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Discussion Starter · #1 ·
I have a set of 11" backing plates from a Caprice and am in the process of changing my rear axle to an 8.5 posi. The original 9" brakes were totally junk so while I'm at it my thought is that putting the 11" won't cost hardly any more than replacing all the 9" parts. Everything I've heard indicates its just a bolt on conversion.

Question is, am I doing the right thing and are there any problems I'm going to run into on my 71 El Camino with this conversion???

Thanks, Ed
 

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I'm not sure about 14" wheels. But if your running 15" wheels, The 11" drums will be no problem. As long as the Caprice had a 8.5 it will be a simple bolt up and you will definitely notice the extra braking.
 

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Discussion Starter · #3 ·
Scott, I'm planning on 15 or 16" wheels so anything over 14" will be fine regardless of style and offset? The rear axle that I took them from is a real mystery to me because I bought it for the posi thinking it was an 8.5 because it had 10 bolts on the cover. When I got the carrier out it seems to be a 12 bolt with 8.875 diameter gear and 12 bolts. Stamped GM on the gears so go figure.

Either way, I was under the impression that brake systems interchanged between 8.2, 8.5, and 8.875 (12 bolt) rear ends. Isn't that true because the bolt pattern appears to be the same to me.

Ed
 

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That is odd Ed. I know that some BOP rears have 12 bolt covers and 10 bolt ring gears, But I don't recall a 10 bolt cover with 12 bolt ring gear.
You need to post the #'s on the axle tube and carrier, May be someone can shed some light on this.
 

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Discussion Starter · #5 ·
The numbers on the carrier are something like:

R 3
17-2
Y 09 82

I'm working from a photo but tomorrow I'll get it out of the box and check it out. Also, I'll post the numbers for the R&P. I'd post a photo but I don't know how. Also, it is a C clip type so amost for sure a Chevy.

Thanks, Ed
 

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I just put my 10 bolt backing plate on my new 12 bolt moser for my 69 Camaro. I was going to use the backing plates off of my 12 bolt from the 69 ElCamino but they were exactual the same. So I left the line hooked up and no bleeding the brakes for me.
 

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if you're going to buy all the new parts anyways, go with the bigger brakes.
the cost will be close to the same, and more braking power is a good thing.
 

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what donor cars have the 11" brakes that will fit a 69 12 bolt axle? i'm thinking of using the praise-dyno rebuilding kit. i have a 12 bolt rear rebuilt but need to purchase rear brakes. the after market 11" brake kits run about $400 and if i could rebuild a set cheaper that would be great. thanx
 

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76 and 77 Monte Carlos and Chevelles have the big brakes, along with all their A body cousins from the same years.
Carprice wagons, cop cars, and taxi cabs have the bigger brakes- but use the big 5X5 bolt pattern. you might be able to use the Caprice backing plates with Monte Carlo drums.
 

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Discussion Starter · #11 ·
I have an almost unlimited source of 11" backing plates if anyone is interested. Will even have them blasted and painted for a little extra $.

I've checked the one's I bought against my early 70's 8.5 and they fit. I'm pretty sure the 69 12 bolt is the same pattern. With a good set of plates you should be able to buy the rest of the parts for under $150. Contact my e-mail if you are interested or reply to this post.

Ed
 

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Discussion Starter · #13 ·
The drums are risky because I can't guarantee they would be usable - and they are expensive to ship. Checker has them anywhere from $29 to 85 for a 78 Caprice - some had 11 and others 9.5. The shoes are a little more but not more than $5 and the springs are about the same so you could buy all new parts for under $120 if you wanted to.

I could sell you a set for $50 plus shipping. They are light so it wouldn't be much. Sandblasting is extra and takes about a week.

Ed
 

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most of the cars with the big brakes also have the big bolt pattern- wagons and cop cars.
but i know for a fact that the 76-77 Chevelle and Monte Carlo had the proper bolt pattern, so those would be the drums to get.
 

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I could sell you a set for $50 plus shipping. They are light so it wouldn't be much. Sandblasting is extra and takes about a week.
Ed,
I'd be interested in a set of 11" backing plates shipped to 30066. No blasting required.
PM sent...
 

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Discussion Starter · #17 · (Edited)
The set I have for myself I've checked the bolt pattern and it matches the 8.5" I'm putting in my El Camino. Jamie, I'll get them and all the hardware I can - can't guarantee everything will be there. Anyone who wants a set send me an e-mail using the website and we'll arrange it - you can send another member a message by clicking on my username. I don't want to post my address for obvious reasons.

Ed
 

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what about 73-87 chevy trucks? they had the 8.5 ten bolt. not sure of the diameter. the drums have 5x5 pattern but you would think that the trucks would have bigger drums.
 

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If I was going to get new, prebent brake lines, (on my '66 Chevelle), I wonder if I should just the slightly longer 68+ lines and tweak the ends (I assume the wheel cylinder will be a little (1") further from the axle tube...

Any one know if the wheel cylinders for the 76/77 Chevelles (or other big drumcylinders) come in US standard, or metric only? Or would regular Chevelle cylinders still work?
 
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