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Rear brake splash/dust guard; significance? Safety related?

13K views 14 replies 10 participants last post by  Ken2004LLBean  
#1 · (Edited)
After 15 years the rear brake back plates on my 07 are rusting. (aka: backing plate, dust cover, dust shield, brake splash guard )

The plate appears to be made up of two parts, a center part, which is clamped between the rear (trailing) arm and the bearing hub, and an outer section that is spot welded to the center and sort of wraps around the brake rotor. In the image below, we can see the spot welds. The rust follows around the center part along the red line but in a wider band that reaches about 1/2-way out to the circumference. (The fact that it's two separate pieces, probably with some gaps, likely provides a space for rust to being and spread out in the thinner outer material.)

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From what I've seen in older Subarus, eventually that outer part breaks away in the shape of a large "C". There's a few posts here about it, in some cases it was being replaced, in others there were suggestions to just leave it off.

Obviously, the center part of the assembly is important, as it forms the interface between the rear (trailing) arm and the wheel bearing hub. But what about the outer section? Exactly what is it's purpose and how does it achieve that, given it's not really sealing anything. (I would imagine there is a purpose/need, otherwise it wouldn't be there.) If it is off, the inboard side of the rotor is exposed, but then the outboard side is exposed all the time. Could it be meant to prevent dust from getting inside the parking brake assembly, or even the hub? Any long term negative effects? Is it safety-related in some way?

I guess my questions are leading to: If it were to come off, should it be replaced? I'm not averse to that if it's reasonably necessary. But I can see it being a challenging job as it requires removing the wheel hub in addition to the brake assemblies (disk and parking). The hub is probably rusted in as well, which could lead to it being damaged on removal and having to be replaced. It won't be inexpensive, and I'll probably have to do both sides.

Your views?

Part details:

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#2 ·
Exactly what is it's purpose and how does it achieve that, given it's not really sealing anything. (I would imagine there is a purpose/need, otherwise it wouldn't be there.)
I used to hang my gopro upside down underneath the rear bumper cover facing forward, and while driving on snow I would notice just how much snow/debris the front tires shoot backwards on to the rear tires/wheels. So a little protection from dirt and even small objects (debris) mixed into the snow wouldn't hurt.

If it is off, the back side of the rotor is exposed, but then the outer side is exposed all the time.
Yes, but I would like to believe the 'spokes' on the outside provide a bit more protection from debris than a fully/largely exposed rotor on the inside. And then the inside simply takes more debris coming from the front tires than the outside. The inside of the rear wheel gets debris from both front tires while the outside of the rear wheel gets a little bit from the front wheel on the same side, but otherwise little to nothing from the front wheel on the other side.

One benefit of not having the plate is that rocks/pebbles won't get stuck between the rotor and the plate, leading to that horrible screeching sound and/or rotor damage. But I'd like to believe that's the evil lesser than having it fully exposed to all the debris that otherwise doesn't get stuck between the plate and rotor. It's hard to say.

If removing or replacing is the same amount of work I would replace, although replacements do seem to be pricey. Perhaps a junk yard may have something intact (more work, cheaper purchase). Or else patch it up as a short/mid term solution (polyester/fibreglass etc.).
 
#3 ·
Isn't that sandwiched between the bearing hub flange and knuckle?
If so, the amount of work to get the bearing hub off should answer the question of whether to replace these or not.
If the rust has eaten through the shield, the hub should be well frozen.
 
#4 · (Edited)
Not unexpected: two differing approaches!

@7stars

Interesting reply . . .

That camera view would have been nice to see; wonder if anyone has posted something here or on YouTube . . . ..

Removing the rusted outer shield part (outside the red line area) is not a problem; in some cases it just falls off, or starts flapping and/or rubbing on the rotor so it's noticeable. Usually can be pulled off (i.e. break the last threads of metal holding it), if it hasn't already fallen off.


@dukey33

Yes, the center part of the "back plate" assembly is sandwiched between the bearing hub flange and knuckle (at the front), or between the rear (trailing) arm and the hub flange (at the rear). (In the photo above, the hub fits in the odd-shaped area in the middle with the four holes.) The hub would probably be seized in the rear arm and would indeed be a challenge to remove in a way that doesn't damage the hub itself. That's why my concern is whether just leaving it without the outer dust shield section could compromise the rest of the components, i.e., affect the brakes (both systems) or the hub itself, due to added exposure.
 
#6 ·
Fascinating to watch, thanks.

Yes, there is a lot of spray from the fronts that carries to the rear wheels. I wonder if the spinning at the rear would throw the snow out/away from the rotor and hub. Probably need a rather sophisticated test. Going to have to consider this.

Also hoping others that are running, or have run, with one or more shields off will comment, especially if there were any effects.
 
#8 ·
Removal of these shields were part of doing the "H6" rear brake upgrades on older Imprezas and WRXs. I don't recall issues with them being removed.

On my old RS, I drilled out the welds and hit it with some primer and paint for some rust protection... tho this was in southern California... so not much rust to speak of.
 
#10 ·
Just did a left rear bearing yesterday on my 06 - I can hear music again! I bought the dust shield part ($95 was best price I could find) but didn't realize the parking brake cable ran through it and so the p-brake would need to be disassembled to replace the shield. That looked like a potential can of worms given the amount of rust, and I was not prepared to spend the whole day doing it so I bagged it and went without. I knew I would never remove the bearing again just to do the shield so it will likely never be replaced (by me). I'd recommend having a new p-brake assembly on hand just in case, if you are going to attempt replacing the shield on a rust-belt car.
 
#11 ·
Hey Notch,

I just went thru an Outback (Gen3, '09 OB 2.5i Ltd) rear brake partial rebuild last week. The car is quite rusty underneath (allegedly lived in W. Va and Pittsburgh in its former life) and these "dust/splash shields" were perforated with rust and crumbling to pieces, but the real problem was the driver's side pb shoes fell off the steel backer so we had to go in.

The caliper bracket bolts were frozen, twisted one head off with the impact and rounded the other off (= an hour of quality time under the car with the die grinder). The hubs were rusted to the back plate and to the suspension arm. The pb actuating arms were frozen to the pin on the primary shoe, so it was hardly actuating the pb anyway. The pb cable housing was rusted to the receiving tube on the back plate, but I was able to separate the receiving tube from the back plate and then split the tube open (both with a cutoff wheel on the die grinder), so we did not have to replace the pb cables. That would have required removing the plastic panels under the car that the cables run behind, which would have been a permanent mod (the nuts are rusted to the studs and there's no hex to speak of, the corrosion is so bad the studs would probably shear off the body).

Surprisingly the guide pins and boots were in good shape and caliper pistons seemed to retract nice and smooth, but now that we're rebuilt (new brackets, new powerstop rotor/pad kit KOE4632, new pb shoes and hardware) the rotors get too hot to touch just rolling down the road. We pulled the pads and opened up the vertical clearance to the bracket, but still they run hot. Wondering if the pistons are not properly retracting.

Reman calipers arriving tomorrow (broke one bleeder screw just trying to crack it loose, and the other felt like I was stripping threads the whole time, it's a miracle I got it closed again), so maybe that will solve the issue.

Going to copy some of this to a new thread on the hot brakes problem...

@plain OM - what did you end up doing with your dust shields?


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#13 ·
Came across this thread just now while researching front dust shields here. 2006 Subaru Outback here. Mine are rusted and chipped (we used to live in the upper midwest but live in the south now). The front left seems fine but the front right is loose and rubbing against wheel (image attached). Is it safe to drive in this condition? Is this a brake related job or tire related job? Could I take this to any repair shop? Just trying to learn and be more informed about my vehicle
 

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#14 ·
Is this a brake related job or tire related job?
To replace the front dust shield? I guess it would classified as a front brake/suspension job because the brake caliper, bracket, and rotor, as well as the wheel bearing hub have to be removed. Might involve having to replace the hub because it tends to get rusted into place and removal involves significant force that could damage it.

The outer part that is rusted could probably be removed to prevent it rubbing the wheel. Check with a local licensed mechanic; in some jurisdictions the car will not pass a safety check if the dust shield is missing.
 
#15 ·
I just removed the dust shields/backing plates on my wife's Gen 2 (2004) Outback, because I am replacing both rear wheel bearings. Shields were pretty badly rusted. Am going to do a total rebuild of rear brakes too.

Will not be an inexpensive project by any stretch, even with me doing the labor.