[PSA/WARNING] - Centerbores out of spec on new Bendix PRT1132 11.75" disc brake rotors
Crossposting this from FBBO, as this applies to big brake A-body swaps equally.
Note: Seeing as rotors are primarily Chinese junk rebadged and sold in everybody's box under different names, there is a possibility that this issue exists with other brands other than Bendix.
Last night, I ran out of daylight working on my '68 Satellite's disc brake conversion (all factory parts) and had to button up the left side as quick as possible - and so I quickly installed one of my new Bendix 11.75" rotors that I had bought from Rock Auto almost half a year ago. No caliper or anything; just a rotor so I could get the car on the ground.
As I tightened the wheel to the rim, I was rather surprised that it seemed as if the lug studs on the disc hadn't been pressed into the drum correctly. Each bolt was loosening up as I went through the torque sequence, as if I were pulling the studs onto their seats as I torqued the nuts. Eventually, all of the nuts seated tightly, and I called it a night.
Enter next morning. I loosened the lug nuts, jacked the car back up so I could start installing the caliper - and the wheel won't come off. PERIOD. One might as well have welded it to the rotor.
Centerbores out of spec on new Bendix PRT1132 11.75" disc brake rotors by cudak888, on Flickr
That rim is lying face up on the ground. Gravity should have made quick work of putting the rotor in its place.
Centerbores out of spec on new Bendix PRT1132 11.75" disc brake rotors by cudak888, on Flickr
Centerbores out of spec on new Bendix PRT1132 11.75" disc brake rotors by cudak888, on Flickr
Centerbores out of spec on new Bendix PRT1132 11.75" disc brake rotors by cudak888, on Flickr
Eventually, it came to light that what my tired-as-heck self didn't notice that evening was that I wasn't seating the studs onto the rotor. I was seating the rotor to the wheel - more permanently than I care for.
And by that, I mean that the centerbores of the Bendix rotor measure out to 71.64mm (and I'm still not 100% sure I had the caliper jaws on the center - the variance may be more!), while the factory centerbore specification is 71.1mm (2.8"). That was just enough for the rim to slide on with the careful application of a 5-lug tightening sequence...and stay there without the assistance of a hydraulic press to get 'em out.
Centerbores out of spec on new Bendix PRT1132 11.75" disc brake rotors by cudak888, on Flickr
That's all ~225lbs of me or so standing on the rotor's hub in this picture; barely putting weight on the rim. You could hold a squaredance on that rotor; it's not coming out.
Needless to say, my mid-1970's Mopar slotted police rims proved the variation difference, and I also verified the fitment issue by checking my second rotor on an early-1980s 15x7" standard Mopar rim (off a B150). Same tolerance problem.
I have a couple of ideas of getting them back apart, but in the meantime, I'm going to email Rock Auto (where I got these from) and Bendix and see what they're going to do about this problem.
Also - in the meantime - I ordered one of Centric's 121.63009 rotors and the (sinfully ugly) drilled/slotted Power Stop AR8309XPR rotors. Though I realize the source of these rotors may be the same place in China, the Bendix parts are starting to look more and more like they bought up some factory seconds and shoved them in a box (with balsa wood to protect the hub area, no less).
So with this said, I warn everyone doing a 11.75" disc conversion: MEASURE your rotors' centerbores before installing. THEY MAY BE OUT OF SPEC. Fact is, it's very easy not to realize something is going VERY wrong when you're installing your rims on these hubs. And if you are lucky enough not to damage your rim on install, there remains the question of safe removal (and I can only imagine how this might damage a restored rim's paint job).
I can only hope that the bulky police rims will do their job and hold up when I finally get this thing removed.
Will report on March 1st or 2nd when the alternate rotors arrive. (And because I'm proud of the unreasonable difficult it took to get this far - long story - here's a self-propagandizing picture of the front end conversion):
Centerbores out of spec on new Bendix PRT1132 11.75" disc brake rotors by cudak888, on Flickr
Crossposting this from FBBO, as this applies to big brake A-body swaps equally.
Note: Seeing as rotors are primarily Chinese junk rebadged and sold in everybody's box under different names, there is a possibility that this issue exists with other brands other than Bendix.
Last night, I ran out of daylight working on my '68 Satellite's disc brake conversion (all factory parts) and had to button up the left side as quick as possible - and so I quickly installed one of my new Bendix 11.75" rotors that I had bought from Rock Auto almost half a year ago. No caliper or anything; just a rotor so I could get the car on the ground.
As I tightened the wheel to the rim, I was rather surprised that it seemed as if the lug studs on the disc hadn't been pressed into the drum correctly. Each bolt was loosening up as I went through the torque sequence, as if I were pulling the studs onto their seats as I torqued the nuts. Eventually, all of the nuts seated tightly, and I called it a night.
Enter next morning. I loosened the lug nuts, jacked the car back up so I could start installing the caliper - and the wheel won't come off. PERIOD. One might as well have welded it to the rotor.
That rim is lying face up on the ground. Gravity should have made quick work of putting the rotor in its place.
Eventually, it came to light that what my tired-as-heck self didn't notice that evening was that I wasn't seating the studs onto the rotor. I was seating the rotor to the wheel - more permanently than I care for.
And by that, I mean that the centerbores of the Bendix rotor measure out to 71.64mm (and I'm still not 100% sure I had the caliper jaws on the center - the variance may be more!), while the factory centerbore specification is 71.1mm (2.8"). That was just enough for the rim to slide on with the careful application of a 5-lug tightening sequence...and stay there without the assistance of a hydraulic press to get 'em out.
That's all ~225lbs of me or so standing on the rotor's hub in this picture; barely putting weight on the rim. You could hold a squaredance on that rotor; it's not coming out.
Needless to say, my mid-1970's Mopar slotted police rims proved the variation difference, and I also verified the fitment issue by checking my second rotor on an early-1980s 15x7" standard Mopar rim (off a B150). Same tolerance problem.
I have a couple of ideas of getting them back apart, but in the meantime, I'm going to email Rock Auto (where I got these from) and Bendix and see what they're going to do about this problem.
Also - in the meantime - I ordered one of Centric's 121.63009 rotors and the (sinfully ugly) drilled/slotted Power Stop AR8309XPR rotors. Though I realize the source of these rotors may be the same place in China, the Bendix parts are starting to look more and more like they bought up some factory seconds and shoved them in a box (with balsa wood to protect the hub area, no less).
So with this said, I warn everyone doing a 11.75" disc conversion: MEASURE your rotors' centerbores before installing. THEY MAY BE OUT OF SPEC. Fact is, it's very easy not to realize something is going VERY wrong when you're installing your rims on these hubs. And if you are lucky enough not to damage your rim on install, there remains the question of safe removal (and I can only imagine how this might damage a restored rim's paint job).
I can only hope that the bulky police rims will do their job and hold up when I finally get this thing removed.
Will report on March 1st or 2nd when the alternate rotors arrive. (And because I'm proud of the unreasonable difficult it took to get this far - long story - here's a self-propagandizing picture of the front end conversion):
