Mazdaspeed6 rear end overhaul begins!

  In this installment, I will cover the major task of removing the rear subframe and differential assembly on my Mazdaspeed6.  First let me itemize the weak points this new batch of parts would be addressing. The Mazdaspeed6 has a couple of known weak points, one is the rear engine mount that I had replaced and covered in a previous installment.  The other is the rear differential mount, of which there are actually two, one fore and one aft of the rear differential.  There has also been a few cases that have been noted online of rear axles breaking under hard launches or increased power levels, but these may be a bit more rare.  Finally, one weak point in the handling department is that this car can have quite a bit of heavy understeer when driven hard, not necessarily unusual for a heavy AWD sedan, but a weak point nonetheless.  Most of the parts slated to be installed, should directly address these concerns, at least in theory.

Nothing like a box stuffed with automotive goodies!

  A part of the motivation to get all of this work done, was to prep the car for an upcoming track day, aside from just the general need to replace old and worn out parts.  So the complete list was as follows:  a Corksport rear differential mount, to replace the old and very worn original OE Mazda mount; a DriveShaft Shop rear passenger side axle to replace the original factory axle that had torn boots and worn joints (the driver rear has already been replaced with a DriveShaft Shop axle for the same reason); a pair of Corksport front upper control arms to replace the worn factory originals; and a Whiteline rear sway bar as an upgrade to the OE Mazda bar since everything would be apart and easy to access.  Whew, thats quite a list of tasks for one sitting!  The front upper control arms would be  a fairly simple and quick replacement, so the focus here will be all of the rear end work.  Dealing with a few different rear end components, dropping the entire rear subframe although a fairly large undertaking, was really the most effective way to address all these repairs at once.

Looks so nice and pretty before install...

    Before getting into this install/overhaul, I must credit the great resource that is this post on nemotorsport.com.  It is a fantastic, step by step guide, that I used throughout the project.  I moved slowly and deliberately through each and every step, which was really a necessity for a job of this scope on my first attempt.  Also bear in mind, this is work being done to a car that is now over 10 years old, with lots of rust and over 100,000 miles on the clock.  Patience is essential in avoiding any broken bolts along the way (which still ended up happening to one bolt).  The how-to from the forum is really as thorough as it gets, and made the whole process relatively easy.  I was able to have the subframe removed and on the ground within a few hours.

After a few hours of battling rust and grimy bolts, the subframe was out!

  With the entire rear end assembly removed, this was to be a good opportunity to replace the rear differential mount, the rear sway bar, and the rear passenger side axle.  Since all these components are anchored to this assembly in some form, in theory at least, the install would be a breeze.  It is worth noting, my H&R sport springs, which have been on the car for at least 70,000 miles and probably about 7 years now, are holding up incredibly well.  The paint on the springs shows no signs of age other than dirt, and I don't see any corrosion setting in as of yet.  That's no small feat for a car driven in Chicago winters with all the slush and road salt it sees annually.

You can see apparent here, lots of rust and lots of CV joint grease spattered on the assembly

  Onward with the install which was, in theory, easier with the entire rear subframe removed, but there were definitely challenges.  Really one challenge, the passenger side axle replacement.  I had not mentioned earlier, but this was actually my second attempt at replacing this same axle.  A previous effort fell short when simply hammering the axle would not free it from the hub.  Being pressed for time, I simply left the job for another day.  So for this go around, the hammering continued, with copious amounts of fire, several rounds of PB Blaster spraying, and lots more hammering (with the help of a friend to basically tag team the damn axle!).  The axle was quite stubborn, and literally moved fractions of milimeters at a time, for a long time the progress was imperceptible to the eye.  The amount of hammering needed, caused the end of the axle to mushroom out so severely that I needed to grind the excess metal in order for it to clear through the hub once freed.  We lost easily an hour and a half to this axle alone.
     Eventually everything was removed that needed to be, and replaced with the new upgraded parts.  Aside from the stubborn axle, it was relatively easy putting the mount in place and the new sway bar in place.  I even did a bit of rust removal on the under body and sprayed on a couple coats of 3M Rubberized undercoating for both it's sound deadening and rust preventative properties.  I also repeated this on parts of the subframe as well, albeit not quite as thoroughly.  It was a bit more of a "quick and dirty" job, as I had lost so much time already and did not want to spend too much time waiting for paint to dry.  After all the paint and undercoat dried, the process of lifting the rear subframe back into place went ahead slowly and carefully.  The theme of taking my time was once again at play, as I wanted to be sure nothing was left loose, pinched, cracked or otherwise broken in some way in the act of sandwiching everything back into the underbody of the car.  Once all the work was completed, it was time for the test drive.  This test drive would reveal a new issue, victory beers would have to wait.  I'll elaborate in the next post.

- written by:  Robert Sixto

-photos by: Robert Sixto