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Brake vibration - totally stumped

I’ve got a 2005 Subaru Outback that has a vibration, not pulsation, only while braking from any speed above 25mph. The frequency of the vibration does not change with speed, but does become more intense at higher speeds. All four rotors have a maximum run out of .002 and the pads are almost new. All suspension and wheel bearings feel tight, by hand and with a 36" pry bar. The vibration can be felt throughout the front of the vehicle but not in the brake pedal. I’m really stumped on this one. Any ideas I’m not thinking of?

NOT IN THE BRAKE PEDAL… Not at all in the brake pedal?

There are a number of non-related brake parts that could cause this. Try raising front wheels off the ground one at a time. Grasp the tire at the 3 and 9 o’clock positions and try to move it back and forth. You should feel no looseness at all. If you feel even the slightest amount of movement, and combined with the max. .002 you have on the rotors it’s possible the inner tie rods are causing this.

Without a doubt, I’ve replaced more inner tie rods by far than any other suspension component on a Subaru.
(And I’m assuming here this vibration can be felt and possibly seen in the steering wheel.)

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I sure wish there were a loose tie rod. Unfortunately the tie rods, control arm bushings, ball joints and wheel bearings all feel tight as can be.

Most likely the problem is with the front rotors. You do not necessarily have to feel the vibration on the brake pedal. I’d buy a new pair and replace them: if you can do it yourself the cost is under $100. But you need to add new pads too.

Take the car out on a deserted, smooth road, run it up to about 50 MPH, and then bring it slowly to a stop with the park brake only.
This will at least narrow it down as to whether the fronts or the rears are the main source of the problem; hopefully.

There are some less obvious things that could cause this but I’d hate to state with any certainty they’re the cause. A problematic tire or a halfshaft (the inner joint) with an odd wear pattern could do it. It’s also possible a faulty upper engine/trans mount (called a pitching stopper) could do it or a brake caliper sticking on a slide.

Those are all just random guesses at this point but with a maximum runout of .002 on all of the rotors one would think these wouldn’t be much of a problem.

You’ve done a pretty good job of narrowing down the source, but you need to do some more.

First, rotate the tires front to back. If nothing changes, then you can eliminate tires/rims/attchment from the list of possibilities.

You should also check the aligment. A bit of toe out, along with a bit of a worn component can do this. Finding that worn component may take some time, but that is where I would concentrate my efforts.

As for the parking-brake test (to isolate front/rear), do Subarus use the brake shoe inside the brake disk? I’ve often used the parking brake procedure to isolate front/rear problems, until I saw brake-shoe style parking brake on the rear disks.

I have the sister car (2005 Legacy GT wagon). No sure if it is the Outback XT in questions, however we had a seizing caliper causing a similar issue. We had the rotors machined(mess), pads replaced and front driver caliper changed it went away.

The brakes calipers on the Legacy GT/Outback XT (turbos) are known to do this. I don’t think it is a common issue on the non-turbo versions.

JoeMario is correct. Because of the rear disk brake design, small brake shoes are used on small brake drums for the parking brake of these cars.

Aside from putting a lot of wear on these little brake shoes, stopping the car from 50 mph with the parking brake will not lead to diagnosis of disk problems.

You’re correct. My mind was so focused on warped rotors and suspension components, etc. I flat overlooked the parking shoe arrangement.