5R55E Valve Body Sonnax Zip Kit Install | Ford Explorer Forums - Serious Explorations

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5R55E Valve Body Sonnax Zip Kit Install

Paul Fithian

Elite Explorer
October 12, 2016
Reaction score
City, State
Long Beach, IN
Year, Model & Trim Level
2007 Job 1 RWD V8 Limited
Thanks to the great information posted in this thread, http://www.explorerforum.com/forums/index.php?threads/5r55e-valve-body-rebuild-diary.140987/ , I had the confidence to dive into my transmission on a recently acquired 2001 Sport Trac with 258,000 miles. Runs great, transmission shifts well, but it did have delayed reverse engagement. No funny stuff in the fluid either. It appears to be original, with non-bonded gasket separator plate.

I removed the pan and dropped the valve body out (see PS below) to install the following on this high mileage transmission.

1) EPC Solenoid BW 50155
2) Valve body separator plate with bonded gaskets 1L5Z-7Z490-HA
3) Solenoid bracket XL2Z-7L491-AA
4) Sonnax 4R44E-5R55E-ZIP kit
5) Low/reverse servo piston D-Ring kit seals 23256K
6) Reverse servo cover gasket 23128
7) Transmission Pan Gasket 23141D

I took resistance readings on all the solenoids once I had the VB on the bench:

Solenoid: Reading (Normal)
TCC: 10.1 (8.9-16)
EPC: 4.5 (3.1-5.7) New and old measured the same
Coast Clutch: 25.2 (22-48)
Shift A: 25.4 (22-48)
Shift B: 25.3 (22-48)
Shift C: 25.3 (22-48)

Installation of the components in the Zip Kit was straightforward and the instructions were clear. I did not replace three items as detailed in the Sonnax instructions:

Step 4D: Plug for Bore 109, Coast Clutch/Converter Regulator Valve, as the OEM plug would not come out and I did not want to drill a hole in the valve body as detailed in the Sonnax instructions.

Step 6: Separator Plate Modifications. I left the plate alone, as built by Ford.

Step 7: Smallest inboard cooler bypass spring remove

The only issue I noticed was the condition of the Low/Reverse Servo O-Rings. They appeared to be degraded, and residue on the metal parts was easily cleaned off with acetone. I suggest you test insert this Low/Reverse Servo piston without new O-Rings to confirm the ****ed orientation of it before final assembly.

No problems with the reassembly. Test run revealed it shifted great in all gears, no more delayed reverse. No leaks either.

The Sonnax instructions have torque, bolt length, and other specifications that are useful for any valve body work in these transmissions. See http://d2q1ebiag300ih.cloudfront.ne...ns/2172/4R44E-5R55E-ZIP-IN_B.pdf?v=1487624733


I dropped my oil soaked valve body in a pile of Oil Dry. Not a pretty sight, looked like the last time I made Schnitzel and dredged the egg coated meat through a pile of Panko. Try not to do this.

I was able to wash it by putting the valve body in the transmission pan and pouring mineral spirits over it. It took a few iterations with filtered solvent before I got all of the granules out. Close inspection of the valve body passages with a flashlight revealed a few more bits as well.
5R55E Valve Body -Parts.jpg
5R55E Reverse Servo O-Ring Deposits.jpg
5R55E Reverse Servo O-Ring Deposits 2.jpg
5R55E Transmission Case Hydraulic Circuits.jpg
5R55E Valve Body Before Disassembly.jpg
5R55E Valve Body -Gasket As Removed.jpg

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After a week or so of driving, one thing that I have noticed is that 3-2 or 2-1 downshifts are a little harsh, I can feel it in the brake pedal.

I will adjust the bands to see if that helps, but I also posed this question to Sonnax, here was their reply:

The Zip Kit for the 5R55E comes with an elevated ratio boost valve. Sometimes the side effect can be downshifts that are a little too firm on some applications, particularly 2wd models with the 4 cylinder engine. The only way to change this would be to install an oe ratio boost valve, or try adjusting the EPC solenoid counterclockwise about an 1/8th turn. Do not exceed 1/4 turn as this will create line rise issues and may damage the unit.

I will post findings once I try one or both of these. Any other advice?

EPC Adjust Screw.png

I will also install a new Dorman 265-831 pan with drain and a Hastings TF140 4WD filter the next time I drop the pan to enable fluid draining. Wished I would have done this the first time I dropped the pan!

I can advise that Sonnax's suggestion to rotate the EPC Torx screw counterclockwise to reduce harsh shifting after installation of a Zip Kit on a 5R55E works.

I initially rotated it 1/8 of a turn counterclockwise. It did reduce, but not eliminate harsh upshifts.

I then rotated it another 1/8 turn counterclockwise, 1/4 turn total. It now shifts up and down like a new transmission, much better than before. It works perfectly.

The Borg Warner EPC solenoid uses a T-15 Torx driver to adjust.

OK, so an update. For the past few months, the transmission has operated perfectly. Except that once in a while, I will get a slight shudder when in reverse.

I have recently started to tow the boat with the truck. Does fine, except when I went to back the boat into its parking space, which is slightly uphill.

The transmission really struggled with this, and would barely move the truck.

Maybe I should up the EPC pressure a bit to see if it improves? Or could this be the broken reverse band tab that we all fear on these transmissions?

The picture you posted of the reverse servo is covered in you reverse band friction material. Probably just finally lost enough that it lost it clamping ability or you may have a broken lug on the band.

I agree with them, I would really avoid high stress usage, like towing. It sounds like it might last many years if it sees normal driving. But with towing, it may not last long. In optimum condition, the 5R55E is a strong reliable trans. But if anything is off a bit, it can go down fast, and be hard to correct to new conditions.

For towing, I suggest a larger trans cooler, added to what's there already. Route it in parallel if you can.

Thanks guys, good advice.

I am thinking about replacing it with remanufactured unit from Rock Auto.

But how do I tell if it has a sensor above the linkage?

Truck is a 2001 RWD Sport Trac, VIN is 1FMZU67E21UA81816 with a build date of 13.06.2000

Low/reverse servo piston D-Ring kit seals 23256K were installed when I did the valve body work.

Further test today, trying to back up a steep hill in reverse. Very little engagement, it was difficult without a running start.

I then tested engine braking in 1st gear. It worked, but appears to be very weak, not as much braking as I would expect.

What could the problem be with it?

That is likely not the hard parts, the clutches/frictions/steels. It'll be one of the many typical control parts of the VB, solenoids or accumulators. If you keep pushing it, the clutches will be worn out, and force you to have to rebuild it.

If it's low mileage, keep at it to find the one magic part to replace. But it's higher mileage right. Consider every part you replaced of what can be without rebuild. I would replace everything that you have not, but still not be confident that the recent parts are fine either.

Read about other issues with the 5R55E on the forums. You should find the same things suggested by others elsewhere. You might also find the less common suggestions, a few Sonnax upgrades, plus for possible pressure losses at the case/VB surface, installing set screws up into the passages where some are very(too) long and can move side to side under pressures.

There is a lot that can be done besides dropping and rebuilding the trans. The problem with 95% of all trans issues is among the owner serviceable parts. I don't know the source of your 5R issue, but I would always go at the used parts not yet changed(and very old(high mileage)), plus possible upgrades available.

Thanks Don, it is greatly appreciated. I will get a pressure gauge and check the line and EPC pressures.

From there I should be able to determine the next step.

Testing actual pressures is an excellent procedure. Most people don't even think of it, and we/I rarely mention it either. I have a gauge and SS line I built about 25 years ago to test/set the pressure for my AOD's back then. It is critical on those to have the right TV pressure, and a gauge seemed like the best way to get it there.

Your EPC is new, Borg Warner I hope, and the main component for all internal pressures. Checking that would be great. Hopefully you find something obvious and clear to do. I would want all of the solenoids to be nearly new, and the Sonnax upgrades too. I forgot if you already did all of the accumulators?

My trans went out due to some kind of part breakage(small part in the pan), and the error code said the EPC was maxed out. It couldn't produce enough pressure to run the trans. I had lots of slippage in 1st gear, leaving my driveway. I never tried to go far, I just backed it up and noted it was the same forward and reverse. I pulled it back into the driveway, and it's hardly moved since then. So my damage should be isolated to the one part, and a normal rebuild should fix it all to be like new. Driving a car with a slipping transmission is really bad, people do that too much.

I can report that a replacement valve body from Shift Rite with an installed TransGo shift kit completely solved the weak reverse issue I was having with this transmission.

I have not done a pressure test, but reverse is strong under load, no slipping at all.

Shifts quickly and smoothly now in all gears, just like new.

Here's the valve body I installed: https://www.amazon.com/Shift-Rite-T..._rd_t=40701&psc=1&refRID=9FR0QBWKGVV8EM96ZDMQ

Well done, that's good to hear.