Last August, we told you that the National Highway Traffic Safety Administration was investigating manual-transmission equipped Ford Mustangs for shifting issues, ranging from binding gears through excessive noise and vibration.

At the time, the NHTSA had amassed some 32 customer complaints, including several that alleged transmission problems had nearly led to a collision. At the heart of the issue was the Chinese-manufactured Getrag MT-82 transmission, used in 2011 and 2012 model year Mustangs.

Now comes word from Mustangs Daily that the NHTSA has completed its investigation, finding that “there is no indication of loss of motive power or unreasonable safety risk associated with the alleged defect in the subject vehicles.” In other words, there’s nothing about the manual transmission used in the Ford Mustang that would prompt the NHTSA (or Ford) to issue a recall.

The agency did cite Ford’s findings that the bulk of the shift effort complaints occurred in cold ambient temperatures. Ford has released a service bulletin recommending a lower-viscosity transmission fluid for customers complaining of cold weather shift problems, which seem to improve as the car (and transmission fluid) come to a proper operating temperature.

A clutch stay-out issue, which may prevent clutch re-engagement at engine speeds above 4,000 rpm, was blamed on the rotating inertia of the clutch components. Ford has  issued a technical service bulletin to dealers on this issue and has revised certain parts within the clutch pedal assembly.

Finally, grinding or notchy shifts were traced back to the loosening of clutch plate fasteners, which the NHTSA links to aggressive shifting. Ford has since revised the fasteners used in production, and the updated fasteners are now available through Ford’s service department.

If you’re a 2011-12 Mustang owner experiencing problems with the six-speed manual transmission, the NHTSA’s findings probably don’t come as good news. We're also curious if any owners have tried the remedies proposed by Ford, with no real improvements. If you have a six-speed Mustang from 2011 or 2012, we'd love to hear from you.

Want to read the full report of the NHTSA's findings? Head on over to the next page.

"The Office of Defects Investigations (ODI) analyzed complaint data provided by Ford as well as complaints submitted to ODI from consumers. In total, there were 364 unique reports indicating various shift quality issues while driving. Ford identified several factors that may contribute to shift quality concerns in the subject vehicles, including cold transmission, clutch stay-out at high engine speeds, gear clash or grinding, and gradual loosening of clutch plate bolts in some early production vehicles.

The largest percentage of complaints indicated higher than expected shift efforts in cold ambient temperatures. These complaints were related to transmission fluid viscosity and the higher shift efforts resolved themselves with the drivetrain warming. Ford published technical service bulletin TSB 11-3-18 to inform technicians that a lower viscosity fluid was available for use to address the cold shift issues.

The clutch stay-out condition typically occurs at engine speeds greater than 4000 rpm. It does not prevent the selection of any gear, but may delay clutch re-engagement depending on how long the driver maintains the higher engine speed. Ford identified rotating inertia of the clutch components as the root cause and replacement clutch pedal parts were made available under Ford TSB 10-19-4.

A number of reports alleged increasing difficulty selecting gears along with gear clash or grinding. Grinding or notchy gear shifts may be caused by gradual loosening of clutch plate fasteners, which is promoted by certain aggressive shifting. This condition is progressive in nature and initially results in symptoms related to shift quality/feel. Clutch plate bolt loosening will not result in inability to select any gear unless the progressive symptoms are ignored until complete clutch failure occurs. ODI’s analysis identified only five complaints alleging an inability to shift into gear due to loose clutch plate bolts. None of these resulted in a stall and gear shifting could occur before engine start. A revised fastener was designed and implemented in production and is available for service through a special service message.

There is no indication of loss of motive power or unreasonable safety risk associated with the alleged defect in the subject vehicles. This preliminary evaluation is closed."