5R55S Won't Shift Into Overdrive: Causes and Fix

A 5R55S that won't go into overdrive is one of the most common complaints on the Explorer, Mountaineer and Mustang. The customer says it "stays in fourth," the engine is turning several hundred more rpm than it should on the highway, and sometimes the O/D light is flashing. On this unit, "overdrive" means 5th gear, and 5th is built from a band, a clutch and a solenoid circuit that are all shared with other gears. That sharing makes it quick to diagnose.

This guide covers the 5R55S and the 5R55W, which use the same geartrain and control strategy. The specs trace to the sources at the bottom. Where something is my own shop habit rather than a published procedure, I say so.

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What has to happen for 5th gear

RatioTek's 5R55W/S rebuild manual gives the apply chart. 5th gear is the forward clutch, the direct clutch and the overdrive band, all at once. 4th is the forward and direct clutches. So the 4-5 upshift is a single change: the overdrive band applies. The 5-4 downshift is that band releasing.

The different 2nd and 5th ratios between the S and the W come from the overdrive planetary. Sonnax's "Figuring Out the 5R55 Alphabet" notes the W uses a 24-tooth overdrive sun gear and the S a 38-tooth one.

Now the hydraulics. ATRA's 2013 seminar material on the 5R55W/S spells out who feeds what:

• PCB (pressure control solenoid B) controls the VFS2 modulator valve, and VFS2 pressure directly applies the overdrive servo and the coast clutch.
• PCC is directly responsible for direct clutch apply in 4th and 5th.
• The forward clutch is applied in every forward gear.

Put the chart and the hydraulics together and you get the shortcut this whole article hangs on: the overdrive band also makes 2nd gear. If 2nd is healthy and 5th is missing, the band itself is probably fine and you're looking at a command problem or a release and timing problem. If 2nd and 5th are both slipping or flaring, you're looking at the overdrive band circuit: band, servo, pin bore, or PCB/VFS2 pressure. If 4th and 5th are both bad, it's the direct clutch side.

Step 1: rule out a command problem

• O/D cancel. These trucks have an overdrive cancel button on the shifter (RatioTek's abbreviation list calls it the TCS, transmission control switch). With overdrive cancelled, the PCM holds 4th on purpose. Check the O/D OFF lamp and the switch state on the scan tool before anything else. A sticking switch or a shorted circuit can hold it cancelled.
• Stored codes. In my experience a flashing O/D lamp on these Fords means the PCM has a transmission fault stored and may be running a failsafe strategy that won't use 5th. Pull codes first, including pending codes.
• Fluid temperature. Watch the TFT PID. Ford's own level-check procedure has you monitor TFT and set the level at 81-120°F, so the PID is there and trustworthy on a good sensor. Compare it with coolant temperature after a full warm-up; a stuck-cold reading can change the shift strategy.
• Speed inputs. The PCM needs believable turbine, intermediate and output shaft speeds to shift and to calculate ratio. Any speed sensor code gets fixed before any shift complaint. Our P0715, P0720 and P0500 guides cover those.

Then road test with a scan tool. Log commanded gear, turbine (input) speed, output speed, TFT and TCC slip. If the PCM never commands 5th, it's a command or input problem, not a band. If it commands 5th and the ratio never gets there, it's hydraulic or mechanical.

Step 2: read the ratio in commanded 5th

Divide input speed by output speed while 5th is commanded. A 5R55S should settle at 0.71 and a W at 0.75. What you see tells you where to look:

• Stays at 1.00: the direct clutch is holding but the overdrive band never applies. Think servo apply pressure, a burned or broken band, or a leak in the apply circuit.
• Drops toward 0.71, then drifts up or flares under load: the band applies but can't hold. Classic worn pin bore or worn band, usually worse hot.
• Engine rpm flares and the unit drops back to 4th: the PCM saw a bad ratio and gave up. That's usually when P0735 (5th gear incorrect ratio) sets.

Pete Luban of ATSG, writing in Transmission Digest ("False Pretenses"), worked a 2002 Explorer with no 2nd and no 5th that had P0732, P0735 and P0775 stored. His point: PCB affects 2nd and 5th, so that circuit sets 2nd and 5th ratio codes together, and P0775 in that pattern is a pressure control performance code, not an electrical fault. Don't replace a solenoid pack on P0775 alone. His culprit on that truck was the servo pin bore.

Cause 1: overdrive servo pin bore wear

This is the big one, and Ford acknowledged it. TSB 09-12-12 covers the 5R55N, 5R55W and 5R55S in the 2002-2009 Explorer and Mountaineer, 2007-2009 Explorer Sport Trac, 2005-2009 Mustang, 2002-2005 Thunderbird, 2002-2006 Lincoln LS and 2003-2005 Aviator. The bulletin describes loss of 2nd, 3rd and 5th, incorrect ratio codes, and overdrive or intermediate band failure caused by servo pin case bore wear that reduces apply pressure. It's generally a higher-mileage condition and gets worse when the fluid is hot. The repair is to measure both pin bores and sleeve the case.

Sonnax describes the mechanism: the apply pin oscillates in a bore machined into the aluminum case and wears it oversize. Apply oil leaks past the pin, and as wear progresses, release oil cross-leaks into the apply side. Their symptom list for the condition includes 1-2, 2-3 and 4-5 flares, gear loss, codes 732, 733 and 735, band lining failure and loss of overdrive and intermediate servo control. RatioTek's manual says the overdrive servo "works 2nd and 5th gears," and that the case usually needs pin bore repair by around 70,000 miles.

Luban's shop test is simple. Back off the band adjusting stud, make sure oil has filled the release side, then air-apply the servo and watch what blows out of the pin bore area. A healthy bore holds. A worn one sprays.

The fix is a reamed and sleeved case. Sonnax's kit 56361J-01K contains an overdrive sleeve and an intermediate sleeve, installed with tool kit S-56361J-TL. The reamer pilots off the pin bore centerline, not the servo piston bore, which matters because the pin bore is the one that's worn. Our servo pin bore wear guide walks through it. Do both bores while the case is apart.

Cause 2: a burned or broken overdrive band

A band that has been slipping on low apply pressure eventually glazes, burns or breaks. The overdrive band has an external adjusting screw, which gives you a quick check before teardown. Seat the screw by hand and count turns. If it runs in much farther than normal before it tightens, the band is worn through or broken.

RatioTek's adjustment procedure is to tighten the screw to 120 in-lb, back off two turns, and torque the locknut to 40 ft-lb. For 2003-up 5R55S units, ATRA's band chart calls for 1-1/2 turns instead; our 5R55S slipping guide has the full table. An adjustment only helps a band that's still healthy. If it buys you a few hundred miles of 5th and then 5th is gone again, the bore is bleeding off apply pressure and the band will burn again.

Cause 3: the servo release side

A band servo needs clean release oil as much as apply oil. Mike Brown's GEARS Magazine article on 5R55 servos explains that when a servo piston is hard, torn or delaminated, release oil leaks across and becomes apply oil, applying the band when it should be off. His check: with the engine running and the selector in Drive, both band adjusting screws should turn freely. If one is tight, that servo is applying its band when it shouldn't.

The overdrive servo also has to release cleanly on the 2-3 and 5-4 shifts. ATRA's seminar notes point at the overdrive and intermediate servo control valves and plugs: worn plugs can leak, especially during engagements and shift timing sequences. ATRA's hydraulic drawings also put a coast clutch control valve in the same VFS2 circuit that feeds the overdrive servo. On the older 5R55E, Sonnax ties a missing 2nd or 5th to a worn coast clutch valve bore, because that valve vents overdrive servo release oil. On a W or S with a missing 5th and good pin bores, I inspect that valve and its bore too.

Cause 4: the direct clutch feed (no 4th and no 5th)

If the unit won't hold 4th either, it's not an overdrive band problem. Both 4th and 5th need the direct clutch, and ATRA says PCC is directly responsible for applying it in those gears. Sonnax's 5R55S unit page lists the reverse modulator valve kit 56947J-23K for no 4th, no 5th and a burned direct clutch. Rebuild the direct clutch without fixing that valve and the new frictions burn too.

The solenoid pack belongs in this conversation. ATRA found that the wrong-design pack for the model year changes solenoid output enough to cause flare shifts. Their part number break: 2002-03 Ford W or S and 2003 Lincoln use 1L2Z-7G391-AG; 2004-on Ford and 2004-06 Lincoln use the later pack, and Ford recommends the updated 9L2Z-7G391-A. If 5th went away right after a pack swap, check the part number first. Our 5R55S shift solenoid guide covers the pack in detail.

Cause 5: low fluid

The 5R55S and W have no dipstick. Ford's procedure sets the level at the check plug with the engine running, in Park, TFT between 81 and 120°F on the scan tool, adding fluid until it comes out as a thin stream or drip. Nobody checks it between services, so these units often run low. Set the level before you condemn hardware. Our fluid type and capacity guide covers the MERCON V spec and the full procedure.

My diagnostic order

This is my sequence, not a Ford procedure:

1. Check O/D cancel and scan for codes, including pending ones.
2. Set the fluid level the Ford way. Note color and smell.
3. Road test with data. Does the PCM command 5th? What does the calculated ratio do? Is 2nd healthy? Is 4th healthy? Is it only hot?
4. Sort by pattern. 2nd and 5th bad: overdrive band circuit. 4th and 5th bad: direct clutch and PCC circuit. Only 5th bad with a good 2nd: command, release timing, or the servo release and coast clutch valves.
5. Check the overdrive band adjuster for turns-to-seat, and for free rotation in Drive.
6. On teardown, measure and air-test both servo pin bores, check the servo pistons for hardening and release-side damage, check the overdrive one-way clutch (RatioTek's check: hold the overdrive carrier and turn the center shaft; it should freewheel in one direction only), and inspect the valve body bores Sonnax lists before reusing it.

Need parts for this job?

Our 5R55 parts page carries 5R55S and 5R55W rebuild kits with bands, valve bodies, solenoid packs, pumps and filter kits for the Explorer, Mountaineer and Mustang units. Checkout is on site.

FAQ

Why won't my 5R55S shift into 5th gear?

5th gear needs the forward clutch, the direct clutch and the overdrive band. The most common cause is overdrive servo pin bore wear, covered by Ford TSB 09-12-12, which bleeds off band apply pressure and gets worse when hot. First rule out the O/D cancel switch, stored codes, low fluid and speed sensor faults, since the PCM will hold 4th on purpose if it sees any of those.

What does P0735 mean on a 5R55S or 5R55W?

P0735 is a 5th gear incorrect ratio code. The PCM commanded 5th but the input-to-output ratio never reached about 0.71 on a 5R55S or 0.75 on a 5R55W. It usually means the overdrive band is not holding, and when it appears with P0732 for 2nd, the overdrive band circuit is the prime suspect because that band makes both gears.

If 2nd gear works, can the overdrive band still be the problem?

Less likely. The overdrive band holds in both 2nd and 5th, so a healthy 2nd usually means the band and its apply circuit are working. A missing 5th with a good 2nd points toward a command problem, release timing, or the direct clutch side. If 4th is also missing, look at the direct clutch and its feed instead.

Can a band adjustment bring back 5th gear?

Only if the band is simply loose. The overdrive band adjusts externally: tighten to 120 in-lb and back off the specified turns (two on most units, 1-1/2 on 2003-up 5R55S per ATRA). If 5th comes back and then disappears again, the servo pin bore is leaking apply pressure and the case needs to be sleeved.

Related guides

• 5R55S Slipping: Causes and Fix
• 5R55W and 5R55S Servo Pin Bore Wear
• 5R55S Shift Solenoid Symptoms and Replacement
• 5R55W P0730 Fix
• Ford 5R55S and 5R55W Transmission Problems