WTF are these? '04 STI rear brake/Weights???

[Dean]

OK, every time I work on the rear brakes on my car I ask myself WTF are these weird things bolted under the bolts for the rear caliper. it appears to be a rubber coated lead weight almost that hangs down below the axle center line.

Other than adding unsprung weight which is not often a design goal, I can't figure out what they are for and they don't appear in the shop manual that I can find.

Any clues.

I took them off and my car was instantly faster.

[sperry]

OMG!!! PUT THEM BACK ON NOW!

...those are muffler bearings, aren't they?

[Kevin M]

Vibration dampers.

[Dean]

Originally Posted by BAN SUVS

Vibration dampers.

In what plane/direction? there is a really big damper for anything vertical and a nice tire for vertical and lateral right next to it. Have you seen discussion of this somewhere?

And I had my muffler bearings serviced last week, those are not them.

WRX didn't have them.

[wrxkidid]

Brake light fluid fliters?

[MattR]

I don't know what those are, but I think I took mine off as well.

[MPREZIV]

Originally Posted by MattR

I don't know what those are, but I think I took mine off as well.

I surely don't remember seeing that shit when we did the wheel brgs...

[knucklesplitter]

Tuned mass damper would be my guess:
http://en.wikipedia.org/wiki/Tuned_mass_damper

"Tuned mass dampers are widely used in production cars, typically on the crankshaft pulley to control torsional vibration and bending modes of the crankshaft, on the driveline for gearwhine, and other noises. They are also used on the exhaust, on the body and on the suspension, as in the 2CV example above. Almost all cars will have one mass damper, some may have 10 or more."

In my college mechanical lab we were given a single-cylinder compressor that practically jumped off the ground as it ran. We had to design and install a tuned mass damper. The compressor barely vibrated once properly dampened.

[Dean]

Yeah, I figured they were a damper of some form, but what I can't tell is in what direction they are damping.

I am guessing they are dealing with a brake related vertical or lateral oscillation and not a suspension travel vibration.

The rear caliper position is a little strange at a trailing 2 O'clock on the driver's side. The mass of this damper would be at about 3 O'clock.

Anybody with an 05 have them? You would know if you have had the rear rotors off for some reason.

[Kevin M]

No direction. Or all directions. It's for tiny amplitude vibration. Smaller than the range of movement provided by the hardness of the rubber in the damper. Remember, "damper" doesn't mean "strut/shock absorber." In other words, it's for the vibrations created by the friction of the pad/rotor contact under braking.

[sperry]

Originally Posted by BAN SUVS

No direction. Or all directions. It's for tiny amplitude vibration. Smaller than the range of movement provided by the hardness of the rubber in the damper. Remember, "damper" doesn't mean "strut/shock absorber." In other words, it's for the vibrations created by the friction of the pad/rotor contact under braking.

If that's the case, it's probably just a damper to quell pedal vibration under braking.

[Kevin M]

Originally Posted by sperry

If that's the case, it's probably just a damper to quell pedal vibration under braking.

Could be.

[knucklesplitter]

Originally Posted by BAN SUVS

No direction. Or all directions. It's for tiny amplitude vibration. Smaller than the range of movement provided by the hardness of the rubber in the damper. Remember, "damper" doesn't mean "strut/shock absorber." In other words, it's for the vibrations created by the friction of the pad/rotor contact under braking.

Looking at the photo I'd guess the "damping" is directional, but I can't tell which direction.

A tuned-mass damper actually uses no "damping" in the traditional sense. It is simply a mass on a spring with no or minimal damping of the spring. You tune the resonant frequency of the mass/spring combo to be equal to the frequency of the vibration you want to damp. A small amount of mass can do a surprising amount of damping in this configuration. The theory is that at resonance the mass tries to vibrate to infinity (and beyond!). It obviously can't do that due to various real-world constraints, but it can counteract a lot of mass vibration, so don't assume it is just for micro-amplitude damping.

Having said all that it wouldn't surprise me if it was for nothing more than reducing brake pad squeel or something mundane like that.

[Dean]

Originally Posted by BAN SUVS

No direction. Or all directions. It's for tiny amplitude vibration. Smaller than the range of movement provided by the hardness of the rubber in the damper. Remember, "damper" doesn't mean "strut/shock absorber." In other words, it's for the vibrations created by the friction of the pad/rotor contact under braking.

All directions requires some level of freedom in all directions which I am not sure is true in this case. I think this likely works in a lateral mode looking at them again.

I think the greater breaking capacity of the rear STI brakes and the significantly larger mass of the vented rear rotor on the STI compared to the WRX and the mounting bracket strength may be part of the issue. This bracket not only has a damper, but also almost doubles the thickness of the mounting surface.

It will be interesting to see if I notice any difference. Laguna is in 2 weeks.

Anybody want to help bleed brakes this weekend if it is warm?

[MikeK]

Originally Posted by Dean

Anybody want to help bleed brakes this weekend if it is warm?

I can help saturday afternoon if you want

[Double Phister]

Originally Posted by Dean

Anybody with an 05 have them? You would know if you have had the rear rotors off for some reason.

I have them. Saw them when i put the dba rotors on.

[Road_Kill]

Those are Subaru's fix for the STI brake noise when backing up.... They were installed for a short period to help eliminate a brake squeak... They are garbage and can be thrown away... Heck they don't even use them on the newer cars.. (05+) Just like everything else Subaru does, it was a half assed attempt to combat a potential complaint from a customer that expected their STI to be a quiet smooth luxury car.

[knucklesplitter]

Originally Posted by Road_Kill

Those are Subaru's fix for the STI brake noise when backing up.... They were installed for a short period to help eliminate a brake squeak... They are garbage and can be thrown away... Heck they don't even use them on the newer cars.. (05+) Just like everything else Subaru does, it was a half assed attempt to combat a potential complaint from a customer that expected their STI to be a quiet smooth luxury car.

If that's the case then these don't do shit, because my '04 has them and it screams when the brakes are applied in reverse. Also R4ND0M_AX3 has them on his '05.

[Road_Kill]

Yeah... I know.... Hence the quote... "Subaru's half assed attempt."

[Double Phister]

Must be working then because I don't get any noise in reverse other than the initial pad rocking.

PS my build date is April 2004.