Can anyone check 3/4 ton disc brake line size for me?

[davepl]

I'm converting a '70 Longhorn over to '72 discs (also 3/4 ton).

I need to know if the factory changed from 3/16 front hard line to 1/4 when they went to disc brakes in the front. I just can't find anything that says anything either way.

I ordered a repro front brake line kit but even though it's sold as 3/4 ton it's clearly for a 1/2 ton and useless to me, let alone to use as an indication of what is "right".

Anyone have a 3/4 ton and a pair of calipers? I'm looking for the diameter of the hard line between the prop valve and the T fitting (the part that goes down to the frame). If you're ambitious it'd be good to know the diameter between the T and the flex hoses too.

Although many argue that tube diameter doesn't really have much if any effect, especially on short runs, I'd like to do this once and do it right. On the other hand I don't want to redo all of that damned stainless if 3/16 is already right for it!

Thanks,
Dave

[airdale94]

Ideally you want 3/16" diameter with front disc and 1/4" for rear with wheel cylinders. The reason I was told was with front disc it's not the volume you need but the pressure. Smaller line, higher pressure. With the rear you don't need the pressure but want the volume. With that being said I just swapped a 14 bolt out of a early 80's and had to use 3/16'' to connect the wheel cyls. so... I would keep the 3/16 because I don't know that they ever switched to 1/4 on the front.

[mgchevyparts]

There is no pressure difference due to line size and either size will work fine.

[JointTech]

ill measure it tomorrow for you. I just put in new lines and still have the old ones.
who did you get your SS from? I got mine from inline tube.

[Tx Firefighter]

Originally Posted by mgchevyparts

There is no pressure difference due to line size and either size will work fine.

That is true. Line size does not affect pressure in any way.

[JointTech]

Hopefully this helps.

[davepl]

Any idea which two are the .255 lines? Since I'm stuck with making my own, I can't ID them easily from looking at them.

[JointTech]

pic #2 is the piece that connects to the long piece that goes down the frame.

it goes across the cross member and then connects to #4 which goes up to the prop valve.

[davepl]

So if I'm reading it right, both #2 and #4 are for the rear brakes then? And they're both 1/4" while everything for the fronts is 3/16?

[JointTech]

yup. you said you wanted the front lines all measured. well those are at the front of the truck but yea they are for the rear brakes.

Im pretty sure #1 goes to the passenger caliper and #3 goes down from the prop valve.
the one to the drivers caliper is just a short L shaped piece which Im not sure why I didn't get a picture. sorry.

[tony58]

Are you doing this so it looks original? Because as already pointed out there is no difference in your brake performance or pressure due to line size.