Brakes Gm (corvette) Pbr Calipers On Sn95 Spindles/cobra 13" Rotors

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
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SO, I posted a few pics of this setup, and got a lot of PM's with questions. I figured a thread would help explain everything better.

I noticed a few years ago, that Baer had moved away from offering the C4 Corvette/Cobra style pad-guided PBR, and instead offered a pin-guided caliper similar to the C5 corvette with some of their kits. In searching, I read numerous sources stating the improvements of these next gen calipers. More pad swept area covering more rotor surface area helping regulate temp evenly, as well as a stiffer caliper in general to help reduce caliper spread under extreme conditions (C6 calipers are even stiffer than c5). Another benefit is they will accept 1.25" thick rotors. Standard cobra rotors are 1.1" thick. Currently researching 1.25" thick rotor options as we speak


SO basically here's how to duplicate the basic baer kits using GM calipers.

As far as I know right now, the calipers that can be used here are C5, C6, 05-06 GTO and '04-09 Cadillac XLR calipers. Only the caliper portion can be used. The brake abutments (portion of the caliper that bolts to the spindle) cannot be used. I believe C5 and GTO calipers are the same, but the C6 calipers are slightly stiffer. Parts shops are offering remans that are BLANK these days, so you can get a plain faced caliper without any ties to it's GM counterpart...if that sort of thing bothers you.

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You can see in the above pic, that the portion that bolts to the spindle is different between the vette and GTO caliper. These abutements are what adapts the caliper to the spindle, and what we need to pay attention to here.

Standard Corvette brakes are 12.75" in diameter. So if you use the standard vette abutment, the caliper won't fit over the cobra 13" rotor. However, GM released a package called the Z51 package, which increased the front brake rotor diameter to 13.4". This will work....sorta.
Standard Base Corvette Caliper abutment (for 12.75" rotors)
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Corvette Z51 Caliper abutment (for 13.4" rotors) part number 88964166
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You can see the additional offset of the Z51 brackets to get proper rotor spacing. (look at the spindle mount holes

So what needs modification? Well, GM uses 14mm bolts to mount the calipers, while the Sn95 uses 12mm. This means you'll need to widen the holes in the spindle just a tiny bit to accomodate the larger 14mm bolts. Also, the bolt spacing is off...by 2mm. SN95 use a 130mm bolt spacing while GM is using 128mm

Here's an OEM Z51 abutment mounted on an SN95 spindle. The upper hole is aligned using the smaller 12mm bolt simply to hold it. You can see here the lower bolt is off by 1mm.
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Z51 abutments usually retail for about $50 each at the local GM dealer. Since i didn't want to modify my spindle, i looked for a more bolt-on OEM solution.

So i went to Baer.

Baer part number CBK332325. Cost is about $130 each (plus shipping). The p/n stamped on the bracket itself is K332-216C1 This is a 100% direct bolt on solution. These are basically Z51 brackets, but drilled for 12mm bolts, and to the proper 130mm spacing for SN95.
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They come zinc-coated, and you can see they feature the Sn95 style 12mm bolt hole compared to the 14mm GM bolt hole on the GM-specific brackets.

Basically, at this point, it's no different than any Cobra 13" brake swap. Slide on the 13" 94-04 Cobra specific rotor of your choice, then the Baer bracket, then pads, and hardware, and finally the caliper. I used my Sn95 SS brake hoses, but with a Corvette specific banjo bolt.
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Piston sizes are 40.5mmx40.5mm, which is practically identical to the 99-04 Cobra/Mach/Bullitt caliper (which is 40x40mm). With rear Sn95 disks, i'm running a 1993 Cobra 1" bore MC, and braking feels great.

Things to pay attention to:

Brake bleeding: The position of the bleeder with respect to the center of the top piston does trap a tiny bi of air at the time. In order to bleed the calipers, i had to upbolt the top bolt on the caliper and rotate it vertically. I was using a gravity bleeder setup, so i did not press on the pedal to extend the pistons. Until i did this, i was having a hard time getting a good pedal

Tape weights. Clearance is tight, so a tire installer needs to position the weights as far forward as possible to clear the caliper. There's plenty of room for the caliper, but the weights get close. C6 calipers supposedly have a bit more clearance at the top of the caliper

Finally, the cobra 13" spare tire will not clear. Perhaps a spacer would work, but i haven't had a chance to explore that.
 
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HotFox

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Jan 5, 2009
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I find it interesting that GM is using larger hardware. The OEM's have pretty good testing and if they could have saved on using a 12mm bolt they would have. Although thinking about this the SN Cobra would have never used the wheel dia. that the Corvette used so maybe the shear forces were not as high.
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
31,692
7,907
224
Massachusetts
Good question. I also wondered why Ford seemed to lag behind in brake tech. The cobra caliper we all know and love debuted around 1988. It's 30 year old tech and Ford finally adopted it when Chevy was moving onto the next generation which improved upon the old pad guide design.