47-55.1 Master cylinder to prop valve

[Matt_50]

I'm concerned if this will work. All I need is rubber line from frame to rear axle to finish brakes but I got to thinking about the small lines going from master cylinder yo prop valve. I used 1/4 line but not all the holes are the same.

[Matt_50]

I'm looking at the port holes. Both on prop valve and left one on MC are the same. Right one on MC is slightly smaller... 3/16?

[Matt_50]

I'm getting mixed results when I Google this.

1984 c10 MC.

Bought a new prop valve.

So I'm searching 84 Chevy brake line sizes and what I'm not sure about is from MC to factory prop. I'm thinking one might be 1/4 from MC to prop and one 3/16 from MC to prop. But the new prop looks like both ports are 1/4.

Then I found this adapter... what do you guys think?

[Kevin Mac]

I am pretty sure you can buy a 3/16" nut for 1/4" line, that way you only have 1 joint and not 2. I had an adapter like that I overtightened and it popped the threads off/ broke so if you use one be cautious.
Kevin

[Matt_50]

I made lines from MC to prop. I got fittings that screwed in to all 4 spots, and I used 1/4 line for both.

My question... can a 1/4 line seat onto a 3/16 spot without leaking? The inverted cones with the hole in the center on both the MC and prop... can they take either line size?

[Kevin Mac]

Matt 50 mine is piped with 1/4" line also and no leaks. I think you will be fine. Maybe others will chime in.
Kevin

[dsraven]

Lots of times the manufacturers used a smaller line with a nut that is special purpose to that, so like a 3/16 line inside a 1/4 nut but the 1/4 nut has a 3/16 sized hole for the tubing to go through. sometimes you gotta go get a piece of line of the donor vehicle with the proper sized nut and make the flared end yourself with the smaller tubing.

[dsraven]

the more adapters you use the more chance of a leak. I try not to use the brass fittings for that purpose. I believe some areas don't allow brass fittings in the brake system.

[Matt_50]

I searched and searched and finally had a conversation with a very knowledgeable guy. I was over thinking this way to much. The inverted cones are the same profile so a 1/4 or 3/16 line will seat and seal on either one.

I got it in my head that the super smart chevy engineers had two different sized lines off the master cylinder for a very very important reason.... maybe to save money??

All I need now is to get the rubber line from rear axle to frame and I can bleed my brakes!

Thanks guys, you guys being iffy on using adapters and stuff made me shy away from that. Now I'm glad I kept looking. I know a bit more about brakes that I did before.

One of you guys mentioned I need a special little tool so i can bleed through my new prop valve... I'll get that too.

[Matt_50]

While we are talking about brakes, I got my E brake mounted under the dash yesterday and I need to run a new cable or modify the old one. E brake and rear axle are both from 84 c10.