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That's probably do-able, silly as it sounds, I'm trying to avoid as many custom one off parts as I can so if something breaks I can just replace it instead of having to make/modify. Axles are kind of a serviceable item so if I can find a 6x5.5 that slides in, that would be preferred.

If I find anything, I'll post it up here.
 

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Guys on the Astro forum are apparently using full-size truck calipers all the time.
 

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That's probably do-able, silly as it sounds, I'm trying to avoid as many custom one off parts as I can so if something breaks I can just replace it instead of having to make/modify. Axles are kind of a serviceable item so if I can find a 6x5.5 that slides in, that would be preferred.

If I find anything, I'll post it up here.
We are on the same mission.

This may be more easily accomplished on a wagon as opposed to a Fleetwood. I spent some time looking at the length of 8.5 axle shafts in other vehicles, and all of them are longer than the 9c1/Fleetwood shafts. The rear skirts on the Fleetwood already present a problem for those of us who want to run wider tires in the back. It seems like no matter what way you go, you have to modify the axle shaft in some way. It's just a question of if you would rather drill the b-body shaft or shorten one of the other shafts.

As you said, axle shafts are only kinda wear parts. It's not one of the more likely parts to break on a road trip. If everything else is a matter of bolting on OEM parts, I will be perfectly content with welding and re-drilling.

Based on the reading I've done over the past couple of days, I think I can say with confidence that the 3-bolt hub mounting pattern is a corporate GM thing. The hubs from the S-10, Trailblazer, Astro, and full-size trucks will all physically bolt to the 2003-2005 Astro knuckle.

Something else I discovered earlier is the S-10 Calipers are interchangeable with those on my 85 Eldorado, which uses smaller rotors. I have an Eldorado caliper and a b-body caliper sitting on the table in front of me, and the b-body caliper is much, much larger than the Eldorado caliper. What I'm getting at, is that I realized Bill was right about the S-10 calipers being smaller. The fact that they have 2-pistons means nothing
 

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The biggest question mark in my head right now is the rotor diameter limitations of the Astro knuckle.

I've confirmed that the Astro calipers are the same as all of the full-size GM trucks, vans, and SUVs. However, I'm not sure if they are an upgrade over ours. Our single-piston front calipers have a pretty large piston, with a contact surface area of about 6.6 square inches or so. The truck calipers, the base C5 calipers, and the Willwood calipers all use dual 2" pistons, which equates to a bit over 6.2 square inches of surface area.

Other people know more about this than me. Maybe there is some advantage to spreading out the load between two pistons, but we definitely wouldn't be gaining any surface area with the aforementioned calipers. I can buy four-piston first gen CTS-V calipers on Rock Auto for under $140, and they have the V logo on them. I would love to use them on my Fleetwood, but I'm not sure if they will bolt up. Again, I still need to figure out what rotors I will be able to run.

I think my ideal setup would be 2003-2005 Astro knuckles, Astro hubs with 6 x 5.5 pattern, 13" truck rotors, and the CTS-V calipers. I hope I can make it work.
 

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The biggest question mark in my head right now is the rotor diameter limitations of the Astro knuckle.

I've confirmed that the Astro calipers are the same as all of the full-size GM trucks, vans, and SUVs. However, I'm not sure if they are an upgrade over ours. Our single-piston front calipers have a pretty large piston, with a contact surface area of about 6.6 square inches or so. The truck calipers, the base C5 calipers, and the Willwood calipers all use dual 2" pistons, which equates to a bit over 6.2 square inches of surface area.

Other people know more about this than me. Maybe there is some advantage to spreading out the load between two pistons, but we definitely wouldn't be gaining any surface area with the aforementioned calipers. I can buy four-piston first gen CTS-V calipers on Rock Auto for under $140, and they have the V logo on them. I would love to use them on my Fleetwood, but I'm not sure if they will bolt up. Again, I still need to figure out what rotors I will be able to run.

I think my ideal setup would be 2003-2005 Astro knuckles, Astro hubs with 6 x 5.5 pattern, 13" truck rotors, and the CTS-V calipers. I hope I can make it work.
What exactly are you looking to do with the car? Are you towing? Open track?

Sent from my moto z3 using Tapatalk
 

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My Fleetwood is going to be a street toy that will see some occasional track use.
 

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Shop owner friend of mine said (just like Navy Lifer recommended) that Moser will build custom axles for well under $200/axle. Given that new stock axles are ~$100 each, one can't spend too much time looking for the unicorn axle that is the same except for bolt pattern.
 

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I've managed to dig up a couple more OEM calipers that are potential bolt-ons. The GM 3500 series vehicles and Cadillac DTS commercial vehicles were available with absolutely massive dual 2.4" piston front calipers. That is over 9 square inches of contact area.
 

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Front to rear balance? How is this any different from doing any other big brake kit?

Keep in mind I'm not operating under the same constraints that you and Sherlock generally do. I will be using 22" wheels and deleting the entire ABS system. Not to mention, I am having loads of fun researching all of these various possible combinations.

A couple more things I have learned: the 2019+ trucks were available with 4-piston fixed calipers, and 13.5" rotors. Also, the Caddy XTS commercial chassis shares a long list of parts with the full size trucks. 6-lug hubs, rotors, calipers, etc. are all the same. There is also a 4-piston Brembo caliper that is unique to the XTS that says Cadillac on it. According to Rock Auto logical deduction, it fits the truck/Astro spindles, but of course sometimes Rock Auto is wrong. Further verification is needed.

I don't want to derail this thread too badly. I will have to make a new 6-lug conversion thread once I actually get into this. Unless a certain someone beats me to it. :cool:
 

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"Front to rear balance? How is this any different from doing any other big brake kit?"

Not to speak for Bill, but,,,,
He is eluding to you are going to step up the rear piston area at least by the equal percentages
Also, the master by the same amount.

Compared to other big brake kits.
They are typically similar if not less piston area.
I have 4 piston Brembos all around and their areas are less than the production piston areas.
My calipers are from a more rear weight biased car but the B (ESPECIALLY THE WAGON) can stand more rear bias as we all know
 

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and I'm still wanting to understand the reference to 9 square inches of "contact area" - pad size, or piston area? It matters. Brake upgrades are really only as good as the tires/contact patch and surface conditions (ie. coefficient of friction) in the operating environment.....big brakes don't/won't necessarily (nor should it be assumed) provide shorter stopping distance - the idea is that greater rotor mass provides a larger operating envelope - repeatibility - compared to the stock brakes. But I probably don't need to tell you that....just re-stating for others to understand.
 

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I was referring to the diameter of the pistons. I have no idea if that's the correct way to measure anything. I do know that giant multi-piston calipers are definitely going to have pretty big pads, too.
 

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for reference, the OE B-body caliper is 2.9375 (2-15/16) which provides 6.77 square inches of piston area. Your truck caliper (2.4" dual pistons) runs 9.04 square inches of piston area. That's 33% more piston area, so it will really screw with the front/rear balance, and the fluid displacement requirement for the master cylinder is going to be quite different to keep pedal travel and rear fluid demand anywhere near what is needed to have the same braking "feel" as the original combination - not the it was perfect, with so little rear braking with the un-modified combination valve. Most of the "big brake" systems actually have LESS total piston area compared to stock B-body, but due to the rotors being clamped at a larger radius, the available brake torque is equal or greater (compared to stock) - and in most cases, the brake pads used with a big brake setup are more likely to be higher friction coefficient than OEM B pads, offering even greater brake torque.
 

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Aren't these just gorgeous? These are the XTS brembos. They would be perfect on a Fleetwood.
 

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Matt, there are a number of "moving parts" to this approach. The photo shows a production brake package that is a mix of OEM parts that fit various platforms - by PN identity, an individual caliper is going to fit right or left, and mount in lead or trail (ahead of or behind axle centerline) on a specific vehicle. The same basic caliper is used on other Cadillac (Alpha ATS/CTS), Corvette and Camaro SS (Alpha models), where the mounting is "trail" - which is correct for B or D-body (GM tall spindle) application.

In the case of the Cadillac caliper in the photo, it would be possible to simply swap sides of the vehicle - just so the bleed ports face up - since the pistons are the same size. The only thing that could differ would be the hose attachment angle using stock hoses, which probably would not work correctly anyway. Aftermarket performance hoses take care of that potential issue.

All variants of this caliper are made to fit 345mm rotors - there's no external fluid transfer line, as found in earlier Brembo designs, common piston diameter for all positions (4-piston) instead of differential bore, and painted for the specific application, hose routing specific to the vehicle (RWD vs FWD), etc. All use 14mm mounting bolts (M14x2.0) to secure to the suspension.

Word of caution--there are similar-looking Brembo front calipers made to fit 321mm rotors, used on Cadillac ATS, which would be an improvement over stock B-body, but given the advantages of the 345 package, if someone is going that route, the larger setup is much more desirable. The one rub in this - the 321mm setup will probably fit inside a stock 17" SS wheel, where the 345mm package will require a minimum 18" wheel. None of these brakes will fit inside a stock 15" wheel. The point is - the rotor diameter determines which caliper can be used.

Brake pads for this caliper family in GM production are either FMSI D1001 (ATS w/321mm rotor) or FMSI D1474A (with small damper weights). The pad specs are interchangeable, and very common on a wide range of fitments beyond GM vehicles, so finding service pads from OEM or aftermarket is no problem at all.

This link shows the XTS front brake package in your picture, clearly in the "lead" mounting position): 2019 XTS Sedan - V-Sport Platinum Trim | Cadillac

Attached photos are same caliper in Camaro trim, for 345mm rotor.

The rotor in your picture is 345mm - 345x30 - with 120mm wheel stud pattern and about 67mm center bore. What I don't have is the inside diameter, or put another way, the maximum hub flange diameter that will fit inside the rotor without some amount of modification (reduction in hub flange size), if it may be needed.

The other moving part in this is to understand that there are several 345x30 rotors with minor offset (hat height) differences and stud pattern/center bore sizing. Using Buyers Guide information (at Rock Auto), it's possible to figure out which is used on which vehicles, but it does seem that GM has chosen 345mm as a common size for a number of platforms. Some applications used the GM DuraLife rotor treatment in production, others may not have.

Rotor examples: all 345x30

Caprice PPV - may not have DuraLife treatment (Zeta platform would also fit 10-15 Camaro or G8, but was not a production configuration)

Buick Regal GS - same as PPV, different PN

Cadillac XTS-V - same as Regal (as shown in your picture)

Camaro SS (2016+) - different offset/hat height (Alpha platform)

Corvette C7 (120.65 & 70.5 center bore)

Corvette C8 (120mm stud pattern)

For use on B/D platform, the rotors will require machining - no big deal - and the hub diameter (inside hat ID) is still an unknown. There is a source (link below) offering a modified GM tall knuckle/spindle, hub and bracket package that should allow the right mix of parts - calipers & rotors - to work. A DIY effort isn't out of the question, but it will require some experimentation to learn which is the correct mix of parts, whether a new hub will be required, or whether a modified/cut-down stock hub (for the ABS ring) can work, is what this comes down to. The other thing about the modified knuckles from the linked source is that they would need to be from a late B-body to include the ABS sensor mounting pad.

1979-96 Tall Spindle Brembo Partial Kit CP Alpha red caliper - 345.JPG Camaro Alpha caliper - 345.JPG
 

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This is the rotor that I have my eye on at the moment: More Information for ACDELCO 18A82458A

The dimensions are basically the same as the normal truck rotors that have been used for years, except this one is 13.5" (343 mm) instead of 13.0". It's similar to the 345 mm rotor that you are referring to, except 6-lug. I think I can use just about any truck caliper that I want with these rotors, and I know they will mount to the hub, of course. The factory calipers that come with these rotors are 4-piston fixed calipers that cost only $71 on Rock Auto, with no core. The dually calipers would also be an option, or even the standard-issue dual-piston calipers that come on basically everything GM has made in history.

Speaking of those standard-issue calipers, GM uses them on the rear of the dually trucks. They are normally front calipers. As I ponder rear brake options, using these calipers in combination with a standard-issue 12" front truck rotor may be a safe option. Those calipers and rotors are used together on all sorts of vehicles.

Of course, none of this matters unless you are converting to 6 lug.
 

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Here's another combination that could be employed - 2nd generation CTS J55 (V6 models) - core fee puts caliper price at about $90, 2-piston cast iron floating caliper.

More Information for CARDONE 18B5117

J55 Caliper for CTS - price is slightly more than your truck package. Same bracket/mount dimension as the Brembo setups.

Buyer's Guide : CARDONE 18B5117 Caliper

CADILLACCTS2008-2014

More Information for ACDELCO 18A2652A

345 rotor used with J55 CTS brakes - same specs as shown below

Buyer's Guide : ACDELCO 18A2652A Rotor

BUICKREGAL2014-2017
CADILLACCTS2008-2014
CADILLACXTS2013-2019
CHEVROLETCAPRICE2011-2017
 
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