Diagnosing uneven pad wear

[steppinthrax]

So last Friday when driving home from work I was getting a squeaking and scraping noise on one of my wheels. I figured it was worn pads (just replace with ceramics a year ago). I went home and took off the driver side wheel. The inner pad on the wheel was worn nearly too bare metal while the outer had plenty of pad (oh shit). I took off the other wheel (both pads OK). So I figured it was a bad caliper or slide bolts were bad. Tore the driver side wheel down and took the pistons out from both calipers. I saw concentric score marks on the inside of the brake cylinder wall??? Don’t know if they were there by design or damage. I replaced that caliper and went ahead and replaced the other caliper as well. A couple of questions.

1. I was reading that inner pad wear (uneven) is likely due to a seized caliper while outer pad wear is due to ungreased slide bolts or bad slide bolts (is this true). I did re-grease the slide bolts, but I re-greased them a year ago as well.

2. Could I simply have honed the brake cylinder to remove the scraping inside? It seems the piston rides on the square seal so the cylinder dimensions are not a very big deal. The square seal sits inside of a groove. The seal is "proud" from the cylinder wall.

3. I replaced the clips, last year I kept the same clips (caliper bracket clips), could this have caused the problem. I didn’t see anything wrong with the old clips vs. the new ones. I even compared them with the new ones and I didn’t see anything different.

4. Could ceramic brake pads be the problem?

 

[SpatiallyAware]

Year/make/model and what area of the country do you live in? (salt etc?)


In my experience uneven pad wear has always been slide pin issues, assembly issues (someone didn't put caliper back together correctly), or seized caliper.

In each case it was fairly obvious... Seized caliper pistons, or slide pins corroded, or clips not installed correctly, etc etc

Personally, I take the time to knock off any burrs on the pad backing plate. I've never had it actually bind, but most of those backing plates don't slide in/out of the caliper all that great right out of the box and I could see how they could get caught up as the pad material wears away.

I like to replace the clips. I'm sure they can be reused quite a bit, but when you compare old vs new the new ones always have more 'spring' to them.

 

[steppinthrax]

Year/make/model and what area of the country do you live in? (salt etc?)


In my experience uneven pad wear has always been slide pin issues, assembly issues (someone didn't put caliper back together correctly), or seized caliper.

In each case it was fairly obvious... Seized caliper pistons, or slide pins corroded, or clips not installed correctly, etc etc

Personally, I take the time to knock off any burrs on the pad backing plate. I've never had it actually bind, but most of those backing plates don't slide in/out of the caliper all that great right out of the box and I could see how they could get caught up as the pad material wears away.

I like to replace the clips. I'm sure they can be reused quite a bit, but when you compare old vs new the new ones always have more 'spring' to them.

1999 Toyota Camry 90K on it. Within the last year I moved to the D.C. area so I have a lot of stop-and-go driving. I would say little salt, mostly city roads and traffic.

I checked the slide pins when disassemling this time. I could physicall move them in and out easily. There was grease there as well.

 

[SpatiallyAware]

1999 Toyota Camry 90K on it. Within the last year I moved to the D.C. area so I have a lot of stop-and-go driving. I would say little salt, mostly city roads and traffic.

I checked the slide pins when disassemling this time. I could physicall move them in and out easily. There was grease there as well.

Then assuming everything is installed correctly I would say it was a caliper issue. You might've been able to pull the pistons out, clean, and reassemble but nowadays calipers are cheap so replacement isn't a terrible option.


Also note, that I've seen people pull those pins out and carefully clean/grease but not clean out the sleeve or rubber boot. Be sure to spray brake cleaner in there to clean out grit and etc or there isn't much point in greasing the pin.

 

[5150MyU]

Most likely the pad/caliper is binding in the slide if the pins are all good.
Think about it, you step on the brakes and some thing is not releasing when you take your foot off the brake.

 

[5150MyU]

By slide I mean where the calipers ride as well as the pads.