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Fossilized Member
1,206 Posts
Discussion Starter #1 (Edited)
First off, I would like to say this is not a shift kit. This modification will not make the transmission shift any harder than it does for the other gears. It will however, improve the delayed or slipping 2-3 shifts on the F4A51 transaxle; assuming your transmission does not have any other problems with it.

Transmission manufacturers incorporate several mechanisms into the design to soften or cushion the shifts for the sake of comfort. They use wave springs, accumulators and flow restricting orifices to name a few. The restricting orifice slows the flow of oil to the clutch pistons and servos. In the following hydraulic schematic, you can see this illustrated.

What I am going to show you is where and how to get to this restriction, and open it up to increase flow. This is not a theory. I performed this modification on my own 3G Eclipse that was suffering the same shift flare that has been described by many others. My car now shifts perfectly and no reoccurrence of problematic shifting has been detected since this modification.

No special tools will be required. You need basic hand tools, oil drain pan, drill and 3/32” drill bit and a clean work area. I strongly suggest you have an inch/pounds torque wrench available. You will also need a tube of silicone gasket maker such as Permatex.

Disconnect your battery, then raise and support the front of the vehicle. Drain the transaxle completely. Remove the air cleaner box and the plastic splash shields under the drivers’ side of the car. Remove the black cover on the front side of the transaxle.

You will need to remove the valve body from the transmission to get to the separator plate highlighted in the illustration below. I am going to instruct you to dissemble only what is absolutely necessary to accomplish the task.

Remove the internal detent spring and retaining bolt. (56 in/lbs upon assembly)

Disconnect the shift solenoid connectors. Some of the shift solenoids can be cross-connected on assembly. Because wire diagrams and the color of wires for your car can be different, make notes or your own diagram of what color wires and plugs go to which solenoid. Yours can be different than the ones in the next diagram. Disconnect or unbolt and remove the fluid temperature sensor. Older models could be unplugged from the wiring harness. On later models the sensor is part of the harness and cannot be unplugged. Remove the bolt holding it in to remove the sensor. Be prepared! When you remove this sensor have the drain pan ready, as another quart of fluid will be liberated when this sensor is removed. (Don’t say I didn’t warn you.) Drape the wiring harness up over the top of the transaxle so it is out of your way.

Remove the 27 valve body bolts. Don’t remove the 4 bolts labeled “E” in the following diagram. Those 4 bolts hold the valve body together. (95 in/lbs upon assembly)

The valve body is held in position by two hollow dowel pins. After the bolts are removed, it will take a little effort to remove the valve body. NOTE the two steel balls in the top of the valve body. The valve body also has a very thin, delicate paper gasket on the back of it. Be careful not to damage it. The manual valve will also become free. It is the valve at the very top of the valve body with a pin sticking straight up. This pin must engage into the slot in the detent plate upon assembly.

There is a small plastic screen behind the valve body. It may fall out when you remove the valve body. That’s not a big deal. It just sits in a small rectangular cavity in the transaxle, and the valve body holds it in.

Set the valve body on a clean work surface. Be sure to remove the paper gasket and set it aside so it won’t get damaged. Remove the last 4 bolts that hold the two halves of the valve body.

Lift off the top plate and the top half of the valve body together and set them aside. Do not turn it upside down or remove the very top plate. Small pieces can fall out. Now you can see the separator plate. I have highlighted the original orifice hole and the added hole. The white outline is of the upper passageway.

Lift the plate straight up and off of the lower half of the valve body. Be careful. There are 3 small check balls and two springs under the plate. They should stay put and not go anywhere if you are careful.

Clean the separator plate off and look for the hole that I have highlighted in the previous picture. Drill a 3/32” (.094) hole next to the original hole. Make sure the position of the new hole is close to what is pictured. The position does matter. If you look at the direction of the passageway underneath the plate, you can see the new hole follows that direction. The new hole you drill is the same size as the original hole. You have just doubled the flow of oil to the clutch pack. There is no need to go overboard. The reason I didn’t just open up the original hole is, because the passageway in the bottom half of the valve body is narrow and a hole twice the size will be obstructed.

Clean the plate off and reassemble the valve body. Install the 4 bolts that hold the valve body together. Leave them finger tight for now. You will torque them down with the others. Install the valve body back into the transaxle. Make sure the paper gasket and plastic screen are in place and the two large check balls are installed in the top of the valve body. Also, make sure as you install the valve body, the pin in the manual valve is engaged in the slot of the detent plate. Finish the assembly in the reverse order from this point using the bolt diagram above.

I disconnected my battery while I did this work. The first drive cycle afterwards had some strange shifting until the PCM finished learning. After the second or third drive cycle, everything smoothened out and works perfectly.

Feel free to PM me with any questions you may have.

Happy motoring.

2011's are gay
4,791 Posts
this is a very good modification if you do it correctly, it is definitely something that you don't want to screw up, there is a very odd shaped and extremely brittle paper gasket in there that you don't want to rip, you won't find another one.

having done this myself there is only one thing i would like to change- the hole that you have to drill: i would suggest drilling it 1/16" instead of 3/32". now i know that seems stupid as both holes are extremely small and it is alot of work just do drill one hole but trust me, it makes a big difference. also make sure that after you drill the hole that you smooth down that lip that is created around the hole from drilling and that you remove all debris. And please, double triple and quadruple check that you drill the hole in the correct spot. mainly just take your dear sweet time and use your head, you don't want to mess this up.
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