Chrysler A413 transmission valve body modifications
Last Updated on July 23, 2024 by Mutiara
Here you’ll find some information on how to take a stock A413 valve body and modify it for performance applications. Most of this information was originally posted to turbododge.com by Joe Dzwil, a big thanks to him for sharing his knowledge on this subject.
Remove the valve body from the trans, turn it upside down and seperate the two halves. The check balls should remain in the top half.
Remove the check ball that is marked in the above image. “This allows second feed oil to bypass a restriction in the v/b spacer plate.” Now it’s time to enlarge some holes in the spacer plate. “Valve body spacer plate feed holes for third gear.
I opened the upper two holes in the pic to .161″ (size 20 drill). For the two holes on the right side of the spacer plate, the outer hole is opened to .161″ and the inner is .157″. The holes are colored red in the picture. MP drilled the two on the right to .125. You can make them bigger (the two on the right) then I did (.157″ and .161″), but the valve body passage walls will be compromised.” Note: When your out shopping for drill bits- .125 would be 1/8 and .157 would be damn close to 5/32.
Notice in the picture of the MP spacer plate (above), that two passages are blocked on the far left. This removes the accumulator from the circuit, resulting in a harder 2nd gear shift. If you can’t get ahold of a MP plate (like most of us), then drill/tap and plug the two holes in the transmission case shown below:
Next, we need to immobilize the shuttle and bypass valves. After you’ve reassembled to two halves of the valve body, turn it right side up and remove the end cover shown below:
Remove the shuttle valve plug and spring, you’ll want to replace the spring with a solid spacer to prevent the valve from moving. “The shuttle valve is held by a steel rod, 1.458″ long by .250 wide. The shuttle valve spring is removed and replaced by the rod.” With the end cover back on, there should be just a little play (maybe .002-.003). See below:
Now do something similar to the bypass valve. “Like the shuttle valve, the bypass valve gets held from moving with a spacer. MP used a .187 steel ball. It gets slipped inside the bypass spring. I think I use a 5/16 steel rod for my last few. When you are done, make sure there is a little free play so the end cover is not held off the valve body.” See below:
Now the line pressure needs to be raised. The hex screw is turned counter-clockwise to raise pressure, however, the stock regulator spring is not stiff enough for high performance applications. “Seven turns of the line pressure screw is not that much extra pressure, around 11-12 psi. (but it is about the max of what the stock pressure reg. spring can handle). Added to the stock 80 to 88 psi you are most likely less than 100 psi at full throttle.” The adjuster will only allow approx seven more turns beyond stock before it runs out of thread. This gives a maximum of about 90 psi with full TV pressure.
This is a much stronger spring that I found at a local Sear’s Hardware store.
If you install it as-is, your min line pressure will be almost 200 psi! I cut four coils off and ended up with a 60 psi min, with the ability to go up past 120 psi.
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Now keep in mind increasing line pressure will also affect the WOT upshift points. With a stock governor, you’ll start hitting the rev limiter even before the stock regulator spring is maxxed out. Check out this page on turbododge.com to learn more about modifying the governor to compensate for the increase in line pressure. In addition to that, increased line pressure will eventually break the low/rev band strut. Sonnax makes a heavy duty replacement, part number 32710-01.
