 Fifth Avenue, it was sidelined by a broken rocker pedestal in the 3.8. The owner decided that was the end of the road. It had engine problems, body damage from two accidents, rusty rocker panels, and rusty spring perches on the rear axle, with 250,000 kilometers on the odometer.

It did have one part in it that made it very useful to me - the transmission. 1991 is the only year that would interchange transmissions with the Imperial, and this particular car had a rebuilt one. Not only that, it was a well documented rebuild. I knew who rebuilt it, what was done to it, and how the car was driven and maintained since. I knew how much mileage was on the rebuild. And the best part was, I got the whole car for $350 Canadian because I happened to be related to the owner.

That's not to say there weren't issues with this rebuilt transmission, because there were. This car had always leaked oil from the axle seals, and I didn't know why. But for $350, I reasoned I would take the gamble. I would buy the car, remove the rebuilt transmission, and just swap it into my Imperial. I would then keep the old transmission, just in case. If things didn't work out, I could then just take my old transmission to a rebuilder and save on the remove and replacement charges.

Now, let me tell you all about swapping transmissions in a 1990s AY body car, because I know now that it is not that easy.


In order to do a job like this, there are a few tools you absolutely need, and some that are not necessary but will save your sanity. The above transmission jack fits into the latter category. Costing me some $200, it has already paid for itself.

Among the tools you do really need, there are the usual suspects. You need a good ratchet for sure, a torque wrench, a breaker bar with a 32mm socket to get the axle nuts off, and sockets in 8mm, 10mm, 13mm, 15mm, 18mm, and 19mm. Deep sockets aren't necessary for most of these, but they don't hurt either. A long offset 15mm wrench helps with the torque converter bolts. A set of decent extensions will help a lot... get an extra long one, like two feet long, and you can remove the bell housing bolts through the left side wheel well when you get to that point. That will make things go a lot smoother.

You also need the usual jacking gear. I ended up needing two jack stands (I had a third handy just in case), the scissor jacks from both cars, my new transmission jack, and my broken but still useful trolley jack with the absurdly low lift range.


Let's examine the above picture of the 1991 for a moment. The engine bay of these cars is rather cramped; it was not originally designed with the 3.8 and A604 in mind. I have already cleared this side of the engine bay. The battery tray, intake hose, air filter box, and cruise servo have all been removed. The radiator overflow bottle has also been removed, but I discovered it isn't necessary to go that far.

All electrical connections to the engine on this side have been disconnected. The shift linkage has been removed, along with the crank sensor has been removed, and you'd better believe this is an important step. Otherwise, you might damage it or the flexplate when you remove the transmission.

All wiring has been disconnected from the transmission. The solenoid pack, speed sensors, range switch, and neutral safety switch are unplugged. Orange arrows indicate the cooler hose fittings - I did those later. This is the new transmission, I wanted to minimize the chance of any debris getting in there. So, I disconnected and duct tape over those fittings just before I dropped the transmission out.

A red arrow indicates a hold down bolt for some of the heater core supply lines. This bracket also holds some wiring. All I had to do was loosen this bolt - the bracket is slotted and will pull off when the transmission drops. Yellow indicates the shift cable clamp. A 10mm bolt clamps the cable in place, while a 13mm bolt holds the assembly to the transmission. This bracket did not have to be removed on the 1991, but did have to come out on the 1992. This is because the 1992 still has its catalytic converter, which limited the amount of adjustments I could make to the angle of the engine and transmission.

Finally, there's a cyan arrow up there. This indicates the one longer bell housing bolt that is used to also hold on the front engine mount. You need to remember where this one goes.


Before going too far with things, there's something else I needed to do - build an engine support bar. Technically, this is one of those not necessary steps, because you could just use a jack and support the engine under the oil pan. But doing so is not really wise. In these cars, the engine has to go down and forward before the transmission will have the clearance to come out. Even with the bar, I still found myself playing with the jacks way too often.

So, here's what I did: I took some 2x4s, some lag bolts, got out the saw and drill, and just built one. I also grabbed myself a 3/4" eyebolt eight inches long to provide some up and down adjustment capabilities, and ten feet of 1300 pound rated chain.


Here's a picture of the support bar installed. It worked beautifully.


Before getting to the major surgery, it was important to make sure it was worth doing. Not only that, draining the transmission fluid does make it a little lighter.

The above picture is what I found when the pan came down on the donor transmission. The magnet has some stuff on it, but it's way far from the fuzz I saw the last time the Imperial's came down. This pleased me greatly. I cleaned off the old RTV, installed the new filter, and replaced the pan.


Before removing a transmission, you must remove the parts the transmission is attached to. Namely, the halfshafts. Pull the vehicle speed sensor first. My 1991 donor had an intermediary shaft, as you see here. While the usual course is to separate the ball joint and leave the struts to get these out, I decided to just pull the struts instead. The Imperial's were shot, and the Fifth's were not. I reasoned I might as well get it all done at the same time.


With the axles out, I found the problem with the leaky axle seals - the seals themselves were at the end of the road. The rebuilders, otherwise competent, had not replaced these. Not to worry - I had factory fresh seals from the dealer on hand. But we'll get to that later.

Meantime, I still needed to get access to the transmission before bolting that big support chain in and lowering the engine. See the red arrows? Those indicate the bolts holding the left side splash guard on. The left one is out of frame in this picture. Once the splash guard is out, we can access the transmission mount bolts.


My new transmission jack is adjusted and ready to go, or so I thought at the time. I put the cart before the horse a bit. The jack must be adjusted after lowering the engine and moving it forward. Angle it so that the leading edge of the jack takes the most weight, or the transmission will fall forward a bit and the torque converter will catch on the flexplate.

This was also before I knew to use a ratcheting tie down strap instead of that safety chain to secure the transmission to the jack. If you don't do that, the transmission will slip on the jack and the torque converter may fall off, as mine did. And the safety chain wasn't really long enough to reach around the transmission, anyway.


Now, there is access to the three transmission mount bolts. But before we monkey with those, support the engine with a jack, bolt that support bar chain in place, and remove the front motor mount.

This is also a good place to stop, get under the car, and unbolt the torque converter from the flexplate. You will need to pull two 10mm bolts and an 18mm bell housing bolt to do that, and then the actual flexplate bolts are short 15mm jobs. There are four of those on these cars. Pull the starter motor while you're at it - this will give you even more access to those flexplate bolts. Also, this will make it easier to line up the transmission again later, as the starter has a peg that fits into the bell housing.

I went just a bit further than this, even, and removed that big bracket on the backside of the engine that was interfering with that 18mm inspection plate/bell housing bolt. That bracket will only make things harder for you if you leave it in, and it's only a couple more 18mm bolts to deal with.


This is a good time to show you another tool that saved my sanity - my 1/2" drive adjustable wobble extension. This guy had me kissing him regularly when it came to removing the bell housing bolts up top, and I'm not normally that kind of guy. The "wobble" part of the extension was already a major help, but the extending part cemented my love for this particular tool. Here, you see me fiddling with my engine support scissor jack.


This is where I got once the transmission mount bolts were removed and the engine jack was down. At this point, the whole shebang is not far down enough to remove the transmission. Another couple inches from here is about where I figure I was able to get it out. Also, I found I needed to put a scissor jack behind the engine, between the cross member and oil pan, and jack the engine forward quite a bit to get the right angle. The cross member will interfere with your efforts once you go down far enough - that's why you have to jack the puppy forward.

Now, this is the hard part. I don't have any pictures of this, as my hands got so greasy I didn't want to mess with the camera, but removing this transmission was a royal pain. My best advice is to go very slow, making adjustments to the jacks as needed to clear the flexplate. You need to move the transmission about an inch and a half to the side to clear it. Jack her up a little now. Down. No, wait, left a bit. Wait... left a little more. Oops, now the TC is caught on the flexplate... let's tilt the jack to the left a bit. Ok, up a little more, and we'll push the tranny jack to the... stop! We're leaking and the torque converter's being pulled off! Jack her up, jack her UP!!! Ok, there we go. Aha! The transmission's clear! But the torque converter's lying over there... rats. And yes, I was talking to myself like that the entire time.

Once I had the donor transmission down, I now had to jack the car's body up to enable removal. I ended up having to put a scissor jack on three blocks of wood and run it to its highest to do it. By that time, that whole side of the car was off the ground. I got my transmission out of there as fast as possible so I could jack it back down. You would think the transmission would come out the front, but that's not the case. The dipstick tube is too high to do that without jacking the car up to the moon. Instead, you pull it out the side through the wheel well.


Now, we'll move to the Imperial. I've skipped the whole clearing of the engine bay picture on this car, because it's pretty much the same procedure as the Fifth Avenue. The ABS computer may have gotten in the way of transmission removal, but that whole system on this car is long gone already, including the computer, which is otherwise bolted to the battery box support right below the cruise control servo.

Here, you see the old transmission losing all its fluid in preparation for removal.


To my consternation, using the crowbar on the wheel studs approach to removing the axle nut on the right resulted in all five wheel studs taking some damage, not to mention deforming the hub just a bit. That nut was on there but good... much tighter than any other axle nut I've dealt with on a Mopar vehicle. It took two breaker bars (the first one broke), a cheater pipe, and all 260 lbs of me bouncing on the end of it while hammering on the breaker bar to crack that nut loose.

Nothing like adding five wheel studs to the list of things to replace on this car. A friend of mine from the Allpar forums by the name of mydodgedip provided me with another helpful tip, having been the one to clue me in on the ratcheting tie down strap trick for the transmission jack: just stick a screwdriver in the brake rotor slots to break the axle nut loose. Or in my case, a really big extra long center punch.


Here we are in mid disassembly. At this point, the front motor mount is gone, as are the axles and struts. The only thing holding the engine and transmission in are the left and right engine/transmission mounts.


Here's a picture of the Imperial's flexplate area. Yellow points at the flexplate itself, through the two areas you can use to access the torque converter bolts. Red indicates the front engine mount bolt I used to bolt the support bar chain to. Behind the engine, I used one of the 18mm bracket bolts I spoke of earlier.


The support bar is in place, and the old transmission is ready to come out.


The left side of the Imperial is a bit different than the Fifth. There is less room for the transmission to come sideways, and I found that the bolt arrowed in red interfered. I had to loosen it up a little.

The blue arrow indicates one of many trim clips you will need to replace if you're doing this job on your AY body. I'll show you the new ones in a bit.


I found to my consternation that this car, with its catalytic converter having had to be re-attached after an emergency pull apart with the rest of the pipe, ended up not allowing the degree of engine movement I enjoyed on the Fifth Avenue. While transmission removal was almost easy on the Fifth, it was not easy at all on the Imperial. In the end, the engine only went down so far and had to be pushed forward as far as it would go to get the transmission out. But at the same time, it did go easier in a way because I now had that ratcheting tie down strap to keep the transmission in place on the jack.

In the above picture, I've pointed out the forward/backward and side to side jack adjustments in yellow. This is when I finally got my transmission removal routine nailed down to avoid having the torque converter (red) drop off. Here's what I did: with the strap securely holding the transmission to the jack, I manipulated the up/down tilt so that, again, most of the A604's weight was on the leading edge of the jack plate. Then, I merely made minute adjustments to the side to side adjustment while jacking up and down to find the perfect angle. Once I did that, the transmission got freed up to the point all I had to do was bring it down.

But not without another bit of aggravation I hadn't seen with the Fifth Avenue. There are two long bolts sticking out of the differential cover on this transmission the 1991 didn't have. These consistently got hung up on the cross member, and would not allow transmission removal. Let me show you another picture.


See the yellow jack? That's what finally got the Imperial's transmission out. What had to be done to get those bolts to clear is, I had to jack up the differential end of the transmission while pulling the transmission jack toward the front of the car. About a half inch is all it took to clear the bolts, and then I could lower the transmission jack the rest of the way.

This is about when I learned I needed my tool bag on the end of the transmission jack. It was just a little end heavy, and the transmission wanted to fall forward.


With the old transmission off the jack, I got this picture of the two bolts in question. It's probably easier to grind these down a bit to not interfere, but I had no angle grinder. Since this transmission won't be going back in, I decided to leave them be.


Before installing the new transmission, I needed to deal with those old axle seals on the rebuilt transmission. Above, you see the new Mopar parts. They are pre-lubed to assist with the axle installation.


Not wanting to spend cash for the official seal installation tool, I went down to the local hardware store and bought this. It's a 2" galvanized pipe adapter. The threaded end is the perfect diameter to install axle seals, and it worked perfectly.


One of the new seals in place.

Installing the new transmission proved to be... well, easy. Or at least as easy as possible. The transmission jack was already pre-set to the right angles, so all I had to do was put the new transmission on the jack, grunting and groaning the whole time because these weigh about 200 pounds, secure my tie down strap, and just jack it back into place. Sure, some wiggling back and forth was needed, but I found that I was able to get it lined up with two of the bell housing bolts tightened within twenty minutes. From there, it was just a matter of bolting everything back together.

Speaking of bolting, there are torque specs for all of these bolts you should adhere to. It was easy torquing the bell housing bolts, because they were all more or less accessible thanks to the adjustable wobble extension. But the flexplate bolts were not so accessible. In fact, I couldn't get the torque wrench on any of them. So, I took my offset 18mm box wrench, the longest I had, and just cranked them down as hard as I could. I used a whole lot of force. They won't move now, especially with blue threadlocker holding them in. Threadlocker is your friend on this type of job, because you don't want the flexplate bolts coming loose. At all. That would be very bad.

More about that torque converter. You do have to take steps to line it up properly when you bolt it back to the flexplate, because it only bolts up one way. There's a trick to it. Look at your torque converter... you will see four bolt holes. One of these will have a circle marked near it, about a half inch in diameter. Now, look at the flexplate. One of the bolt holes will be round at the top and bottom, but flat on the sides. That's your index bolt location on both the flexplate and the torque converter. Match the bolt hole with the circle to the oblong bolt hole on the flexplate, and you're good to go. Note that there may be other oblong holes like that in the flexplate - take care not to try bolting to those by accident. They won't line up.

If you do manage to mis-align things, don't panic. You can still rotate the torque converter by reaching through the starter hole in the engine block, getting your fingers in behind the flexplate. I was pretty close to lining it up the first time, but I did have to do this too just a bit.

And one more little tip before I continue. Perhaps some of you have had the torque converter fall off, as I did, on the donor transmission. I want to help you get that back on the input shaft properly. Here's what I did: first, I tipped the transmission on end with the input shaft reaching for the sky. Then, I gently set the converter into place, and began to spin it on the shaft. When you do this, the converter should drop down when it lines itself up properly. It will drop a couple times, until it should be just barely scraping on the bell housing. It sits way down there on the shaft, and that's how you want it for installation. Worry not - once you put the bolts in, nothing will scrape anymore. The bolts pull it back out just enough to be in perfect alignment on the input shaft.


Not a required step but a useful one is to use this here dielectric grease to seal up the solenoid pack connector. It's a big connector that faces the hood - it's a given that water's going to try and get in there. I just squirted a bunch of this in the connector and bolted it together.


These are the trim clips used on the splash guards on this car.


Now, with the new transmission in, I decided a flush was in order. The rebuilt transmission was about 50,000 kilometers into its one and only (since the rebuild) supply of ATF+3, so I was anxious to get the really good stuff in there. And let's face it - I wanted the old Lucas permeated fluid out of the transmission cooler, too.

The red arrow indicates what I do to provide a quick ignition kill - I put some duct tape on the ASD relay, flush until I reach my target level, and yank the relay. Engine dies immediately, no more transmission fluid comes out. That's the idea, anyway. In reality, I was so tired by this point I put the tape on the fuel pump relay without thinking, and it sputtered for a bit before dying; still pumping some fluid out.

My flushing supplies were ten liters of ATF+4, a rapid flow funnel, and a measuring funnel. I used the measuring one to do the initial 3.8 liter (4 quart) fill, then used it again to dump 200mL into another container. Now I knew I had six liters to flush.

That's where the bucket comes in. It is graduated at one liter intervals, so I put a strip of duct tape at the six liter mark so I could see it easier. I put the bucket under the car with it still up on the jack stands, dangled the cooler return line above the bucket, readied my fluid, and started the engine for the first time with its new transmission. It purred like a kitten.


This is my rapid flow funnel in place. I found that it doesn't really flow much faster than a normal transmission funnel, and I was not quite able to dump it in as fast as it was pumping out.

It's all good, though - the transmission never went dry.


All done the flush. Now it's time for the real fun - get the car off the stands, take it for a spin, and top off the fluid level.

How did that go, you ask? Well, I ended up going to the next town and back. I had no major issues with anything. Especially with the new transmission. It is currently shifting like... well, a new transmission. There are no problems with it whatsoever, except a few random harsh shifts that come with the TCM now having to learn it's not working with a slushbox full of worn parts and clutches any more.

As for fluid level, I was still a liter low after checking several times during the drive in 30 degree Celsius weather. But, as I found out the hard way on the old transmission, it's better to be too low on these than too high. It's running in the correct fluid level zone now. Even better, the new seals have totally stopped it from leaking at the axles.

My Imperial is now 100% reliable for the first time since well before I bought it. My total investment on this job is somewhere in the neighborhood of $800 Canadian, including the cost of the parts car. I'm happy. That's just over half the dollar amount it cost in 2007 to have this transmission rebuilt. I had to work hard to save that kind of money, but it was well worth it.

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