A friend has a track day Miata with lots of power (over 300 HP) and it's equipped with some 4 pot Wilwood calipers. The brake pads will wear at an angle, lead edge thin, trailing edge thick.The difference will be an eighth of an inch ,or more. I don't think Wilwood calipers would flex so what else could it be? I'm assuming that this wear pattern is not normal.
sounds like something that is supposed to slide is sticking
Maybe, but the calipers have inner and outer pistons, so it shouldn't have to slide.I don't even know if there are slide pins.
If it is a multi piston unit it probibly Is a stuck piston
If it is a slider type it could be a stuck slider.
Which calipers does they have? Dynalites do flex some, more than the Superlites. Even so, the Superlites I have came with a warning not to exceed 1200 psi. Being 4-pot, they would be fixed calipers, so it may be piston issues if not a flex issue.
Look for pads binding in the caliper or on their mounting pins. Sometimes the stamping on the pad backing plate is poor and there are burs that need to be filed down so the pad moves freely within the caliper box. I also suspect that the calipers have differential piston sizes. Make sure the smaller piston is to the rear of the rotating direction. These calipers can be installed "upside down" or "backwards" depending on your frame of reference.
Yes, it is possible that the pistons are sticking too. Many wilwoods do not have seals and the brake dust can build up causing them to bind. Pull them, clean them, run them.
Time for a caliper rebuild. A lot of Wilwood 4 pot racing calipers have no rubber booties because they burn from the heat - so they need more frequent cleaning and rebuilds than a street car's calipers due to dirt & pad material build-up (which in some cases is pretty damn corrosive) gumming up the works. It is an easy job and the parts are available cheap from Wilwood if a good old fashioned cleaning does not put it right.
If the pistons are the same size the issue arises from a temperature difference across the pad form leading to trailing edge. This is the reason most professional motorsport calipers have staggered piston designs with the piston size stepping up in the direction of rotation. That does mean different calipers left to right, but also reduces pad taper wear.
The short term solution is to replace the pads more frequently or find a pad that has a different operating temperature range. You will not be able to completely remove the pad taper, but you can reduce it.
would flipping the pads after each session help ?
I'll have to contact him and get more info. I'm not sure which calipers from Wilwood he has. I doubt it's anything stuck because he said both left and right sides are doing the same thing. I wasn't aware that there are two different piston sizes in the calipers and he may not be either. I do know he has them installed with the bleed screws up because I asked that question.That means the thinnest part of the pad is at the piston furthest from the bleed screw and is the leading piston on the rotor.
Outgassing will also do this. Common on corvettes. We find that slotted rotors eliminate the problem. We also found that to not be a cost effective solution with the amount of rotors we go through. Ill usually just let my customers know what is happening and why, and we replsce pads as needed.
Stafford1500 is right.
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