front brake grinding, one side only, good pads

[scottmcphee]

Scratching my head.... When applying medium to firm brake pedal pressure the driver's side front wheel makes a gritty grinding sound. The newish MBenz pads are still good at maybe 75% remaining, the discs are just at their wear limit (I think 20mm, but whatever, I measured and checked FSM so I know they are due but not an emergency to replace). Anyway there's enough meat on these pads so the piston is not over-extending for brakes to do their job. Discs have smooth wear surfaces both inside and outside faces and are fairly evenly worn on both sides. If anything the wear surfaces have a slight bulge shape mid-disc rather than perfectly parallel flat wear. The noisy side seems to produce more brake dust, as compared to the quiet side. All front wheel bearings have been replaced and packed with MBenz grease tightened per spec... and both wheels are are free wheeling when spun by hand, no wobbles or wiggles or play. No dragging brakes, not warped, no pulsations. Just when brakes are applied, it grinds. I thought maybe the raised "lip" that forms on the disc running around the outermost edge (where the pads don't touch and don't wear it down) was causing the sound by hitting some part of the the calliper, so I used a grinder to remove that disc lip material, but nope not the problem.

Is this a symptom of a half-sticking or non-floating caliper?
Do I have a rock lodged somewhere in the brake caliper that hits "something" when brakes are applied?
Or is the rock lodged in my left ear?

[Brian Carlton]

Did you pull the pads out of the caliper to inspect their contact faces or are you simply judging the amount of material remaining by observing the edge?

[scottmcphee]

I have not pulled the pads out to inspect surfaces. I guess I'm going to have to take a closer look at everything. Was just hoping someone knew fur shure what the issue was, then I could do one-trip in to R&R instead of the two step process.

[Brian Carlton]

Originally Posted by scottmcphee

someone knew fur shure what the issue was,

Has that ever happened on here with symptoms by wire????

[rrgrassi]

Have you also checked play in the wheel bearings? HAve checked to male sure the caliper is mounted good and tight? How about the rotor to hub bolt tightness?

[barry123400]

I would inspect the area where the actual disk is joined to the hub of the disk itself. I have seen the disk separate at that cast area. So it is possible that it might crack along there before it does.

Although no member has mentioned the issue in a long time. Neither am I certain even if cracked it would make that noise. When mine totally let go there was no previous noticeable indication the separation was underway. The physical cross sectional area of the cast gets pretty small right there.

[Renntag]

I have experienced similar and it was defective pads. Crazy I know.

If you know the grinding is on one side rather than the other, swap pads left/right. If I am correct, and your assessment is accurate, the noise should move to the other side.

The next step would be to simply install a new set of pads. You may or may not have warranty recourse. This will depend upon your sourcing of the suspect parts.

I have gotten pads warranted in this situation.

[Mad_Matt]

My rear caliper outer piston was working fin and the inner was stuck. needless to say that the break dust was more on that wheel. i'm going to take a shot and say is most likely the cause of the extra break dust. The grinding noise could be from floating pads and the pads getting out of their normal groove on the rotor.

My Passatt has that issue when the rotors start to corrode and wear a bit. when you step hard on the breaks the pads squirm a bit and then get into the outer edges of the wear groove. Sounds like a set of failed pads even though pads were good and had plenty of meat left on them.

I finally replaced the pads and rotors because the noise was irritating.

[Renntag]

Mad Matt had a similar experience.

Just for the nay sayers, the first time I replaced a perfectly good set of new pads (bedded in properly) resulting in no more noise/grinding feedback, I couldnt believe it either.

[HammerWerfer]

Had the same situation at Christmas. Daughter driving our '85 300td in the bay area. Had the front brakes and discs replaced in Sept. By early Nov, she was telling me about a grinding noise when she applied medium brakes. Had her cousin yank the wheel, and found the top edge satisfactory. At the same time she was telling me the brake wear sensor was flickering.

Got it home, and we went into testing. Yep, grinding noise as described. pulled the wheel, top of pads looks ok. pull the pads, and find the inner on wore down to the backing plate.

The inner caliper piston was hung up in the out position, accelerating the wear. Rebuilt caliper went on, and I haven't heard about any noise since.

Hammerwerfer