sbp to bbp

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AlaskaJeff

AlaskaJeff

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On my 70 Duster I currently have a stock 8 3/4 with sbp (5 on 4) axles. I recently picked up a set of bbp (5 on 4.5) axles to swap out. Will I need to swap out the entire drum brake assembly, backing plates and everything else?
 
AlaskaJeff said:
On my 70 Duster I currently have a stock 8 3/4 with sbp (5 on 4) axles. I recently picked up a set of bbp (5 on 4.5) axles to swap out. Will I need to swap out the entire drum brake assembly, backing plates and everything else?
Click to expand...
In general, yes. Which axles did you get?
While there are a few aftermarket offerings of what amount to redrilled 4" axles that require you to redrill your original drums, most are axles that require you to swap to B/E/C/FMJ/truck-van-Dakota w/5x4.5BC and some Jeep Cherokee drums.
The difference is in the flange offset- the distance that the axle flange protrudes from the housing end. Factory A body rears through '72 use a unique offset that was not used on any other Mopar offering, necessitating the use of their own style of backing plate and drum, which dimensionally do not interchange with any other Mopar. Most 4.5 BC conversion axles use the standard Mopar offset, and require the use of the backing plates and drums listed above.
All that being said, most suppliers will specify in their spec sheets which brakes their axles are compatible with.
 
"Depends"

SBP and BBP use different flange offsets...
b87e8cda-4826-4290-8e9e-7915b82ff6b5-jpeg.jpg


BUT, there are aftermarket axles that use the SBP offset but have the 5x4.5" pattern. So, if your axles are BBP and have the BBP flange offset, you need new brakes. If your axles are BBP but have the SBP flange offset, you have to re-drill your drums.
 
72bluNblu said:
"Depends"

SBP and BBP use different flange offsets...
View attachment 1715977175

BUT, there are aftermarket axles that use the SBP offset but have the 5x4.5" pattern. So, if your axles are BBP and have the BBP flange offset, you need new brakes. If your axles are BBP but have the SBP flange offset, you have to re-drill your drums.
Click to expand...
I'm not near the axles right now. From your provided (very informative) picture I believe that they appear to be A-body sbp axles that have 2 sets of holes in the flanges. Would they be aftermarket?
 
AlaskaJeff said:
I'm not near the axles right now. From your provided (very informative) picture I believe that they appear to be A-body sbp axles that have 2 sets of holes in the flanges. Would they be aftermarket?
Click to expand...

If they have 2 sets of holes in the flanges they're probably not aftermarket. The aftermarket axles I'm familiar with typically only have once set of holes for the 5x4.5" pattern but still have the SBP offset, which is why they can be tricky. If there's two sets of holes they're probably just factory axles someone re-drilled. But I suppose they might also be re-drilled aftermarket axles.

Either way you'll have to confirm the flange offset, since it can only be right for one of those patterns.
 
I think you're going to need to measure them well. I have a set of Dr.Diff axles that came with 2 sets of holes, both are 5x4.5 but one is for press in press in studs and the other set is screw in studs
For what it's worth, the 5x4.5 axles I've seen (both stock and aftermarket) have a thicker flange than my sbp axles so it might be worth checking that too
 
Quick and easy way to tell if they're legitimate 5x4.5 axles or redrilled 5x4 axles: measure the center register. If they're 5x4.5 axles with two sets of holes (for press in and/or screw in studs, for example) the center register should be ~2.825" IIRC. Redrilled 5x4 axles would have a much smaller center register, I don't recall the exact measurement offhand- maybe 2"?
 
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