Preventing and removing brake pad deposits on rotors? Topic is solved

Post by **FireFox31** » 11 Jul 2021, 22:00

Is there a way to prevent my brake pads from leaving deposits on my rotors when the car sits unused for a few days? This happened over the July 4th weekend when it rained a lot. My new OEM front pads left a deposit on one of my new Zimmermann rotors. Now it thumps on every rotation while braking.

Or is there a way to remove the deposit from the rotor without getting it turned at a machine shop? If this will keep happening, I need a simple method like scraping it with a chisel. Thanks.

Post by **mecheng** » 12 Jul 2021, 04:06

FireFox31 wrote: ↑11 Jul 2021, 22:00 Is there a way to prevent my brake pads from leaving deposits on my rotors when the car sits unused for a few days? This happened over the July 4th weekend when it rained a lot. My new OEM front pads left a deposit on one of my new Zimmermann rotors. Now it thumps on every rotation while braking.

Or is there a way to remove the deposit from the rotor without getting it turned at a machine shop? If this will keep happening, I need a simple method like scraping it with a chisel. Thanks.

I’ve used a wire wheel attached to a drill

Post by **scot850** » 12 Jul 2021, 12:53

Most deposits I find normally wear off after a short drive and application of the brakes a few times. What brake pads are you using as I can't recall having ever had this issue over 45 years of car ownership? So maybe it is the pad material that is the issue?

Neil.

Post by **Chuck W** » 12 Jul 2021, 15:34

scot850 wrote: ↑12 Jul 2021, 12:53 Most deposits I find normally wear off after a short drive and application of the brakes a few times. What brake pads are you using as I can't recall having ever had this issue over 45 years of car ownership? So maybe it is the pad material that is the issue?

Neil.

Same. The flash rust on rotors is normal. A few days of sitting shouldn't cause any permanent issues.

Post by **FireFox31** » 18 Jul 2021, 23:09

This just happened to my rear brakes after sitting for four rainy days, causing a terrible thumping. I blame a rear caliper since this happened once before. I confirmed that the caliper pistons extend and retract smoothly. Could a caliper piston not be fully retracting, keeping a pad too close to the rotor, letting it rust in place? How could that be identified and resolved? How do pads retract from rotors anyway?

Cookeh · Post by **Cookeh** » 19 Jul 2021, 02:42

Bilt Hamber Atom Mac will prevent the trusting from rain/humidity when standing. The deposits thing sounds like a different issue, though I must echo Neil's thoughts there.

Post by **FireFox31** » 13 Aug 2021, 12:24

Here's a picture of the rear rotor with the pad deposit on its inner face. Both rear rotors (Zimmermann) and pads (Volvo) are eight months old with 4000 miles on them. The rotors came with about 13/1000" run-out and I have replacements ready from FCP.

The deposits happened July 4th and July 19th when the car sat a few days in the rain. I heard the rust break loose when I drove both times. The rough spots are barely raised at all yet the cause a terrible shudder and loud banging even under light braking. The spots at 9 and 10 o'clock have clear rectangular pad outlines from the rainy days. The spots at 1 and 3 o'clock are oddly wider, perhaps caused by the bad run-out. The other rear rotor has the same bad run-out and has two similar vague rough patches on its inner face.

I blame the parking brake shoes dragging against the rotor hat, causing excess heat, bubbling the caliper piston boots, making the pads sit closer to the rotors than they should (causing more heat and ruining everything faster). See the attached picture. Before removing the caliper, the wheel was somewhat hard to turn because the pads were pressed to it. However, this same problem happened to the previous owner 14 months and 4000 miles ago when the piston boots were in much better shape. Seven months ago, the inner boot had two small bubbles and the outer was fine. Could two small bubbles have pushed the pad too close to the rotor for the previous owner?

Why do you think the pads are leaving deposits on the rotors, knowing these facts?

The track racing forums have lots to say about removing brake pad deposits. The Flex-Hone for Rotors seems to be the most reasonable method. At $42, it's more than a single rotor, but I'm going to try it on these as a test. What do you think about this method?

Post by **volvolugnut** » 13 Aug 2021, 17:35

Get some salvage yard calipers installed until you can rebuild yours?
volvolugnut

Post by **abscate** » 13 Aug 2021, 18:02

I think the pistons are corroded in the cylinders.

New calipers and 2 year brake fluid changes

Post by **FireFox31** » 13 Aug 2021, 21:13

The pistons expand and retract fully and easily. In January when I inspected them, the boots weren't bubbled and I saw no cracks in the boots which could let water in. So I'm hoping the pistons are good.

I would like to get a caliper from the junkyard in order to use its pistons if necessary. They are what always seems to go bad but they're not available separately.