New pads and rotors...pulsing?

[drano]

i just replaced my pads and rotors.

they are pulsating when i hit the brakes.

any ideas?

[blackgtbeauty]

were the rotors sitting around a while before they were put on? have you washed you're car since they were put on and the car was hot?

[drano]

nope no washing, they were sitting in the back of my wagon today and yesterday.

[Huffer]

Pads not lined up right, sitting level, or the rotors are not flat either. They could be warped, defective manufacturing.

When you installed them, did you take the time to bed them in, or first run out did you stand on the stop pedal?

[drano]

i didnt slam the brakes, how does bedding work? ive read a little about it on here, ill do some more research. could be that the pads arent sitting right, my friend had a time with the drivers side caliper going onj.

dumb question....im still a newbie, but when i removed the old pads, there were two metal plates on the back of the pads, are these shims? and i put them on like they were on the old ones, i just want to make sure that i was supposed to put them back on.

and the old inside driverside pad was worn very oddly. worn more at the top and towards the rear. there was a nice chunk of pad left near the front bottom of the pad.

[shazapple]

sounds like one of your calipers has a seized bolt. take it all apart and grease it up

[llaprad1]

were the rotors sitting around a while before they were put on?

I've searched pretty thoroughly, and have only found a couple of references to the question above on the web. And those guys were guessing, plus they were dealer salesmen.

I don't think rotors sitting around will cause warping. I have a car I drive maybe twice a month, and the rotors are as true as day. Plus they are much smaller than my LGT's.

---

I just installed new pads and rotors, and the rotors were open but stored in the baggie, plus showed no sign of oxidation.

I still have a pulse that is assumed to be brake-related, and it is not reproduceable with only the e-brake (to factor out the improbable rear rotors).

Is there anything else (specific to Legacies) that may cause pulsing when brakes are activated?

Wheel bearings?
Tie Rods?
ABS stuff?

I'm relatively new to Subaru stuff, but I am a thorough and competent mechanic with my SE-R. But I've noticed sometimes with Subaru things are not logical.

[ivwarrior]

I still have a pulse that is assumed to be brake-related, and it is not reproduceable with only the e-brake (to factor out the improbable rear rotors).


You didn't rule anything out with the parking brake, all you did was wear away at the parking brake shoes. The problem very well could be the rear rotors.

Hint: Your parking brake is a drum style brake in the hat section of the rear rotors. Pulling up the lever doesn't engage the rear service brakes.

[steven_esworthy]

Did the rotors come with a zinc coating? I have heard of new rotors pulsing when they are coated unit you wear the zinc coating off of the contact area. Just a thought.

[llaprad1]

Your parking brake is a drum style brake in the hat section of the rear rotors. Pulling up the lever doesn't engage the rear service brakes.

I'll be damned...checked my Haynes, and you're right. Evidently most cars are like this now. That's what I get for dinking on early 90s cars.

Regardless, I'm still not convinced it's the rear anything. So little braking is required from the rear, and I have never heard of someone warping rears through heavy use. (The diagnosis is all over the net, but no one has a 'yup, that's what it was' answer)

I'm going to check for sticky sliding pins and look up that zinc coating thing.

[Perdue]

I'm going to go for defective rotors too. Doesn't sound like the rotors are true to me. Pulsing usually means warped rotors, and if it wasn't doing it before the brake install, it's probably from something installed. If it's only doing it when you're on the brakes, it probably has to do with the brakes. Not a subie thing...just common mechanical sense, if that.

[Huffer]

Could be installation error too.

[boxerpower]

were they new rotors? if so were they from a reputable company? do you have any discoloration of your rotor that would indicate warpage?

[llaprad1]

They were decent rotors from NAPA. No discoloration.

I had the pulsing beforehand, that's why I got the rotors.

I also bedded them in correctly.

I looked up the zinc coating thing, and saw that its mostly an added value option to keep the appearance up..I doubt these have that.

I'm going to go ahead and rule out installation error...I've done this several times over, and how can you mess up a rotor install? It's disassemble, remove, reassemble.

I'm going to go in and check the sliding pins. While I'm on the car, I'll get the rears apart to check for glazing on the pads/rotors.

And seriously, Subaru does do some nonstandard stuff (like thread the brake line thought the strut), so I thought maybe I'd ask here if there's something Subaru-specific that I should be looking out for.

[ivwarrior]

I'm going to go ahead and rule out installation error...I've done this several times over, and how can you mess up a rotor install? It's disassemble, remove, reassemble.


Let's see.
1. Not paying attention and getting something between rotor hat and hub on car.

2. Not properly/evenly torquing lug nuts....

3. Well, you get the point, people can find a way to screw up anything.


Now, another thing to check, while you have the rear wheels off is to see if there's anything with the back rotors that just doesn't look right. Rust, discoloration, whatever. You may not personally have experienced rotor pulse from a set of rears, but I've seen it with customer's vehicles before. Do you feel the pulsation through the brake pedal only, or (when braking hard/long enough) through the pedal and the steering wheel. If it's really pulsing bad, and you don't feel anything at all in the steering wheel, I'd bet it's in the back. If you can get some feel through the steering wheel, definitely front issue. (My work van is bad enough to shake the steering wheel coming down long mountain grades.)

[jeremod]

The rear rotors are warped on my car. This is the second time they have warped since I've owned the car. They cause a slight pulse in the pedal and some shaking from the rear end (not in the steering wheel.) The stock rear rotors aren't vented (at least on my L) so they could over-heat pretty easily.

[jmgtp]

Did you overtighten the lug nuts? Perhaps with an impact gun? That has been known to warp rotors though uncommon.

Even so, as mentioned above, unevenly torqued or worse loose lug nuts can cause your symptoms.

If you had the rotors machined maybe they were done so incorrectly. I think you're forced into removing wheels and doing a visual inspection of the hardware, especially the sliders that allow the calipers to 'float.' Using a torque wrench to tighten the lugs to spec helps too, torque limiting bars are available to impact guns too.

[warrior]

1. Not paying attention and getting something between rotor hat and hub on car.

My guess is this. This happened to me and the slightest bit of rust on the hub will cause a rotor to warp. You should sand any rust off the hub with light sand paper to make it feel smooth as a mirror.

The subaru mechanic that did my head gasket said this is the number one cause, especially on subaru's that causes rotor warp.

[llaprad1]

Let me reiterate, the pulsing was there before the new rotors, so I doubt an installation error replicated the old problem.

Let me also say, I have done HPDE track days (read: heavy, repeated breaking), and I do all my own maintenance, and I have yet to see a warped rear rotor.

---

After quite a bit of reading, I'm going to check the sliding pins. The LGT has 120k miles on it, so it probably needs it. This is what I meant earlier by 'something specific to Subarus or Legacys.' I've never had pulsing from stuck calipers on Nissans.

This is not a knock on Subaru, Nissan has their own 100k mi.+ repair quirks.

[danci1973]

There is no such thing as 'warped' rotors - it's pretty much a myht.

Stoptech has some excelent info on brake systems - anyone wrenching on their vehicles should read their stuff:

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

If changing the rotors didn't cure pulsing, it's probalby not brakes fault.

D.

[LeggoMyLeggy]

^ Good read.

[sharky nrk]

that article from stoptech is a good one, and so is their bed in procedure. you can still warped your rotors though and the rotors can still be defective

[llaprad1]

UPDATE:

1. Measured front and rear rotors, they are all perfect.

2. Checked for negligent assmebly 'debris.' Nope, none.

3. Partially disassembled the front pass. caliper and there was slight rust inside the sliding mechanism.

Chalk one up to sticking slider.