Front dust shields grinding after rotor replacement - Nissan Forums : Nissan Forum
 
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post #1 of 5 Old 08-31-2017, 04:33 PM Thread Starter
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Front dust shields grinding after rotor replacement

I've got a 2011 Sentra SR and I changed the brake pads and rotors on it over this last weekend. Afterwards it has a nasty screw-driver-on-concrete grinding noise when you drive the car now. I went back and tried resetting everything down there a couple nights ago (took off wheel, took off brake pads, took out the little mounts the pads sit on). I manually rotated the wheel to try to hear the grinding noise and after bending the dust shield (baffle, backing plate, there seems to be a lot of different names for it, but this is the part: https://www.nissanpartswebstore.com/...1151ZW80B.html)

After putting everything back on the other night, it has gone from a constant grinding noise, to more of an oscillating grinding noise (like it only grinds at a certain wheel position). Could this mean the rotor isn't on correctly or something? The car brakes work perfectly (I replaced them in the first place because the car had a bad shudder when stopping hard).

I'm to the point where it feels like I need to just replace this part. I went down there and bent the part to try to get that noise to go away. It sounded like it was gone when I manually rotated the wheel on the driver side, the passenger side still had a slight grind and I decided it probably wouldn't be noticeable. After putting the wheels back on, the noise was still there and just oscillated instead of being constant. This picture shows how the front brakes are assembled: http://i.ebayimg.com/images/i/112405...-1/s-l1000.jpg. It seems like if I were to replace this part, I'd have to remove the big nut in the middle of the rotor (heck, it's probably a 35-40mm nut, and then there is a cotter pin to keep that nut from slipping out accidentally).

I guess I have two questions...

1) Is this anything to worry about? It's awful embarrassing to drive around but if it's not gonna hurt anything, it's not THAT noticeable.
2) Is this something that'd be easiest to just contract out to a mechanic since he'd have all the tools already? I hate paying labor costs, but I think I hate having something obviously wrong with my car as well and I'd just shell out the money to fix it. (On an off note, I'm -never- buying a Nissan ever again with the sheer amount of issues I've had with this car in the year and a half I've owned it, that's a story for another day though)

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post #2 of 5 Old 08-31-2017, 04:57 PM
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You don't want to have to take the axle nut off...probably $10-20 just to go buy the socket.

You can bend that plate to your hearts content...it's just a splash shield to keep spray and dirt off as much of the rotor as possible. Round here...the winter salt pretty much starts to erase them after about 8 years anyways...

Now, of more concern is the rhythmic scraping sound. We can reasonably assume that the splash shield plate is fixed relative to the knuckle, so for the rotor to rub in any kind of oscillatory way, means that the rotor is not spinning perfectly parallel to the plate and this can be for a number of reasons (at least off the top of my head)

-warped rotor
-rust/dirt/contamination on the hub face (the spinning plate that the studs are mounted in)
-worn bearing
-stuck or sticky caliper pins and/or slides

Given how new the rotor is, more likely the second and/or third options.

Question...when replacing the rotors, did you clean up the hub face to ensure there were no hard deposits left on it...if not, those could be causing the rotor to sit at an angle relative to the plate/bearing geometry and would cause the rub rub rub sound. I use a round brass wire brush mounted in my drill to do the initial clean up, then I go over it with a finger nail to check for ridges/deposits, then a slap some high temp anti-seize on for the next time I have to take it all apart.

Having just replaced my own front bearings I can attest that 'good but well used' bearings can allow too much play. I would notice, particularly on on-ramps, that I would get a rubbing sound from the front disc as the corner tightened (because play in the bearing allowed the rotor alignment to change relative to the fixed geometry of the caliper/pads bolted to the knuckle). This has completely stopped with my new Timken hubs.

Usually the reason for that throbbing braking effect is that a caliper has partly seized causing issues with one side of the rotor (usually the inside face, but not always). I would hope that as part of the rotor/pad job, you also removed, cleaned and re-lubed the caliper slide pins and guides. If not, your new brakes may soon look and perform very much like the parts you just threw out.

HTH

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post #3 of 5 Old 08-31-2017, 05:03 PM
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Last point...

It is normally for brand new rotors and pads to make a shhhhshhhshhhh sound as you drive. Once you bed them in (repeated accelerate/hard brake cycles until up to temp (ie you can smell the resin/hot brake smell)), they typically go silent. My slotted rotors made this kind of sound for the first few tens of km until the rotor surface was buffed smooth by contact with the pads during braking.

You may just want to read through my notes from the BBK: install link in my .sig below. There are pics where you can see the cross-hatched surface of the new rotors that caused that shhhshh sound...

Nissan OEM HID, Morimoto bulbs/harness, RacingLine Y-pipe, Strut Brace, Stillen Swaybar, ETI LED Fogs,
BBK: PowerStop Powder Coated Calipers: M45 Front/Stock Rears w/StopTech slotted sport rotors
BOSE Headunit w/USB & BT (2012 update), Dunlop Signature HP (summer) / Blizzak WS80 (winter)

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/ Spurious ABS / Audio Power / ABS Diag / Steering Lock / Lower VQ rad hose / VQ Belt Squeak /
/ Brake Job / RA 5% Discount

Last edited by d0ugmac1; 08-31-2017 at 05:06 PM.
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post #4 of 5 Old 08-31-2017, 05:08 PM Thread Starter
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Quote:
Originally Posted by d0ugmac1 View Post
You don't want to have to take the axle nut off...probably $10-20 just to go buy the socket.

You can bend that plate to your hearts content...it's just a splash shield to keep spray and dirt off as much of the rotor as possible. Round here...the winter salt pretty much starts to erase them after about 8 years anyways...

Now, of more concern is the rhythmic scraping sound. We can reasonably assume that the splash shield plate is fixed relative to the knuckle, so for the rotor to rub in any kind of oscillatory way, means that the rotor is not spinning perfectly parallel to the plate and this can be for a number of reasons (at least off the top of my head)

-warped rotor
-rust/dirt/contamination on the hub face (the spinning plate that the studs are mounted in)
-worn bearing
-stuck or sticky caliper pins and/or slides

Given how new the rotor is, more likely the second and/or third options.

Question...when replacing the rotors, did you clean up the hub face to ensure there were no hard deposits left on it...if not, those could be causing the rotor to sit at an angle relative to the plate/bearing geometry and would cause the rub rub rub sound. I use a round brass wire brush mounted in my drill to do the initial clean up, then I go over it with a finger nail to check for ridges/deposits, then a slap some high temp anti-seize on for the next time I have to take it all apart.

Having just replaced my own front bearings I can attest that 'good but well used' bearings can allow too much play. I would notice, particularly on on-ramps, that I would get a rubbing sound from the front disc as the corner tightened (because play in the bearing allowed the rotor alignment to change relative to the fixed geometry of the caliper/pads bolted to the knuckle). This has completely stopped with my new Timken hubs.

Usually the reason for that throbbing braking effect is that a caliper has partly seized causing issues with one side of the rotor (usually the inside face, but not always). I would hope that as part of the rotor/pad job, you also removed, cleaned and re-lubed the caliper slide pins and guides. If not, your new brakes may soon look and perform very much like the parts you just threw out.

HTH
Thanks for the quick response. To answer your question about cleaning up the hub face, no I did not, didn't even strike me to think about it to be honest. When I remove the caliper, the rotor was free already (as in I didn't have to bang on the rotor to break it free, which I took as a good sign, but it's possible that my hammering on the caliper mount bolts loosened it up before I got to the rotor).

So it sounds like I have some homework to do now. I need to get back down there, remove the caliper again (do I need to remove the brake pads when I take off the caliper, or can I just take off the entire assembly, those pads are a pain the rear to install?), clean up the hub with a brush, and then I need to lube up the caliper pins/slides since I neglected that.
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post #5 of 5 Old 08-31-2017, 05:13 PM
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You can remove the entire caliper assembly as a unit and I would recommend doing it like that. I found it handy to have a small piece of clean cardboard (corrugated box stuff) folded 3x or so which I jammed between the two pads to simulate the presence of the rotor and prevent the pads from sliding out of position. You can safely tie back the entire caliper as you clean up the hub surface. If you find ridges, and I did find a few, I used a flat bladed screwdriver to gently scrape them off.

After it's remounted, you can then just remove the piston portion from the caliper bracket, remove the pads from that, clean your guide pins and slides and reassemble. It's much easier to get the pads in quickly with the piston portion detached from the bracket

Don't forget to re-torque all those bolts!

Nissan OEM HID, Morimoto bulbs/harness, RacingLine Y-pipe, Strut Brace, Stillen Swaybar, ETI LED Fogs,
BBK: PowerStop Powder Coated Calipers: M45 Front/Stock Rears w/StopTech slotted sport rotors
BOSE Headunit w/USB & BT (2012 update), Dunlop Signature HP (summer) / Blizzak WS80 (winter)

Altima FSMs 94-09 Useful posts: Bose Upgrade / Alternator / Bad Ground / Rear Brakes / TPMS Reset /
/ Spurious ABS / Audio Power / ABS Diag / Steering Lock / Lower VQ rad hose / VQ Belt Squeak /
/ Brake Job / RA 5% Discount
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