Brake Line Size

[thebearded1]

I am going to be redoing the brake lines in my hot rod this fall/winter since i'm having some issues with leaks and components in areas tough to get to. Currently the system is: 1940 Ford hydraulic drum brakes up front, 1995 jeep rear drum brakes and 3/16" lines going to the front and the rear. I'm thinking about going to a 1/4" line for the front brakes since that is what originally used for those brakes but keep the rears 3/16". Has anyone done a setup like this before? I assume there shouldn't be an issue using different line sizes on a brake system.

 

[Spanky]

I've heard of it being done the reverse of what you suggest (3/16 front, 1/4 rear) but . . . who knows? It may work fine.

 

[Neshkoro]

A way to address it might be to look at the car the front brakes and the rear end came At least it would be a good starting point. See what size lines the manufacturer used. I'm using what Spanky suggested. 3/16" front and 1/4" back. I have drum front and back. It's a 40 year old build!! Never had any stopping issue.

 

[fletcherson]

You want more bias to the front so what you propose may be fine. There are some very good but technical websites for brake components. I would look at them to try to keyboard engineer the system to the best of my ability, lol.

 

[thebearded1]

Thanks yall it looks like the car the front brakes came off would have had 1/4" brake lines, and the jeep rear brakes used 3/16". The Ford wheel cylinders have a bore diameter of 1" and the Jeep wheel cylinders have a diameter of 13/16" so I bet the larger lines up front will help. If not I get some extra practice doing flares haha.

 

[Indycars]

The Ford wheel cylinders have a bore diameter of 1" and the Jeep wheel cylinders have a diameter of 13/16"

That sure seems like a big difference in wheel cylinder bore going from 1.0" down to 13/16". I guess it's been stopping good in the past, the fronts are not touchy about locking up early. I know the fronts are suppose to lockup first.

 

[thebearded1]

That sure seems like a big difference in wheel cylinder bore going from 1.0" down to 13/16". I guess it's been stopping good in the past, the fronts are not touchy about locking up early. I know the fronts are suppose to lockup first.

Braking has been alright but i'm sure it could be better. I don't have much to compare it too as this is the first hot rod I've built but i can't get the brakes to lock up at all and thats why closing the rear valve to the brakes all the way. Hopefully the larger lines up front will help.

 

[Indycars]

You should definitely be able to lock up your brakes !!!

I'd be VERY suppressed if the new lines help! That's not going to change the pressure seen at the wheel cylinders.

What is your brake peddle ratio ???
What size is your Master Cylinder ???

Pedal Ratios and How to Find Them
What is brake pedal ratio?

 

[thebearded1]

You should definitely be able to lock up your brakes !!!

I'd be VERY suppressed if the new lines help! That's not going to change the pressure seen at the wheel cylinders.

What is your brake peddle ratio ???
What size is your Master Cylinder ???

Pedal Ratios and How to Find Them
What is brake pedal ratio?

View attachment 24528

Pedal ratio is 6.25:1
Master Cylinder bore is 1"

I was hoping since the 1/4" line would move more fluid it would help require less pedal travel to actuate the front brakes. I have the front brakes properly adjusted as well with a slight drag

 

[Indycars]

I was hoping since the 1/4" line would move more fluid it would help require less pedal travel to actuate the front brakes.

No, that not going to help. The MC bore and the stroke length will determine how much fluid is moved thru the system.

You should have enough pressure for drum brakes, but going to a smaller MC would help with the braking force generated at the wheels. The pedal travel with also increase some. Are you sure you don't have a problem somewhere. How old are your flexible line? Teflon-lined, stainless-steel braided hoses are best. They would give you a harder pedal.

• Disc brakes require a minimum pressure of 800-1000 psi
• Drum brakes require a minimum pressure of 400-500 psi

Reading thru this article will provide a wealth of information.
BillaVista.com-Brake Bible Tech Article by BillaVista


.

 

[thebearded1]

No, that not going to help. The MC bore and the stroke length will determine how much fluid is moved thru the system.

You should have enough pressure for drum brakes, but going to a smaller MC would help with the braking force generated at the wheels. The pedal travel with also increase some. Are you sure you don't have a problem somewhere. How old are your flexible line? Teflon-lined, stainless-steel braided hoses are best. They would give you a harder pedal.

• Disc brakes require a minimum pressure of 800-1000 psi
• Drum brakes require a minimum pressure of 400-500 psi

Reading thru this article will provide a wealth of information.
BillaVista.com-Brake Bible Tech Article by BillaVista

View attachment 24529
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I just recently started having the lines leaking going into the MC so I was going to cut and reflare them to see if that helped. I also had a brake light pressure switch leaking which I took out and plugged but it was in a pita location so that's what lead me to want to replace the front lines and go to 1/4" while i'm at it. Everything else appears good. I bled them until several rounds of no bubbles. the front flexible lines appear to be newer braided lines with a vinyl covering. I had a set of ss braided lines made for my motorcycle and it made a huge difference over the original rubber line. I will read through the article and see if i can come across anything thing else. They are new shoes that I installed up front a while ago and finally have some miles on the car. Maybe I will pull a hub and drum to look at the shoes to see how much contact they are making. I have heard of issues of 40 ford shoes not being the same arc as the drums.

 

[thebearded1]

The front and rear lines also have a 10 lb residual valve in them as well.

 

[Spanky]

The front and rear lines also have a 10 lb residual valve in them as well.

Personally I would ditch those. They make some sense in a disc brake setup, but I can't believe they do anything except provide another place for a leak in a drum brake application.

 

[Indycars]

I guess you have a double flaring tool ? What kind of flare does the Jeep use, there are different kinds of flared lines. I wold think the 40 Ford is a Double flare.

How to find what type of flare is on your brake line
Besides the two flares below there is also the AN flare at 37°.


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[HenrysT]

I think you should be more worried about how and where to run your lines instead of the slight increase in tubing size. The MC is only going to push so much fluid, the only thing the bigger line would do is lower the line friction, but it's only a little bit of fluid getting pushed anyway, I'd be more concerned about bends and transitions in the line. That's my 2 cents

 

[Indycars]

I think you should be more worried about how and where to run your lines instead of the slight increase in tubing size.

I would also agree with that statement.

I would also add that the 3/16" line are easier to find compatible fittings for than the 1/4" fittings. But the 1/4" lines might be a better choice when it comes to bending the lines since if there is any kink in a 1/4" line, it will have more room for flow.
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[thebearded1]

I think you should be more worried about how and where to run your lines instead of the slight increase in tubing size. The MC is only going to push so much fluid, the only thing the bigger line would do is lower the line friction, but it's only a little bit of fluid getting pushed anyway, I'd be more concerned about bends and transitions in the line. That's my 2 cents

The previous owner had lots of up and down bends when he ran the front line so I was.going to make itore of a straight shot to avoid air bubbles getting trapped in a high spot.

The 1/4" line already arrived so I will see if the fittings with it will work for what I have if not I should be able to return it

 

[thebearded1]

Personally I would ditch those. They make some sense in a disc brake setup, but I can't believe they do anything except provide another place for a leak in a drum brake application.

My master cylinder is under the floor and lower than the wheel cylinders should I still leave them out?

 

[Spanky]

Yes I would (and did on mine). The theory that they prevent fluid from "draining back" towards the M/C seems a little goofy to me when you consider that the system is completely closed with no air bleed possible to allow drain-back. And self-adjusters on the drum brakes should keep the shoes close enough to the drums for good braking as the linings wear.

 

[lincolnuT]

Those resudal (sic) valves are a good selling thing for the companys, but do not put them in the system they are not in any way needed. Like Spanky said it is a closed system or you have a problem with air getting in.......