The Stovebolt Site Forums The Shop Area Engine Shop 3/16 " vs 1/4" rear axle brake line

The rear end of my truck has the real small 3/16" diameter brake line. If I was to change it to 1/4" to match the rest of the brake lines, would I also need to change the two brass blocks that connects between the rear wheel cylinders and the lines as we as the brass "T" connector that is clipped onto the rear axle housing? I would think that the threaded nuts on the 1/4" line would have larger diameter threads, yes?

Who's a good sourse for these brass fittings?

Yes,Craig, the brass junction blocks would have to be changed. The tube nuts are larger on 1/4" lines than 3/16". My 50 has all 1/4" lines while my 51 is all 3/16" except for the main line from the master which is 1/4". I believe this was because of the change in brake systems from 50 to 51. Along with going from the Huck brakes to the Bendix, they also changed the master cylinder,1" bore in 50 to 1-1/8" bore in 51.

Weren't you changing your front brakes to Bendix also? I would run all the same line, but I'm not sure if it would be better to go all 3/16" or 1/4". If your master cyl. is a 50 it should be a 1" bore.

I think if you have a system that has dissimilar sizes now and change it you actually change the operation of the brakes.
If you imagine the master cylinder displacing X amount of fluid. If that fluid is pushed through a narrower opening it will travel further. So with rear brakes at a smaller diameter, the rear brakes would operate unequally from the front. This may be intentional or not.

My '52 has 3/16 everywhere except the line that goes from the master cylinder to the brass junction on the right hand side of the frame. This piece is 1/4 and is mounted on the crossmember.

Craig: If you need some brass fittings for the rear axle for 3/16 I have a complete, extra set from a rolling chassis I have used for parts.

Looking for the junction blocks in 1/4", thanks

Tony M - you are scaring me man!

The difference in 1/4 vs 3/16 tube sizes plays no role in distribution of pressure to the wheel cylinders at the fluid flow rates experienced in any normal braking system.

Using the 1" 1950 master cylinder will result in less brake pedal effort, but also less margin for acceptable brake shoe adjustment.

You will have to pay slightly more attention to how the shoes are adjusted - if you let them go for too long, you will bottom out the master cylinder before you reach maximum braking effort at the wheels.

So at present, you need the 3 rear axle brass blocks in size 1/4"?

My theory is wrong? I was wondering about it for a while.

Ken is correct. The displacement of the wheel cylinder is so small with respect to the brake line flow capability that it is safe to ignore the dynamics of fluid flow. The pressure at each of the 4 wheel cylinders essentially identical at all times. Of course, we are all talking about single (non-split) braking systems.

Yes,
3 1/4" rear axle brake blocks.

C