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Discussion Starter · #1 · (Edited)
I'm posting this in the Wagon category rather than Brakes because I'm specifically referring to the unique wagon rear end.

I've spent a LOT of time reading up on rear brake upgrade options for my '93 Roadmaster wagon. Seems like the main documented options involve either swapping in a 9C1/Impala SS rear end, or going with a retrofit with Z06 calipers, either of which involves switching to 17" wheels [edit: correction, the former option will work with 15" wheels]. I REALLY, REALLY wanted to stick to OEM 15" wheels, and I wasn't interested in swapping rear ends.

Enter the SSBC rear disc brake kit (A125-4). While technically intended for sedans, SSBC has a service bulletin that calls for swapping out the flange brackets to accommodate the larger wagon bolt spacing. The service bulletin refers specifically to older full size models ('71 to '76), but appears to potentially work for our more recent wagon rear ends as well. I figured I'd give it a try and placed an order a couple months ago. The big skepticism I got as feedback when I was considering this kit was that no commercial rear disc brake kit has ever taken wagon rear ends into consideration. They were always intended for sedans, where the flange bolt spacing and axle offset are different.

I received the kit a couple weeks ago (there was a backorder on calipers for the kit), and today I had time to take some initial measurements to gauge the feasibility of the swap.

The kit consists of backing plates that bolt to the rear end flanges, a couple of brackets to attach the caliper on each side, what appear to be Ford rear calipers (from late 80s/early 90s Thunderbird, Taurus and Mustang, I think), and some spacers and hardware to make it all fit. There's also brackets for the parking brake cables, some hydraulic tubing and lines for hookup, and brake pads of indeterminate brand or type. This would be one side:



Basically everything one needs to do the conversion, with the exception of rear end stuff (gear oil, cover gasket, etc). There's nothing included for modifying the line layout at the master cylinder, so changing the metering and bias will need to be done with more parts.

I have not yet begun installing the kit, I still need to acquire the extra bits first. But my initial assembly and measurements are very promising.







Note that I may have some orientations wrong for some of those parts, but the overall dimensions are correct.

The backing plate that attaches to the rear end flange appears to have the bolt holes at precisely the proper spacing, so that's a great first step. Measuring the rear end flange to axle flange offset is a little more difficult without taking out the axles, but my rough measurements tell me that it's either spot-on or within 1/4". I got about 2.25" from the backing plate to the axle flange, and pretty much the same while hand-holding the rotor in the assembled disc brake setup. There's shims in the kit to get the caliper centered over the rotor. If they're insufficient, it's a very simple matter of swapping out the spacers for different ones to achieve the axle flange offset I need.

So near as I can tell, this kit should work just fine without modification. It'll retain the e-brake functionality AND fit within 15" wheels, and it uses very commonly-available calipers and pads. Now I just need to gather up the other extra bits to complete the swap. I'll try to document everything and add it to this thread... but beware, I'm terrible at remembering to take photos.
 

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1993 RMW, 1996 RMW, 1992 OCC
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Discussion Starter · #2 ·
It just occurred to me that the kit pictured on the product page has the backing plate in 2 pieces, while the kit I received has it in a single piece. The 2-piece setup would allow installing the kit without removing the axles (if one didn't mind cutting off the old drum backing plate), while the 1-piece setup requires the axles to be removed. I dunno if the kit was updated in recent months to the single-piece backing plate, or if it's a consequence of accommodating the larger rear end flange. A single piece plate would be significantly stiffer, based on what I'm seeing in the product picture of the 2-piece plate.
 

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If you have easy access to a scale, consider weighing the old vs the new. I’m curious how much weight this sheds.
 

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If you can measure the piston diameter, that'd be great for comparison to the 9C1/SS caliper. Does the rotor trace to anything common?

I think it was their kit I used on the 9" rear in my 70 Mustang. As I recall they used the 85-86 SVO Mustang rotors, which I think are the same as the Lincoln VIIs. They look redrilled for our bolt pattern. Some measurements of the rotor would be nice too.
 

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Discussion Starter · #6 ·
If you have easy access to a scale, consider weighing the old vs the new. I’m curious how much weight this sheds.
I plan to. The disc brake setup weighs 26.2 pounds per side, for a total of 52.4 pounds. I'll try to remember to weigh the drum brake setup once it's off.

If you can measure the piston diameter, that'd be great for comparison to the 9C1/SS caliper. Does the rotor trace to anything common?

I think it was their kit I used on the 9" rear in my 70 Mustang. As I recall they used the 85-86 SVO Mustang rotors, which I think are the same as the Lincoln VIIs. They look redrilled for our bolt pattern. Some measurements of the rotor would be nice too.
The rotors are 11.3" diameter (vs 11.6" for 9C1/Impala) by 0.8" thickness (about the same as 9C1/Impala) and have a really nice casting for the vents. The caliper has a piston diameter of 1.75", which is a bit smaller than the 9C1/Impala's 2.125". The D347 pads used on the SSBC calipers have a radial height of 1.46", I don't know what it is for 9C1/Impala rear pads. I might switch to grippier pads for the rear if I can't get the bias I need without resorting to an adjustable combi valve. I guess some compromises need to be made in order to retain fitment inside 14" wheels, which is what this kit is intended for.
 

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The SVO rotors are 11.3 also but a little thicker at .945 nominal. Can't find info yet on the piston size in their calipers. So the pad and caliper could be a good match if need be.

If you don't get enough squeeze and IF you can forego the parking brake, might not be that hard to adapt the kit for the stock SS calipers.
 

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Discussion Starter · #8 ·
...I might switch to grippier pads for the rear if I can't get the bias I need without resorting to an adjustable combi valve...
Or maybe switch to Wilwood front calipers... they have options with single 2.75" or dual 2" pistons, either of which would be a better match for the 1.75" rear calipers.
 

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You can get the stealth bolt to mod the proportioning valve. It will give you more rear brake bias.
 

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Discussion Starter · #10 ·
That was my initial plan, but I ended up buying a disc/disc proportioning valve with 3 outlets and a set of lines for a non-ABS car so I can eliminate the giant cluster of brake lines that's stuffed under the steering column. The ABS on this car has never worked anyways. When I bought the car, it had a piece of electrical tape over the ABS warning light that had clearly been put there YEARS ago. I got rid of that warning light bulb last fall after determining that the front sensors were both bad. And when I installed the HD12 front rotors, I didn't bother with the ABS tone rings. At this point, all that's left is getting rid of the ABS pump altogether.
 

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As far as fronts, Wildwood single 2.75" piston would be smaller than OEM, and the dual 2" piston calipers would be the same as GM truck, Astro, etc.

Props for digging up this kit. None of the budget brake parts I've looked into take wagons into account.

It seems in this application, the backing plates are pretty much the entire kit. There are lots of vehicles with rear discs that use the smaller flange, but the bigger flange pattern is more tricky. If somebody just started producing backing plates in the correct size, it would open up your selection for rotors and calipers.

I'm not sure what makes you think the SS/9c1 rear brakes require a 17" wheel. The 9c1 has 15" wheels. Also, swapping a sedan rear into a wagon is not considered a good option. The suspension geometry is not the same.
 

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Discussion Starter · #12 ·
Huh, you're right. Then why do Impalas require 17" wheels? I never understood that. I do know the retrofit kits with Corvette calipers DO require 17" wheels. In any case, I wasn't interested in swapping rear ends, for the reason you mention among others.

I'm really liking the idea of having a bolt-on brake kit that does what I need it to and retains the e-brake. It's nice to have found one that's basically just a backing plate and spacers. The whole thing is super beefy and looks like it could take a beating without any flexing, and it's easily adaptable to different axle flange offsets. The bolts that go through the spacers are significantly larger than the ones that bolt the backing plate to the rear end flange, and the spacers themselves are substantial and have a large OD.

As far as front calipers, from what I can tell, the big Wilwood dual piston caliper has a piston area of 6.28", while the OEM calipers have a piston area of 6.77", so even Wilwood's biggest bolt-on caliper has slightly less raw clamping force. The big single-piston Wilwood has 5.94" of piston area. That might be useful for balancing with the inherently-smaller piston area of the Ford caliper in this kit. With the hydroboost setup I'm planning, the overall clamping force will be higher anyways, so losing a bit of front grab relative to the rear won't matter. I'll still have plenty of grab to lock up all 4 wheels at will. But this means finding the right bias will be even more important.
 

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Impalas do not "require" 17 inch wheels. You can use wheels from a Caprice or Roadmaster.
 

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Discussion Starter · #14 ·
Ah, then it must just be the retrofit kits I'm thinking of. Would be interesting to have a backing plate that can accommodate an Impala caliper and brake rotor. That would open up available parts significantly, and would avoid requiring custom rotors. Also would simplify bias tuning.
 

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Backing plates can be easily fabricated or modified if you don't mind going to a machine shop. I mean, we're talking about a piece of sheet metal with holes drilled in it. You could also probably take backing plates that are meant for the smaller flange and modify them to bolt to the larger one. Trailblazer, S-10, etc. There may even be adapters, but I haven't looked.

I shouldn't get too far away from discussing this kit. I have another thread for discussing factory brake parts. 😂
 

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Discussion Starter · #17 ·
This is the weekend I chose to install the rear disc brake kit. I'm not quite done yet, because I hit every imaginable obstacle along the way. But it's coming along nicely, and I can at least confirm that it does in fact fit perfectly on wagons.

First I raised the back and allowed the rear end to droop:

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The jacks under the rear end aren't supporting it, they just exist. They're very meta.

My first obstacle was the rear end cover bolts... they were super rusty:
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I ended up having to torch and use a bolt extractor for every single one. The bottom 3 wouldn't even come out with the extractors. I ended up slotting 2 of them and removing them with an air chisel. The very bottom one I had to grind away until the head was small enough for the rear end cover to just slip over it, then I was able to take it off with vice grips:

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Luckily I wasn't planning to keep the rear end cover, it got pretty mangled. But the rear end itself is fine and all the threaded holes survived unscathed! The bolt that holds the center pin of the differential in place was being super stubborn, that ended up requiring the torch too. But it did eventually come off without breaking and the pin slid right out.

At that point I could remove the C clips, pull the axles, disassemble the rear drums and remove the backing plate. Then I trial fit the new backing plate, and it fits super perfectly!

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(ignore the failed bearing removal attempt, that's one of the obstacles I came across, my slide hammer broke)

The holes line up flawlessly, and everything is very snug. There's a groove on the back of the backing plate that slips over the lip around the axle tube. I spent a bunch of time trial-fitting all the brackets and bolts to make sure everything was done right, and this is the final configuration

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And here it is with the brake rotor and caliper installed:

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I slid the pin back into the differential to get the axle situated properly, then checked the brake pad clearance:

Automotive exterior Bumper Gas Auto part Audio equipment


I don't think it could possibly be any more perfect. Once I've got the lines hooked up and I can pump the brakes, that should settle in flawlessly.

So that's as far as I've gotten. Both sides are setup, I just need to get a new slide hammer to finish the bearing removal.

Some notes:

- I did not need shims. The included spacers are exactly the proper length

- the kit includes new wheel bearings... BUT NO SEALS?!? That's so not cool, of all the cheap omissions... I would've loved to receive one of those nice Timken one-piece bearings/seals, but no. Just regular Timken bearings and NO SEALS!!! :mad::mad::mad:

- the printed instructions are ok... there's nothing explaining how to determine if you need to use the shims. The illustrations are wrong about at least 2 very important things, though the words are more accurate

- weight of all the drum brake parts (drum, backing plate, shoes, all the springs and bolts, etc, etc): 38 pounds per side

- weight of all the disc brake parts (backing plate, brackets, rotor, caliper, pads, etc, etc): 26 pounds per side
 

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Discussion Starter · #18 · (Edited)
Further notes:

- I just put an OEM 15" wheel back on to check fitment. Everything fits with plenty of room to spare. This kit is intended to fit inside 14" wheels, so that makes sense

- The brake rotors have a thicker mounting surface. THIS INCREASES THE TRACK WIDTH! I had not expected that. My 255 tires still fit with room to spare, but I'm not sure that 275 tires would fit without trimming the inside edge of the wheel skirt

- Side effect of wider track: the wheel studs aren't long enough anymore. My lug nuts aren't threading in all the way, only about 2/3 of the way. I don't think I trust them that way. So I think I'll look into longer wheel studs before I re-install the axles
 

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- The brake rotors have a thicker mounting surface. THIS INCREASES THE TRACK! I had not expected that.
My 255 tires still fit with room to spare, but I'm not sure that 275 tires would fit without trimming the inside edge of the wheel skirt.
In the early 2000s I replaced 235/70R15 with 255/65R15. The installer said they were 'close but acceptable'.

Back in the 2000s I looked for many excuses to corner very enthusiastically; so enthusiastically that I managed to 'anonymize' most of the markings on the widest part of the rear tires' sidewalls. This happened very slowly, and after about 4 months it stopped once I could no longer recognize the brand name.
Just FYI.
 
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