Rear Drum Question

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e50095

e50095

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Some years ago I bought a pair of 8 3/4 axles that were redrilled for bbp. My thinking was change the axles and buy new 10" drums from a 73 up car and I'm on my way. Now I'm not so sure. My 8 3/4 has 10x1.75 shoes on it, and it looks like the 73 up shoes are 10x2.5. Am I missing something or is this more of a complicated mission than I thought.

I appreciate any expertise you can offer.
 
No its not that easy. The SBP 8 3/4 has a specific brake offset or brake spacing. Your only solution when redrilling a SBP axle is to drill the original drums. Your best solution now is to buy a set of BBP axles.
 
CRAP!!!! I was afraid you were gonna say that. It appears Dr Diff has them on ebay for $348 with shipping. If I go that route I assume I can use the 11" drums and backing plates I got from the Upullit years ago from a B body, although I wonder if that causes an issue with emergency brake cable length.
 
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SGBARRACUDA said:
No its not that easy. The SBP 8 3/4 has a specific brake offset or brake spacing. Your only solution when redrilling a SBP axle is to drill the original drums. Your best solution now is to buy a set of BBP axles.
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Or you could redrill your drums for BBP.
 
I could, but mine are out of spec, and the small bolt drums are getting tougher to find, tougher being defined as rockauto doesn't have them. I think they can be had for around $150 a pair. I wonder how much the machine work would be, and whether the 11x2.5 is worth the extra money compared to 10x1.75.
 
You said "Years ago".About how long? At one time they were making big bolt pattern axles that were direct replacement using the 1.75'' shoes and backing plates. I bought 2 sets of axles from Mancini and did my Dart and my friends Duster.All we had to do was re-drill the drums for the pattern.They even had the small hub register.That was 20 years ago. I'm not sure when they stopped making those axles but now it looks like the only ones on the market have the 10''x 2.5'' backing plates and drums AKA "B'' body parts.So look at your 4''BP axles and the replacements to see if the hub register matches.If so you got the "old style axle" for lack of better wording.If not then you can use the 10''x 2.5'' or=
"Yes" on using the 11'' drums and matching backing plates as long as they are 11x2.5'' Chrysler also made 11x2" sets. I believe your brake cables will work as I've done several 11'' changeovers and used the cables over again.
 
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ster.All we had to do was re-drill the drums for the pattern.They even had the small hub register.That was 20 years ago. I'm not sure when they stopped making those axles but now it looks like the only ones on the market have the 10''x 2.5'' backing plates and drums AKA "B'' body parts.So look at your 4''BP axles and the replacements to see if the hub register matches.If so you got the "old style axle" for lack of better wording.If not then you can use the 10''x 2.5'' or=
"Yes" on using the 11'' drums and matching backing plates as long as they are 11x2.5'' Chrysler also made 11x2" sets. I believe your brake cables will work as I've done several 11'' changeovers and used the cables over again.[/QUOTE]
 
thanks for the info brother, I bought mine probably 15 years ago off ebay. I think they were stock axles that were redrilled, but I'm gonna measure to be sure. Did you notice any real gain on the 11" swaps you did. I've read some folks say the difference is clearly noticeable and others say no change whatsoever.
 
e50095 said:
I could, but mine are out of spec, and the small bolt drums are getting tougher to find, tougher being defined as rockauto doesn't have them. I think they can be had for around $150 a pair. I wonder how much the machine work would be, and whether the 11x2.5 is worth the extra money compared to 10x1.75.
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Check with Napa
 
Can't say that it was noticeable. We are talking about rear brakes.Can't hurt.Bigger is always better so I've been told.Now that I see yours were re-drilled (my bad I read it too fast) then have your drums drilled and all will be good.Also the most inexpensive way to go.It's all up to you.
Now of course you can't use the 11'' brakes with those rd-drilled axles.Just the stock 1.75''.
 
e50095 said:
CRAP!!!! I was afraid you were gonna say that. It appears Dr Diff has them on ebay for $348 with shipping. If I go that route I assume I can use the 11" drums and backing plates I got from the Upullit years ago from a B body, although I wonder if that causes an issue with emergency brake cable length.
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There's no issue with the e-brake cable length using the 11x2.5" rear drums. I have 11x2.5" drums on my Challenger, on my Dart and previously used them on my Duster before switching over to rear disks. I used the stock e-brake cables on all them without issue. Obviously you need to re-adjust the e-brake, but there's more than enough adjustment to deal with the minor difference in the size of the drum.

You can't mix and match backing plates, shoes, etc between the SBP 10x1.75" drums and the BBP 10x2.5" drums. The axle flange offset is different. If you have re-driled SBP axles, or the Moser axles that have the SBP axle flange offset (despite have the 5x4.5" pattern) then you have to use 10x1.75" brakes with re-drilled drums.

bbp-axle-shafts-copy-jpg.jpg

If you switch to BBP axles (with the BBP axle flange offset) you have to use the 10x2.5" or 11x2", 11x2.5" or 11x3" rear brakes. 10x2.5" and 11x2.5" are most popular. Keep in mind if you just buy a set of 11" backing plates that the backing plates are specific to the shoe width, ie, 11x2" backing plates are different from 11x2.5" backing plates. They have a different offset from the housing because the axle flange offset is the same for all of them.

The 11x2.5" brakes are a pretty significant upgrade from the 10x1.75's. Which is great, but they work best when paired with larger front brakes as well. I use them with the later 11.75" B/R rotors that work with the 73+ BBP spindles. And the really nice thing is that they came on cars and trucks up into the late eighties, so, parts are easy to find. Unlike for the SBP stuff, at least at times.

This is a listing from eBay for a set of used, loaded 11x2.5" backing plates. I've bought from this seller before a few times and haven't ever had an issue with them, they're a good seller.

11 x 2.5 brake plates loaded drum MOPAR DODGE 8 3/4 8.75 new yorker 8 9 1/4 used | eBay
 
I got longer axles out of junk yard 2 1/2" wide brake style and told Moser Engineering to shorten and respline to fit my 68 A-body. Lot less money at the time .
 
AJ/FormS said:
When your rear brakes get to be too powerful,
and they lock up the rears before the fronts do;
then you are just micro-seconds from spinning out.
This really sucks in traffic.
Click to expand...

Which isn't a problem with 10x2.5" brakes if you use the matching 73+ BBP disks. Or the 11x2.5" drums with the later 11.75" B/R body disks. Both of those combo's are better matched than anything that the SBP cars came with IMO.

And honestly, if you're really bothered by that possibility, you should plumb in an adjustable prop valve so you can dial the brake bias in to match your car. Because once you start doing things like staggering the tire widths front to rear, changing the suspension or moving things around that will change the weight bias front/rear or move the CG the factory valve won't be as accurate as it should be anyway. All of those things can change the required front/rear brake bias, and many of those things are pretty common to do on these cars. Especially the tire stagger.

What you shouldn't do is just run around with little bitty rear brakes because you're worried about making the brakes "too powerful". Most guys run wider tires on the back of their cars than they do on the front, which makes them harder to lock up. Which means that more powerful rear brakes can be pretty helpful as long as you do it right.
 
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