my left rear brake rotor, the pads don't seem to contacting it well. It got rusty after a recent thunderstorm and the rust on the rotor isn't going away near the center.

The old brake pads worked fine, and contacted the rotor surface well, so I am somewhat confused.

The caliper seemed to be fine, and moved fine. It's like the top of the pad is contacting but not the bottom of it.

EDIT: just to add, I put the e-brake on and drove a very short distance and it seemed to grind at the rust spots.

 

hows all your hardware? and slide pins?

 

Try swapping the pads, inner to outer.
Make sure the pad pins are clean and the pads are free to move on them.

 

slide pins are fine, thus why I am confused.

Clokker, I'll try that but, the springs are clean and the caliper is working as it should. Tommorow, if it isnt raining, I'll take it back apart and maybe the pad lost some of its lining?!

 

You mentioned "old pads"...so you changed pads recently? Did you change rotors? If not, were they machined? Maybe the old rotors didn't wear evenly and the new pads aren't getting to the low spots.

 

Slide pins need grease.

 

Good idea. I was in a hurry and didn't have them machined, nor changed them.

I'll take a pic today. Just seems like a strange way for a rotor to wear, especially on just one side with perfectly working slide pins.

As i said, the slide pins moved freely.

I'll take some pics today. It's raining like a **** so no car work today.

 

I should add...check to make sure the backing plates and pad material is/are straight. You never know...

Story time: Once a mechanic at a place I worked at (I worked in parts in another life) jammed my brake pads in and somehow I ended up with a bent pad!

Yours are/were new and you said the grooves on the pad support are fine are ok, and I doubt the factory messed them up, but still good to check.

 

It rained, and rained, and rained all ******* day. Now that the sun is out, I am tired and I don't feel like messing with the car anymore. Thus, I didn't have time to inspect the pads (jacking a car up and doing brake work in the rain SUCKS!).

I did get a good picture though. This is the driver side rear that is having the issue. YES, the pins where fine when i installed these, so please stop making me repeat this. Also, the passenger side rear brakes are not having this issue.

Picture time!

 

Have the rotor resurfaced.

 

I have planned on doing that, but...

I do have to ask why you say that? Don't you find it strange that maybe a rotor wore down toward the center and not so much at the top, on only one side of the car?

I went to college for automotive technology, and work in the field, but I am no wizard when it comes to brake systems. I ask because I want to learn.

 

I guess i suggest that because you insist that everything else is fine (not that I don't believe you) and the rotor is about the only thing left.
Judging by the lip at the outer edge, that rotor is pretty well worn, so who knows what it's done.

 

I just went out and did an experiment.

I pulled the emergency brake level up a bit and drove a very short distance (a few parking spaces and back) and that seems to grab the entire rotor face. How confusing considering the E-brake pushes on the piston just like the hydraulics do!

I am going to try and mic the rotor out tommorow, and see if there is a wear difference between the center and outer edge of the rotor. I have to borrow my fellow techs mic, as I don't have one, so hopefully he lets me use it (he borrows **** from me, so it shouldn't be an issue).

 

try sanding down your pads enough so that it levels out. dont go crazy on it, just grab some sand paper, lay it on a flat surface like a bench, and sand the pad down untill the whole surface looks flat and even. sometimes pads can wear out unevenly and causes stuff like this. also if you have some spare cash, change your rotors.

 

Maybe you just don't brake hard enough to make the rear brakes engage enough to scrape all the rust off? Either that or the rear hydraulics aren't working so well.

 

Judging by the picture, the rotor has hard spots on it. Without going into too much metallurgy, basically the pads have a harder time cleaning/wearing them down cuz those spots have a higher hardness. Similar reason to why it's good to machine a flywheel when you get a new clutch.

So either machine the rotors to give the new pads a nice surface so they wear evenly with the rotors or get new rotors.

You're right, the rest of the system is probably ok.

 

I went to college for automotive technology, and work in the field, but I am no wizard when it comes to brake systems. I ask because I want to learn.

When replacing pads you should machine the rotor and then bed in the pads.

It is quite possible the old pads were worn more at the top of the pad than the bottom and the new pads are flat.

The slider is at the top of the caliper and the rest of the caliper that pulls the pad to the rotor is unsupported on the outward facing side of the caliper. Expect flex and uneven wear on a sliding caliper. Not to mention clearance and wear for the sliding pins will introduce slop in the system and the further from the pivot the more movement you have.

Since it was raining you probably weren't breaking hard enough for the rear to grab the disk hard enough to wear the rust off. Pulling the ebrake on the drive wheels while moving kept you from locking up the tires in the rear and canceled out front weight transfer so it is as if you are braking harder.

There are no mysteries except why you did not do a brake job correctly, but it is good you trying to figure out how things work!

Your homework-
Mic the rotor, new and old pads. Put squish tape for measuring bearing clearance between the pads and rotor vertically and stand on the brakes with the booster working (stationary of course) and see how the pressures are distributed.

 

I know I did an improper brake job, as I pointed out in my first post (or maybe second). I needed pads, got some good ceramics but didn't have the funds for the rotors. The pads HAD to be changed like yesterday so it had to be done.

with that said. I mic'd the rotor and the rotor is more warn toward the center than it is up on the outer friction surface. not by much, but enough to cause the pad to barely grab that area.

I am going to measure a few more times to make sure, but for now, I am financially destitute, so it'll have to stay this way until I can afford new rotors.

 

Yup, confirmed, rotor more warn on the inner friction surface.

I applied the parking brake half way full wheel lock and while the top of the pad I couldn't get a feeler between the pad and rotor, but I could get it under the pad toward the inside of the rotors surface.

 

Although most of the post was right on, the quoted part begs correction for people reading with less experience. There are two sliders on each rear caliper. The top one is a pin type one, the bottom is actually the bolt that works with the bushing and sleeve on the caliper ear at the bottom. When the piston pushes out, the caliper reacts by pushing itself away and sliding on the pins towards the center of the car. As it does this, the outside fingers of the caliper push the outer brake pad against the disk, at an equal force to the one on the inside (piston side) brake pad. This, of course, as long as both sliders move evenly. When one of the sliders is more stuck is when you get different wear on the outer pad, top to bottom.

 

I know how floating calipres work for the effin time! (this isn't directed to you pfsantos).

The slides are FINE.

The outer radius of my rotor is worn less than the inner radius. uneven sliders cause uneven pad wear, and would not cause the situation that I have.

This is what I think caused it. I believe the retractor spring at the top of the pad was doing its job of pulling the pad away from the rotor, but the bottom parts of the pad stayed slightly more engaged with the rotor surface. Strange how this would only occur on one rotor, but that is my hypothesis.

 

Here is a better picture. My micrometer showed (I kinda forgot, but this is close) about a couple of hundreds of an inch difference, so not much, but enough to cause this.

Does my hypothesis make any sense? I know i need to machine or replace the rotor, but now I am just curious of what might have caused this.

 

What, wait wait wait. Maybe the bottom sliders on the pad aren't working well? The pins i keep getting all pissed about work fine, but maybe the little slider ears on the bottom might be seized?

****, I got the wheel back on and back home, so i won't be able to **** with it for another 5 days.

 

Maybe its the slide pins.

 

The bracket area where the pad ears slide sometimes accumulates rust from old pads. Make sure this area is ok and lube with a little brake caliper slider grease or anti seize. Oh...also sometimes the pad backing plate is a little big and the ears end up a little long or too wide.