Uneven Front Rotor Wear

bubbeck · Post by **bubbeck** » 03 Oct 2017, 09:49

Hey everybody,

I was just noticing that it looks like my front rotors are wearing unevenly - the left rotor has a much larger rust ridge than the right (see photos). It also appears to me to be a much wider rust ridge than I should have, period. Rear rotors are polished pretty much all the way out to the edge. I do notice some vibration when braking at highway speeds.

Any idea what could be causing this, and do you think its an immediate safety problem? I replaced pads and rotors front and back about a 1.5 years ago (15k miles), and made sure to lube pins and slide when I did it. The outer pads all look good. I'll have the whole front end disassembled to work on the suspension in a couple weeks, anything I should be checking for then/in the meantime?

Thanks!

Post by **scot850** » 03 Oct 2017, 11:17

Either seized pistons in the calipers, frozen pads (not very likely in fronts but can happen on the one mounted to the piston), worn out slider pins and finally, collapsed front flexi-pipes not allowing the pistons to get sufficient pressure to compress the brakes via the piston.

Has the car been sitting for a long period of time?

You could have the front rotors machined smooth if there is enough material left, but rotors are fairly cheap so replacing is the way to go. First though, check the cause(s) of why it is happening as listed above. When was the brake fluid last flushed?

Neil.

Post by **oragex** » 03 Oct 2017, 13:37

I have the exact same thing, both on front and rear wheels.

My caliper pistons all function well, the sliding pins and boots have been replaced and greased with the Volvo special grease.
Brakes have been bleed in all corners, fresh Dot 4 synthetic fluid. The pads also slide easily on the caliper. The front flexible hoses are new.

In my opinion, this comes down with two potential problems: either a slight leak in the brake booster, either an issue with the ABS valve body. I tend to believe it's rather the ABS body valve, because when I open the caliper bleeders and press the brakes, the fluid doesn't come out with a good jet, it leaks rather slowly.

Btw, I've seen at the dealership a recent XC70 with the same issue, on all four breaks.

Mechanically speaking, it is not an immediate safety problem, but you surely have noticed the braking power is less than optimal in emergency situations. By the way, replacing the disks and pads is a waste of money, you will have the same issue with the new ones.

The vibration is most often times caused by uneven wheel lug torque, have the wheel lugs tighten down in 3-4 steps.

Post by **bmdubya1198** » 03 Oct 2017, 21:59

That's strange, my front rotors don't have any rust ridge. If the brake hoses look suspect, change them. Cheap and easy.
My next idea would be the calipers are a little frozen or have a leak. You can either replace the calipers with new or reman units or rebuild them yourself. I rebuilt all four of my calipers, it's not too hard. CN90 has a great writeup. You can find the seal kits on FCP, eEuro, or Rock Auto. I found the Centric seals from Rock Auto work well, believe it or not.

Post by **abscate** » 04 Oct 2017, 02:02

That does look like a caliper hanging up. If you have been changing brake fluid every 24 months, I would first grease the slides again, then check piston for smooth operation. With the bleeder slackened you should be able to move it smoothly with firm hand pressure.

I don't fool around with brakes. Winter will be when uneven braking will make life interesting

Post by **BEJinFbk** » 04 Oct 2017, 08:02

OP - What are you using for pads?

Post by **bmdubya1198** » 04 Oct 2017, 08:41

abscate wrote: ↑04 Oct 2017, 02:02 That does look like a caliper hanging up. If you have been changing brake fluid every 24 months, I would first grease the slides again, then check piston for smooth operation. With the bleeder slackened you should be able to move it smoothly with firm hand pressure.

I don't fool around with brakes. Winter will be when uneven braking will make life interesting

I agree, I was fighting with my brakes for a long time, and now I have them nearly perfect. I still get a "popping" feeling in the pedal every now and again, and I don't know what it is, but the pedal is very firm and tight otherwise. My cousin doesn't like it because the brake pedal in his S70 had almost no feel at all or it was coming and going from no feel to very firm before I finally bled the brakes for him.
Anyway, my brake problems were solved with rebuilding all four calipers and replacing front flex lines. I plan on replacing the rear hoses soon, but I'd rather just get stainless lines all around and do it all in once shot.

bubbeck · Post by **bubbeck** » 04 Oct 2017, 08:43

Not sure the last time the brake fluid was changed - definitely more than 2 years, probably more like 4. Does that point you one way or another? Could it just be in need of a fluid change and bleed?

So I guess to check if the piston is seized I can open open the bleeder and push it in and out? Will I need to bleed the system after I do that?

Thanks folks, so many helpful ideas!

bubbeck · Post by **bubbeck** » 04 Oct 2017, 08:45

Oh, and for pads I have the Bosch Quietcast in the front

Post by **erikv11** » 04 Oct 2017, 10:06

To check if the piston is seized, open the reservoir and compress the piston (pull the caliper and remove the pads - basically inspect the whole thing). Then you don't let any air into the lines.