Mazdaspeed 6 Rear Subframe Project Posted on 05 Jan 23:04

  I realize I left this topic hanging, and never really had a complete conclusion to this piece, so here is my updated revision on the topic:

     In this installment, I will cover the major task of removing the rear subframe and differential assembly on my Mazdaspeed6.  The complete removal of the rear subframe makes replacing many of the parts easier as an individual job, but even more so when replacing several of them at once.

Nothing like a box stuffed with automotive goodies!

       Most of the parts being installed will be employed to replace old worn out original components. The Corksport rear differential mount, replaces 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.  Finally, some Prothane sway bar bushing brackets would eventually go in place as well, an important step with this combination of parts.  More on that later.  The front upper control arms from Corksport, are some great looking pieces, they offer some additional camber adjustment, and increased rigidity in the bushings they employ.  Install was a snap, with no real mishaps in the process.  Long term, I had noticed the adjusting bolts develop some surface rust rather quickly, but they appear to be holding up OK.

 

Looks so nice and pretty before install...

 

  On to the real meat of the job, the rear subframe removal.  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 car is now over 10 years old with over 100,000 miles on the clock and many winters worth of salted streets.  The rust is plentiful!  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, even with a relatively slow and cautious pace.

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 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. Fitment of all the aftermarket parts was spot on, and went together with ease.  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 the subframe, giving it a healthy coating of Rust Bullet.  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 would reveal a critical issue that is key to having both the Drive Shaft Shop axles and the Whiteline rear sway bar.  What you might not notice in the photos above is just how close the axles sit to the sway bar, the bar essentially wraps around the axle.  When you have these beefed up versions together, the clearances become almost zero, to the point where the axles will bump against the original factory sway bar brackets.  Luckily the bumping merely tore a CV boot and caused no catastrophic damage.  The remedy is simple, Prothane makes a universal sway bar bracket and bushing set that fits perfectly and restores factory like clearance.  I have been trouble free for over 15,000 miles since.

 Long term driving impressions:

    I have really no complaints with almost a year and 15,000 miles of driving, everything has held up well.  As for performance, nothing in my opinion took away from the performance or comfort.  Little, if any, noise or vibration was created with the addition of these parts.  The real performance stand out, is the Whiteline rear sway bar.  I can say emphatically, that this is how it should have been delivered from the factory.  The cornering grip and the way it rotates now is better than I would have imagined it could be simply from replacing the rear sway bar.  I would consider this modification a must if you really want to extract the best handling from this car, even if you already have lowered and stiffened it via springs/shocks or coilovers.  The customer service stand out, was definitely Drive Shaft Shop.  You may have picked up on the fact that I was not aware my new sway bar would rub against the Drive Shaft Shop axles, and sure enough I tore open a CV boot as a result.  A call to Drive Shaft Shop, just to price out the replacement boot and ask about how to replace it, was met with courteous and eager help from the staff.  Not only that, but they even ended up sending me that replacement boot kit free of charge!  I never asked for even a discount, as I took full blame for the mishap, but they made the gesture anyway.  That is something that really makes an impression for me, and I would never hesitate to use their products and services in the future.  Be sure to check out more Mazdaspeed 6 modifications, like my big brake upgrade! 

 

-photos and writing: Robert Sixto