Strange Pilot/ hub size on 8.75 Rear drum brakes

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Nitrocide595

Nitrocide595

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Hey guys, I've been here for a while but haven't posted much.

I've converted my '69 Dart to a large bolt pattern 8.75 rear, and I finally got it all together and in the car and I noticed an issue regarding the axles, which has an impact on the brakes. This is a little lengthy, so please bear with me!

These drums came with the rear, off a show car, hence the chrome... they're temporary, just for fitment purposes at the moment, so don't worry about those.

The Axles I picked up are Mosers and go by the part number "A30-CST-A45" (Moser Engineering A30-CST-A45: Alloy Race Axle Set Chrysler 8.75" 30-Spline | JEGS)

Right when I put them on, I noticed that everything fit on fine, but the hub on the axles is about a quarter inch in diameter smaller than the drum and wheel. After some digging, a facebook post, emails to Jegs AND Moser, it would appear that the common school of thought is that the center hub on the axles are machined for the A-body rear drums, but the bolt pattern is for larger drums (and wheels).

So my question here is this: Where can I find 10" drums (and hardware) that are the proper size for the A-body center hub, but have the big bolt pattern? Will I have to just find 10 inch drums for an A-body and drill my own holes for the wheel studs? Can I just put a cut down piece of pipe in there as a spacer to fill the gap?

I'm completely open to ideas and solutions, and I appreciate your time!

1015161747a.jpg
 
Your probably going to have to find some std a body 10" brake set up for an 8 3/4 and redrill the drums out to 4.5 BP. That smaller register is only found on the small bolt stuff. If you use the a body drums your going to have to use the backing plate assy's to match the smaller brakes of the small bolt pattern drums. A bit of a PITA but workable or see if they will send you what axles you need.
 
the 4'' bc axle reg hub is smaller as well as the measurement from the flat of the flange to the axle housing as well . a 1/4'' different spacing . so your fix is a tubing spacer , but it must be tight on that short hub are they will far of while your driving the car . guess you could mig weld them in place on the inside of the ring and axle hub . they will have to be right on center if the rim is to reg on them .
 
thanks for the input, guys!

I emailed Classic Industries about the size of the hole on their 10" A/B/E body rear drums they have available... we'll see what that yields I suppose.

I thought I would have to drill out the pattern on some A-Body drums... Rockauto.com has a lot of 9" options, but 10's are Front drums. Kinda new to the whole drum brake thing... what's the difference between the front and rear drums?
 
RockAuto has the correct SBP 10" rear axle drums --- Centric 123.63044 10 inch rear 5x4 sbp are plentiful. Check under 1971 Plymouth Duster brakes.

These will have the proper axle register --- if you wish to convert these to LBP, drill them.
 
You MUST use redrilled SBP brakes with those axles. Those axles are for the SBP brakes, the axle flange offset is different than standard BBP axles. You can't use those axles with standard BBP brakes. Personally, I would see if you can return them. If you're going BBP there is no real reason to keep using SBP brakes and have to mess with having them re-drilled to fit.

This is the real problem you have, SBP axles had a different axle flange offset and therefore the backing plates can't be interchanged. The register problem is minor compared to the offset issue.

***edit***
Fixed, here's the picture

882BE0F2-CCE7-45CD-9309-1EC5A901EB5A_zpsrqarvzox.jpg
 
Last edited:
72bluNblu said:
You MUST use redrilled SBP brakes with those axles. Those axles are for the SBP brakes, the axle flange offset is different than standard BBP axles. You can't use those axles with standard BBP brakes. Personally, I would see if you can return them. If you're going BBP there is no real reason to keep using SBP brakes and have to mess with having them re-drilled to fit.

This is the real problem you have, SBP axles had a different axle flange offset and therefore the backing plates can't be interchanged. The register problem is minor compared to the offset issue.

***edit***
Fixed, here's the picture

View attachment 1714981339
Click to expand...


ok, that's great info, I didn't know that... Didn't realize there was that much going on with those axles.

Just to be clear, what exactly do you mean when you say "SBP" and "BBP"?

As far as the brakes go, they came with the rear which I got from a friend, so I was going to junk them anyway. For the cost of a whole new drum setup, I'm pretty sure I could find a disc setup for a little more. Does anyone know of a disc kit that would be a compliant alternative for these axles?

If not, I'll email JEGS and beg them to take them back in exchange for the correct ones... I don't have high hopes for that though... I bought them a while ago and finally had the time to install them last weekend... That's how a project goes I suppose.
 
i see some use of the jeep rear disc's fit 4 1/2 bc , wrecking yard stuff . just going to make some caliper brackets .
 
BBP= big bolt pattern, the 5x4.5" pattern used on pretty much every other Mopar car of the era and most of the later A-bodies, 73+

SBP= small bolt pattern, the 5x4" pattern used almost exclusively on A bodies before 1973 (and some /6, front drum equipped A bodies after '73 too)

As for the drums, you don't need to junk them. What you have are BBP drums, otherwise they wouldn't fit over the wheel studs. And that's why the center register is larger on those drums too. They should be 10x2.5" shoes right? So, those will work with BBP axles as long as the axles have the normal BBP flange offset. The axles you have use the larger bolt pattern, but have the SBP axle flange offset, so the axles must use redrilled SBP drums (10x1.75"). So if you get standard big bolt pattern axles, you can keep those drums. If you keep the axles, you'll have to find a disk kit for small bolt pattern axles, because the ones intended for big bolt pattern axles won't have the right offset either.
 
72bluNblu said:
BBP= big bolt pattern, the 5x4.5" pattern used on pretty much every other Mopar car of the era and most of the later A-bodies, 73+

SBP= small bolt pattern, the 5x4" pattern used almost exclusively on A bodies before 1973 (and some /6, front drum equipped A bodies after '73 too)

As for the drums, you don't need to junk them. What you have are BBP drums, otherwise they wouldn't fit over the wheel studs. And that's why the center register is larger on those drums too. They should be 10x2.5" shoes right? So, those will work with BBP axles as long as the axles have the normal BBP flange offset. The axles you have use the larger bolt pattern, but have the SBP axle flange offset, so the axles must use redrilled SBP drums (10x1.75"). So if you get standard big bolt pattern axles, you can keep those drums. If you keep the axles, you'll have to find a disk kit for small bolt pattern axles, because the ones intended for big bolt pattern axles won't have the right offset either.
Click to expand...


Yeah the "SBP" and "BBP" clicked for me about 5 minutes after I posted, just forgot to edit lol thanks!

I'll be looking online and I'll see what I can find. Thanks for all the help, and I'll be sure to follow up with whatever happens next!
 
After getting in contact with the appropriate parties, It would appear that JEGS won't take the axles back because they've been installed, they have the bearings pressed on, etc... fair enough, it's in their written policy. I don't really get why Moser would make an axle in this configuration, or why people would want this over getting a full BBP 10" drum set up, but I guess there's something for everyone out there.

I think, just for the ease of making changes down the road, I'm going to sell these axles to someone who is looking for them and I'll buy the correct ones for my application and take the hit of whatever the price difference is. I'm sure I'll be posting in the For Sale section when that time comes.

Thanks for all the help!
 
....you could have the drums machined to fit.....on second thought, yeah I see where this is a big snafu... finding the right backing plates and all....I do see that the drums you have are drilled for both patterns, that seems strange. Did the axle's come with both patterns? Good luck.
 
Yeah, the trouble comes with finding replacement parts in a pinch, or going disc brakes down the line. It makes more sense to do it right the first time and find the correct brake parts rather than chasing down a million different leads, re-drilling for a bigger pattern, etc. It's not that it's "too much work", I think it just makes more sense to do it right the first time :)

The axles came drilled for the Big Bolt Pattern only, and the center register was for A-body brakes (Small Bolt pattern style with a re-drill) but the drums were from a different application originally.
 
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