Rear wheel cylinder bore

[Mori]

Looking to replace rear wheel brake cylinders but in doing some research I see they come in different cylinder bore sizes. Is one bore size recommended over another?

 

[Apogee]

What year EB are you working on? What front brakes are you running, disc or drum? If disc, which ones? GM...Ford...standard caliper piston bores or oversized?

 

[jckkys]

The size would determined by the whole brake system. The last thing you want is rear end lockup. It's distressing to have your truck swap ends in an emergency stop. Ford put different rear brakes in EBs over the years.

 

[Rustytruck]

its really not an easy swap as the hole register in the backing plates are different. in my year bronco there were 2 different bores the larger one for the 3300 11x1-3/4 drum and the smaller bore lighter duty 10 x 2 inch drum then another one for the front drum brakes.
earlier broncos had the small bearing rear axle for yet another size.

 

[Mach]

What year EB are you working on? What front brakes are you running, disc or drum? If disc, which ones? GM...Ford...standard caliper piston bores or oversized?

Sorry late to the party. I’m looking for drum cylinder bore size as well. I’ve got disk fronts with the larger Torino calipers from duff. I’ve got small bearing axle. Running drums in the rear.

 

[Broncobowsher]

I think you missed that the different bores are matched to the backing plates. They are not interchangable. Whatever wheel cylinder that matches the backing plate is the one that works. They did this so you can't put the wrong bore wheel cylinder on for the given backing plate.

 

[DirtDonk]

That being said, there are fittable units out there, if you have a friendly counter person at a well stocked store, willing to let you go through the boxes. Or have an book with specifications.
I had the former when I put larger wheel/slave cylinders on my '71. But as the others were saying, if you are looking for replacement cylinders, you need to specify the brakes and year of Bronco, so you get the "one single" size that was specified for your particular Bronco.
They are different front to back and left to right, and whether you have 10" or 11" inch brakes, and what year range your Bronco falls in to. Different line fitting sizes and angles, different register sizes, different bolt spacing, etc.
So for Mori the OP, if you specify your exact setup, you don't actually need to know the size. Just that it's for your setup. For all I know, the bore sizes for the rear are all the same?
The problem comes now, if your components have ever been swapped to another model!

Here's our web page with the choices: https://www.wildhorses4x4.com/66-79-ford-bronco-rear-drum-brake-wheel-cylinder
Unfortunately it looks like we made a change to how it works. The old page used to show a list of the different part numbers within the category for the different applications. Now you just click on the specifics and add it to the cart. Does not show details. Just the base part number. I thought it used to also show the bore size, but I could be wrong about that.
The brake book from Centric lists the size of the master and of each part number wheel cylinder. But I don't have it handy at the moment.
I see that RockAuto does not have that capacity. They list the size for them, but simply list them as "front" or "rear" and don't break down the rears into the two different categories. Too bad for them...
Still, the bottom line is if you're just replacing the existing ones for the same ones, you need to drill down in the specifications.

Paul