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Discussion Starter #1
GM (Corvette) PBR Calipers on SN95 spindles/Cobra 13" Rotors

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 state the pad area of the newer caliper was increased 30%, as well as the caliper being stiffer overall.

You can see the various calipers at the bottom of the page here
https://baer.com/Replacement-Brakes-Pads/

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 and 05-06 GTO 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 C6 and GTO calipers are the same, but the C6 calipers are slightly stiffer. Haven't confirmed though, and pricing of C6 calipers leaves the cheaper C5 and GTO calipers as a more likely alternative. There may be a model of early/mid 2000's Cadillac that uses these calipers as well, but I haven't confirmed.


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)


Corvette Z51 Caliper abutment (for 13.4" rotors)


You can see the additional offset of the Z51 brackets to get proper rotor spacing. (look at the spindle mount holes)

The part number for the Z51 brackets is GM 88964166


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 1mm

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.




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 spacing for SN95.

EDIT 5/15/2018: Have been informed that Baer no longer offers the above brackets. You'll need to track down a set of used ones or Baer calipers, or modify the Z51 brackets.


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.



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.

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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Discussion Starter #2
Keep in mind, you can grind off the lettering, or paint the calipers to mask the original lettering. These are physically the same as the BAER calipers in the link above minus what they say on them, so don't let the fact that they say corvette or GTO on them stop you. They are all made by PBR who pretty much makes all the OEM calipers for a lot of domestic cars these days. Keep in mind that C4 calipers are pretty much the same as Cobra calipers anyway, and the 99-04 GT calipers, and 05-09GT calipers are pretty much the same type of design.

EDIT: Also just noticed Rockauto.com sells remans that are void of all lettering completely.


I chose to leave the lettering on just for a bit of controversy and visual pop. I've driven around a bit with them and they get noticed. I don't mind it.


 

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Nice writeup! So the benefit here over Cobra brakes is more pad area?
 

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As far as I know right now, the calipers that can be used here are C5, C6 and 05-06 GTO 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. Haven't confirmed though, and pricing of C6 calipers leaves the cheaper C5 and GTO calipers as a more likely alternative. There may be a model of early/mid 2000's Cadillac that uses these calipers as well, but I haven't confirmed.
Using Hawk's catalog (which is pretty handy for this sort of parts cross-referencing) the only other vehicle that I see using the same caliper is the '04-09 Cadillac XLR. Makes sense, as it was a Corvette chassis with a Caddy body and Northstar engine. Not a particularly common car, so folks are probably better off shopping for Vette/GTO parts, as used XLR parts will probably carry a "Cadillac tax".
 

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Discussion Starter #5
Nice writeup! So the benefit here over Cobra brakes is more pad area?
More pad area, which should translate into even heat into the rotor, and better pad modulation. Also, the caliper is stiffer.

For a street car, probably wouldn't really notice this in normal driving.

However, one big advantage for track guys is that you have the ability to run 1.25" thick rotors up front, vs the 1.1" rotors from the Cobra. This would likely require a 2-peice rotor from Baer, or using Cobra center hats, with the outer rotor of a vette from other manufacturers.
 

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This is a really good write up, thank you for taking the time to document this. At least it gives us another choice of brakes to go to.

Thumbs up
 

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Interesting parts combinations, thanks for the research.

Do any of those PBR or Corvette calipers have larger pistons similar to the 99-04 GT calipers? I've got a heavier Lincoln to put the SN95 spindles etc, onto, but I might need the bigger calipers too.
 

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Discussion Starter #8
Do any of those PBR or Corvette calipers have larger pistons similar to the 99-04 GT calipers? I've got a heavier Lincoln to put the SN95 spindles etc, onto, but I might need the bigger calipers too.
From largest to smallest caliper pistons

99-04 GT: 44.5mm x2
C5/C6/GTO/XLR: 40.5mm x2
99-04 Cobra/Bullitt/Mach1: 40mm x 2
94-98 Cobra: 38mmx2

The last 3 of those 4 however would be run with an 13.1" rotor, vs 10.9" on the 99-04 GT.
 

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From largest to smallest caliper pistons

99-04 GT: 44.5mm x2
C5/C6/GTO/XLR: 40.5mm x2
99-04 Cobra/Bullitt/Mach1: 40mm x 2
94-98 Cobra: 38mmx2

The last 3 of those 4 however would be run with an 13.1" rotor, vs 10.9" on the 99-04 GT.
Thanks. I'll try the front Cobra rotors and matching caliper first and see where that gets my car, with the Crown Vic 03-10 rear brakes, which are easy to find versus Cobra parts. The CV's do have bigger rear pistons, 1.9" versus 1.5", my stock rears now have 1.8" pistons.
 

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Discussion Starter #10
Just updating with some info on wheel fitment.

13" Cobra spare tire with spacers does not clear. By the time you add enough spacers, you have run out of useful thread on the lugs. Perhaps extended lugs would work. My next option is to try a large (1" or 1.25") bolt-on style wheel spacer, or pick up an 18" spare tire out of an S550 and try that out. (P/N FR3Z-1K007-C). Tire size on those is 185/55/18, which is 26" in OD and about 20mm wider than the cobra spare, so it may not sit flush in the well. I'll try the spacer first.

I've tried 3 OEM 17" wheels with the setup. 01-04 bullitts, 99/01 Cobra wheels, and 94-97 Cobra wheels. While clearance in terms of diameter is fine, there is a big difference in clearance to the spokes. The bullitt wheels were by far the tightest of the 3. Not sure i could get tape weights in behind the spokes there. The 99/01 cobra wheels have a bit more clearance, and tape weights fit fine. I've driven 300 miles or so on this setup without issue.

The 1997 cobra wheels i put on as rollers for the winter fit with tons of space, as seen here.

Reason i bring this up is because this fit is with the 1.1" cobra rotor. These calipers will take a 1.25" rotor however, like what would be included with them if one were to purchase the Baer kit. I want to look into buying a set of 1.25" 2-peice rotors that fit the Mustang, so i've been double checking clearances. May look into this over the winter.

Oh and the brakes work fantastic. Once they bedded in, i've been hard on them and the entire brake setup performs quite well on the car. Very little pedal effort to slow the car down from 65MPH or so. Reactions are mixed. Most people see them and just think they are Cobra calipers. Some notice and, for some reason, get very angry that a GM part is on a Ford.
 

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Thanks Mike. I got a pair of 05/06 GTO calipers the other day. They are heavier than the Cobra PBR's, and these had nice thick pads still in them.

I'm using 94/95 Cobra wheels now on my Lincoln, with 255/45/17" DWS tires.

I'd like to consider a 1.25" rotor, but after I mock up the SN95 spindle with a rotor. If it could use the meat, that sounds like the caliper would need to go inboard a bit, maybe .075" inboard. The caliper bracket bolts to the spindle from the back. These brackets have 14mm holes in them I'm sure, so the brackets I have aren't the best choice.

The Baer CBK332325 bracket is the first option, and are those the entire caliper bracket for the caliper to fit into? These GTO brackets don't have threads in the holes, I'm guessing the bolts go through them from the back, into a spindle. I'm imagining which parts would be best to mount the calipers with, which bracket and which bolts.
 

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Discussion Starter #12
You pretty much are scrapping the black abutments from the GTO caliper. The mounting points are offset like the picture in the above post of the GTO caliper in my initial post, so they are useless to you. You keep the caliper and all the hardware however.

True 100% bolt on solution is the baer brackets. These are what bolt to the spindles. Pic below shows you what i mean. Just replace my 'vette caliper with your GTO caliper. The black bracket is what you will get from Baer. This is direct bolt on to the SN95 spindle, and the GM PBR will bolt to this using the same hardware from your GTO calipers.

The spindle bolts you see on my baer bracket are not included. These are the standard SN95 front spindle bolts, and yes, they slide THROUGHT the caliper bracket and thread into the spindle. If you need any hardware, just use a 1998 corvette as your reference. You'll need GM specific banjo bolts. I am using SS braided lines with round heads that worked with my old Mach 1 calipers as well as these.



Since you have the GTO versions, there is no raised lettering. A quick coat of paint and you'd never know it was a GM spec PBR, which is ironic considering the Cobra caliper also appeared on the corvette first, so does it ultimately really matter here?

What your end result is, is basically the Baer GT plus kit, which i believe is discontinued.

As for the 1.25" rotors. Provided you get the correct application rotors, the difference would be split 0.075" each side over the standard cobra 1.1" rotor. The caliper abutment that bolts to the spindle would stay fixed, but the caliper would slide out that 0.075" further. If the pads are worn, the caliper will actually be located further inboard as it centers on the rotor. As you can see from my pic above with the '97 Cobra wheels, there is plenty of room for the red caliper portion of my brake to move outboard to accomodate a 1.25" rotor.


I think with the rotors, there aren't that many vendors that make a 1.25" rotor for the mustang given the cobra style PBR can only accept a 1.1" rotor. Baer makes a rotor, since they package this caliper as a kit for the Mustang, but i beleive the strategy here is to buy the center hat of a 2-piece rotor for a SN95 Mustang cobra, and purchase the outer wear ring for a Z58 corvette which uses a 13.4" rotor ring. I'm not 100% on this, so i'll be looking into it.
 

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Thanks for clarifying what the Baer bracket is, and the mix of which parts go to which car etc. I like that these are smooth and just painted.

I will repaint these with the "O" altered to a "C", since I just brought home the GTC body kit for my Lincoln. That'll work.

The rotor hat is the key component to get a rotor we want. The offset has to be right to work with the caliper etc. I wonder if another hat exists with a little less offset(.075" or close), which moves the rotor inboard. If we use a Mustang offset rotor hat, then a thicker rotor moves inboard .150", which won't work with the calipers and brackets. The stock offset is already very low, .350", unlike the Corvette which is .850" offset. How much of a washer is allowed to mount a caliper bracket to the spindle, I've forgotten what Todd(TCE) told me? I used very slim(.030-.060) shims with my SUV custom brakes, to center the caliper over the rotor.
 

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Discussion Starter #14
The rotor hat is the key component to get a rotor we want. The offset has to be right to work with the caliper etc. I wonder if another hat exists with a little less offset(.075" or close), which moves the rotor inboard. If we use a Mustang offset rotor hat, then a thicker rotor moves inboard .150", which won't work with the calipers and brackets. The stock offset is already very low, .350", unlike the Corvette which is .850" offset. How much of a washer is allowed to mount a caliper bracket to the spindle, I've forgotten what Todd(TCE) told me? I used very slim(.030-.060) shims with my SUV custom brakes, to center the caliper over the rotor.
I see what you are saying.

If you were to place a washer between the spindle and caliper bracket, you would move the caliper outboard, which is opposite of what you want. You'd actually need to machine 0.075" off the backside of the bracket to position the caliper inboard to account for the offset created when you bolt a 1.25" ring to a mustang AL hat.

I'd have to think we are overthinking it, as i've seen it's been done.

http://forums.corral.net/forums/road-racing-auto-x/1160634-13x1-25-cobra-rotors.html


I forget what size rotors came in the Baer GT kit that was for the Sn95 mustang that used these calipers. They were 2-peice, but unsure if they were 1.1" or 1.25" thick. I almost want to give baer a call and see what they would have recommended for a 1.25" setup with that kit.
 

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Sounds good. I'll give Baer a call when I'm close to do the brakes. I'll ask them what brackets they have for the SN95 spindle, for which rotors/calipers. I expect the clearance to be fine in any case, but I wouldn't mind to have the thicker rotor. I'm very tough on brakes. As a mail carrier, I've found the limits of lots of various pads, rotors, stock, aftermarket etc.

I need to soon get on my redesign of my SUV brackets, to use the bigger Wilwood calipers I found a while back. My mail truck eats brakes, by my standards. Some people don't mind doing brakes every few months, I'd rather not have to for a year or two under severe duty. My current 98 with stock brakes has managed about 9-10 months on the brakes. The first rears went in about five months, both rear calipers were dragging a bit. Now this time after six months the rear pads are still half there.
 

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Good work guys. Awesome reference.
 

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Well I too got consumed in this thread and picked up a used pair of C5 (base) calipers/brackets off eBay.

I have Baer modified Fox spindles with GM sourced C4 HD J55 brackets (14mm bolts), thus I thought these newer GM brackets might bolt up. Turns out my assumption was wrong! Lesson learned. The new brackets are 1mm to short, just like the problem with SN95 spindles. GM obviously didn't want mixing and matching.

So I searched all over the internet for C4 to C5 brackets and just couldn't find a solution that wouldn't break the bank. Back on eBay they went, but I must say, the C5 calipers are pretty darn beefy compared to the C4 PBR versions.
 

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Discussion Starter #18
but I must say, the C5 calipers are pretty darn beefy compared to the C4 PBR versions.
They really are. They may have the same size pistons as the 99-04 Cobra/mach/bullitt PBR, but the caliper surrounds the rotor more and does sweep the entire face of the rotor, which i always disliked on the Cobra PBR's (they seem to only grab the outer 2").

Sucks you couldn't get it to work. When i was using the Z51 brackets, i was tempted to whip out the drill and hog the hole out to make it work. I really didn't want to permanently alter the Sn95 spindle to do this though, so i can understand not wanting to do the same.
 

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Sucks you couldn't get it to work. When i was using the Z51 brackets, i was tempted to whip out the drill and hog the hole out to make it work. I really didn't want to permanently alter the Sn95 spindle to do this though, so i can understand not wanting to do the same.
Ha! I consider the same thing, but then thought otherwise. LOL
 

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for the guys not liking the corvette or gto logos i found ones without

CENTRIC 14162128
Front Left; Except Corvette Logo

CENTRIC 14262128
Front Left; Except Corvette Logo
 
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