The wagon specific axle flange to housing flange stand off dimension is likely going to through a wrench in your plan.
While it might be doable, not going to be a drop in swap, methinks.

 

The wagon specific axle flange to housing flange stand off dimension is likely going to through a wrench in your plan.

I was kinda hoping that the difference in width is accomplished through a deeper inset of the drum, as opposed to more positive offset from the axle, hence the need for a new backing plate. Especially since the Fleetwood commercial chassis was apparently available with both sizes of drums.

 

Well, look at this in reverse.
You can take a large flange 11-2 wagon drum off a wagon and toss the shallow flange sedan drum right on.
I did this when drag racing to lose some weight .

BUT you can not swap backing plates wagon to sedan or sedan to wagon.
Both because the offset and flange bolt circle is different.

The Fleetwood limo stuff you are speaking of, not positive, but thought the stand off was more sedan like.

I am thinking to mount a Fleetwood limo backing plate on a wagon there would be , minimum, a machined spacer .
Is the big limo backing plate available ?

 

Is the big limo backing plate available ?

Yep, readily

 

A set of high performance shoes would probably get the rear axle to lock up without any modifications. The internet shows many companies that could reline a set of shoes with better material than the mass market offers.

 

This is very true, but I'm also thinking of heat management. Bigger drums and shoes can soak and dissipate more heat, and drums tend to run hotter than discs, especially when hauling heavier loads

 

Link to backing plates please ?

 

Link to backing plates please ?

More Information for GM GENUINE 15650129

Doesn't look like it's offset any more than the 11x2 backing plate...

Ironically, the 11x2 backing plate seems to be less common than the 11-5/32x2-3/4 one

 

Being that braking plate shows to also fit a plethora of 1/2 ton gm trucks, pretty confident it is a no go for our shallow wagons.

Cadillac Fleetwood 4DR Brougham
1991, 1992, 1993, 1994, 1995, 1996
Chevrolet BLAZER
1992, 1993, 1994, 1995, 1996
Chevrolet C1500
1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000
Chevrolet C2500
1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000
Chevrolet C3500
1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000
Chevrolet EXPRESS
1996, 1997, 1998, 1999, 2000, 2001, 2002
Chevrolet G10
1996, 1997, 1998, 1999, 2000, 2001, 2002
Chevrolet G1500
1996, 1997, 1998, 1999, 2000, 2001, 2002
Chevrolet G20
1996, 1997, 1998, 1999, 2000, 2001, 2002
Chevrolet G2500
1996, 1997, 1998, 1999, 2000, 2001, 2002
Chevrolet G30
1996, 1997, 1998, 1999, 2000, 2001, 2002
Chevrolet G3500
1996, 1997, 1998, 1999, 2000, 2001, 2002

 

Mind you I do not know your fab skills.
Anything is possible with a mill, lathe, tig, smarts

 

Meh, not that desperate. I have all those things, but I was kinda hoping for a quick and easy upgrade that doesn't cost much more than refreshing with stock parts. If I really went that far into it, I'd probably find a way to fit discs under my 15" wheels, instead

 

Ended up ordering the SSBC rear disc brake conversion kit instead. When I contacted them directly, they said they have an option for caliper brackets that fit the bigger wagon rear end flanges. Adding up the cost of new drums, wheel cylinders, backing plates, etc, etc, the disc brake conversion ends up being only slightly more costly. Seems worthwhile.

A125-4 Rear Disc Brake Conversion Kit, GM-10 & 12 Bolt

REAR DISC BRAKE CONVERSION KIT , 1971-1996 GM FULL SIZE 10 & 12 BOLT WITH 11" DRUMS, 5 X 5 WHEEL BOLT PATTERN This kit contains all the parts you need to convert your 1971-1996 GM- full size, 10/12 bolt pattern vehicle from drum to disc brakes. Manufactured from quality materials, these rear...

ssbc-usa.com

And best of all, it fits inside stock 15" wheels!

 

Hope I am wrong but i think your are going to be disappointed 😞

The wagon has a specific axle standoff dimension and a different backing plate bolt circle, bolt size, bearing register dia

 

Yeah I'm aware, that's why I asked them about it first. The only rear disc conversions I ever hear mentioned are the Kore3 kits, which are too big to fit under 15" OEM wheels and are only meant for sedan rear ends. It'll be interesting to see if these can be made to fit without too much effort. Honestly, I'm surprised SSBC exists at all... apparently they made a return last year after their bankrupted assets got bought by a new company.

 

The wagon is unique enough a lot of aftermarket lump it in with the sedan.
Impala- Caprice rear disc fit under the 15 wheel, but you have to mod, backing plate bore and pattern.
The, setup leaves the axle being short.
Custom length axles are avaliable.
Others have put spacers between axle and rotor and not had issue.
I personally do not subscribe to that method.
The corvette based rear rotors many of us use , the spacing is the other way.
It gets tricky and close in there.

Thing is, the impala rotor don't have a lot of mass.

If you are willing to explore the old horrific park brake in caliper avenue, there might be other choices.

Years ago , I did the late 70s Seville swap on a, wagon housing.
Had to section and weld the bracket for the stand off difference.
BUT we were saddled with the crap GM caliper.

Good luck with your quest

 

Sill question here - what makes rear discs better than drums?

 

They dissipate heat faster, they engage more quickly, they have a lot less rotating weight. That's about it.

OEM setup has a delay on the engagement of the front brakes in sudden braking situations to allow time for the rear drums to engage at about the same time as the front discs. That delay bugs the hell out of me. With rear discs, that delay is no longer necessary and can be eliminated by modifying the proportioning valve.

 

That seems reasonable - thanks

 

Truth be told, the cars (drum rear wagons ) are perfectly happy with the front hold off and hydralic rear proportioning removed.
In bench testing a combination valve with a pressure guage on in and out, all the rear prop was doing was "clipping" the higher end.
The reason I say perfectly happy,
My combination valve is gutted, only serves as a front to rear pressure, differential warning lamp switch.

This because I run fixed caliper 4 piston Brembo calipers whose sizing does not need "help"

My rear 15" drag slicks do not clear my big rotors.
When I am doing the drag race thing, I go back to drums
Because I am also doing a new diff, the drums have been on the car again for some time.
I have noticed no ill braking with the drums and gutted combo valve and have had some emergencies on the street.

Granted my front to rear bias is different than most , but the same setup seemed happy when the iron block was in place.

 

Speaking of calipers, what is the piston size on your, SSB calipers

 

Dunno yet! Guess I'll find out when the kit gets here, someday. They don't stock the brackets for the larger rear end flange, so they have to fabricate them

 

They say they are 1.75., basically same as C5 Vette
Stock Impala rear is 2.126
Sooooo, if you are using with corvette 2x 40.5 mm or similar area front calipers you will be starting in the neighborhood.

If you are using Impala, or similar area fronts, your bias will be out to lunch.

 

They say they are 1.75., basically same as C5 Vette
Stock Impala rear is 2.126
Sooooo, if you are using with corvette 2x 40.5 mm or similar area front calipers you will be starting in the neighborhood.

If you are using Impala, or similar area fronts, your bias will be out to lunch.

If they're 1.75" diameter, I suspect they might just be C5 rear calipers. The pictures look VERY similar to that on the product listing, with a slightly different casting at the rear where lines thread in. I won't be finding out for at least another month, though. SSBC is really far behind on shipping...

In the meantime, I did some quick math. Assuming they are in fact C5 calipers or use the same pads:

• running front J55 calipers (2.8125" diameter piston)
• pads with similar friction front/rear (currently 0.5 cf in the front calipers)
• disable proportioning in the combination valve
• disable front metering in the combination valve

I end up with a front/rear brake bias of about 70/30. That sounds pretty darn close to perfect and safe. This is based on the pad sizes listed on the Hawk website for those specific calipers. I could switch the rear brake pads to something slightly less grippy, say 0.4 cf, and end up with 75/25. While maybe less efficient, it would be even safer. Anything within that range is still way more efficient and reliable than the current rear drum setup, which I'm pretty sure has seized adjusters.

 

Fronts are J55 calipers, so basically stock diameter pistons. I'm putting in an adjustable proportioning valve and converting to hydroboost, so I'll need to adjust the bias from scratch anyways

 

What are you doing in front to use J55 calipers - missed it if you already covered it.

 

You probably have researched this all, all ready,
Below the knee point , the outlet pressures are basically the same.
With a large mech size mismatch, below the knee point you will be way imbalanced.

Example, wildly mismatched components,
you adjust the prop valve so under hard breaking you have great braking , no early lockup on either end.
light and moderate braking the front to rear balance is way out of wack.

We experienced this years ago in a Mustang Lincoln disc diff swap before we had a clue what we were doing or how a adjust prop valve worked .
GMPP, Ford Motorsports Mopar all marketed the same valve as the "fix all" for brake and diff swaps
Car seemed fine to drive, panic stopped great.
Would lock up one end all the time in the rain.

Adjustable prop valves are great to TRIM pressures and offset weight transfer at threshold braking. They are not made to fix mech mismatches .
You have likely seen this before

https://tiltonracing.com/wp-content/uploads/2013/07/98-1261-Brake-Proportioning-Valve.pdf

 

If we are on the same page and I am looking at the correct stuff, the discription has them as cast iron with integral park brake,certainly not Corvette.
Makes me wonder Ford. 🤔

Bias, not to belabor this.
Thought the J55 was 2.94 or 3
The Impala has,
a much bigger rear piston, than this kit
Larger dia rear rotor , than this kit
Less rear weight, than the wagon
and still happy with the combo valve gutted.
Personal opinion, I question tuning bias with brake material .

 

A cast iron caliper is even better! I need to spend more time reading the product description for this thing I just dropped hundreds of dollars on I'm so sick of stripping threads on aluminum calipers. I just got done replacing two rear aluminum calipers on my B5 A4 wagon because the bleeders were seized solid and all the threads ripped right out like soft cheese when I tried to bleed them.

I don't know what the J55 caliper piston size is. I assumed it was the same as the OEM calipers I just removed from the car, and those are the ones I measured to get the 2-13/16" dimension. RockAuto lists it as 3", though I always take their specs with a grain of salt. But if it is 3", it barely changes anything. Just adds 2-3% to the front bias

I used to adjust brake bias with pad changes all the time for autoX events many years ago. For street use, I'd run a "reasonable" 0.4cf rear pad to make sure there were no surprises on varying road conditions, like in rain. But for events on dry pavement, I'd run a grippier 0.5cf rear pad since I knew grip would be abundant and the car wouldn't get tail-happy with hard braking. Good quality street pads tend to have a very stable cf throughout their usable temperature range, unlike race pads which vary greatly with temperature.

Typically if I stick to 70/30, I have good results on the street. Going beyond 65/35 can get a little squirelly in wet weather, especially with a lot of weight over the rear axle. At 75/25, everything is super stable, but I'm approaching the point where rear discs aren't much of an improvement over drums. But then, every car is different and everything's a compromise. Especially when trying to stay with small OEM wheels.

 

I don't know what the J55 caliper piston size is. I assumed it was the same as the OEM calipers I just removed from the car, and those are the ones I measured to get the 2-13/16" dimension. RockAuto lists it as 3", though I always take their specs with a grain of salt. But if it is 3", it barely changes anything. Just adds 2-3% to the front bias

Don't forget that area is the square of diameter so 3" is ~12% more area than 2-13/16...

 

Yeah, rudimentary math, no hydraulic intervention,
Impala is roughly 69-31
I see you at 77-23 based on piston and rotor dia with a car that weighs more on the rear than the front.
Gunna be perfect with your diesel 😉

 

Yeah, rudimentary math, no hydraulic intervention,
Impala is roughly 69-31
I see you at 77-23 based on piston and rotor dia with a car that weighs more on the rear than the front.
Gunna be perfect with your diesel 😉

That brings up a question I haven't been able to find an answer to.. . what's the approximate weight distribution of a B-body wagon?

 

The opposite of a diesel swap

45.7 front 54.3 rear with alloy engine

 

opposite of a diesel swap
View attachment 198452

45.7 front / 54.3 rear with LS7 V8

Are those numbers with you sitting in it?
Because if you're NOT sitting in it, why is the left front heavier than the right front?
Did you relocate the battery?

 

No driver
The car is only 22 pounds heavy left.
Add a driver, it will be much more.
At that point it becomes a nose crossweight vs diagonal compromise.
Lowering the RR will "fix" the heavier LF but it shifts to LR.
Stock form,
auto level, steering box, steering column, major brake components are all left .
Engine - trans are 1/2 " offset right stock to help.

My battery is right rear location , but only weighs 21 pounds
My dry sump tank is where the battery was and with oil weighs a similar amount.

At 4500 pounds, 20 pounds bias here or there on a street car,,,,, well ,,,
Even the purpose built cars I work with , sometimes driver weight is difficult.

 

For future reference - Some additional discussion on the subject...

Rear sprung weight of wagon

Hi guys, the Moog 6101's in the back of my wagon are compressed to a length of 11.0" installed. They've got an advertised free height & rate of 13.12" & 389 lbs/in, respectively. That would indicate a sprung weight of 2 x (13.12-11.0) x 389 = 1650 lbs. Seems a bit low, considering wagon is about...

www.impalassforum.com

 

For future reference - Some additional discussion

Nice, even a post of mine with my weights from 2002 !


Discussion Starter • #3 • Sep 30, 2002

Ok here goes,
My wagon on Longacre scales weighs in at 4541 with some? gas.
LF 1158
RF 1161
LR 1135
RR 1088
That comes to,
50.4% left
49.5% right
51% front
49% rear
Because of the wagons overhang and heavy components at the extreme rear it actually weighs less on the front than the sedan.
Before you get all juiced up about the cool 51-49 front rear bias remember hanging weight outside of the wheel base might make for good numbers but does not make for good handling in corners. Straight line ok . Regards, Gerry

 

Look at that, I knew you were an overachiever, but a 199.9% car is pretty good!

 

Sides and ends NOT corners
In 2002 , My scales showed
Left side of car was 50.4% of total
Right side of car was 49.5% of total
Front end of car was 51% of total
Rear end of was 49% of total