rear brake swap question

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fishy68

fishy68

Tyr Fryr's Inc.
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I just acquired a nice set of 11x2" brakes. Not sure what their off of other than some other Mopar. My plan is to replace the small 10x1-3/4 brakes on the back now with them and hopefully have better holding rear brakes cause the stock ones suck. Question is has anybody done this and if so what brake drums did you use? My axles are stock but Moser re-drilled them to the large pattern and installed 1/2" studs so the drum would need to be large pattern.
 
fishy68 said:
I just acquired a nice set of 11x2" brakes. Not sure what their off of other than some other Mopar. My plan is to replace the small 10x1-3/4 brakes on the back now with them and hopefully have better holding rear brakes cause the stock ones suck. Question is has anybody done this and if so what brake drums did you use? My axles are stock but Moser re-drilled them to the large pattern and installed 1/2" studs so the drum would need to be large pattern.
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11"x2"? That's what the front of my B-body has. The 11" rears I have are all 3". That's the Dip, the Ramcharger, and the Sport...
As for the conversion Pop and I've done the 11" brake upgrade on the Dip using the backing plates from an 11" car. From there it was just a matter of ordering shoes, hardware, drums, etc, for the cop car. Seems to me that if you have the backing plates you could order up the drums for a 11" brake B-body.
 
I just dont know :(
11 inch drums that have the 4.5 bp may require a larger center register. I can go and measure the register in both early a Sbp wheels and later Lbp wheels if that would help. Or just call a parts store and ask them to pull the 11X2 rear drum for a 73 A-body and measure the hole for you.
 
ramenth said:
11"x2"? That's what the front of my B-body has. The 11" rears I have are all 3". That's the Dip, the Ramcharger, and the Sport...
As for the conversion Pop and I've done the 11" brake upgrade on the Dip using the backing plates from an 11" car. From there it was just a matter of ordering shoes, hardware, drums, etc, for the cop car. Seems to me that if you have the backing plates you could order up the drums for a 11" brake B-body.
Click to expand...

Yeah their 11x2 and they are rear brakes. Apparently their an oddball size. I didn't know it or I wouldn't have bought them. At least I got them cheap. I went to NAPA and me and the guy dug all through the books and couldn't come up with any rear brakes that were 11x2. All the 11" rear brakes were 2-1/2 or 3" wide and these are just 2" wide.

RedFish said:
I just dont know :(
11 inch drums that have the 4.5 bp may require a larger center register. I can go and measure the register in both early a Sbp wheels and later Lbp wheels if that would help. Or just call a parts store and ask them to pull the 11X2 rear drum for a 73 A-body and measure the hole for you.
Click to expand...

Thanks for the offer Red but for now I don't know what I'm gonna do since they seem to be such oddballs. I can't even find parts for them. Guess I'll wait until I run onto a set that'll fit. Going to Monster Mopar this weekend so hopefully I'll find something.
 
Just a question, but would the backing plates for an 11" 8 1/4 or 9 1/4 work on the 8 3/4? I'm asking this because I'm not sure. I've had no need to do a swap like this (for the reasons posted earlier.) If they do fit, then what's to stop anyone from finding a junk Dip or Fury cop car and scarfing up the parts to do the swap? The M-body has the BBP and you might find the parts easier to locate. The earlier trucks would work, too.
 
I think your right Robert. From everything I've read their all the same bolt pattern on the housing ends. I have not proved that in person but that gives me something else to look for. In fact it's entirely possible these came from a vehicle with something other than an 8-3/4 and that's why I couldn't find parts for them because I only had the guy at NAPA look up parts for an 8-3/4. Good idea Robert. Thanks
 
fishy68 said:
I think your right Robert. From everything I've read their all the same bolt pattern on the housing ends. I have not proved that in person but that gives me something else to look for. In fact it's entirely possible these came from a vehicle with something other than an 8-3/4 and that's why I couldn't find parts for them because I only had the guy at NAPA look up parts for an 8-3/4. Good idea Robert. Thanks
Click to expand...

I'm gonna go up to my parts storage today and you got me curious enough to take some measurements. I'll let you know what I find.
 
Tracy, took some measurements off one of my 8 1/4's. The backing plate bolts are as follows (on center's, approximates, I may be off a 1/16 or so)


< 3 1/2">

^ 0 0
1 9/16"

v 0 0

the center surrounding the axle is 3 7/8".

Didn't pull apart one of my 8 3/4s to check. The 'Cuda is off to a new home tomorrow and the Satellite is just a pain in the butt...
 
Here is the housing end dimentions to some popular rears (and some not so popular ones too!) I thought the 8.25 was on this as well but I was mistaken.

I have read that the 8.25 backing plates have the same pattern with the exception of the bottom bolt hole that can be drilled out. What I dont know is if 8.25 complete brakes will work on an 8.75 because I dont know the measurments of how far the axle face is from the housing ends bolting surface (does that make sense? lol)

Oh! The housing ends on my now trashed 7.25 (1976) was the identical pattern as the 8.75. The brakes were 9" and I should have for curiosity sakes made some measurments.... oh well it's gone

Though I have not checked, I do beleive the 9.25 (1974) also has the same housing ends as the 8.75

What was the question again?

Axle Housing Ends 2.jpg
 
My two cents from my personal experience...

I've swapped complete brake set ups between 1974 7.25 and 1968 B-body 8.75 and between 1973 A-body 8.25 and 1970 A-body 8.75. The swaps involved the 10x2.5, 11x2.5 and the 10x1.75 brake set ups. All were direct swaps with no modification and all were large bolt pattern axles.
 
You may also need to look into whether the 11 x 2 brakes you have will suit the modified SBP axles that you currently have. With stock A body SBP axles, the distance bewteen the axle bearing and axle flange is less than large bolt pattern axles - by a total of 3/4 inch overall or 3/8 each side. Assuming your 11 x 2 brakes would have come a LBP car, this length variation may effect the mounting/working relationship between backing plate and drums (ie. when mounted on your SBP axles the drums may hit or rub the backing plates because they would be moved closer in towards the drum by that 3/8 inch).

As for your general question, I've nearly completed a big brake set-up for my 8 3/4. I bought some Raybestos 11 x 2.5 drums from Rockauto (about $43 USD each). I already had the correct backing plates though u see them on ebay regularly.

CIMG1844.JPG
 
the center register on sbp drums is smaller than lbp drums. they are not interchangeable because of that. the register needs to fit the axle correctly.

I have swapped complete rear brake assemblies from 7-1/4's to 8-1/4's and 8-3/4's (ALL lbp assemblies) worst case I have run into is you have to drill one hole in the backing plate for the fifth mounting stud.
 
Yes this is alot of great info and I really appreciate it. The only 2 things I knew for sure was they would bolt up to the rearend housing cause their (7-1/4, 8-1/4, and 8-3/4) all the same flange pattern and I knew the register had to match the axle. I figured their would be an offset diff. but had no idea what it really was. I have to take the left axle out next week to replace it (bent) so when I do I will do some measuring and see how much diff. their is in the offset of them and the stock brakes and go from there. Again thanks for all the info gents.
 
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