[Savagesubie]

‘16 Forester Prem 79k mi. Subaru says brakes are good. My brakes shudder/vibrate only when slowing from 60mph+ and I think only going downhill, vibration stops below about 40mph. Vibration is moderate, gets worse the harder I brake, and does appreciably extend stopping distance. I can slow from 80mph fairly rapidly with no detectable vibration as long as it’s not downhill. The exit off the freeway to my house is downhill, so I experience it every time from work unless if I brake much more gradually. I followed instructions to temporarily disable my ABS, and there was no more vibration anywhere from any speed even with heavy braking, so thinking it’s not a rotor/pad issue. Maybe an ABS issue, or maybe a suspension issue the ABS reacts poorly to. Any input helpful, thanks!

 

[donkpow]

I don't have this model car. It sounds like to me you may have a problem with something in the communications system or like in the steering angle or yaw rate and G force sensor.

 

[Savagesubie]

Thanks for the reply!

I goofed

I did a test drive and discovered the downhill off-ramp made me apply the brakes at just the right pressure, at just the right speed to induce the most shake. When I did the test at 80mph flat freeway, it was a lot of pressure (not quite “emergency” pressure though), and very little to no shake. I just did that again both flat and on hill with same results. I tested braking from 80 on flat freeway and was able to reproduce the same shake only with moderate pressure (not heavy, not light). Shake stops at about 50, but I’ve felt it down to 40, I guess with the right pressure. So it has to do with the specific pressure on brake, so I will have to test again with my ABS disabled. I guess it could be slight warped rotor at this point.

 

[donkpow]

Okay then. Now I would also consider front end suspension components along with the brakes.

 

[DockingPilot]

Rotors might be warped


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[donkpow]

You know, it's possible to check run out on a rotor. Cheap and easy with a Harbor Freight dial indicator kit.

 

[bman400]

I had a similar problem years ago with my 2001. Steering wheel oscillating as I drove, worse as speeds increased, worse during braking. Cause by runout as @donkpow mentioned, except in my case it was caused by damaged front hub/bearing. Basically the rotor was wobbling as it rotated.

 

[whobodym]

dry pavement?? it's very hard to imagine the ABS system being involved at all in any braking short of flat-out panic stops. I vote for brake rotors and/or suspension bushings.

 

[GuusV]

I had this issue on our 2009X. It got worse the longer I was travelling at higher speeds. The first time I would apply the brake would cause weird shaking and vibrations.
At the same time my front brakes would always squeal when going backwards slowly.

I ended up going to a higher quality slotted and drilled rotor. Not only did I notice a significant improvement in braking performance, the shake/vibration went away, as well as the squeal in reverse!

 

[Savagesubie]

Thank you ALL so much for the relies and help.

I was able to test again with ABS “disabled”. I removed 15a “STOP” fuse in cabin, there is also a 30a fuse in engine bay, but reports of limp mode with that one removed. Anyway, I was able te recreate vibration, but did seem less intense, and also at even more specific pedal pressure & speed, most intense from 70 to 60mph moderate pressure. Probably slightly warped rotor, but could be suspension issue as I read those can sometimes mimic a warped rotor. Unfortunately I have about 40% pad life left but don’t want to damage system so will replace sooner than later to see if fixes problem.

Thanks again everyone!

 

[Savagesubie]

A warning on slotted/drilled rotors.

It is usually better to get good quality solid rotors. Drilling is for better heat dissipation on many repeated hard stops such as in racing. Slotting is for better bite into pads, wearing them out significantly faster, but it does help in racing when you replace pads and rotors regularly anyway. There are more problems with drilled/slotted rotors for the street as they tend to be cheap (not thousands of dollars) and are cast instead of machined, and use cheap metal, so introduces more chance of a cracked and warped rotor down the road. The slots/holes can damage rotor/pads if little rocks get in there too when off roading.

I bought my subi two years ago and the dealer had just replaced the brakes, probably cheapest they could get their hands on, and why they’re most likely warped already.