unequial drag from front (disc) brakes

Question

'07 Cobalt LS. No ABS, no traction control.

I have (IMO) excess drag when I manually rotate the passenger side front wheel. Inspecting, those pads have lost a lot of material. (inner & outer equally; over ~1500 miles.) The driver's side rotates (IMO) too freely, and the pads have not worn significantly. I don't see anything obviously wrong with either side. There is no discernible pull, either braking or not.

I suspect I need a new caliper. Even so, (a) is there a way to tell which one, and (b) I'd like to get a better picture of what would cause this mix of symptoms.

Answer 1

I would suggest the caliper piston not retracting correctly, mainly because pads are being worn equally, just with one side being worn a lot more than the other ... the worn side is where I'd look for the caliper issues. While cleaning and servicing the pins and/or slides is never a bad idea, I don't think it will cure the issue. Usually when the caliper is not sliding correctly, it will wear one pad more than the other on a single caliper. Considering both pads on a single caliper are equally worn, as well as the fact there's no pulling while braking, leads me to this suggestion.

Answer 2

Textbook No.1 causes for drag on disk brakes are calipers seized by dirt.

Just disassemble them, clean thoroughly -especially the slides- with a wire brush, lubricate where needed (depends on model) and replace pads while you're at it. If necessary you might replace guide pins or bushings, but that is only necessary on severe cases.

Every once in a while, it happens that the dust shield got damaged, water entered the piston and damaged the bore beyond repair. In that case it is necessary to replace the caliper.

Answer 3

Just for the record:

The brakes are now working. Both front wheels now have similar (and normal-feeling) drag. IMO, the problem was that the 'free-rotating' (driver's) side caliper was sucking air past the piston.

However, it was a roundabout path to get here, so I could be wrong about the cause. In (excessive) detail:

1. I changed the 'dragging' caliper. After (manual) bleeding, I had no pedal resistance. I decided to bleed all wheels.
2. The rear wheels (IMO) spun much too freely. The shoes were very worn, so I replaced them.
3. I replaced the master cylinder, which was (as I'd suspected) leaking into the booster.
4. When I now bled the 'other' caliper, it never stopped producing air in the bleed.
5. I changed that 2nd caliper. It now bled as expected.
6. While the brakes then 'worked', there still was what I'd call excessive pedal travel. This improved after further adjusting the rear brakes.
   I am continuing to adjust the rears by hard-stopping when backing up. (I normally brake very lightly.)