Converting rear drum brakes from SBP to BBP

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I just ordered my BBP Moser axles ... i will remove exisiting SBP Moser axles .. install volare 10X 2.5 backing plates and hardware.. install new BB Moser axles and order my volare bbp drums .. i will let you know results ... thanks for input
 
A lot of information to digest. I am beginning my build so let me make sure I have this right. I want to go to BBP just for the better options of wheels. For the front my option is to swap the front spindles, rotors and upper A arms from a 73-76 B body? that would have to include master cylinder and proportioning valve? which while I'm there I might as well get the booster (did I miss anything, like linkage)? Now for the rear I can use the axle from the same car but I need to relocate the spring mounts 1/2 inch inboard? If I just want to swap axle shafts I have to drill the drums for BBP? I can't swap drums and backing plates from the donor car and install BBP axles unless I use the axle housing from the donor car, right?
 
Update -... make sure when you order BBP moser axles you get the ones for a B body.... due to locating axle in correct location to accept BBP drums and not contacting backing plates ..
 
M67cuda said:
A lot of information to digest. I am beginning my build so let me make sure I have this right. I want to go to BBP just for the better options of wheels. For the front my option is to swap the front spindles, rotors and upper A arms from a 73-76 B body? that would have to include master cylinder and proportioning valve? which while I'm there I might as well get the booster (did I miss anything, like linkage)? Now for the rear I can use the axle from the same car but I need to relocate the spring mounts 1/2 inch inboard? If I just want to swap axle shafts I have to drill the drums for BBP? I can't swap drums and backing plates from the donor car and install BBP axles unless I use the axle housing from the donor car, right?
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Couple of things- you need UCA’s from a 73-76 A-body. Not B body. B-bodies use totally different UCA’s. That may just have been a typo.

If you use a 15/16” master cylinder, there’s really no need for a booster, you can run manual brakes. Not a fan of the power brakes on these cars.

Rear axle- I’m not sure what rear axle you’re even talking about. B-bodies used several different widths (and different type axles!). Some can work with A-bodies if you’re talking about a Demon, Dart Sport, Duster, or Barracuda. But some of them are way too wide. All B-body housings will need the perched moves. When you start talking about swapping axle shafts I’m not even sure what axle you’re talking about. You can’t mix and match SBP and BBP brakes and axles.
 
Obviously I am confused. I'm new to this and I've been trying to gather information from around the web so any help is appreciated. I'm wanting to convert to BBP in the most cost effective way.

The UCA's have to come from a 73-76 A body equipped with disc brakes? Do all these models have the BBP?

I assume that the spindles, rotors and calipers must come from the same A body?

Do all 73-76 A bodies use the 15/16" master cylinder? What other models should I be looking at?

Why don't you like power brakes on these cars?

As for the rear of the car, any suggestions? I would like to come out with a larger diameter drum in the process.
 
M67cuda said:
The UCA's have to come from a 73-76 A body equipped with disc brakes? Do all these models have the BBP?
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No, not all of those models have the 5x4.5" pattern, only the disk equipped cars starting in '73. Drum cars still had the SBP. But, the control arms are the same. From 1973-1976 A-bodies used upper control arms with a larger ball joint than they did from 67-72.

On that note, you don't NEED to have UCA's from a 73-76 A-body. You can use tapered adaptors on the ball joints to match the 73+ spindles. The only difference between the 67-72 and the 73+ UCA's is the size of the ball joint. Doctor Diff sells the adaptors if that's the way you wan to go Mopar A-Body Upper Ball Joint Tapered Adapter

M67cuda said:
I assume that the spindles, rotors and calipers must come from the same A body?
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Nope. Mopar changed the spindle/brake package starting in '73, and they basically made it uniform across all the body styles except the C-bodies and trucks. It's pretty common to use FMJ body parts for this swap. The A-body spindles were slightly shorter than the E/B/R/F/M/J spindles, but the change in geometry is almost negligible. So, if you have a wrecking yard locally, you can check for all kinds of later cars on the F, M, or J platform. Diplomats had the right spindles for the swap up until '89 I think.

Swapping Disc-Brake Spindles - Mopar Muscle Magazine

M67cuda said:
Do all 73-76 A bodies use the 15/16" master cylinder? What other models should I be looking at?
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No. Most of the A-bodies used a 1-1/32" master cylinder. The 15/16" I use is an aftermarket piece, also from DoctorDiff. I think the power brake A-bodies were the ones with 15/16" masters, but if you go manual the power m/c may not have the right cup on the piston for the push rod.

M67cuda said:
Why don't you like power brakes on these cars?
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Because the pedal feel is terrible. Soft and squishy. Modulating the brakes isn't as easy as with manual brakes. And with a 15/16" master cylinder, pedal effort isn't that bad at all.

M67cuda said:
As for the rear of the car, any suggestions? I would like to come out with a larger diameter drum in the process.
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What rear axle is in the car currently?
 
Thanks so much for the information. Currently the car has a 7 1/4 rear axle with 3.23 ratio. The drums measure 11" though, does that sound right?
 
M67cuda said:
Thanks so much for the information. Currently the car has a 7 1/4 rear axle with 3.23 ratio. The drums measure 11" though, does that sound right?
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Nope. No such thing as SBP 11" brakes, they were all 10". Only way they could be 11" brakes is if that's a BBP 7 1/4. They wouldn't have been there stock in that case, but they fit.

With a 7 1/4 you're pretty much screwed too. The SBP and later BBP 7 1/4's are different, you can't swap BBP 7 1/4 axles into a SBP 7 1/4". You'd have to have the SBP axles drilled for BBP, and then do the same with the SBP brakes. Or swap out the rear axle entirely.
 
I was trying to measure the brakes from the ground under the car. Again thanks for the information. I haven't had any luck finding a salvage yard with pre-90's anything.
 
M67cuda said:
I was trying to measure the brakes from the ground under the car. Again thanks for the information. I haven't had any luck finding a salvage yard with pre-90's anything.
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The diameter should be stamped on the outside of the drum somewhere, usually as a "max 10.090" for the maximum serviceable diameter. The backing plates are also about 1" larger in diameter than the inner diameter then the brake surface, so, 10" drums would have 11" diameter backing plates.
 
Suggestion on models that would be easiest swap to 8 3/4 axle with 5 x 4.5 and larger brakes?
 
Please let me know if my research is correct for the rear end. To install a 8 3/4 my options are:
Find a 8 3/4 from a 65-72 A body then change the axle shafts to BBP and either drill the drums or change backing plates and drums from BBP car.
Find a 62-70 B body rear end and move the spring perch in 1/2" which will require new perch with 1/2" locating pin hole.
Are these my options?
 
If you order axles from Moser .. they will need to be 28 inches long ... register hole of 2.825 - 2.830 , and distance from front of axle face to bearing snap ring or exposed part of axle is roughly 2.4 inches ... then you can use volare backing plates and drums... hope this helps ..
 
M67cuda said:
Please let me know if my research is correct for the rear end. To install a 8 3/4 my options are:
Find a 8 3/4 from a 65-72 A body then change the axle shafts to BBP and either drill the drums or change backing plates and drums from BBP car.
Find a 62-70 B body rear end and move the spring perch in 1/2" which will require new perch with 1/2" locating pin hole.
Are these my options?
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Um, sort of.

Yes, a 65-72 A-body 8 3/4 should bolt right in. If you change to BBP axle shafts (with the BBP flange offset) then you must change to BBP backing places and drums. If you have the stock SBP axles drilled for the larger bolt pattern (or you buy Moser axles with the SBP flange offset), you have to drill the SBP brake drums for the larger bolt pattern and use the re-drilled SBP brakes. You can't mix and match parts between BBP and SBP brakes and axles, has to be either all BBP or all SBP, even if the SBP stuff is drilled for the 5x4.5" pattern.

The 62-70 B body axle thing- first, I know exactly what chart you're looking at if you say 62-70 B-body 8 3/4, and that chart is totally wrong. Completely wrong. Use this chart An accurate 8 3/4" rear axle width list

There are literally 4 different width B-body rear axles from 62-70, and anything before '65 has a tapered axle set up that you do NOT want. So, you have two real options that don't involve major pain, both will need the spring perches moved to the A-body perch width.
65-67 B-body 8 3/4 = 59.5" drum to drum
68-70 B-body 8 3/4 = 60.125" drum to drum

So, you can see these are wider than an A-body 8 3/4. If you move the perches the axles will bolt right in, and you'll have BBP brakes, but you will need rims that have more backspacing than a stock A-body. Especially you use the 68-70 B-body 8 3/4, you may have a hard time finding 15" rims with enough backspace to run wider tires. If you want to run 17" or 18" wheels, no problem. In fact, the wider rear axle will be beneficial, because there are a lot of off the shelf 17 and 18" rims with enough backspace, especially for a Barracuda. But if you want to run 14" or 15" rims and anything wider than a 225/60/15, you will have limited options for 15" rims, and almost no options for 14" rims, unless you have them custom made.

For example, I have a 68-70 B body rear in my Duster. I did a 1/2" spring offset when I installed it (have to move the perches anyway, might as well), and I run 18x10" rims with 7" of backspace (+38mm offset). But before I bought those rims, I ran the car with 15x7" cop wheels with a 4.25" backspace and 225/60/15's. They barely cleared the quarter panels. And finding significantly positive offset 15" rims isn't that easy. So, you may not want to use a B-body 8 3/4 if you plan on staying with 15" stock style rims.
 
thanks. I found a front disc setup from a 73 Duster so I got the rotors, spindles and calipers from it and the master cylinder from a manual disc 76 Duster yesterday. No luck on the rear. I plan to run stock style 15" wheels with 4" backspace either 8 or 10 inch width.
 
Do you or anybody have the drum to drum measurement of a F-body. seems to be missing from the chart.
 
72bluNblu said:
Assuming that you're buying a set of BBP axles that will work.

Also recall that 11" rear drums came in 11x2, 11x2.5, and 11x3" varieties, and you can't swap drums and backing plates with those either. Since the BBP axle offset was the same for all of them, the axle flange is in the same place for all of those and therefore the offset for the backing plates on each of the 11" drum set ups was different. Meaning, if you have 11x2" backing plates, you can't just buy 11x2.5" drums and shoes and run those. Somewhere I have those measurements to tell which is which.

***Edit***
Found the measurements.

To measure the backing plate offset you want to set the backing plate flat on a bench. You'll need to hang the bottom 1/3 of the backing plate off the edge of the bench so that the mounts for the e-brake cables don't keep the backing plate from sitting flat. It isn't much, but they do change the measurement. Then, measure from the bench to the top of the backing plate through the center hole (for the axle) in the backing plate.

If you get ~1.75", you have 11x2.5" plates. If you get ~1.5", you have 11x2" plates. Those I know for sure, as I've measured them. I don't have a set of 11x3" backing plates, but the math would say you'd get ~2" measuring them as I described above. This is because half of the additional width is on the inside of the axle flange and the other half is on the outside to keep the axle flange in the same spot, as there was only one axle offset for BBP 8 3/4 axles.

View attachment 1715019208

Also, if you have a set of 10" backing plates without any hardware, shoes etc you can measure those to determine if they're BBP 10" backing plates or SBP 10" backing plates. BBP plates will measure 1.75", they're 10x2.5" and have the same axle flange offset as the 11x2.5" brakes so you get the same measurement. The SBP 10" backing plates will measure roughly 1.25"
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