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Changing AX4N Valve Body   


Symptoms: My 96 AX4N transmission would hesitate engaging at a stop sign and eventually completely failed with no forward or reverse gears. There was absolutely no engagement, so the clutch pack was not suspected as a problem.

Diagnosis: Before I did anything else, I checked to see if the pump was working (based on telephone advise from a helpful tranny shop). With the car cold and NOT running, I checked the tranny fluid and made note of how high on the dipstick it was (it should be VERY high). I wiped the dipstick off, but did not replace it yet. I then started the car and inserted the dipstick back in within 10 seconds, and rechecked the level. Since the level dropped, I thought the pump was working. Actually, I think if I had re-checked the level when the engine was warm I would have found the level to still be high (
I later discovered the pump had failed).

I next towed the car to an AAMCO shop that read the computer tranny codes at no charge. He came up with three codes indicating incorrect gear ratios and a fourth code (the root-cause code) indicating that the torque converter control valve was stuck.

The technician (very helpful) suggested that the retaining clip on the control valve was broken, and this caused the valve to get stuck. This is apparently a common problem because the valve slams into the retaining clip fairly hard. He then took me down to the repair area and showed me an AX4N valve body, the location of the control valve, and what the retaining clip looked like.

Research: Before I began, I went to the library and accessed the "AllData" web site. This is a mechanic's resource site with a very expensive subscription, but my library provides it for free. I located the procedure for removing the pump and valve body from a Taurus. The procedure was not very clear, but it did show a drawing of what bolts need to be removed. (I have a better picture shown below though).

I also checked out a copy of the Haynes manual (not Chilton) for the Taurus. It doesn't describe how to remove the valve body, but it did show me how to remove the motor mount and sub-frame. However, it failed to tell me I needed to remove the main cross member (neither did AllData).

Postscript After posting this and re-reading it, I realized that the rest of this discussion seems one-dimensional. What you should note is that most of the AX4N tranny problems are related to the valve body. The same procedure and discussion is useful for ANY valve body problem even though mine was the pump. Getting the valve body out of the tranny is $1800 worth of the total repair!

Final Cause: It wasn't until after I got the car apart that I discovered the real cause of my problem. All of the symptoms pointed to the control valve. However, I discovered that the pump shaft had sheered and the pump was fouled up with metal pieces. There was enough friction between the two halves of the broken shaft to make the pump turn slightly, and this is why I didn't detect it earlier.

Inside the pump are two guide rings. These broke and the metal pieces were trapped inside the pump body. The pump would still function properly under high RPM even without this rings. However, at some point the metal pieces jammed into the vanes and seized the pump. This caused the pump shaft to sheer off. The inset photo is an Internet picture of what the pump is supposed to look like.


Repair Options: For $200 I could get new pump parts, but there is a risk that metal got into the solenoids (which are electromagnets). Or for about the same price, I could get a complete valve body and pump at a junkyard. I chose the junkyard. (The junkyard would have provided a completely rebuilt valve body for $350.)

When I took on this project, I assumed that with the $2000 savings I could buy some additional tools. I bought a bunch of tools, but the ones listed below are what I really needed.

Metric socket set with a wide variety of extensions and universal joints.
Air ratchet is helpful but not required.
Impact wrench with metric sockets.
Jack stands are mandatory.
At least one floor jack.

To help me reassemble the car, I took a bunch of pictures.

1. Clean the engine compartment to prevent dirt from falling into the open tranny.

2. Remove the battery, battery box, and battery support bracket.

3. Remove the air intake box and sensors.

4. Disconnect the main wiring harness that is sitting over the tranny control cover. This is a large rectangular connector with a bolt running down the center to hold it together--remove the bolt. You also need to remove this connector from its mounting bracket. I think there is a retaining tab, and then it just slides off. This took a little while to figure out.

5. Do what ever else is necessary to get the rest of the wiring out of your way. Go have a beer, relax, and try it again. You need to have the whole area directly above the tranny side cover clear in order to remove the cover. It will be a tight fit as it is.

I noticed from the new batch of photographs that there was another harness connector I removed. (I suspect two of them actually). This connector is located above the shift link shown in one of the photos below. It may have been the one leading to the tranny solenoids.

6. Jack the car up and remove the driver's side wheel.

7. Turn the steering wheel to give you better access to the wheel well.

8. Place at least one jackstand under the car behind the wheel. Important: Make sure the jackstand is under the unibody frame and NOT under the main cross member supporting the engine. I had to place an additional jackstand under the front of the car to keep the right-rear wheel from lifting.

8.5 (Missing Step) Remove the inner plastic splash guard from the wheel well.

9. With the car's frame supported by jackstands, relocate the floor jack to support the driver's side of the engine (support but don't lift).

10. Remove the isolator (1-nut and 2-bolts) and motor sub-frame (3-bolts and 2-nuts I think). (You won't be able to remove the parts yet.)


11. Raise the engine slightly (mainly to know it is supported).

12. Remove (at least partially) the two bolts that secure the main cross member to the unibody frame. (The main cross member is what the isolator is sitting on. You'll know it when you see it--it is the main support for the whole front of the car.) This is necessary because you don't have enough clearance between the cross member and the unibody frame to remove the engine mount. I found that lowering the cross member an inch or so was all I needed (I did not remove the bolts). I also found out that my cheap impact wrench was not strong enough to loosen these bolts. A friend brought his Ingersol-Rand impact wrench over and made quick work of the bolts.

13. Raise the engine until the engine sub-frame touches the wheel well (as far as it can move) and remove the isolator by moving it toward the rear of the car (big hammer helps).

14. Using some finesse, remove the engine sub-frame from the engine first, and then the transmission. Raise and lower the engine a couple inches as needed to give you the clearance. Be careful. The reason why this is tough is because there is a stud on both the engine and transmission that you need to clear before you can move the frame. Don't bend these studs.

15. Drain the Transmission fluid. I removed the main pan and drained the fluid before I removed the side pan. I thought I had done this with almost no mess, but the next morning I discovered that the transmission had hemorrhaged more fluid over night. I later realized that the cooling lines had drained over night.

16. Remove the nearly two dozen screws that secure the side pan to the transmission. Some screws are accessible from the engine compartment and some are accessible from the wheel well.

17. If the gasket is a thick, ribbed rubber then it is reusable, so be careful not to damage it. If it is cork, then throw it away.

18. Carefully remove the side pan through the top of the engine compartment. It will be a tight fit, but it will fit. Remember, the front face of the valve body has solenoids on it and you don't want to damage these (see picture below).

19. Disconnect the wire connectors at the 5 solenoids (3-right and 2-left) and the temperature sensor at the very bottom. (My wiring harness was stiff enough that replacing it later was a no-brainer--all of the wires lead straight to their respective solenoid.)



20. Disconnect the linkage arm at the top-rear of the valve body (near the wiring harness you just removed).


21. If I remember correctly, there were 25 screws holding the valve body to the transmission. The 4 screws across the bottom are shorter than the others. The 5 of 7 screws through the pump cover are longer than the others. If you remove a screw that seems too short, stop and put it back in before removing any others (especially on the pump cover, you don't want the internal parts to fall out).

22. With the screws removed, the valve body should pop off the transmission with just a little effort. Pull it straight back toward the wheel well. Note that the pump shaft is fit tightly, so cocking the valve body may cause it to bind. The pump shaft MUST stay with the transmission or you can't remove the valve body (it extends into the torque converter by about 8 inches). Because my pump shaft scored the sleeve in the valve body, I had a hard time pulling the shaft out of the valve body, and thought there might be some type of retainer--there isn't. It is a slip-fit spline, so everything should come apart easily.


23. With the valve body removed, if you need to replace any of the 3 right-hand solenoids, press in on the retainer, rotate them slightly, and lift them straight out.

24. The two analog solenoids are held in with brackets. Remove the screws and lift the solenoid out.

25. If you need to replace any of the valves, I would recommend bringing the valve body to a tranny shop for a rebuild. This should still be pretty cheap.

26. When you replace the valve body and cover, I recommend counting the number of screws as you torque them down so you don't miss any.

27. After refilling the transmission with fluid, recheck it after running the engine for a short time, and again after it has warmed up. For me, I forgot about the fluid that drained out of the tranny cooler, and ended up running low in the first minute or so.
If you like this type of information, you might be interested in some of the articles I've written. The most popular is "Electricity in the Woodshop" (a comprehensive discussion about electricity and wiring). Click on the link below to go to my main web site.

Rick Christopherson
Waterfront Woods
This came from TCCA and all props and thanks to Rick for one hell of a write up.



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