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The 5R55S and 5R55W are close cousins. The 5R55W (wide-ratio) showed up first in 2002 behind the Explorer, Mountaineer, and Aviator. The 5R55S (synchronous shift) came right after in the Mustang, LS, Thunderbird, and select Jaguar applications. Internally they share the same case, the same notorious servo bores, and most of the same failure points. If you are diagnosing one, the tips here apply to both unless noted.
These transmissions are not bad designs, but they have two structural weak spots that almost every high-mileage unit eventually hits: the aluminum servo bores wear oval and the pressure sensors and solenoids inside the valve body drift out of spec. Get those two right and a 5R55 will run another 100k. Ignore them and you chase phantom shift complaints forever.
The Five Most Common Symptoms
| Symptom | Most Likely Cause | Typical Code |
|---|---|---|
| Harsh or banging 1-2 shift | Worn overdrive/intermediate servo bore | none or P0741 |
| No reverse, or delayed reverse | Reverse servo bore wear, cracked overdrive band | P0733/P0734 |
| Slips or flares between gears | Failing shift solenoid, low line pressure | P0750/P0751/P0760 |
| Limp mode (stuck in one gear) | Solenoid pack or TR/range sensor | P0708/P1702 |
| Wrench / "Check Transmission" light | Internal pressure/speed sensor fault | P0715/P0720/P0791 |
If you only remember one thing: on a 5R55, a harsh 1-2 shift combined with a soft or missing reverse is the classic servo-bore signature. That is not a solenoid problem and no fluid additive fixes it.
Problem 1: Worn Servo Bores (The Big One)
The 5R55 case uses aluminum servo bores that the steel servo pistons ride in. Over time the pistons hammer the soft aluminum oval. Once the bore is worn, the servo cannot hold pressure, so the corresponding band applies late, slips, and bangs. The overdrive servo bore and the intermediate servo bore are the usual culprits.
You diagnose this by ruling out everything electronic first (clean codes, good line pressure at the test port), then dropping the pan and valve body. The fix is not a band-aid: the bore has to be machined and a Sonnax oversized servo cover and pin installed to restore the seal. This is the single most important upgrade on these units, and a rebuild that skips it will come back.
The Sonnax servo bore repair kits are the standard fix. The overdrive and intermediate kits are sold separately by position.
Check Sonnax 5R55 servo bore kits
Problem 2: Shift Solenoid and Pressure Sensor Faults
The 5R55S/W carries its shift solenoids and pressure control solenoids in the valve body, plus an internal Transmission Range (TR) sensor and turbine/output speed sensors. When one drifts, you get codes in the P0750-P0791 range, intermittent limp mode, or shifts that wander with temperature.
- P0750 / P0755 / P0760: shift solenoid A/B/C electrical fault. Resistance-check each solenoid cold; spec is roughly 11-15 ohms. Out of range means replace.
- P0791 / P0715 / P0720: internal speed/turbine sensor or its harness. These sensors live inside the case, so a real fault means dropping the pan.
- P0708 / P1702: Transmission Range sensor. Often just the external TR sensor on the side of the case, which is a far cheaper fix than the internal work.
A full solenoid pack with a fresh updated TR sensor and a Master Glide-style overhaul kit is the right way to address a high-mileage valve body rather than chasing one code at a time.
Check 5R55 solenoid packs
Problem 3: Cracked or Worn Overdrive Band & Pump Issues
The overdrive band and the direct/reverse band are the friction elements that take the abuse when the servo bores wear. By the time a customer notices a slipping or missing reverse, the band is usually glazed or cracked. On teardown you also commonly find pump bushing wear and a worn stator support, which bleeds line pressure and makes every other problem look worse.
This is why a 5R55 is rarely worth a partial repair once it is slipping under load. The right move is a full rebuild with new frictions, steels, bands, the servo bore corrections, an updated solenoid pack, and a pump rebuild or replacement. Done right, it is a genuinely durable transmission again.
Fluid: Get This Right First
The 5R55S/W is fussy about fluid. Ford specifies MERCON V for these units (not the older MERCON, and not a universal that only claims compatibility). Low or burnt fluid will mimic almost every symptom above, and people throw parts at problems a fluid-and-filter service would have solved. Before any diagnosis: confirm level on a level surface at operating temp, and confirm the fluid is red and not brown or smelling burnt.
Check MERCON V fluid
Rebuilding a 5R55? Parts Ship Same-Day
Once it is on the bench you need frictions, steels, bands, the servo bore correction parts, a solenoid pack, and a master overhaul kit. gearboxinsider.com stocks 5R55S and 5R55W rebuild parts with same-day ship before 2pm Eastern and free shipping.
Shop 5R55 Parts →FAQ
What is the difference between the 5R55S and 5R55W?
The 5R55W is the wide-ratio version used mostly in the Explorer, Mountaineer, and Aviator. The 5R55S is the synchronous version used in the Mustang, LS, Thunderbird, and similar rear-drive cars. They share the same case and the same servo bore problems, but the valve body calibration and some internal parts differ, so always order parts by the exact unit and year.
Is the 5R55 worth rebuilding?
Yes, if the servo bores are corrected with the Sonnax kits during the rebuild. A 5R55 rebuilt properly is a reliable transmission. One rebuilt without the bore correction will develop the same harsh shift and reverse complaints again within a year or two.
Can a servo bore fix be done without removing the transmission?
No. The bore correction requires removing the servo covers and machining the case, which means the valve body and pan come off at minimum, and a proper job means the unit comes out and onto the bench.
Why does my Explorer go into limp mode intermittently?
On a 5R55W the usual suspects are the Transmission Range sensor and the internal speed sensors. Pull the codes first. A P1702 or P0708 points at the range sensor; P0715/P0720/P0791 points at the internal speed sensors and means the pan comes down.