65 GMC 1/2 ton brake line question

[CPO1]

Hey
I've read and I can't find the answer.

I have drum/drum. Currently, the line from the single master cyl to the front brakes is 1/4 but from the right front Tee to begin the rear, the line reduces to 3/16. Is that correct??

I am swapping the single master cylinder to a dual master cylinder with booster.
I question if I should run 3/16 all the way to the rear, or run 1/4 and connect to the 3/16 with a reducer. This reduced connection would remain at the location of the right front tee.

I suspect the PO (my deceased brother) altered the sizing back in the 90's when he restored this truck. At that time, he added a booster but kept the single master cylinder.
Thanks for your suggestion.
Cheers.

[Lugnutz65]

Originally Posted by CPO1

Hey
I've read and I can't find the answer.

I have drum/drum. Currently, the line from the single master cyl to the front brakes is 1/4 but from the right front Tee to begin the rear, the line reduces to 3/16. Is that correct??

I am swapping the single master cylinder to a dual master cylinder with booster.
I question if I should run 3/16 all the way to the rear, or run 1/4 and connect to the 3/16 with a reducer. This reduced connection would remain at the location of the right front tee.

I suspect the PO (my deceased brother) altered the sizing back in the 90's when he restored this truck. At that time, he added a booster but kept the single master cylinder.
Thanks for your suggestion.
Cheers.

I seem to remember buying new brake line in two different sizes. What you describe sounds like a stock setup. If you have 3/8" coming back from the T then I'd stay 1/4" up front and 3/8" to the rear brakes. Let's see what others say.

[Monte's62]

On my 62 the backs were different than the front, but I don't remember the exact size. My bleed valves were also different. Not sure if that is the stock design or not.

[CPO1]

Right 3/8. Not 3/16. im still not sure what size line to run to the rear.
Posted via Mobile Device

[Lugnutz65]

Originally Posted by CPO1

Right 3/8. Not 3/16. im still not sure what size line to run to the rear.
Posted via Mobile Device

Actually, I think the rear lines are smaller, so 3/16" sounds right. My bad. It was a typo. 3/16" sounds right.

[pwrbrkpadguy]

When I did mine I left the 3/8 line alone going to the rear and ran 3/16 line for the front.

[Lugnutz65]

Originally Posted by pwrbrkpadguy

When I did mine I left the 3/8 line alone going to the rear and ran 3/16 line for the front.

Well shoot! I guess just ignore my size references. My memory obviously stinks. Haha!
But basically I'm thinking that the line size would not change even though you are running a dual master. I'm gonna look for a thread on the subject and post it here when I find it.

[pwrbrkpadguy]

Lugnutz, we may all be wrong but if I remember right the rear brakes on a drum drum setup do most of the work
Unlike disc brakes. Mine stops great with this combination and I think key word being THINK I read this on the forum somewhere. I hope I'm right cause I don't want to have to change mine.

[61K10]

my 61 k10 (4x4) had 1/4" front to rear then split to 3/16" to each rear wheel cyl.

[KVB]

What make or brand or year of dual master are you installing?

Ken

[CPO1]

Originally Posted by KVB

What make or brand or year of dual master are you installing?

Ken

Ken, I picked up a "MBM" brand master cylinder and dual chamber booster for a 1967-72 C10, C20 truck. I found it at a local brake shop. Im in the process of installation but it will be another week before Im finished.

[sharkskinman]

I'm going to measure between 3/16-1/4"
Can I just use either or??
How much do I need?
8' front?
Rolls come on 25' I believe.. Will that be enough?
What's the thread pitch 3/8-24?
I would like to get all I need before I dig in

[Monte's62]

Sounds like your making your own lines from a roll. If you buy the straight pieces at a parts house just make sure you get the American threads on your couplings. They used to all be American and now they are made with threads from 5 different countries!!!