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The Ford 5R55S is a five-speed rear-wheel-drive automatic that Ford built from the early 2000s into the early 2010s. You find it in the Explorer and Mercury Mountaineer, the Explorer Sport Trac, the Ranger, and the V6 Mustang, and its close relatives the 5R55N and 5R55W appear in the Lincoln LS, Thunderbird, and Jaguar S-Type. The three variants share a case family and a lot of parts but are not interchangeable, so identify the tag before ordering anything.
The 5R55S has one dominant failure that defines the whole platform, plus a handful of electrical faults that get mistaken for it. Understanding the difference is the whole game, because one is a $400 to $1,400 repair and the other is a rebuild.
Servo Bore Wear — The Signature 5R55S Failure
This is the one. The 5R55S applies its bands using servo pistons that ride in bores machined directly into the aluminum case. Over time and heat cycles, the aluminum bore wears oval where the servo pin passes through. Once that clearance opens up, apply pressure bleeds past instead of holding the band, and the band slips.
What it feels like
- Slip or flare on the 1-2 shift, or a delayed, mushy 2nd gear engagement.
- Loss of overdrive or a shudder entering the top gear.
- Symptoms that get worse when the transmission is hot and are barely noticeable on a cold start. Hot aluminum expands and the clearance grows.
- Gear ratio codes in the P0731-P0736 range for the affected gear.
- The vehicle otherwise drives fine, with clean fluid and no burnt smell.
The fix
The bore is repaired, not replaced, because the case is the bore. Sonnax makes the widely used servo bore repair kit for this family: the worn bore is reamed oversize and a hardened sleeve or an oversized servo pin restores the correct clearance. Good news: on many of these vehicles the repair can be done with the transmission in the car through the servo cover on the side of the case, though access varies by chassis and some builders prefer to pull the unit for a clean job.
This is why a 5R55S with a slipping band and clean fluid is worth repairing rather than replacing. Catch it early and you are fixing a machined bore, not a burnt transmission. Ignore it and the band material wears away, contaminates the fluid, and turns a bore repair into a full rebuild.
Cost: Bore repair kit and labor at a shop $600 to $1,400 depending on whether the transmission has to come out. The kit itself is a fraction of that; you are paying for access and for reaming the bore straight.
Check servo bore repair kits
Solenoid Pack and Electrical Faults
The 5R55S uses a solenoid block that controls shift timing and pressure. When one of those solenoids sticks or goes electrically out of range, the transmission shifts at the wrong time, shifts hard, or drops into failsafe. These faults are common, and they are cheap compared to internal work.
- P0750, P0755, P0760, P0765, P0770 — shift solenoid A through E circuit faults.
- P0745 — electronic pressure control (EPC) solenoid. This one drives harsh shifts and elevated line pressure.
- P0715 — turbine shaft speed sensor. A dead TSS causes harsh shifting, no overdrive, and failsafe. It is an external sensor and one of the most satisfying cheap fixes on this transmission.
- P0720 — output shaft speed sensor. Similar story: erratic shifting and a speedometer that may act up.
Because a bad TSS produces symptoms nearly identical to real internal slip, always read codes and check the sensors before authorizing a rebuild on a 5R55S. Shops replace transmissions on this platform every year that only needed a $60 sensor.
Cost: Speed sensor $150 to $320 installed. Solenoid pack $350 to $750 installed. EPC solenoid replacement is usually done with the solenoid block.
Check scan tools
Failsafe / Limp Mode
A 5R55S in failsafe holds one forward gear (usually a high gear), the shifter indicator may flash, and the vehicle feels like it launched in third. Ford's failsafe strategy on this unit is aggressive, and it triggers on a wide range of inputs, which is good news for the owner because most triggers are cheap.
Work in this order before assuming the worst: read all codes including manufacturer-specific ones, check fluid level and condition on a level surface at operating temperature, check the turbine and output speed sensors, inspect the transmission range sensor and the wiring at the case connector, and verify charging system voltage. Only after all of that does an internal fault become the likely answer.
Delayed Engagement, No Reverse, and Harsh Shifts
A long pause before the vehicle moves after selecting drive or reverse, especially cold, usually means fluid is draining back or apply pressure is not building. On a 5R55S the usual suspects are a worn pump, hardened seals, or a cracked/worn valve body separator plate area. On a higher-mileage unit with dirty fluid, it means the transmission is telling you it is near the end.
Harsh shifts that arrive suddenly and affect every gear point at the EPC solenoid or line pressure control rather than at a clutch pack. Harsh shifts on one specific gear point at that gear's apply circuit. Harsh shifts right after a battery disconnect or fluid service are often just adaptive relearn and settle within a few dozen shifts.
Cost: Valve body replacement $600 to $1,300 installed. Pump work is done as part of a rebuild, not on its own.
Fluid Spec and Service
The 5R55S uses MERCON V. This is one of the few areas where the platform is forgiving on cost, since MERCON V is inexpensive and widely available. Do not substitute MERCON LV, which is a different friction package used on later Ford units, and do not use a generic ATF that is not licensed to the MERCON V standard.
| Spec Item | 5R55S Requirement |
|---|---|
| Fluid type | MERCON V |
| Do NOT use | MERCON LV, unlicensed generic ATF |
| Drain-and-fill (pan) | ~5-6 quarts |
| Full dry fill with converter | ~13-14 quarts |
| Filter | In the pan, replaced with the gasket at every service |
| Service interval (severe/tow) | ~30,000 miles |
Heat is the accelerator for servo bore wear, so on an Explorer or Sport Trac that tows even lightly, an auxiliary cooler plus a shortened fluid interval is genuinely protective, not just upsell advice. If the fluid is already dark and burnt, a fluid service will not save the transmission and may expose a slip that the old sludge was masking. Be realistic about which situation you are in.
Check MERCON V fluid
Check 5R55S filter and pan gasket kits
Rebuild vs Replace — Realistic 2026 Cost
The 5R55S is old enough now that vehicle value drives the decision as much as the repair itself. An Explorer or Sport Trac in rough shape may not justify a full rebuild, while a clean, low-mile Mustang V6 or a well-kept Mountaineer absolutely does.
| Job | What It Covers | Typical Cost (USD) |
|---|---|---|
| Fluid and filter service | Maintenance, mild shift complaints | $180 - $340 |
| Speed sensor (TSS/OSS) | Harsh shifts, failsafe, no overdrive | $150 - $320 |
| Solenoid pack | Solenoid circuit codes, wrong-time shifts | $350 - $750 |
| Servo bore repair | Band slip, 1-2 flare, lost overdrive | $600 - $1,400 |
| Valve body replacement | Harsh or erratic shifting, pressure faults | $600 - $1,300 |
| Torque converter replacement | Shudder, lockup slip | $900 - $1,600 |
| Full rebuild | Frictions, bands, servo bores, seals, converter | $2,400 - $3,800 |
| Reman/replacement unit | Complete reman transmission installed, warranty | $3,000 - $4,800 |
How to decide
- Repair when the fluid is clean, the failure is isolated to one gear or one circuit, and there is no friction material in the pan. This is the common and correct answer on a servo bore complaint caught early.
- Rebuild when the fluid is burnt, the pan has debris, or the unit slips in multiple gears. Insist the builder addresses the servo bores during the rebuild, because a rebuild that reuses worn bores will come back.
- Reman unit when you want a warranty and a single predictable price, or when the case itself is damaged.
DIY vs Shop
- Fluid and filter service: yes for a capable DIYer. Pan drop, filter, gasket, refill, check level warm on a level surface.
- Speed sensors: yes. External, inexpensive, and the highest value-per-hour job on this transmission.
- Solenoid pack: reasonable with the pan down, if you are careful with the connectors.
- Servo bore repair: only with the correct reaming kit and experience. The bore has to be cut true or the repair fails.
- Rebuild: shop work. This unit has bands, servos, and setup dimensions that reward experience.
Check transmission jacks
Rebuilding a 5R55S? Parts Ship Same-Day
Servo bore repair components, solenoid blocks, friction and steel kits, filters, pan gaskets, and seal kits for the 5R55 family. Same-day ship before 2pm Eastern.
Shop Gearbox Insider →FAQ
My Explorer slips in 2nd only when hot. What is it?
That is the textbook 5R55S servo bore wear pattern. Aluminum expands when hot, the worn bore clearance opens up, and the band loses apply pressure. Check the fluid for debris; if it is clean, a bore repair is the fix and it is far cheaper than a rebuild.
What is the difference between the 5R55S, 5R55N, and 5R55W?
They share a case family and general architecture but differ in valve body and control strategy, and parts do not freely interchange. The 5R55S is the Explorer/Mountaineer/Mustang V6 unit; the 5R55N appears in Lincoln LS and Jaguar S-Type applications. Always verify by tag.
What fluid does a 5R55S take?
MERCON V. Do not use MERCON LV. The two are not interchangeable, and the wrong fluid causes shift-quality complaints.
Is a 5R55S worth rebuilding?
If the vehicle is otherwise sound, usually yes, especially when the failure is a servo bore or a solenoid rather than burnt clutches. At $2,400 to $3,800 for a rebuild against the cost of another vehicle, a clean Explorer or Mustang is worth saving.
Can a bad speed sensor really feel like a failing transmission?
Yes, and it is the most common misdiagnosis on this platform. A failed turbine shaft speed sensor throws the vehicle into failsafe and produces harsh shifts and no overdrive. Read the codes first. It is a fraction of the cost of any internal repair.
How many miles should a 5R55S last?
With clean MERCON V, a cooler, and no towing abuse, 180,000 to 220,000 miles is realistic. Servo bore wear is a heat-and-time failure more than a mileage failure, so a low-mile vehicle that ran hot can show it early.