Blazer Spare Tire Carrier
When the GM engineers looked at spare tire locations for the 2-door
Chevy Blazer, its short wheelbase made for a difficult design
compromise. The underside of the vehicle has no room for a
full-sized tire. So they offered two solutions:
Time + Wear = Noise
May 2012
Inside Mount
Outside Mount
Neither option is ideal. Cargo space gets eaten up with the inside
mount, and the outside mount requires the spare tire carrier to be
swung out whenever you want to open the tailgate. On stock ZR2
Blazers like mine, you can't even open the rear glass without swing
open the carrier, because the tire is in the way. Plus, it blocks the
rear view. Another common issue with the outside spare is the
carriers occasionally come unlatched, which usually results in the
carrier swinging open all the way while you're driving down the road.

I addressed these issues with help from the ZR2USA website, first
by lowering the spare tire mount and then by adding a secondary
latch. The square metal plate in the photo below is the lowering kit.
It's just a metal plate mounted to the carrier, with studs positioned a
couple inches lower. Washers are used to space the tire further
back, which helps provide enough gap from the rear glass that it can
be opened without having to swing out the carrier.
Secondary Latch
From left to right: 1) Carrier open; 2) Carrier closed; 3) Latch unhooked by
squeezing the latch handle;  
4) Carrier tries to open; secondary latch engages.
The main weakness of the outside-mounted spare tire is the weight of
the wheel and tire on the carrier. If I had to guess, between the wheel,
tire and carrier, there's at least 100 pounds mounted to the rear
quarter panel. When the carrier is swung all the way out, the hinge
and brackets are supporting a pretty large load.

A couple things can cause problems here. First, if the carrier breaks
free from the latch while the vehicle is in motion, odds are it's going to
swing open rapidly, all the way to the stops. The force of this can
actually dent the quarter panel. If you do a lot of off-roading, all the
bounding and jostling may even cause the body panels to crack.
The pictures above are probably extreme examples of how the carrier brackets can
damage the body. I'm not sure what conditions this Blazer was driven in, but I would
guess there was some off-roading involved. There's really no good way patch-fix this.
Most carriers that end up this way probably aren't carrying a spare tire anymore.

On the left is a more common example of what happens when the carrier swings out
all the way to the stops. We'll see below why the body panels can dent so easily
when this happens. There just isn't much support behind those panels.

I've seen plenty of Blazers
without the tire on the carrier, probably because of some
of these issues. When Blazer owners give up on the carrier, most spare tires end up
taking up room in the cargo area. Others end up
on the roof rack. Neither method is
ideal, although that roof rack looks pretty cool.....
On my Blazer, the carrier started rattling and thumping pretty
severely. Before I figured out what the noise was, I thought
something might explode back in the rear passenger side quarter
panel area. When the noise disappeared with the spare tire
removed, I knew it must be the carrier mounting brackets. The
mounting bolts were snug but not super tight, so I torqued them
down a bit. That only made the problem worse.

After a long period of Internet research, using forums like
s10forum.com, zr2USA.com and blazerforum.com, I couldn't find
much help. Nobody had any photos of what the carrier mounting
brackets connected to on the other side of the body panel. The best
I could find was a diagram (click on diagram for larger view):
Some of my Internet research pointed to the hinge pins and bushings
as potential noise makers, but my hinges had very little play. The
inside brackets (#6 and #7 in the diagram) had to be the problem.

When I took apart the inside body panels and exposed the inner part
of the rear quarter panel, I saw only this:
The inside bracket was sandwiched between the inner and outer body
walls. I could just barely make out the bolts poking through the
rear-facing part of the bracket, but not good enough to tell anything
about what was going on in there.
You can see that the bolt threads into what is basically a nut welded
onto the inside bracket. The reason I chose to expose this particular
bolt was because that nut thing was pushed in slightly. With the
carrier removed and the M10x1.50 bolt threaded about a third of the
way into the nut,  the bolt would move just a little as I jerked on it. The
other bolts did not give very much when threaded into the other 5
holes (the brackets appear to be tack welded to the outer body).

When I exposed the bracket, the lower left corner had a small gap
between the bracket and the outer body wall. Not much - probably
about 1/16" of an inch. On a hunch, I shoved a nylon washer into the
gap, put some electrical tape around the bracket to make sure the
washer stayed put, and then gave it a test drive.
Outside bolt holes. The one of the right had been pushed in just a bit. This can be
fairly common, especially when the carrier opens all the way to its stops. There's a lot
of weight pushing against the body and the brackets. For as much weight as there is
on these brackets, I was surprised how not beefy this is.
Washer shoved between the bracket and the body wall, with tape to keep it from
falling out.
All back together, with subwoofer and amp (out of sight behind the sub)
Like magic, the noise went away. Apparently the flexing of the body
wall against the inner bracket was enough to cause some rattling
and thumping. At some point I will spot weld the bracket for a more
permanent solution.
To improve my view, I drilled a small hole to locate the upper bracket
(#6) and then made it bigger with a 1.75" bi-metal hole saw. With a
larger opening, I could see the front-most bolt sticking through the
opening. It looked like this:
The secondary latch is visible on the left side of the latch plate. It's an
ingenious little device plumbed into the stock latch mechanism. If the
stock latch somehow releases (or wasn't closed properly), the
secondary latch catches and prevents the carrier from swinging open.

Unfortunately, neither of these products are available anymore,
although the lowering kit would be pretty easy to make with plate
steel, studs, a drill press and a welder.