The Bullitt Mustang – another upgrade

Over this past weekend I was able to do some more work on one of my favorite project cars, the 2009 Bullitt Mustang.

2009 Bullitt Mustang

In the last write-up on this car we executed a large suspension transformation that resulted in a significant improvement to the car’s handling capabilities.  It removed the nose dive on braking and the exaggerated squat on acceleration.  The changes brought the ride height to a reasonable level and provided roll stiffness that vastly improved the steering response and road feel.

Much of the improvements were things that eliminated the overly compliant factory bushings and inadequate factory bracing.  With the additional stiffness and more precise locating of suspension points came indicators of the wide tolerances typical of a mass produced drive train.  This manifested itself as some drive train clunks, particularly between the transmission and rear differential.

The owner and I had considered what options were available.  Some that occurred to us unfortunately would be a substantial financial investment.  So the owner did a lot of research and came up with a modification that would prove to be nearly miraculous.  His research uncovered a company called Shaftmasters that produces replacement driveshafts for 2005 and up Mustangs.  They convert the heavy two-piece steel stock shafts to a single-piece light aluminum version.

Certainly there are other companies out there with similar options, but this outfit’s solution is particularly attractive because it uses neither adapter plates nor flanges that can easily be installed out of alignment.  I have plenty of experience with driveshafts that use those methods and it can be very tricky to line up without misalignment occurring.  The Shaftmasters drive shaft is a direct bolt-in design where alignment is not a variable. 

 

Shaftmaster kit

I was particularly impressed with the quality of their driveshaft when I unpacked it in preparation for installation.  The welds and finish were excellent.  It was also impressive that they packed a set of replacement bolts for the rear flange, along with anti-vibration Vibra-tite, and a twelve-point socket for installation. 

 

Fastener Kit

 

With everything sorted out we got the Bullitt Mustang up on the lift and had time to look over all the suspension upgrades that we had installed prior.  Everything was still in excellent shape and tight as it should be.  I was using a friend’s shop and he had not had an opportunity to see this project car so we went stem to stern going over all the parts and improvements that made the Bullitt the sweet handling car it had become.

 

the factory driveshaft assembly

 

Then we got down to the project at hand first unbolting the drive shaft at the transmission flange.  Four twelve-point bolts hold it on and we used a battery powered half-inch drive impact gun to loosen up the bolts.  A large screw driver was inserted in the rear U-joint to ensure the torque from the impact wrench wouldn’t spin the shaft assembly.  The transmission flange actually has eight threaded holes so the four that were originally used to bolt to were marked so that they would be re-used when the new driveshaft went in.

 

The front of the factory drive shaft

 

Then we did the same at the rear flange that had six six-point bolts to remove.  After that we zipped out the two bolts holding the carrier bearing assembly to the driveshaft tunnel, easing the center of the shaft down onto the exhaust for support while we finished removing the front bolts.

 

Rear flange with factory bolts

 

Ford had used red Locktite on the front driveshaft bolts which made the impact wrench a necessity, but once they were broken free we could complete their removal with just finger torque.  The front of the old shaft also rested nicely on the exhaust system while the rear bolts were completely removed.  The rear bolts came with flange plates that tied a pair of bolts together.  Neither the bolts nor the plates would be reused.  We put them aside.

carrier bearing mounted

At this point the driveshaft was completely free and could be slide to the rear between the exhaust pipes and removed.  It is always surprising just how heavy a driveshaft assembly is.  The new shaft being made from aluminum tubing and minus a carrier bearing was considerably lighter

 

rear flange of the new shaft

 

 We checked the flanges front and rear and they were very clean.  There was not rust or dirt so with a quick wipe they were ready to receive the new driveshaft.

the front nose of the new shaft

 

Even without the benefit of a flexible center the Shaftmasters driveshaft went in easily the same way the stock shaft had been removed.  The front flange was bolted up using the original bolts and Vibra-tite from the kit was applied on their threads prior to bolting them up.  They were snug, but not tight.  We would save that final step for after the rear flange was bolted together.

 

the front flange of the new shaft

 

 Shaftmasters has an excellent set of directions that calls for two of the new bolts to be screwed in first.  They are placed opposite each other (at 12 and 6 o’clock positions on the flange).  The new shaft has a spline coupling at the front covered by a rubber accordion boot.  It is normal for it to be compressed some and it actually aids in the initial positioning of the new shaft. 

front spline joint stretched

 

We stretched the joint so that the rear flanges would meet enough for us to get the two bolts snugged up.  Then we applied Vibra-tite to the other four bolts supplied in the kit and bolted them up to the rear.  The two bolts we first put in were removed and had their threads coated with Vibra-tite as well before they went back in. 

     

setting the first two bolts so the flange was seated

 

 Our attention then returned to the front bolts that were torqued to 75 lb/ft.  Again a large screw driver was braced inside the u-joint to keep the shaft from turning while these were tightened. 

front of new shaft with bolts installed

 

The rear bolts were also torqued, but there was not sufficient room to get a socket and torque wrench in place so we used a twelve-point box wrench and brought the torque up as evenly as we could using another wrench on the end to add torque.

 

rear flange with new bolts provided in kit

 

We then boxed up the old driveshaft and fasteners and took the Mustang out for a test drive.  I was impressed with the lack of vibration and almost complete elimination of drive line clunk.

 

the new shaft in place

 

The Bullitt’s owner remarked that “Thanks again for installing the driveshaft.  It’s about 80% quieter than it was, still knocks a little in 1st or 2nd shift but I can live with that for now.  I’ll eventually chase it out of there one way or another.  The car seems a bit smoother, not as much harshness, seems smoother.”

So there you have it, a very effective change and improvement to a really enjoyable Mustang.