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Discussion Starter #1 (Edited)
[editor's note: This is a transcript of the article I wrote for the ISSCA SScene for the winter/spring 2011 edition. I have made a few updates since that article went to print.]

Ever thought about upgrading your brakes but didn’t have the cash to buy one of the nice but high-dollar big brake kits available? Want a little extra margin for occasional high-heat situations without radically altering your vehicle? You will find this article enlightening and enjoyable.
The impetus started back in 2005 at the “Mountain Madness” Impala SS Nationals which included a road race on a portion of Pocono International Raceway. I can honestly say that this was one of the most exciting driving experiences of my life – to be able to drive full-out and enjoy my 9C1’s LT1 and suspension in ways not possible on the street. Before I drove the 3 hours to the Nationals, I carefully prepped the car by rebuilding the front suspension, installing fresh rotors and street pads all around and purchasing new tires. I followed up by doing the proportioning and metering mods to the proportioning valve, flushing the brake fluid and refilling with a high-quality synthetic, and had an alignment done. And off I went.



Figure 1: Mountain Madness 2005 at Pocono with my Light Driftwood Metallic 9C1 in the foreground. Dave Wilson's LDM 9C1 is behind mine, and to the left is Chris Pustizzi's two-tone SWT SS.



Figure 2: Another shot of Pocono 2005 with the B-cars ready to roll. Turn one is in the background.

The car did fine, but I remember how tremendously hot the front brakes were when I completed each 5-lap session (it feels a lot longer than it sounds!). I could hear a “shhhh” sound echoing off the paddock buildings, so I drove around the infield service roads at low speed for about 10 minutes to cool them down a bit and avoid putting hard spots on the rotors. All in all, a great day, but I never forgot those hot brakes.
Well, 6 years and several small children later, the 9C1 has served exclusively in street duty as a summer car, its racing days on hold for now. But this year, I was thrilled to be able to get my schedule lined up to attend the 2011 Impala SS Nationals in Detroit, MI with my father, who grew up in the area. By the way, the benefit of this event being held simultaneously with the Woodward Dream Cruise cannot be overstated – it will be worth your while to attend! As a plus for me, the Waterford Hills racetrack (www.waterfordhills.com) was where my Dad, while in high school, helped out a Chrysler engineer who raced in his spare time. What a great event to take him to! Then I thought about those brakes.
 

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Discussion Starter #2 (Edited)
In those six years since the ’05 Nats, I have gotten involved in the B-car wagon scene with my ’95 Roadmaster (since scrapped due to rust) and ’94 Roadmaster wagons, and had the privilege of meeting Jay Doughty through that. Jay and I are both engineers by trade and tinkerers on the side. He taught me a lot about how to use parts catalogs to cross-reference parts by application and by dimensions, and it is his experience and searching which has yielded the solution you are about to read about. I am merely the scribe (and guinea pig!).

For reference, the stock ’91-96 GM B-car front brake system uses a single-piston floating caliper on a rotor which has an integrated hub on which the wheel bearings ride. The rotor also has a pressed-on ABS reluctor wheel on the inside face with 34 teeth on it. Finally, it uses wheel studs in a 5x5” pattern. In the family of vehicles of which the B-car shares most parts commonality with (GM trucks, vans and large rear-wheel-drive cars of earlier years), the B-car rotors are among the largest diameter that GM used at the time excluding Corvette and heavy truck/van applications. Through the 1980’s, 1990’s and on, the auto industry has since migrated to sealed wheel bearings integrated into self-contained hub assemblies which in turn bolt to the suspension uprights. The brake rotors then fit over the hubs. GM front wheel drive platforms have been built this way since the late 1980s. Unfortunately the “B” platform was scheduled to be terminated by the end of 1996 and never received the chassis upgrades other models have.

THE PROBLEM
B-car brake performance upgrades that retain the stock rotor and caliper sizes are generally limited to different pad materials, larger (police) calipers, rotors of upgraded quality, and increased airflow to the brake area. But for those who really exercise the brakes (such as road racing applications), the primary complaint quickly becomes this: Under repeated heavy braking, the stock rotors cannot dissipate braking energy quickly enough and overheat. Looking at the rotors themselves, a big reason becomes apparent: the vane area is very small. It’s what I experienced at the 2005 Nationals at Pocono.

This problem can be solved either by using rotors with a higher “thermal mass” or heat capacity (which reduces the amount of temperature increase for a given braking effort), increasing airflow through the vanes (which improves the convective cooling), or both. There are a number of excellent brake upgrade kits for the B-car that all utilize significantly larger rotors. Beginning back in 1998, the “Mov’it” kit sold by a German company started the ball rolling by essentially adapting Porsche 911 turbo brakes to the Impala, and still produces kits for the SS (http://www.movitbrakes.com/en/applicationlistegallery/chevrolet/impala-ss/). Other suppliers have since developed similar setups using larger rotors, and now a kit exists by which a two-piece hub and an oversized rotor of the stock diameter are substituted for the factory unitized hub-rotor assembly, providing for those who want to retain 15” wheels. These kits are all well-engineered and solve the heat problem, but for my basically “one-time use” at the 2011 Nationals, they are quite a substantial investment as they require custom hubs, different rotors, different calipers, and sometimes different pads. Additionally, they use a significant number of one-off parts and that adds to the cost.

Jay and I often marvel at how GM and other auto engineers will often use “parts bin” approach by utilizing pieces already in production, rather than designing different pieces for newer cars or even performance/trim option packages. In this fashion, Jay has pieced together a very impressive big brake kit for his ’96 Buick Roadmaster wagon using Mercedes ML55 calipers (purchased used on eBay) fitting over 340mm C6 Z51 front rotors. Since I run 15” wheels on my 9C1 and he uses 17” Impala SS wheels on his wagon, going this route was not an option for me. We reasoned that there is possibly some existing combination of parts, which, if they could be combined, may yield an inexpensive solution without a lot of custom work, so to the parts catalogs we went.
 

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Discussion Starter #3 (Edited)
The Search

The Internet is a goldmine of information regarding components and cross-references, especially if you know which catalogs to search in. Jay extensively searched the online catalogs to find rotors that might be candidates for a B-car. Napa Auto Parts also has a very detailed online catalog with component images and technical information, which we consulted after the initial candidates were found. For a rotor to be useful for our purposes, it must have:

1. Proper diameter (stock B-car diameter is 11.86”) in order to fit radially inside the B-car caliper and mounting ears on the steering knuckle.

2. Increased thickness (stock is 26.4mm) to help with heat handling.

3. Correct axial offset relative to where the wheel bolts to (this is called the hub face). The rotor must fit inside a stock caliper without moving it too far in either direction on the slider pins. This is the same idea as a wheel offset if you’ve shopped for wheels. The B-car offset is approximately 73mm from the wheel mounting face to the backside of the rotor.

As a secondary concern, an optimal rotor would:

4. Have a 5 on 5” bolt pattern and 12mm lug nut holes

5. If it didn’t include a hub, it should have an inner opening (called a “register”) diameter of 3.0625” or only slightly greater, so as to center the rotor on the hub.



Any rotor that met the first three criteria could be modified by any machine shop for the latter, but this adds a continued cost every time you have to replace rotors. Low-effort rotor replacement was a key factor in this search, as I live in Syracuse, NY which has probably one of the most severe moisture environments in the USA. Not only does Syracuse get a lot of lake-effect moisture from Lake Ontario, but it also experiences freeze-thaw cycles almost daily and the highway departments use a rock salt mixture which is not kind to bare metal. As a result, it is not uncommon for winter-driven FWD vehicles to require rotor replacement every 18 months due to corrosion damage (the lousy metallurgy of replacement rotors nowadays doesn’t help either). In case you are wondering, Syracuse is about 250 miles or 4 hours from New York City. New York is a big state!

The investigation went in two directions. The first was to see if a stock GM integrated rotor & hub application similar to the existing B-car design might fit with little modification. The second was to see if a stock B-car rotor was machined down to a hub with wheel studs, could a hat style rotor of the Impala SS / 9C1 rear, or typical GM FWD design be used.

Jay started with the Centric and Brembo catalogs, which provide detailed drawings, or allow you to search by various rotor characteristics independent of application. Using rotor diameter as the starting point, we selected several units that were close to the existing diameter. Then checking the width, we eliminated all rotors that weren’t thicker than the B-car rotor. The next step was to find offsets that would be within the range of B-car slider pin travel. For the non-hub rotors, Jay calculated the effective offset needed from the B-car rotor with the rotor portion removed.

The search turned up several candidates from applications we had suspected: GM trucks and full-size vans in the 1990s, and Cadillac commercial chassis vehicles (limousines and hearses) otherwise known as the ’91-96 Fleetwood with the option code “J55” for the brakes. As the search continued, Jay verified that the J55 setup uses the same rotor and part number as the 1971-1976 Caprice. Neither of these vehicles have ABS, in part because the rotors lack the provisions for it. If they were to be used, the rotor would have to be machined and B-car ABS tone rings pressed onto the rotors. Additionally, the inner wheel bearing is larger (both Inner Diameter (ID) and Outer Diameter (OD)) than the ’91-96 B-bodies, so this too would have to be addressed.

GM truck and van rotors were also investigated. The 1997 Suburban 2WD rotors (these fit a variety of truck applications of this era) are 6.4mm thicker than the B-car rotors, have the correct bolt pattern and offset, and have provisions for an ABS tone ring. But they also use the same large inner wheel bearing that the J55 package does, and the 56-tooth reluctors (common to most GM trucks and vans) are incompatible with the B-car ABS system unless you create and install a custom reluctor in your rear axle. This option was also set aside and the alternate rotor approach was explored.

Jay found a Porsche rotor that had a matching diameter and desired thickness along with an offset that is close to what is needed, but the wheel bolt pattern (often referred to as pitch circle diameter or “PCD” in the industry) is 130 mm vs. B-car 127 mm (5"). Additionally, it had a much larger hub diameter of 103 mm (4.06”) vs. B-car 78 mm (or about 3.06 inches). This would require the inclusion of a hub-centering ring to ensure concentric mounting. A Mercedes rotor also had a similar offset and thickness, but the outer diameter would need to be cut down in a lathe from 330mm to 301mm (B-car size) to fit, the bolt pattern re-drilled and hub register diameter opened up. Additionally, both of these rotors were used on low-volume applications and as I searched several well-known parts chains’ websites, they showed ZERO local availability, despite a price that wasn’t actually that high.

We stopped and reviewed what the parts searches had turned up. To date, we had come up with two options. The GM J55 or Suburban options required some sort of adaptation to retain the B-car ABS reluctors, and either an alternate inner wheel bearing that used the smaller B-car inner race with the larger truck outer race (if available) or a pressed-on sleeve that allowed the truck bearing to be used. On top of that, you still had to deal with an additional sleeve for the inner dust seal, and the prospect of repacking the wheel bearings each time you changed a rotor. The Mercedes/Porsche option, while eliminating the bearing packing process, required significant machine work to be performed on each rotor before it could be used, as well as no immediate availability. Neither solution was appealing.
 

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Discussion Starter #4 (Edited)
The Solution

Then, Jay remembered seeing something on Wikipedia about Chevy Astro / GMC Safari minivans using some of the same suspension components as B-bodies. He started searching parts catalogs and determined that 1990-2002 Astro 2WD rotors were essentially the same as the B-car with only a few minor differences. Wanting to move away from an integrated-hub design, Jay then looked at the 1990-2002 AWD Astro model, and found the solution. The rotor is a hubless design with the correct bolt pattern and offset. They do have a slightly smaller diameter (11.61” vs. 11.86”). The 0.25” difference across the diameter equates to 1/8” or about 3mm around the radius, which was a concern at first, but if you’ve seen the stock B-car wear pattern, this is the amount of unused edge anyway, so it wasn’t a deal-breaker. Furthermore, the rotor is a full 32.7mm thick versus the stock B-car 26.4mm, an increase in thickness of about 25%. Measuring the thickness of the wear surfaces vs. the vanes, almost all of the added width is in the vanes!



Figure 3: B-car rotor (26.4mm) top vs. Astro rotor (32.7mm) on bottom showing vane thickness increased by 50%.

In terms of the cooling area, the vane thickness is increased by 50%! The real icing on the cake came when we found that Astro rotors are typically about 50% of the cost of a comparable B-car rotor, are readily available everywhere, and need no modifications at all to fit!
Jay and I began to look at what else it would take to make this setup work.
 

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Discussion Starter #5 (Edited)
Hub Mods

First, the B-car hub/rotor needs to have the rotor portion machined off. This can be done on a brake lathe that many auto repair shops have.



Figure 4: Brake lathe cutting setup.

If you do not have access to a brake lathe, but do have access to a smaller lathe, you can cut the rotor off yourself. This leaves you with a roughly 6.9” hub diameter which will fit into most benchtop lathes. Use a reciprocating saw or similar cutting tool meant for cutting metal. One such blade is “The Torch,” a 6” diamond grit blade made by Milwaukee, part number 48-00-1440 and available at Home Depot. Be aware that a signficant amount of the rotor may be surface hardened and the cutting speed will be slow until you get deeper into the metal. A plasma cutter can be used as well. Measure 23.7mm (or 15/16”) back from the hub face, and then plunge cut through the rotor hat. The B-body rotor/hub I cut down had significant surface hardening; once we made it through that, the metal began cutting away much more quickly. You will then need to have the outer diameter of the hub face turned down to roughly 6.75” diameter to fit underneath the Astro rotor. On the brake lathe, we actually did this step first.



Figure 5: B-car hub outer diameter being turned down prior to removing the rotor.

As an alternative way of measuring (if you’re like me and only have 6” calipers!), if you measure out from the hub register (the place where the stock wheels locate on the hub), you should have enough clearance at about 1.95”. Be aware that there are two types of rotor constructions: “one-piece” rotors in which the entire rotor is one piece of metal, and “composite” rotors which are made from two different pieces of metal and then fused together. Composite rotors visually have a rounded, flat/satin hat surface, while one-piece rotors look uniformly shiny everywhere.



Figure 6: Astro rotor comparison: composite on left (with B-car hub in place) vs. one-piece on right. Note that I found the composite rotor was more accommodating of a larger hub outer diameter than the one-piece rotor was.

As I completed turning the first hub down, I discovered that the composite rotor could handle a larger hub diameter than the one-piece rotor, which had a smaller inside diameter. It is wise to add a chamfer to the outer edge to provide clearance for any fillet on the inside of the rotor. The important thing is that this outer surface dimension is not critical; as long as the rotor fits squarely & concentrically to the hub, it’s good. A final photo of the hub on the lathe is shown here. Note: do not turn this outer diameter down until you read the entire article.



Figure 7: Cutting chamfers on the cut-down B-car hub.

Since the Astro hat thickness across the hub face is 5.5mm, you will need longer wheel studs, Dorman P/N 610-323, which are 13mm (or ½”) longer than the stock ones (54mm vs. 41mm). Press the studs in (one trick is to use a lug nut, an impact wrench, and several greased “sacrificial” washers to keep the lug nut from grinding against the hub). Once the new studs are installed, the hub modifications are done.
 

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Discussion Starter #6 (Edited)
By the way: Wheel bearing clearance improvement

Jay also suggested another mod while I was assembling this new setup. The stock B-car spindle nuts are castellated for a cotter pin locking system to secure the wheel bearings and properly tighten them. This is important because too much pre-load dramatically shortens bearing life, but too much free play causes brake pad knockback, excess lateral wheel movement and imprecise steering feel. To illustrate this, here’s a picture from the internet (thanks Internet!) showing the effect of slack or preload on bearings:



Figure 8: Bearing Life vs. slack/preload. Note that too much pre-load (positions 4 and 5) drastically shortens bearing life. Positions 1-3 are vastly different clearance and steering feel, but little effect on life. Position number 3 is optimal, but only slightly better than position 2. The stock B-car adjustment nut doesn’t give you much ability to optimize between positions 1 and 3.

The stock setup, having only a limited number of adjustments, doesn’t allow you to fine-tune wheel bearing clearances as much as other methods. So the differences between positions 1, 2 and 3 may be beyond your control. That said, Jay did some digging and found that the ’91-92 Camaro & Firebird used a special retainer (of the same design that Ford and Chrysler have been using for years) which allows for a more precise adjustment and lock. The part numbers are 18018567 (nut) and 18018568 (retainer). Both are discontinued by GM, but Dorman makes a replacement retainer available as PN 615-154. Dorman & NAPA carried replacement nuts at one time, but again, are currently discontinued. Several other options were explored but ultimately none turned up as being feasible without significantly more effort. This narrows the available options to finding used nuts at the wrecking yard, or reworking the castellated nut. Replacement B-car nuts can be sourced inexpensively – look for Dorman PN 615-065 or equivalent. If one has access to a lathe, it is a relatively simple process to cut down the standard nut so it may be used with the retainer. Shown is a comparison of the F-Body nut, the B-body nut and a B-Body nut with the castellations removed. Note that the cut down nut still retains the dimensions of the F-Body nut, ensuring that sufficient material remains for proper thread engagement.



Figure 9: Stock B-car castellated nut on left, F-car nut on right, cut-down B-car nut in middle.

Installation of the new parts are as follows: Adjust the bearing preload per the factory service manual, then slip the retainer over the nut, oriented so that the tangs fall on either side of the cotter pin hole. Insert the pin, and you’re done! Now your wheel bearings are precisely tightened with no additional work needed!



Figure 10: Install lower-profile nut onto hub. Note that F-car spindle nut is shown.



Figure 11: Add nut retainer and cotter pin to complete installation
 

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Discussion Starter #7 (Edited)
Caliper mods

The stock B-car caliper is not wide enough to accommodate the thicker rotor. Use the thicker J55 calipers instead. The J55 calipers uses what is essentially a 9C1-spec caliper casting, but with a shorter piston.

Table 1: Caliper Measurements. Note - 9C1 piston did not retract all the way - casting clearance would have been around 64mm had it retracted as far as the J55 piston did.



If your car is a 9C1, or has 9C1 calipers on it, you may get away with using stock D52 pads or even worn 614 pads, but I would recommend you upgrade to the J55 calipers for several reasons. First, given the age of these cars, your calipers may be in worse shape than you think. Just for grins, I’ll include this pic of one of my 9C1 calipers – this “bubble” in the dust boot is actually brake fluid that has leaked past the seal.



Figure 12: Funky bulge in the dust boot around the retracted piston on my 9C1’s caliper reveals brake fluid had leaked past the seal and was being retained only by the dust boot. 160k miles, time for new J55 calipers!

Second, 9C1 calipers with Astro rotors will likely only leave you 27.6mm for pads, which drastically limits which new pads you can use (to basically none!). Finally, the fully rebuilt Fenco 18-4126 / 18-4127 calipers I got from Advance Auto Parts (and these units are rebadged as Duralast from Autozone for about the same price) come with brand new slider pins as well. You can buy these for around $13.50 apiece plus tax, not including cores. It’s literally quicker and cheaper to replace the calipers than to rebuild them!
 

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Discussion Starter #8 (Edited)
BRAKE PAD CHOICES: D52 vs. D614 vs. D153

One of the things I discovered in the course of measuring everything is that there are certain manufacturing tolerances that allow parts to vary slightly from “published numbers.” One aspect of this appeared during measuring of brake pad thicknesses. As I was measuring pads at Autozone (thank you counterperson!), it was not uncommon to find up to .15mm thickness variation between a pair of pads that had come out of the same box. While this sounds insignificant, clearances were so close, that one set 0.1 mm thicker than another was unable to fit into the J55 caliper with the Astro rotor. I have a set of Bendix Fleet MetLok 614AFM pads I was hoping to use but they are too wide to fit, unless I first pass them over a belt sander or run them against the stock rotors for awhile to wear them down slightly.

Table 2: Brake Pad Thickness of actual measured pads: D52 is thinnest, then D153, then D614


*Note that Performance Friction has discontinued these pads and Autozone was clearancing them for this price as of spring 2011. Once remaining store stock is gone, warranty replacements will be the gold-level house brand pads.

The D52 pads tend to be the thinnest averaging 28.3mm for a set. The D153 truck pads can and do fit, and while they cataloged at about 31mm, an actual set measured 29mm. 614 pads are the next thicker at 31.5mm, and lastly the 614A pads which were the thickest at 33mm. Remember that measured J55 caliper + Astro rotor clearance is roughly 30.8mm, so you can see why pad choice becomes very important. You may end up getting a good combination by mixing and matching several different sets of 614 pads at the parts store to come up with two pairs that will fit. Yes, it’s that close!

For what it’s worth, the D153 pads have just about the same total surface area as the D614 pads, but the material is distributed a bit differently. Note that although the drawings below seem to show that the D153 pads are wider radially, most of it is placed towards the inside radius (hub side) and not towards the outside radius (outer edge) of the rotor. Brake pad material distribution is an issue that goes far beyond the scope of this article. You can learn more online at one of the many brake science articles such as this one: http://docsdrive.com/pdfs/ansinet/jas/2008/3583-3592.pdf



Figure 13: D153 pads on B-car rotor with 9C1 caliper.



Figure 14: D153 pads inside 9C1 caliper on B-car rotor; all mounting points line up.

I also spent some time tracing out pad layouts on top of one another. The results are shown below.



Figure 15: Inboard brake pad overlay D52 vs. D153 vs. D614



Figure 16: Outboard brake pad overlay D52 vs. D153 vs. D614
 

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Discussion Starter #9 (Edited)
Assembly and shimming

There are two places the Astro rotor will need to be shimmed to provide a perfect fit. The first is against the hub face to locate it laterally (or axially, depending on your point of view), and the second is around the hub register to locate it concentrically.

Another instance of production values and tolerances varying from catalog data is the axial offset of the Astro rotor. Given that it was an additional 6.4mm thick, the published numbers of the thicknesses and offsets of both the Astro and the B-car rotors led us to the conclusion that this extra thickness would be evenly distributed across the inboard and outboard sides. During test fitting, we found that most of the material tended to be biased towards the inboard side. Actual measurements seemed to imply that the published B-car rotor offset may be incorrect by several millimeters. This becomes a critical issue because the inboard pad must fit between the inboard side of the rotor and the steering knuckle’s mounting ears. The outboard pad depends only on the slack of the slider pins for its clearance. As a result, you will need to install 5mm disc brake spacers such as the ones shown below. These are readily available via Ebay or online for around $10-$15 shipped for a pair. The spacers shown in the Figure 17 are not listed as accepting the 5 on 5” bolt pattern in their sales literature, but actually do fit. Be aware that if you purchase this style spacer, you will likely have to open up the inner diameter to ~3.060” in order to fit the B-car hub register.



Figure 17: Disc brake spacer (5mm) mounted on cut-down B-car hub. Note that the inner diameter (ID) has been opened to match the B-car 3.060"

If you do not install these spacers, you will find that the Astro rotor crowds the inner pad area at the pad/caliper mounting ears and in extreme cases may also contact the inner shield mounting bolts and prevent you from installing the inboard pad.

[One other tech note after the article went to print: I discovered that one of the B-car hubs I cut down was SIGNIFICANTLY inboard relative to the other one by almost 3mm. I ended up adding extra shims to that one to space the rotor out properly. This could have been an oddball bearing race or an oddball rotor/hub. I do not know how prevalent this is, but be aware of it. In a pinch, you can take a pair of measuring calipers to a hardware store and find 5 stacks of washers with uniform enough stack height to work as shims. I kept tolerance to within 0.007" and had no run-out issues. Lest you question the feasibility of this approach, the washers are under compression load which is relatively easy for them to handle, and the car successfully road-raced with no problems. I brought a torque wrench with me, checked the torque on those lugnuts often, and did not encounter any loosening. ]

Remove the stock caliper, pads and rotor, and install the cut-down hub and spacer. Next, the second shim area comes into play – the concentric mounting. You have three options. One option is “lug-centric” – using the lug nuts to center the rotor. Astros use 14mm diameter lug studs while B-cars use 12mm, so it is necessary to add thin (about 1mm thickness) bushings that fit around the studs. We were unable to locate exactly what was needed, but a suitable sleeve can be fabricated by using McMaster-Carr steel-backed bearing PN 6679K17 (12mm ID / 14mm OD by 20mm long). This is too long as supplied and will require some lathe work prior to use. With careful cutting, you should be able to get 3 sleeves out of each piece, which will be enough to ensure the rotor is properly positioned.

Another route, which is “hub-centric” – using the hub to center the rotor much like GM uses the hub to center wheels. On the hub register itself, the B-body diameter is 3.060” while the four Astro rotors I obtained measured 3.084-3.088”, a difference of about 0.025” across the diameter, or 0.0125” on the radius. All you really need to do is locate the rotor until the wheel can be installed and the lugnuts tightened down. Once the wheel is tight on the hub, the rotor won’t be going anywhere. Shim stock cut to size and wrapped around the hub register will work well here. Use McMaster-Carr brass sheet PN 9011K8 (8” x 12” by .012” thick). This method will center the rotor long enough for you to assemble the caliper and then bolt the wheel on. You may notice the black material protruding from the hub in the picture below. When test fitting parts for this article, neither the shim stock or bushings were readily available, so I used several wraps of electrical tape, carefully cut so there were exactly enough layers of tape with no overlap at the ends. It sounds cheesy, but it works. I bolted the rotor in place using several lug nuts, and then installed the J55 caliper and 614 pads. The final assembly looks like this.



Figure 18: Astro one-piece rotor with J55 caliper and D614 pad on cut-down B-car hub.

If you use the hub-centric method, make sure to cut the shim material so that it doesn’t protrude beyond the outer surface of the rotor, so as not to interfere with the wheel mounting face.
The third method of ensuring the rotor is properly centered is accomplished by turning down the B-body hub diameter only enough to allow the rotor to slip fit over the hub; this will force the rotor to be concentric with the hub via the inside of the rotor hat, eliminating the need for shims or sleeves. This will require continued use of only one type of rotor (one-piece vs. composite) so that is something to keep in mind, but it’s an elegant solution.
A group of final installation pictures is shown below.




Figure 19: Stock (worn) 9C1 setup on top, Astro Rotor, J55 caliper, 614 pads, reused stock 9C1 slider pins on bottom.



Figure 20: Side views of Astro rotor, J55 caliper, 614 pads & reused 9C1 slider pins. Note tight clearances on inner pad.

One note: you need to make sure that your slider pins are fully engaging, at a minimum, the rubber o-ring inside the outboard ears of the caliper. A close-up of this is shown below. Do not attempt to reuse stock JB9 slider pins as they will be too short.



Figure 21: Caliper slider pin outboard engagement short of the minimum allowable. Note rubber o-ring is visible. This is unacceptable. The OEM 9C1 slider pins were cleaned up and reused.
 

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Discussion Starter #10 (Edited)
Other points - q&a

1. Why did you choose to recommend this method to upgrade my brakes? Answer: This solution is inexpensive, and although some initial machine work is required to make it happen, once the conversion is complete, any expected maintenance can be accomplished by purchasing readily available replacement parts.

2. Will this setup change my braking feel? Answer: No. Only larger-diameter rotors or more aggressive pads will do that.

3. How much weight does this add? Is it all in the rotor? Answer: I measured about 2.8 LBS difference per side (25.0 LBS to 27.8 LBS) when the hub, rotor, bearings, castle nut and washer were measured together. Only a small amount of that is attributed to the additional Astro hub face material. Most of it goes into the rotor. Dimensionally, the Astro rotor is 50% thicker in the vanes, 10% thicker on the outboard wear surface, and 5% thicker on the inboard wear surface.

4. Does this affect my track width? Answer: Yes. Each side gets spaced out 5.5mm (rotor hat thickness) + 5.0mm spacer = 10.5mm or 0.413”. This is slightly under 7/16”.

5. I saw that the Astro rotor is only 11.61” in diameter vs. the B-body 11.86” diameter. Is this a problem? Answer: No. In fact, all of the test-fitted D52, D153 or D614 pads in J55 calipers resulted in a perfect alignment along the outside radius of the rotor. The stock B-body rotor/pad setup has a rust ridge of roughly the same amount as the difference in radius.

6. Will this rotor keep me from boiling my brakes at the Nationals this year? Answer: Possibly. Based on the numerous scientific papers available online, brake boiling occurs primarily due to fluid heating. You can lessen fluid heating by using cast-iron calipers (aluminum ones are more susceptible to heat conduction, note that all stock B-car calipers including JB9, JA9 and J55 are cast iron), inner pads which have at least 12mm of friction material on them, fresh high-quality brake fluid, and larger rotors with the most airflow you can fit within your design/budget constraints. Compared to B-car rotors, AWD Astro rotors will heat up more slowly due to their greater mass/thickness and (most importantly) dissipate heat more quickly due to the larger vane openings. The other item to note is that rotors cool both inside AND outside at roughly equivalent percentages according to scientific research, since their hottest parts are located right at the wear surfaces. Directing air to the rotor area and using wheels that block airflow as little as possible (such as Impala SS or the N97 police-spec wheels vs. base-level Caprice wheels) will also help. It should be noted that numerous fluid dynamics studies of airflow around brake rotors have found that increasing the passageway size is what increases cooling, not directional or intricate vane geometry. Anything you can do to ensure that fresh air can get to into the center of the rotor and exit out through the vanes will be helpful. Real world situations being what they are, don’t kill yourself trying to make it perfect, just do the best you can.

7. Is there anything else I should do while I have everything apart? Answer: It would be a good time for cars with rear disc brakes to do the brake bolt mod. Discussion is beyond the scope of this article, but instructions and vendors can be found on the Impala SS Forum (http://www.impalassforum.com/vBulletin/).

This setup was in use on my Light Driftwood Metallic ’95 9C1 at the 2011 Impala SS Nationals. I had no problems after repeated lapping and then drove the car 400 miles home. I've now got almost 2000 miles on this setup with no problems.
 

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Discussion Starter #11 (Edited)
Parts list & cost

Here’s a parts list (prices as of winter 2011):
1. 1999 Astro AWD rotors ($40 each - 2 req’d).

2. J55 calipers ($15 each - 2 req’d). (Advance Auto Parts sells these as Fenco 18-4126 & 18-4127).

3. Cut-down B-car rotors (free, plus the cost of machining)

4. Longer wheel studs - Dorman 610-323 ($1.50 each - 10 req’d).

5. Lug-Rotor bushings – McMaster 6679K17 ($3.23 each – minimum 4 req’d).

6. Brass shim stock to center rotor (alternate method) – McMaster 9011K8 ($7.22 each – 1 sheet req’d).

7. (Optional): Castle-nut replacement with fine-adjustment setup:
Retainers – Dorman 615-154 ($3.50 each - 2 req’d). Replacement spindle nuts – Dorman 615-065 ($4.00 each – 2 req’d). Total - $15.00, plus the cost of machining.

8. (Optional for 9C1 & Impala) brake bolt mod – Ford Motorsport M-2450-A ($17.95 each – 1 req’d).


Total cost: $80 + $30 + $15 + $13 + $15 (optional) + $18 (optional) = $138 + options, core charges, shipping & taxes (as required) & machining.


Necessary ancillaries you should budget for: New pads, high-quality brake fluid, brake cleaner.


Now that’s a budget brake setup! As has been stated, none of this could have happened without Jay’s detective work. Thanks Jay!




Figure 22: Final assembly after components were painted. (rotor is BBQ painted, Hub and Caliper were painted with caliper paint from Autozone and then cured for 12 hours in an oven. Random factoid: The rotors I road-raced with were actually sourced from a local u-pull junkyard for $10 apiece, in Syracuse, NY no less!



Figure 23: My 9C1 on Waterford Hills in August 2011. My dad and I put 60 miles on the car at the track that day, then drove the car 400 miles home. Picture courtesy a1awind.


Figure 24: Turning into the curve. Road racing is so much fun! Picture courtesy a1awind.
 

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No, as I'd have to either buy new rotors and then cut the rotor part off, or locate junkyard cores (cheaper) and then clean them up. By that time, it wouldn't be cost effective.

Just do what I did - use your old worn-out B-car rotors and cut them down. Be aware I used both methods; the brake lathe is significantly quicker but you have to cut carefully because the bits on them are not designed for plunge cuts. The sawzall cutting method took almost an hour for one rotor.
 

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Great Post

This was very informative! Really enjoyed reading this. Will be a future mod I hope. Thanks!
 

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Figure 23: My 9C1 on Waterford Hills in August 2011. My dad and I put 60 miles on the car at the track that day, then drove the car 400 miles home. Picture courtesy a1awind.


Figure 24: Turning into the curve. Road racing is so much fun! Picture courtesy a1awind.
Heavy positive camber on the outside front wheel there! Yeesh! Were all the front end parts relatively fresh? What kind of alignment were you running? I hope that's not all just due to flex! However, looks like the inside front wheel has some heavy negative camber gain, so maybe it is?

Anyway, serious thanks on the write up! This might be just the ticket for the occasional hot lapper such as myself not looking to trade an arm and a leg for a little less brake fade.
Well done!
 

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Discussion Starter #18 (Edited)
I should have made mention that we had no heat-related brake fade the whole day, and anyone who was there can testify that this car was on the track quite a bit. Brake fluid was fresh ATE Super Blue.

Now, we didn't exactly drive it at 100% either, but Waterford Hills is a tight track so it's typically gas - brake - gas - brake and the car was on the track for 20-30 minutes at a time. Then we'd come off, switch drivers, and get back out there.

The alignment is a typical street alignment to factory specs (basically neutral camber and toe). The front end was rebuilt about 24k miles ago with a ProForged predecessor kit, mostly polyurethane but some rubber as well (I think UCA bushings). The rest of the suspension was all stock 9C1 with Bilstein 1104/0929 shocks riding on evenly worn-out Yokohama Avid ST 255/60R15s on Suburban 15x8 steel rims. The pictures here are showing the car going probably 35mph at nearly the edge of grip. The front tires' tread blocks distorted like somebody took a blowtorch and melted them. I should post those pictures!

Next time I do an event like that, I might add some shims to the UCA bolts when I get to the track to get a little more negative camber, then take them back out at the end of the day before I drive home.

Man that event was fun. I hear the ISSCA Nats is back in Detroit for 2012 - if you get the chance to go, go!
 

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Joel:

Awesome write up. I have looked into the Astro suspension in the past for B-car uses as well... though it was to consider building an AWD Caprice :)...

I totally missed the AWD pre-02 stuff. When I looked, I looked at the 02+ setup, which is 6-lug, but uses 99+ Silverado 13" brakes with 2-piston iron calipers).

Anyway, did you consider the possibility of using the AWD knuckle completely? I wonder if they use the same ball joint and steering arm points?? If so, you can use the complete Astro corner assembly and avoid nearly all the machine work. The only thing I would recommend is to cut down the outer CV joint, and use the splines and thread to maintain pre-load on the unitized bearing.

Now, I just need to figure out how to convert either option to 5x4.75 for my 79, or change over to 5x5. I happen to have a set of old b-car rotors I cut down MANY years ago to build my own brake kit..

On a personal note, where in Syracuse do you live? I lived in Manlius (Go F-M Hornets!!) when I was a kid, but now live in Motown. PM me if you'd like.
 
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