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Originally Posted by roger0080
...4x4 Poet, thanks for the detailed info. You don't say what years the HO52's are from.
I am going to venture to say that one of those was switched from a 4WD Drum setup to the 2 WD drum setup of 11x2-1/2.
Could you/Do you know if the backing plates are the same/same size on both those vehicles???
The GM parts manual says that ALL the 4WD backing plates are the same part numbers.
My 71 K20 Eaton uses 5/16" brake line.
Does your 11" HO52 have 3/16 or 5/16? I wonder if that is the difference in the wheel cylinders for 2WD vs 4WD...
Guess I learned that 12x2 drums are non-existent....
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I added the year above. It's a '72 K20 pickup, but it's a hodgepodged truck, so it could have an H052 or parts of an H052 from anywhere. You may be right about my '72 K20 having swapped backing plates to get 11"x2.5" brakes. Maybe someone was running away from the 12"x2" brakes. When I ordered the brake parts, I gave the vehicle app and also told them it's got 11"x2.5" brakes.
With that info, the wheel cylinders were different and the rear brake hose did not match. Carquest books said that the wheel cylinders that did work (after returning the ones that didn't match) were for coil spring trucks even though my '72 K20 pickup obviously has leaf springs as did all 4x4s. The difference is one has symmetrical wheel cyl mounting bolt holes and one has asymmetrical mounting holes. So whether the backing plate has symmetrical or asymmetrical bolt holes or slots drives what wheel cylinder is used. According to my local Carquest, asymmetrical are for coil spring trucks.
I don't know for which model they ordered the rear brake hose that turned out to be correct. I think they made a mistake on the first hose they gave me because the correctly fitting hose matches my K10 burb's rear brake hose and my Classic Industries catalog lists Skyjacker SS hoses as being all the same part # for all 67-72 4x4s. I have one of their rear 4x4 SS brake hoses which matches the correct hose Carquest finally gave me. Anyway, don't take my word for it. Just be wary.
The 12" brake backing plates are definitely larger diameter because on both 11" and 12" brakes, the brake drum double lip fits over the backing plate lip to make something of a overlap fit without touching, of course. More importantly, there's the symmetrical vs. asymmetrical wheel cylinder bolt hole/slot differences. For the same year, maybe all 4x4 backing plates are the same if all 4x4 H052s originally have 12"x2" brakes. Maybe all 2wd are the same. Don't know.
Don't take my word for the lack of availability of new 12"x2" drums. I haven't tried to source them in years. I'd definitely convert the rear to discs if I had 12"x2" brakes in need of refurbishment to avoid future parts availability concerns. My K20 burb has 12"x2" or 12x2.5" (I forget, but the hub lines up) drums from another vehicle app that a brake shop turned part of the lip off of to help them overlap with the backing plate. Don't know the app. This was in '94 way before I knew one could convert the H052s to discs. The 12"x2" drums are fine for now since they have Praise Dyno Brake shoes mated to them.
My '72 K20 pickup's hard brake lines are 3/16" (EDIT: Wrong! They're 1/4"). The fittings take a 7/16" wrench. I haven't looked at my '71 K20 burb's H052 hard lines. The fittings for the H052 hard lines on my '72 K20 fit both the "symmetrical" and "asymmetrical" wheel cylinders. I know, because I had a few threads of the fittings started with the wrong wheel cylinders before I noticed the bolt holes didn't line up. I thought I was being smart to start the threads before tightening the cyls.
