OEM parts bin fun

[Caddylack]

The primary focus of this thread will be the discussion of converting the B-body to a modern hub and slip-on rotor setup using OEM parts that are affordable and easy to find. From there, the secondary focus will be the discussion of multi-piston brake calipers, larger diameter rotors, and bolt pattern changes. Let's see what we can do to freshen up an old chassis.

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Things that we know:

• All 91-96 B-body and all 85-05 RWD Astro/Safari use the same front upper control arm
• All 85-05 RWD Astro/Safari use a front lower control arm that is virtually identical to the 9c1 lower that uses a 5/8" ball joint... the only difference is the steering stop, which may be only cosmetically different
• All 03-05 Astro/Safari use the standard GM truck caliper of that era, which features dual 2" pistons, like the C5 Corvette
• The dual-piston truck caliper likely requires a minimum 16" wheel

[li]All 03-05 Astro/Safari use slip-on rotors in the standard 6-lug truck pattern; we are likely only interested in the RWD knuckle[/li]
[li]Pre-2003 Astro/Safari used the same 5x5 bolt pattern as our cars; AWD models used a slip-on rotor, while RWD models used a spindle that is similar to ours, however with a larger bearing size[/li]
[li]Based on the above, the entire 85-05 Astro/Safari RWD front end is a direct bolt-on for our cars; 6-lug conversion is just as simple as transplanting the van parts onto the b-body[/li]

• OEM 6-lug truck rotors are available in diameters ranging from 12" to 14"

• NOTE THAT YOU WILL LOSE ABS unless you figure out how to make it work

[li]If you want to run a slip-on rotor and change your bolt pattern, the easiest way is to use the 03-05 Astro/Safari RWD knuckle; this enables you to use any modern GM hub that you like...[/li]

• For the 6x5.5 truck pattern, use the 03-05 RWD van hub

• For the 5x4.75 Vette pattern, use the Blazer/S-10 hub

• If you want to run a slip-on rotor and keep 5x5, use the pre-2003 AWD van hub

[li]You have 3 different options for changing your rear bolt pattern to match the front:[/li]

• The best option is to just buy new axle shafts in the pattern of your choice; Moser is a safe bet

• The next best option is to find a pair of axle shafts from another GM 30-spline rear and have a machine shop modify them so that they are the correct length, etc.

• If you are on a tight budget, your other option is to get your existing axle shafts re-drilled

[li]As far as rear disc conversion, you can use the backing plates and calipers from virtually any GM 8.5" rear, with the exception of vehicles that use the larger axle housing, such as the wagon, etc. The most common will be 97+ Blazer/S-10 4WD and 02+ Trailblazer, Envoy, etc.[/li]

• Again, ABS is not taken into consideration

• Parking brake setups will vary from vehicle to vehicle, and that is something else I have not explored; I am speaking only about physical fitment of the brakes themselves[li]

[li]Outside of GM, the most common vehicles that utilize the 5x5 pattern are Mopar products such as the Grand Cherokee, Pacifica, and mini-vans.[/li]

• The 3rd generation Grand Cherokee uses a slip-on rotor in 5x5 pattern that is 12.9" in diameter and 2.1" in "height"; this is within about 1/10th of an inch of the height of the GM truck rotor

• The Grand Cherokee rotor, as well as the rest of the Mopar rotors, will require slight opening of the center hole, as Mopar uses a standard size that is slightly smaller than the standard 3.06ish used on many GM vehicles

[/ul]
Unanswered questions:

• What is the maximum rotor diameter for the unaltered 03-05 RWD Astro-Safari knuckle and the dual-piston truck caliper?
• How much more can be gained by minor clearancing?

[li]Will the center bore of the 03-05 RWD van knuckle need to be enlarged to accept the earlier AWD hub?[/li]
[li]What kind of practical "plug" can we come up with to fill the splined hole in the AWD hub?[/li]
[li]What other calipers will easily bolt to the 03-05 RWD Astro/Safari knuckle?[/li]

• Brembos?

[/ul]
Why this stuff is relevant and important:

• The B platform is objectively outdated (obviously)
• Aftermarket support for our cars is dwindling
• This could be a motivation for switching bolt patterns

[li]Our cars are becoming more and more rare, while other GM products such as trucks and vans are still a dime a dozen in any junkyard; in many cases upgrading to "parts bin" stuff will be cheaper and easier than sourcing "genuine" B-body parts[/li][/ul]

[Caddylack]

I figure I should share that one of my good friends just got his stock B rotors machined into hubs that fit the SRT Jeep front rotors.

As mentioned previously, the center bore is slightly smaller on the Jeep rotor. You could open the center bore, but machining the hub allows you to use unmodified rotors, which is quite advantageous.

He is using Camaro Brembos with mounting brackets designed for this exact application.

He said he is using 330 mm rear rotors, which I believe would be a front rotor from a late-gen 5.7L Jeep.

The only issue I can spot so far is the increased track width up front. I will post pics when he is finished.

[Caddylack]

Mar 12, 2022 5:07:43 GMT -6 Caddylack said:

He said he is using 330 mm rear rotors, which I believe would be a front rotor from a late-gen 5.7L Jeep.

The only issue I can spot so far is the increased track width up front. I will post pics when he is finished.

Just an additional note: That 330 mm 5.7 GC rotor is almost 3/4" taller than the OEM rear rotor. It will be interesting to see how that works out.

I already let my buddy know that the Pacifica front rotor is also 330 mm, but it is closer to OEM height.