Brake Roaring

[browney]

Hi,
My mother has a Subaru outback and her brakes make a roring sound and feel a bit off (the feedback when you are coming to a stop just doesn't feel quite right/progressive).

I would have thought this is likely to be brake disc warping? Does that sound right?

She says she has had the pads change and the discs machined before but the problem has come back again. Can anyone give me some other ideas of what it could be?

[Peter...]

Probably ran over a lion.

[Peter...]

PS we have a "tech" section.

[MR-PUNANNY]

Probably ran over a lion.

hahahahaha :rotflol::rotflol::rotflol:

[tremolo]

Probably ran over a lion.

:rotflol::rotflol::rotflol::rotflol::rotflol::rotf lol::rotflol:

[ZENNON]

can you feel the pedal pulsating at all?

[GTSBoy]

It will be pad binder material stuck to the discs. They need a good hard flogging to get them hot and burn it off then a nice cool down.

Tell her not to brake like a MoFo when stopping at the lights then sit with her foot on the brake pedal and tranny in drive.

[browney]

Pedal pusating, as in ABS, no it's not necissarilly under hard braking.

Brake like a MoFo?

The car would be driven about as sedately as possible (it's a bloody subaru outback).

[GTSBoy]

Brake like a MoFo?

The car would be driven about as sedately as possible (it's a bloody subaru outback).

I've noticed that regardless of how sedate women drive, they all brake like mental cases and sit at the lights with their foot on the still hot disc transferring binder material from the pad to the rotor - in just the one place. Makes for lumpy and noisy rotors.

Rotors are probably also undersize. They get worse at this stuff as they get thinner. Ours is actually having new rotors in today, as it has been having a throbbing pedal for the last [too many] months courtesy of all of the above points.

[browney]

That may well be the case but it is odd that this is the first vehicle she has diven that has had that problem occur, repeatably, after 20 odd years of driving. I guess there are factors like the type of materials used for the pad and the way the cooling is set up for the brakes in an outback?

[RB30-POWER]

small brakes, too much vehicle weight, high friction pads all equal more heat.

seems to be the trend these days on most cars to warp rotors and all the rest of it.

auto's can not help the situation either, if the fuckers downchanged and allowed some engine brake effect, might help some.

[browney]

Possible, i guess.

It does feel like warped rotors I haven't seen that happen to anyone multiple times in the same vehicle when it had been fixed.

I would have thought that i have done a lot more hard braking in my cars and motorcycles and have only ever had a warped disc on my old S2 RX7 and it didn't come back after being fixed, although I used other brake pads after that.

I've only just come back from intersate and she's been getting it serviced at a dealer who don't sound like they have been helping her much with answers (and she probably doesn't ask enough either!).

Has anyone else seen anything similar on Subaru Outbacks?

[Madhatr]

how long has it been (how many km's) since they were machined?

[GTSBoy]

Rotors don't warp. It's almost always pad material transfer.

[bigmuz]

Check the wheel bearings.

[Steve]

And, don't do up your wheel nuts with a rattle gun,
do up your wheel nuts by hand/with a torque wrench, because if you don't you can end up with DTV i.e. disc thickness variation due to odd torquing of nuts resulting.
I've heard a hundred ways of adjusting wheel bearing pre-load, want to go down that path?
The way I was shown was to tighten the nut till the bearing just starts to bind, then release it till it turns freely, maybe 5-10 minutes on the clock. My wheel bearings last approx 200k kms when greased and serviced regularly approx 50k intervals.

[jmac]

+1 for it being transfer from the pads unevenly, and the discs not being warped.

wheel bearings - they are typically supposed to have around 2thou clearance (application dependant) but the big problem is it's next to impossible to perceive such clearance by eye or feel so a dial indicator is key (unless there is another way, read on) - the assosciated problem is the fact that the forces any person could put on a hub or disc/hub assembly (heck even with the wheel attatched) is stuff all compared to the weight of the car pushing sideways around a corner against the tyre grip etc. So we can't 'really' measure it or get a good feel by hand.

I'm of the opinion that the tighten then back of procedure is doable if one has the experience, but a combo of the factors above as well as the tackiness of wheel bearing grease, finding the sweet spot is harder than it sounds, and a hell of a lot of people do them too loose. the bearings are tapered and with the load spread across the full width of the roller they can handle massive loads, but a little bit of slack and there's angularity and force focussed on a small section of each roller = massive wear.

An alternative AND ABSOLUTELY DON'T DO THIS, OR IF YOU DO, DO SO AT YOUR OWN RISK, THIS INFO IS FOR DISCUSSION PURPOSES ONLY, that I employ is to tighten till it binds a little, then back off around 1/4 of a turn, then re-tighted, but by hand, and assuming that hand still has some grease on it from backing the bearings etc, then do it up as firm as one can by hand. This probably amounts to something like 1Nm. For whatever reason, creeping up on the tension seems to get it 'closer' than tightening and then loosening.

But, as I said, I know plenty of people who get it 'right' by using the former method, I'm just mentioning the method I use. I've _never_ had a set of bearings that were stuffed or even borderline - I've _always_ gotten them to last the life of the discs (and further to that, I've _never_ had discs machined, so the life of the discs tends to be longer than it might otherwise appear I'm talking about).