Uneven Brake Pad wear

[Yardsale]

’01, Job 1, 4WD



So, I check the brake pads (front) and the left side have uneven wear. The inner pad is about gone and the outer is almost new. (Pads on the right side are evenly worn with about half remaining.)



I removed the pins, cleaned and greased several months ago and they still move freely. I checked for an obstruction that may be hindering the movement of the caliper. I found a couple of possible areas where the caliper may contact the spring clip and filed them smooth.



I can’t think of anything other than sticking pins and some sort of obstruction.



Any other ideas?

 

[Fudged Undies]

I've had the same problem on the driver side and potentially it's a sticking caliper. I did my brakes in march for the second time and didn't notice this problem the first time around. There is a caliper rebuild kit which you could use or you could replace the caliper. I've seen this on other fords and it seems to be a bit common.

 

[Yardsale]

I considered a sticking caliper, but the caliper works (the inner pad is worn). The symptom is that there is uneven wear between the twp pads and, since the pad on the piston side is worn, I suspected that the caliper assembly was not moving, or not moving beyond a certain point.



I removed the pads and installed the caliper to check for smooth operation and it seems fine. While sliding the caliper in and out and pulling up on it, it did once hang a bit on the upper spring, but it’s not in the area of travel where the wear of the pad has stopped.



I’m baffled. Do you know what's included in the rebuild kit - is it piston seals?



I am going to replace the pads to see if still doing this. It’s a long-term experiment though, as I have to wait for noticeable wear.

 

[Fudged Undies]

Not familiar with the rebuild kit. The Limited Lifetime warranty on my pads is two years and that is about what I got on the last set of pads so I figure the uneven wear will keep me from having to buy new pads. I am keeping an eye out for other issues though. I really do like being able to stop when I need to. I suggest going to a local autoparts to check out the kit. I know autozone carries it.

 

[Richard L]

Yardsdale,

if the caliper bore is rusted and pited the piston will be forced out by the hydrolic pressure, however the corrosion in the bore will not allow the piston to retract fully. This causes the pad to constantly drag and wear. As the pad wears the piston is for out further but still cannot retract enough to prevent the constant dragging.



The best solution is to replace both calipers with rebuilt units. Often times the caliper bore is too badly pitted to just use a rebuilding kit, and frankly it's just easier and cheaper to just buy rebuilt calipers rather than attempt to rebuild them. I recommend replacing both since the usual case is that, If one is bad the other is not too far behind.



I usually just replace the calipers with rebuilt units everytime I replace the front brake pads (usually about every 50K miles).



...Rich

 

[Yardsale]

Rich,



Interesting (I should have thought of this). But, I have a question - assuming that the hydraulic force of braking is far greater than the force of the rotor pushing back on the (pad and) piston, if the pistons are (two pistons) moving out, wouldn't the wear be more equal between the inner and outer pads (pistons on inner pad side? The inner pad has about 1mm left and the outer appears almost new (at least 6-7mm left).



It may be just as you indicate. It seems odd to me that there would be so much difference between the two pads. This noted, the two pads on the other (right) side are worn about equal with about half remaining so, as an average, it's about the same as the unequal side. Also, there is a bit of uneven wear on the thinnest (inner) pad - the most rearward portion, or lower, of the pad is worn to about 1mm with the lesser worn portion at about 2mm. This may indicate that only one of the pistons is sticking. (doesn't change the solution though).



Thoughts?



Oh, on caliper brands, any preferred?

 

[Yardsale]

 

[Richard L]

Yardsale,

First, the Sport Trac caliper is a single piston, floating caliper design. That means that as the piston pushes outward aganst the pad and rotor. This simultaniously causes the caliper to slide inward forcing the outside pad inward against the outside of the rotor. When you release the brake pedal, the retracting fluid will release the pressure on the pads and rotor. This movement is only a fraction of an inch and there will usually always be some contact or minor drag.



if either the caliper or piston cannot fully retract, one or both pads will drag excessively and cause premature wear. Most cases of uneven brake pad wear are caused by hydrolic problems which can usually be traced to the caliper since that's the lowest component and that's were the water and moisture settles in the brake system (water is heavier than brake fluid). It can also be caused by sticking caliper slides/pins, but since you claimed that you cleaned and filed the burrs on caliper pins and slides, then my next guess would be that the piston is sticking.



Why does the inside pad wear more than the outside pad? Who knows? It just happened that way this time. Sometimes it's the outer pad that wears more than the inside, and sometimes it's the inside pad that shows the wear. Perhaps if the piston is sticking in the front or back, or top or bottom effects whether the inner pad or outer pad will drag more or less than the other? Perhaps it was caused by a full moon, or sunspots, or maybe it was high tide?? There is really no specific explaination.



...Rich

 

[Yardsale]

I think it's the full moon.



My calipers have two pistons, both on the inner side. Is this an "off nominal" setup (for a '01 Job 1 4WD)?

 

[Richard L]

Yardsale,

I changed the pads on my old 2001 Sport Trac, Job1, 2WD, about 2-1/2 years ago and it had thought they were single piston calipers. I stand corrected. I just checked my old pads (still have them) and I can see the marks from the dual pistons on the back of the pads and they are dual piston calipers.



Either way, it has no bearing on the fact that your caliper is sticking. whether it's one piston sticking or both makes no difference since the end results is the same problem.



...Rich