So I've done some research over the last day or so...summary of my findings is below - apologies if this is "common knowledge" and please correct me if your experiences conflict with mine.

Commercial Chassis front spindles
- Use a "Set 5" inner front wheel bearing which has a 1.375" spindle diameter whereas the wagon/sedan spindles use a "Set 6" which is 1.250"
- The outer wheel bearing is common between the two - "Set 3" with a 0.8437" spindle diameter (for the later cars)
- Need to verify if the commercial chassis hub bearing spacing is different than the wagon/sedan - is it just a larger inner bearing or are there other dimensional/positional differences as well
- Tie rods (both inner and outer) have different part numbers vs the wagon, but share the same 11/16-18 thread at the adjuster
- Need to verify if rear dust shields are same between wagon/sedan and commercial chassis. If so, there's a chance at one of the big brake kits being able to be used
- Need to verify if the Commercial Chassis spindle has provisions for ABS sensors - is a must have for my application.

At this point I'm considering the Commercial Chassis front brakes a "nice to have" - I'd like to have the larger wheel bearing size, but in reality, it's only 300lb heavier than stock (on the front end) which doesn't feel like a lot. So if I can make one of the big brake kits work with the larger spindle bearings without reinventing the wheel, then I'll probably do that, but otherwise guessing it will be fine as is.

The hearse is 2900lb front and 3100lb rear - empty with a full tank of gas
The stock RMW is 2360lb front and 2560lb rear with a 1/2 tank of gas
The Duramax RMW is 2650lb front and 2750lb rear

Commercial Chassis 9.5" 12/14 bolt rear end
- Used in many GM trucks through the late 90's - heavy 1/2 ton and light 3/4 ton
- Is a semi floating design (C-Clips) and has 14 bolts in the cover but 12 bolts on the ring gear
- Big disc brake kits for these are not common, but need to look into the truck market closer and see if anything adapts - Possibly a factory 454SS application used 5x5 bolt pattern and same rear end
- Parking brakes in almost any wagon rear disc brake upgrade are not common - Baer has one and the WRDC from Navy Lifer seem to be the only ones I've found.

I'm more nervous about the 8.5" 10 bolt and surviving long term sustained loads - we'll have to see how/where it measures up unless someone has measurements of one of these rear ends (9.5" 12/14 bolt from a commercial chassis).

I think I'll go with a crown vic type RSB that mounts to the axle and frame (skipping the control arms) - regardless of which rear axle is used.

 

Commercial Chassis front spindles
- Use a "Set 5" inner front wheel bearing which has a 1.375" spindle diameter whereas the wagon/sedan spindles use a "Set 6" which is 1.250"
- The outer wheel bearing is common between the two - "Set 3" with a 0.8437" spindle diameter (for the later cars)
- Need to verify if the commercial chassis hub bearing spacing is different than the wagon/sedan - is it just a larger inner bearing or are there other dimensional/positional differences as well
- Tie rods (both inner and outer) have different part numbers vs the wagon, but share the same 11/16-18 thread at the adjuster
- Need to verify if rear dust shields are same between wagon/sedan and commercial chassis. If so, there's a chance at one of the big brake kits being able to be used
- Need to verify if the Commercial Chassis spindle has provisions for ABS sensors - is a must have for my application.

At this point I'm considering the Commercial Chassis front brakes a "nice to have" - I'd like to have the larger wheel bearing size, but in reality, it's only 300lb heavier than stock (on the front end) which doesn't feel like a lot. So if I can make one of the big brake kits work with the larger spindle bearings without reinventing the wheel, then I'll probably do that, but otherwise guessing it will be fine as is.

I'm more nervous about the 8.5" 10 bolt and surviving long term sustained loads - we'll have to see how/where it measures up unless someone has measurements of one of these rear ends (9.5" 12/14 bolt from a commercial chassis).

If the chassis you're getting does not have ABS, (assuming model year is 91 or newer), the front end is going to be J55. If it has ABS, it's the same as all other "B" applications, right down to 9/16" lower BJ. 1/2" wheel studs is the other giveaway for J55.

See photos below--I do have a pair of new-in-box J55 knuckles - 18021054 & 18021055. Lower ball joint is 5/8", and the casting is otherwise identical to JA9 for 95-96 9C1. Only differences are the larger spindle pin for Set 5 inner bearing, the tie rod taper, and the ABS sensor bosses are there, but blanked--it would require a machinist to bore the hole in the casting and thread the hole for the sensor retaining screw.

I'm confident there's sufficient material on the J55 rotor to cut the step on the back to add the 34T ABS tone ring from a standard 91-96 B-body rotor.

I haven't read the entire thread to grasp what your objectives are, so it's not clear what would be of the most benefit/bang for the buck to get you there. I do also have some modified original 9/16" ABS knuckles (18021052 & 18021053), ready for 5/8" lower ball joints, if that helps.

I see that HD12 and Astro mod have both been mentioned. HD12 uses the KORE3 billet HD hub that also is part of their big-brake kits. Astro uses a cut-down stock rotor, turned into a hub. Both are standard Set 6 inner, Set 3 outer.

The dust shield holes on the J55 knuckle are the same, so everything is there to do something "big brake", but it would take a cut-down J55 rotor, or a custom KORE3 hub for the larger inner bearing--and I still don't know the answer as far as inner/outer bearing seat distance being the same or different.

One last thing--if you stay with the B-body knuckles, for improved strength, probably equal to J55, get the bearing pre-load spacer kit from KORE3.

I can't help with the rear axle--the wagon 8.5" is pretty beefy, with 1.6" diameter axle shafts at the bearing journal, compared to 1.4" for sedans. Swapping in a Limo 9.5"--no idea where that takes you. WRDC takes care of the park brake function, if it was not clear.

Photos 1-3 are of the FW non-ABS knuckle for J55 brakes. The area for mounting an ABS sensor is blank.

Photos 4-6 are of the standard B-body knuckle with the provision for ABS, and JA9/JB9 or JM4 spec brakes. The area for mounting the ABS sensor is clearly different, as it has been machined to accept the sensor and bolt.

Same casting, minor machining differences for tapers & ABS sensor, and the spindle pin is larger at the inner bearing on the J55 version.

 

ABS can be added to J55 limo brakes, but Navy Lifer's HD12 kit is likely a better solution if ABS is required.

Don't remember if
the Astrafari front brake upgrade
has bigger front wheel bearings. It does improves front rotor ventilation [but not rotor diameter], and also keeps ABS.

Is it of any help to mention that the Cadillac Fleetwood V4P 7000lb tow pack option came with 4 wheel ABS, the same brakes, the same front suspension kit, and same axle assembly as any & every Caprice LT1-V92 sedan?

Said another way, the Cadillac Fleetwood V4P
did NOT use the wagon's rear assembly with its thicker tubes and axles
did NOT use the 9.5" ring&pinion
did NOT use the J55 [front or rear] brake package
did NOT use any limo suspension upgrades whatsoever
and yet, somehow, still managed a 7000lb tow rating.

Think the GVWR for 96 Impalas SS is about 5100lb, he GVWR for V92 sedans is about 5300lb, and the GVWR for wagons is about 5700lb, but whether that's for V92 wagons or 2.56 wagons I don't know.
Don't know the GVWR for Fleetwoods V4P.

 

Marky, I googled this off MotorTrend and it looks like 12,100, - which sounds about right given the car's weight and 4 fat old bluhairs. Adding to your point I considered the V4P ain't nothing more than a Brougham with belt fans, stiffer tranny line pressures and different rear gear. Also, urban legend I've read is the Impala SS tow capacity was rated lower than otherwise due to its wheels.

 

Marky, I googled this off MotorTrend and it looks like 12,100, - which sounds about right given the car's weight and 4 fat old bluhairs.
Adding to your point I considered the V4P ain't nothing more than a Brougham with belt fans, stiffer tranny line pressures and different rear gear.

Don't forget the shift strategy.
V4Ps' normal shift points were set to prevent pensioners from needing to access a separate 'Tow/Haul' shift map.
In so doing, V4P's BARELY avoided the CAFE Gas Guzzler penalty - by 0.1MpG.

Anyone whose V4P has been reprogrammed with the understanding that towing was no longer on the menu, gained about 2-4MpG when driven conservatively.
(Why GM did not bother with a 'Tow/Haul' mode button, is lost to posterity …)

Also, urban legend I've read is the Impala SS tow capacity was rated lower than otherwise due to its wheels.

Lack of belt fan, lack of sidewall margin to protect the wheels, lack of spring travel margin.
(A set of 235/65R17 (103), 255/60R17 (105), or 275/55R17 (109) would have enough sidewall margin, but then the springs would need to be as tall as 9C1 springs, ruining the SS aesthetic.)

 

Awesome info guys, Thanks a lot for sharing! I'd seen the Astro Brake mod earlier, but was one of those things where when you read it a 2nd time (with more background knowledge) you get a lot more out of it .

One of the little tidbits of info I gleaned from the write-up was this:

..........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...........

This might be a good cheap solution if I decide to put the large hearse spindles on the wagon to get tone rings for the ABS. I don't have a rear ABS to worry about so no problems there and I'm pretty sure that the 2012 ABS is looking for 56 tooth reluctors (though it seems to be just fine with the 36(?) tooth wagon/sedan rings).

Also great to learn about the 12k gross, 7k net weight ratings on what is effectively the 8.5" 10 bolt rear end and factory wagon/sedan front brakes. That gives me confidence that the "do nothing" option might be more viable (if not as much fun ).

Another little tidbit that I stumbled upon is that 2006-2009 Chevy Trailblazer SS's came with the GM 9.5" 12/14 bolt rear end with factory disc brakes. This would provide a basis for rear discs and parking brake on the commercial chassis rear end. Still TBD if the commercial chassis width and such is compatible with the wagon. I was incorrect in my above post about the Chevy 454SS trucks - those have this rear end, but drum brakes.

Trailblazer SS rear discs specs
Diameter (mm) 324
Height (mm) 85.1
Nominal Thickness (mm) 20
Hub Hole Diameter (mm) 97.79
Number of Holes/Studs 6
Bolt Circle (mm) 127

The diameter is good, thickness is a bit thin compared to some of the aftermarket options and the 6 bolt pattern is a "bolt in" issue. Guessing that this would machine out to a 5 bolt just fine.

Other than being relatively ugly behind a 22" wheel, is there a significant performance difference between the commercial chassis big drum brakes and any (wagon, sedan, etc) of the rear disc brake options?

One more week until I can get some hard measurements on the commercial chassis and then finally bring this idea in for a landing.

 

Ok - In short, after all the discussions and considerations, I'm going to follow the advice of everyone here and exercise the "Do Nothing" option.

Given the above GCVW info, that the 8.5" 10 bolt in the wagon is already a beefed up version (30 spline axles, larger wheel bearings, etc) and the brake options are readily available for the wagon (and not for the commercial chassis), I think the best thing to do is run it as it is. Front brakes would be upgraded to something larger than the J55 brakes anyway so not much point in putting those on. Rear brakes would be tougher with the 14 bolt (though it looks like Trailblazer SS uses the same rear end with factory disc/parking brake). I am compromising on the front inner wheel bearing and spindle diameter. If it becomes a problem down the road, there are several options to deal with it at that time.

The 9.5" 14 bolt is more/less a "Sedan" rear end. Why they did this on the commercial chassis, no idea. The spring perches, LCA mounts, Shock Mounts, frame rails, overall flange/flange dimensions, etc are all 2-3" narrower on the commercial chassis as compared to the 8.5" 10 bolt on the wagon. The 9.5" 14 bolt should more/less bolt into a sedan though and be a killer tough rear end for low $$ (compared to building a 8.5" or going to a Ford 9" or something like that).

Things that would have to change or be modified on a wagon to install a 9.5" 14 bolt from a commercial chassis
- No rear ABS provisions
- ~3" narrower flange to flange width
- Brake drums will hit frame as suspension compresses on wagon so would need to notch the frame (a lot)
- Use soft rubber LCA bushings and pull them in or re-locate LCA mounts on the frame inward 1.5" per side. Can't widen LCA mounts on axle to match the wagon frame, will run into backing plates.
- Relocate spring perches ~1.5" wider on each side of the axle (there is room for this, barely)
- The rear end cover will be nearly touching the gas tank

If I'm going to go to that much work, I may as well put a 10.5" 14 bolt in out of a 1 ton truck - full floater design, front and rear pinion bearing, rear disc brakes, won't even sneeze at the power/torque this duramax will make or the loads it will haul. Just need to weld in the control arm mounts and buy a set of high ratio (low number) gears.

I didn't dig into the front as much, but it looks pretty plug and play
- No front ABS provisions
- Might need to change tie-rod ends and lower ball joints, but should be a direct exchange
- I didn't measure bearing spacing or anything else on the commercial chassis.

Thanks to everyone who provided ideas and opinions on this, I really appreciate it. I hope I have been able to help you out with some solid info and reasoning for any future applications.

 

Hey guys sorry I’m late to the party. I have a 94 fleetwood brougham with stock gearing and was wondering what would take to get 3.73s would be like. I found a 93 fleetwood limo in a junk yard close by and believe it has that gearing. I’m guessing since the b body can be done, would it be an easier to swap the rear end in a d body brake to brake? I don’t see my self affording gears any other way. Since it’s the bigger rear I’ll need a new driveshaft/ modify from what Ive read. What else could I be missing?

 

Hey guys sorry I’m late to the party. I have a 94 fleetwood brougham with stock gearing (2.93) and was wondering what would take to get 3.73s would be like. I found a 93 fleetwood limo in a junk yard close by and believe it has that gearing. I’m guessing since the b body can be done, would it be an easier to swap the rear end in a d body brake to brake? I don’t see myself affording gears any other way. Since it’s the bigger rear I’ll need a new driveshaft/ modify from what Ive read. What else could I be missing?

If you have in fact found a 93 Fleetwood (RPO V4U), the good news is it should have RPO GT4, which is 3.73.
You can confirm by turning the driveshaft once, & watching the rear tires turn extremely close to 3 & 3/4 times.
The bad news is those gears are 26yrs old, & have sat idle for whoknows how long.
Did the limo's 3.73 come with a limited slip differential? If not, you'll want the tallest AND widest rear tires / absolutely largest rear contact patches possible, to mitigate the lack of a posi:
255/70R15, 255/65R16, 255/60R17, 255/55R18, etc. You already know 235 width tires fit just fine -235/75R15, 235/70R16, 235/65R17, 235/60R18, etc.
275 width tires are harder to find, more expensive, have sucky rubber compounds, and will force alterations to those removable rear wheellwell thingies.
(Any tire taller than 29" will probably need custom- or adjustable length rear control arms.)

V4U's J55 rear brakes are nonABS, that's only a downgrade if you care about ABS. Don't know if front ABS keeps working if rear ABS quits …
Limo rear brake drums [and shoes] are larger than normal civilian rear drums, so upgrade there. Definitely compare those brake lines!
You may also need to take - or replace and use - the limo's master cylinder assembly.

Maybe you can take the limo driveshaft & trim it to size; would that be cheaper than buying another driveshaft? Make sure you don't downgrade the U-joints.

 

Limos do not get TC and ABS. As a result brake lines scheme, routing and ends may require rework. Drums and pads are bigger, but not really something that's considered 'missing'.



I recall there were 2 limo rears. Just confirm the ratio is the one you're hunting. And can't vouch for the drum-drum width of either v. sedan. If you do the mod put up a thread about it eh.

 

For sure verify that it has 3.73's and count the bolts on the differential cover to make sure it is what you think it is - mine has 3.08's

Not sure about 94 Fleetwood Brougham's, but a 96 Roadmaster Wagon will fit a 33x12.50-15 tire with no modifications on stock wheels. This tire actually measures 32" diameter and about 11" wide. A taller tire will put more tire in contact with the ground, but will also mitigate the effect of the deeper gears (making it more like a 3.42 gear instead of 3.73).

I wouldn't be too concerned about the age of the gears - Have used 50+ year old gears that sat for 30+ years without issue - there's nothing age dependent about steel . If you pull the cover and find that they're rusty/pitted than you'll have to do something, but unless they're literally filled with water, I've never seen that happen.

I'd definitely grab the whole limo driveshaft including the carrier bearing in the middle. Typically they're a 2 piece driveshaft so shortening isn't really an option, but at least you can walk into a driveshaft shop with all the pieces they'll need and say - make it XX" from center to center of the u-joints.

 

Wow thanks fo the help guy! I remember reading a while back that the 93s had 3.73 and posi. The traction control is my biggest annoyance on my car( maybe after the finicky trunk pull down).
The junkyard owner said he’d help pull my old rear and put in the new one for $400. I’m beginning to realize that I probably won’t be able to drive away from there without a working driveshaft!
My car has 22s and with 265/35/22 tires(rubber bands that probably shouldnt be trusted with holding air).
I’m gonna take measurements of everything before I start the work. Hopefully get things going next week. And that’s only if I can get this harmonic balancer off to check my optispark. Damn thing already came off and went back on and now won’t budge. Btw what’s the SPID for posi in the 93?

 

Here's a list of codes. You may find more info for your swap too. Caprice Classic dot COM -- Some SPID codes for 9C1 Caprice's

Mark: Snowman-33

 

Please post up the measurements (wheel mounting flange to flange as well as control arm widths) for both vehicles to continue adding to the info in this thread.