Shaftmasters 3.7L Mustang Driveshaft Issues Resolved

As most of you know stopped production on their driveshafts for the 3.7L V6 Mustangs after a couple of them failed. The failures were very peculiar as they only happened on an automatic V6 Mustang while running on a Dyno. After several weeks of investigation and testing has come to a conclusion. Here are the findings.

The driveshafts were tested by member Frank R. (westcoastsc) who is a metallurgical engineer. He found some very minor shrinkage cavities in the shaft material.  He then recommended that each shaft be ultrasonically inspected, because before they were inspected on a lot basis.  The failures occurred at the same location on the shafts. It was previously thought that harmonic vibration during sustained 6900 plus RPM run was to blame. The failures occurred at speeds far above what the stock shaft from Ford was designed for. Ford has set a limit of 118MPH from the factory. However most guys who re-tune their car move the speed limit of the car much higher.

There have also been several examples of Ford 2011+ V6 mustang stock drive shafts failing at speeds over 135MPH. This just added to all the confusion and speculation. Many were double guessing if the driveshaft was properly constructed using quality materials. It turns out they were. I have personally punished their original driveshaft on the dyno and at the drag strip. I broke a flywheel and not the driveshaft on one run even. It is very stout.

halted production of their 3.7L V6 mustang drive shafts. After the metal testing came back, it was confirmed that the metal and welds were of sound structure. They then proceeded to consult with some professional racing shops. It was brought to their attention that on automatic transmission cars while on a dyno have a small known complication. When making a high RPM run it is imperative that the dyno operator slowly reduce the RPM versus just letting off the gas. Apparently doing so is equivalent of hitting a brake on the drive line. This shock load on the driveshaft was the primary cause of the failures.

Problem solved. However the team, in their consummate professionalism, wanted to make sure such a problem could not reoccur. The have revised the design with a longer yoke that effectively shortens the main tubing itself. The shorter tubes makes the driveshaft stronger and at the same time increases the critical speed approximately 300 rpms for every inch shorter. They then sent the new designed shaft off to be torque tested. Here are the findings of that test. 

3.7L v6 mustang driveshaft testing


The sample was set up in the torsion machine. The output of the torque cell was read by a data acquisition computer and plotted in relation to the angular displacement of the axle. Angular displacement was read by an encoder and recorded by the data acquisition system as well. The accuracy of the load cell is +/- 100 Ft Lbs and the accuracy of the encoder system is +/- 0.75 degrees. 3.7L v6 mustang driveshaft torque test

Ultimate failure was achieved at 3973 Ft/Lbs. at 24.3 degrees. Failure was at the weld near the slip coupler.

3973 Ft/Lbs of torque before failure is of high enough quality to receive certification for use in Nascar. A Nascar race car will normally have twice the torque and spin at several thousand more RPM than a 3.7L V6 Mustang will ever produce. has offered to trade in any existing Revision One 3.7l V6 Mustang driveshafts and send back a Revision 2 driveshaft. All new sales will include a BMR driveshaft front safety loop, just to be on the extra safe side. I have to applaud the team at for going the extra distance and continuing to support the 3.7L V6 mustang community by building their driveshafts.

shaftmasters redesigned 2011 v6 mustang driveshaft