Ford 6F50 and 6F55 Problems: Harsh Bump From a Stop, 2-3 Flare, Delayed Reverse and P0741

Ford 6F50 and 6F55 Problems: Harsh Bump From a Stop, 2-3 Flare, Delayed Reverse and P0741

Ford 6F50 and 6F55 Problems: Harsh Bump From a Stop, 2-3 Flare, Delayed Reverse and P0741

Sonnax lists the 6F50 and 6F55 applications as the Ford Edge, Taurus and Taurus X, Flex, Fusion, Escape and Explorer, the Lincoln MKX, MKS, MKT and MKZ, the Mercury Sable, Milan and Mariner, and the Mazda Tribute - the 6F50 introduced in 2007, the 6F55 in 2009. Same family, same weak spots.

The complaints come in a predictable set: a sluggish crawl from a stop that ends in a harsh bump, a 2-3 or 4-5 flare, delayed or slipping Reverse, and P0741 with converter shudder. Those are four different circuits. Swapping a solenoid body at the first code is how people spend the money twice.

First: confirm which unit you actually have

Per Sonnax's 6F50/6F55 training material, the vehicle certification tag on the driver's door B-pillar carries the transmission code in position 8: 6 = 6F35, C = 6F55, J = 6F50, with the axle ratio in position 7. Check it before ordering anything, because several of these vehicles were built with more than one transmission depending on year and engine. The same material lists the 6F50 at 4.484, 2.872, 1.842, 1.414, 1.000 and 0.742 with a 2.882 Reverse, roughly 9.5 liters (10 quarts) of fluid, and six variable-flow solenoids plus one on/off.

Symptom 1: Sluggish from 0-5 mph, then a harsh bump

This one has a factory answer. Ford TSB 11-12-10 covers sluggish acceleration from 0-8 km/h (0-5 mph) followed by a harsh bump, or a slip on take-off followed by a bump, on 2009 Edge, Flex and MKX built on or after 5/4/2009, 2010-2011 Edge, Flex, MKS, MKT, MKX and Taurus, and 2011 Explorer, built on or before 4/15/2011. The bulletin supersedes TSB 11-9-11.

The gate is the dipstick: Ford states the modification is only available for transmissions originally built with MERCON LV listed there, and if it is not listed the bulletin does not apply. Where it does, the repair is to reprogram the PCM to the latest calibration using IDS release 73.04 or higher, replace both separator plates, and remove one check ball in the area of the eliminated plate hole. Ford's warning is blunt: performed incorrectly, the procedure creates loss of Reverse or a 2-3 shift flare - worth knowing when buying a used valve body of unknown history.

Symptom 2: 2-3 flare, 4-5 flare, delayed or slipping Reverse

Sonnax ties this exact symptom cluster - 2-3 flare, 4-5 flare, delayed Reverse, Reverse slip, burned 3-5-Reverse clutch, ratio codes and bind-up - to wear at the Direct Clutch (3-5-Reverse) Regulator Valve bore in the upper valve body. Their repair is the oversized 3-5-R clutch regulator valve kit, offered in two versions because the unit changed: part 124740-26K for the 1.35 ratio valve with a .390-inch spool, and 124740-21K for the 1.83 ratio valve with a .335-inch spool.

That same 1.35 versus 1.83 split defines the valve bodies themselves. Sonnax's remanufactured valve body sheet lists FD6F50E for '07-'09 units with the 1.35 ratio 3-5-R and FD6F50L for '09-later units with the 1.83 ratio - and warns that the two look very similar and must be verified before installation. The FD6F50L is the six-checkball design. If the 3-5-R clutch is already burned, the valve fix alone will not restore the shift; that is a teardown, and the clutch pack goes in with it.

6F50 6F55 transmission friction clutch kit for Ford Edge Taurus Flex and Lincoln MKX
6F50 Friction Clutch Kit - the frictions that go back in when the 3-5-R or 2-6 pack is burned.

Symptom 3: 1-2 or 5-6 flare, no 2nd, no 6th

Different valve, same idea. Sonnax attributes 1-2 flare, 5-6 flare, 2nd and 6th gear slip, no 2nd or no 6th, ratio codes, erratic shift timing and a burned 2-6 clutch to the Intermediate Clutch Regulator and Gain Valve, repaired with oversized kit 124740-17K. Each clutch has its own regulator valve and a worn bore burns exactly the clutch it feeds - the 2-6 clutch covers 2nd and 6th, the 3-5-R clutch covers 3rd, 5th and Reverse. The gears that disappear tell you which bore to vacuum test first.

Symptom 4: P0741, P0742, converter shudder, overheating

Sonnax splits the lockup circuit into two wear points. The TCC Regulator Apply Valve is tied to codes P0741 and P0742, harsh TCC apply, TCC slip, low TCC apply pressure, lost fuel economy and overheated fluid and lining; the repair parts are 124740-24K or 124740-31K. The TCC Control Valve is tied to excess TCC slip, low cooler flow, overheating, apply and release concerns and TCC apply codes, repaired with 124740-14K.

Both bleed converter and cooler flow, which is why a lockup complaint here so often arrives with cooked fluid. Replacing the converter without addressing the bore that starved it is the classic repeat failure.

Symptom 5: Harsh shifts that are not load sensitive

If shift feel does not change with throttle, Sonnax points at the latch valves - Forward Clutch Latch, Direct Clutch Latch and L/R-Overdrive Clutch Latch in the lower valve body - listing harsh shifts, slips and flares, delayed engagement, burnt clutches, slide shifts and slip codes. One part, 144740-23, fits any of the three locations. Separately, low line pressure, no line rise and line pressure instability point to the Isolator Valve (kit 124740-03K, spring 124740-16), while erratic line pressure with low converter and lube flow points to the Pressure Regulator Valve (124740-12K). Solenoid performance codes, wrong gear starts and clutch failure point to the AFL (actuator feed limit) valve, 124740-01 or kit 124740-32K.

The solenoid body trap

Per Sonnax, the solenoid body tag on the case carries a solenoid body strategy - always 13 numeric digits - and a solenoid body ID made of digits and the letters A through F, and those must match the lead frame attached to the valve body. Any time a new solenoid body goes in, a new strategy file has to be downloaded into the PCM with a scan tool and a replacement tag placed on the case. Skip it and you have built a brand new shift complaint on top of the one you were chasing.

Replace while you are in there

  • The solenoid filter plate. Sonnax states the seals will leak if it is reused - discard and replace it every time the solenoid body comes off.
  • Valve body end plugs. Worn plugs cause pressure loss, shift concerns, burnt clutches and TCC apply concerns; the O-ringed end plug kit 124740-02K includes nine.
  • Checkballs. The Sonnax Zip Kit replaces seven, with the caution that an OE valve body may contain seven and that TSB 11-12-10 calls for removing one on the affected units.
  • Filter and overhaul gasket and seal kit. Non-negotiable on any pan-down or valve body job.
  • Frictions and steels if any clutch is discolored. Browse the full clutch packs and rebuild kits selection, or go straight to the 6F50 master rebuild kit if the unit is coming apart anyway.

Cost and effort, honestly

Ford's published warranty operation for TSB 11-12-10 - remove and install the main control, replace the separator plate, remove the check ball and reprogram the PCM - is 3.0 hours. Treat that as the floor for valve body work here; a home mechanic on jack stands should plan on more.

Torque matters. Sonnax specifies 106 in-lb for the valve body reassembly bolts, the ten 62mm bolts holding the valve body into the case, and the eleven solenoid body bolts, each in the published sequence. One more Sonnax caution for anyone installing a Zip Kit: it requires drilling and plugging the separator plate to block the solenoid pressure regulator balance port, and failure to block that orifice results in no movement of the vehicle.

If the fluid is black and the pan has friction material in it, valve work alone will not save the unit. Sonnax's air-check list for a valve body install covers Low/Reverse, compensator feed, 3-5-Reverse direct, 4-5-6 overdrive, 2-6 intermediate and 1-2-3-4 forward. Air check each with low regulated pressure while the valve body is out; a circuit that will not hold air means the teardown is already decided.

FAQ

Can I just replace the solenoid body and be done? Only if the fault is genuinely electrical. A worn regulator bore produces the same slip and ratio codes as a bad solenoid, and a new solenoid body pushing fluid past a worn bore behaves like the old one. Vacuum test the bores first, and load the strategy if you do install one.

Is the 6F55 different enough to need different parts? Sonnax publishes its valve body layout, Zip Kit and vacuum test guidance for the 6F50 and 6F55 together, so valve body repairs are shared. The split that matters when ordering is the 1.35 versus 1.83 ratio 3-5-R valve and the early versus late casting.

The TSB was already done and it still flares on the 2-3. Ford warns that an incorrectly performed 11-12-10 causes exactly that. Verify both separator plates and the check ball count against the bulletin before condemning the 3-5-R regulator bore - on high-mileage units both can be true at once.

Related reading

The GM 6T70 and 6T75 share this architecture and fail in a comparable pattern: GM 6T70/6T75 slipping, no Reverse and P0776. The smaller Ford sibling has its own tells: Ford 6F35 bind in Neutral, P073D and P177F. And before replacing any solenoid, read how to find the actually failed solenoid.

Sources