Converting rear drum brakes from SBP to BBP

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rrvolare

rrvolare

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Wondering ,,,,, is it possible just to change axles to BBP and then install 10 inch bbp drums on rear ?... Keeping the same backing plates ..shoes and wheel cylinders ?.
Is there a p/n drum BBP that will work with SBP original shoes and backing plates ?
thanks
 
That's exactly what I did.
Specify if you want the "wide offset" for the later drums if you're ordering axles for an 8 3/4. Strange knew exactly what I wanted.

My 8 3/4 is running Aspen/volare rear drums from drum to drum.

Edit: I mis- read the original post.
I don't think the spacing will work for any backing plate from the narrower shoes.
in other words, I think it's a one way street.

That said, I'll never run the sbp brakes ever again. The later model parts are way more available
 
rrvolare said:
Wondering ,,,,, is it possible just to change axles to BBP and then install 10 inch bbp drums on rear ?... Keeping the same backing plates ..shoes and wheel cylinders ?.
Is there a p/n drum BBP that will work with SBP original shoes and backing plates ?
thanks
Click to expand...
Yes, I redrilled my axles and drums. You can get the template to drill them from Art Morrison.
 
Which design of axle bearings prohibits moving axles from one to the another also. They aren't all the same.
 
rrvolare said:
Wondering ,,,,, is it possible just to change axles to BBP and then install 10 inch bbp drums on rear ?... Keeping the same backing plates ..shoes and wheel cylinders ?.
Is there a p/n drum BBP that will work with SBP original shoes and backing plates ?
thanks
Click to expand...

No, there isnt. The large bolt pattern drums have a larger center register and dont come in the narrow width you'd need.
Just swap out the entire rear brake assemblies. Ditch those tiny shoes.
Your already going to replace the axles so why not replace the brake backing plates, etc. with 10x2-1/2"?
Very little cost difference over what your thinking of, if it was even do-able.
 
well the axles stick out of the housing more on a 4 1/2bc axles and yes the center reg huds are different dia as well . and there is a brake shoe width difference as well . got to change it all , you get special axles to redrill your 4'' brake stuff . one member said he redrilled axles n drums .
 
if you have good sbp drums, have them redrilled and get new axles from Strange or Moser to match
 
I've been wondering the same thing, so if I'm reading correctly I can't use the OE 70 Dart 10" backing plates, cylinders, shoes and just install new axles and say 70 challenger 10" LBP drums?
 
how much wider are the lbp drums than the Dart drums? you can get axles that stick out .36" more than A body axles
 
I appreciate all the replies .... moving forward , it looks like i will be easier if i switch over to big bolt pattern backing plates and drums... i do know i have 76 volare setup ... my NEW question is that i will need to redo my steelies ... i will have stockton make me new 15 X7 steelies ... any of you can tell me after installing new moser axles ( being there longer ).. what offset did you use on steelies ?

Thanks
 
76 F stuff will work. Might have to drill hole number 5 in the backing plate but thats cake.
Sent a dozen or more sets of em to A body guys converting over to large bolt pattern...along with F front disc set-ups.
Parts are plentiful and cheap...about 10 ea for wheel cylinders, 20 for good shoes, etc.
 
Talked to Moser ... he stated that he could redrill my existing Moser SBP axle and install new studs for under 100... as long as the face of the axle flange is larger than 5 3/8 of an inch .. I will pull the wheel and check ... Thanks
 
Yup, you can do that....and get the sbp drums you have redrilled too.
And you'll still have the small brakes.
 
It's been mentioned, but I wanted to make this clear. If you use re-drilled SBP axles, you MUST use re-drilled SBP brakes (10x1-3/4") No major parts of the BBP brakes will work. That also applies to aftermarket axles with the SBP flange offset but the 5x4.5" bolt pattern. And conversely, BBP axles must use BBP brakes (10x2.5").

The offset on axle flange is different between SBP and BBP axles, so the backing plates are different and can not be interchanged.

882BE0F2-CCE7-45CD-9309-1EC5A901EB5A_zpsrqarvzox.jpg
 
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72blunblu...
in vehicle now is sbp "MOSER" axles ... i was going to have these redrilled to lbp and then upgrade to F body backing plates and drums/shoes ... i asked Moser about axle length when comparing SBP and BBP .. he told me they were the same length ... ?? I will ask again ..
 
rrvolare said:
72blunblu...
in vehicle now is sbp "MOSER" axles ... i was going to have these redrilled to lbp and then upgrade to F body backing plates and drums/shoes ... i asked Moser about axle length when comparing SBP and BBP .. he told me they were the same length ... ?? I will ask again ..
Click to expand...

The axle length isn't the problem, the axle flange offset from the housing is different. You can not use BBP backing plates or drums with SBP axles regardless of the bolt pattern you have drilled on them. If you're currently using SBP brakes you'll have to have those drums re-drilled and re-use those brakes if you have the axles re-drilled.
 
Not once did anybody mention, or question just which rearend it is that we're talking about here!! Info please!!!
 
cosgig said:
Not once did anybody mention, or question just which rearend it is that we're talking about here!! Info please!!!
Click to expand...
Not sure on original poster but my question was for an 8 3/4, I have OE 10" drums with SBP and was wondering if I can use my backing plate and buy 70 challenger 10" drums and shoes to make LBP, if that would work.
 
cosgig said:
Not once did anybody mention, or question just which rearend it is that we're talking about here!! Info please!!!
Click to expand...

Definitely an oversight, but for the topic of the brakes it really doesn't matter. You can't use any BBP brakes with any SBP axles, regardless of which rear axle it is. It does make a difference for the axles of course, because if I'm not mistaken the SBP 7.25" rear axle can't swap axles with the later BBP 7.25 rear axle for other reasons. That's just going off of what I've read though, I've never had a SBP 7.25" in any of my cars. All of my A-bodies either had SBP 8 3/4's or BBP 7.25's, and I got rid of the BBP 7.25 pretty quickly.

Sublime Swinger said:
Not sure on original poster but my question was for an 8 3/4, I have OE 10" drums with SBP and was wondering if I can use my backing plate and buy 70 challenger 10" drums and shoes to make LBP, if that would work.
Click to expand...

Nope!

You can not interchange SBP and BBP backing plates or drums. SBP backing plates must be used with SBP axles and drums. If you re-drill the SBP axles to the 5x4.5" pattern, you must re-drill the SBP drums as well. You cannot use stock BBP drums (10x2.5") with SBP backing plates or re-drilled SBP axles.

It's a matched set. If you want to use the 10x2.5" BBP drums, you must use the 10x2.5" backing plates and BBP axles (not SBP axles redrilled to BBP!!!). If you want to use 10x1.75" SBP drums, you must use 10x1.75" backing plates and SBP axles. If you re-drill a set of SBP axles to 5x4.5", or buy a set of aftermarket axles with the SBP axle flange offset, you must still use the 10x1.75" backing plates and drums and re-drill the drums for 5x4.5.

The BBP axles have a different flange offset, as shown in the picture I posted above. That means the backing plates also have a different offset, because the drums are a different distance from the axle housing where the backing plates mount. The difference in the axle flange offset is not the same as the difference between the width of the BBP and SBP shoes either, so, there's no combination that works other than keeping the SBP brakes paired with SBP axles and the BBP brakes paired with BBP axles.
 
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72bluNblu said:
Definitely an oversight, but for the topic of the brakes it really doesn't matter. You can't use any BBP brakes with any SBP axles, regardless of which rear axle it is. It does make a difference for the axles of course, because if I'm not mistaken the SBP 7.25" rear axle can't swap axles with the later BBP 7.25 rear axle for other reasons. That's just going off of what I've read though, I've never had a SBP 7.25" in any of my cars. All of my A-bodies either had SBP 8 3/4's or BBP 7.25's, and I got rid of the BBP 7.25 pretty quickly.



Nope!

You can not interchange SBP and BBP backing plates or drums. SBP backing plates must be used with SBP axles and drums. If you re-drill the SBP axles to the 5x4.5" pattern, you must re-drill the SBP drums as well. You cannot use stock BBP drums (10x2.5") with SBP backing plates or re-drilled SBP axles.

It's a matched set. If you want to use the 10x2.5" BBP drums, you must use the 10x2.5" backing plates and BBP axles (not SBP axles redrilled to BBP!!!). If you want to use 10x1.75" SBP drums, you must use 10x1.75" backing plates and SBP axles. If you re-drill a set of SBP axles to 5x4.5", or buy a set of aftermarket axles with the SBP axle flange offset, you must still use the 10x1.75" backing plates and drums and re-drill the drums for 5x4.5.

The BBP axles have a different flange offset, as shown in the picture I posted above. That means the backing plates also have a different offset, because the drums are a different distance from the axle housing where the backing plates mount. The difference in the axle flange offset is not the same as the difference between the width of the BBP and SBP shoes either, so, there's no combination that works other than keeping the SBP brakes paired with SBP axles and the BBP brakes paired with BBP axles.
Click to expand...
Okay thanks for the info since I'm not able to use those I think I'm just going to upgrade to the 11-inch Challenger drums instead.
 
Sublime Swinger said:
Okay thanks for the info since I'm not able to use those I think I'm just going to upgrade to the 11-inch Challenger drums instead.
Click to expand...

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.

img_2848-jpg.1714942228.jpg


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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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"
Click to expand...
Great info, really appreciate the extra attention to detail!
 
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