Weird brake pads issue

[UNGN]

I ran into this recently on my Jag XK8 with Rockauto "close out" pads. I couldn't argue with $10 ceramic pads.

On that car, there are Different Pad thickness specs with the same backing plate dimensions. Rockauto lists them as fitting (and they will fit if your discs are worn). With the caliper opened to max I had to dremel a chamfer on the ID of the pad to get it to go over the rotor, after I threw away the shims.

Another XK8 owners showed me the that the thinner pad version was the actual Jag spec version and the thicker one was something rockauto figured could be made to fit (and they were right, I made them fit).

 

[pagrunt]

I do wonder if this is a issue with the Wilwood 154 calipers is using O.E. type pads

 

[Bonnewagon]

That's interesting. If the rotors were worn, or had been cut, they would have fit no problem. Maybe my new-at-the-time rotors were thicker than stock specs? I never even thought to check that. But I do remember that not long ago most pads didn't have those shims on them. Relatively newer cars did, but not our antiques. Maybe the manufacturer just slapped on some shims and didn't think to check if there was enough clearance? They were barely stuck on, and I popped them right off with a big knife.

 

[Bonnewagon]

Update: I asked my cousin the Engineer about this and he shot me back an interesting dialog he had with an old buddy. Here it is-
"I called a Bud of mine from long past, at our regional G-M Training center, and asked him about this phenomenon of Inner Pad’s wear.


His comments were a bit enlightening, to say the least, which you can appreciate.


According to “Instructor George”, Factory 4- Piston, and even those Hi-Zoot 4- & 6- piston Aftermarket System calipers also experience Accelerated Inner Pad Wear.

This issue is apparently not exclusive to Single Piston calipers, though it seems that it is More Pronounced with a Single Piston system.


His experience is that, with a Single Piston Caliper System, the inner pad gets the “Hit” a bit before the outer pads, and that the clamping pressures are rarely ever Equalized between them during Normal Braking, though Performance Braking does not exhibit this odd wear pattern.

So, as to the “Why” of it all...


1. With Rear Wheel Drive cars, with accessible front wheel bearings, this is usually caused by Improper Bearing Torques, though most folks “think” they did a proper Pre-Load torque on these front wheel bearings.

George says that for smaller GM cars with 10.5” to 11” rotors, like Chevelles, Novas, and perhaps even your Poncho Wagon, et. al. after packing the bearings, they should be Torqued with a Reliable and Calibrated (which I do yearly) “Clicker” Torque wrench, to 13 to 15 Lb Ft while turning the rotor by hand, and it will be Stiff, but stay with me.

Then he says to back off the nut 2 turns, all while turning the rotor, and set the Pre Load to 5 to 6 Lb Ft for smaller GM cars, and 7 to 8 Lb Ft for larger GM cars with the “Clicker” torque wrench, again, all while turning the rotors by hand.

Note that most shop manuals say to place the Nut’s Cotter Pin’s Slotted Retainer where the cotter pin will almost align with the spindle’s hole, and Back Off the nut for the cotter pin to fit.

Well, George says that No Matter What, the Pre Load should Never go Below the recommended Minimum Pre Load Torque.

He says it is better to get that slotted retainer to Almost Exactly Match the cotter pin’s hole, even if you must Ever So Slightly Tighten the preload nut, so that you Never Go Below Minimum 5 Lb Ft preload on smaller GM’s, and 7 Lb Ft Minimum for larger GM’s"

Odd? Yep, I’ll say. But, Timken-Style Tapered Bearings are Designed to Run Hot and with a Lot of Preload. Very, very interesting. I will need to check my bearings again and adjust accordingly.