How do I find out if I have 11 or 13 inch brakes

[Nasty-LSX]

1985 4x4 k20. I noticed some brake master cylinder replacements say for 11in and 13in brakes.
Im replacing the brake master cylinder and want to get the correct one. Not sure if they are
talking about the front or rear brakes

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[squaredeal91]

Measure your drum for size

 

[AuroraGirl]

if you have a 16 inch wheel, the 13 inch drum fills almost the entire back of the wheel
If you have 11, there is extra room
13''

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11 inch

These are both 14 bolt full floats and both have the same kind of wheel, same tire size

mine are 13 because I have c6p, heavier duty 3/4 ton which includes larger diameter shocks and thicker frames(noticeable looking at them thats why I included the shock pic next to the 13 inch drum)

im sure you can get 13 inch drums just having a better braking RPO, but im not 100% certain on that or what years. What RPO for brakes do you have?
I also notice you have a 14 bolt semi float which im not sure what brake options they had

my instinct is to say you prob have 11 inch

 

[Nasty-LSX]

If you look at the last picture there is almost no gap. I have 16.5x8 wheels. Dont think they make this tire
size anymore for a 16.5 rim lol. I have almost No gap between drum and rim.

So it's a 13in. Thanks aurora

 

[AuroraGirl]

If you look at the last picture there is almost no gap. I have 16.5x8 wheels. Dont think they make this tire
size anymore for a 16.5 rim lol. I have almost No gap between drum and rim.

So it's a 13in. Thanks aurora

The lighting was bad and I didnt see the it as well as you lol youre right

 

[Nasty-LSX]

The lighting was bad and I didnt see the it as well as you lol youre right

Here are some better pics!

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[HotWheelsBurban]

Yup that's what the 13" drums look like inside my crew cab's 16" wheels too. Not much room for cooling air to flow around them....