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.

[Lugnutz65]

Originally Posted by 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.

OK, so this bothered me enough that I went out to the garage. I measured the OD of my brake lines with a digital caliper. My factory style single reservoir has a 1/4" OD hard line that runs to each front brake hose. There is a T-junction block on the PS front line that has a 3/16" line that runs to the rear brakes. The hard line that runs to the back is definitely smaller than the front line. It can't be 3/8" because 3/8" is larger than 1/4". My caliper confirmed it's a 3/16" too.

I'll be able to sleep better now. Haha!

[pwrbrkpadguy]

Thanks a lot Lugnutz, I'm still at work won't get out till 10:00 then have to be back at 9:30 in the morning with no sleep cause I got the wrong brake line setup!

[CPO1]

Ok Cool. Thanks for everybody's discussion. No worries Lugnutz65- even I mixed up the dimensions. Agreed 1/4 to the front brakes, 3/16 to the rear.

So.... now that I'm swapping the single master to a dual... do I run 3/16 hardline right from the master for the rear brakes??

[pwrbrkpadguy]

Originally Posted by Lugnutz65

OK, so this bothered me enough that I went out to the garage. I measured the OD of my brake lines with a digital caliper. My factory style single reservoir has a 1/4" OD hard line that runs to each front brake hose. There is a T-junction block on the PS front line that has a 3/16" line that runs to the rear brakes. The hard line that runs to the back is definitely smaller than the front line. It can't be 3/8" because 3/8" is larger than 1/4". My caliper confirmed it's a 3/16" too.

I'll be able to sleep better now. Haha!

Lugnutz, you are absolutely correct. Just got home from work and checked my setup and it is just as you say 3/16" line that runs to rear and I used the existing 1/4" line on the front. It's tough not remembering things sometimes! Anyway CPO1 that's two people that finally agree on how to set up your drum drum brakes. It was easy to do just hard to remember!

[Lugnutz65]

Originally Posted by CPO1

Ok Cool. Thanks for everybody's discussion. No worries Lugnutz65- even I mixed up the dimensions. Agreed 1/4 to the front brakes, 3/16 to the rear.

So.... now that I'm swapping the single master to a dual... do I run 3/16 hardline right from the master for the rear brakes??

I recommend using a piece of 1/4" line and then a reducer. Some people, even me, would install a brake pro portioning valve. If you can connect a 3/16" line to the master cylinder then that seems ok to me. Most folks would just plug the junction block right where the 3/16" line starts to run back and then run a new piece of hard line straight from the master to the 3/16" line. Give the pro portioning valve a thought. I know they are usually just for disc/drum setups but it gives you some adjustability.

[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 Lugnutz65

I recommend using a piece of 1/4" line and then a reducer. Some people, even me, would install a brake pro portioning valve. If you can connect a 3/16" line to the master cylinder then that seems ok to me. Most folks would just plug the junction block right where the 3/16" line starts to run back and then run a new piece of hard line straight from the master to the 3/16" line. Give the pro portioning valve a thought. I know they are usually just for disc/drum setups but it gives you some adjustability.

Cool,
Then that's my plan. I'll plan to go disc next year so a portioning valve now would save headache later. Thanks.

[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.

[OldGMJon]

Well, in fluid dynamics, when you go from a larger diameter line to a smaller diameter one, the pressure increases. So the smaller line to the back is intended to increase efficiency to the rear brakes and should remain.

[sharkskinman]

Ok..65 c10..drum-drum
Went to replace 1 rubber hose and I know Need to replace all!
1-MC to first T 32"?
1-short T to drvr rubber 9"?
1-long(about as long as MC to T) from 1st T to psngr side T 28"?
1-short from T to psngr rubber 9"?
1-long to back T. ?"
1-short to psngr rear rubber
1-long to drvr rear rubber

Have I got them all?
Will probably have to cut them off
But hopefully can at least keep og to rear from psngr T

Should I buy length and bend as needed
Or buy a roll and make them myself? (seems immensely cheaper)

Anyone have or can get me measurement so if I do them myself I know how much I need?
And the new MC has 2 places for hoses?
1 for front and one for rear??

[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!!!