4-Wheel Disc Brake Line Bore
 

Hoping CaptFab or someone else can lend some expertise/experience:

I am wondering if I need to route new brake lines and if so what bore size to compensate for the change from drum to disks.

Basically wanting to make sure i have proper pressure everywhere needed.

Current Set-up:
- Front : ECE Drop/Disk Brake Kit
- Rear: CaptFab D52 brakes (with the astro van rotors and caddi e-brake calipers)

Master Cyl :
- Wilwood Manual Master - Part # 260-8556-P

Currently I have the stock Drum/Drum Lines front to rear

Should I route new lines either with a pre-bent kit or bend my own, and what size line should i be looking for?

Re: 4-Wheel Disc Brake Line Bore
 

I don't know for sure what's "right", but I can tell you what I'm doing on mine...

I have Wilwood D-52 calipers up front, and D-154's out back. Piston area in front is 6 something, and the rear is 2 something. I'm hoping that will get me pretty close on the front/rear bias without the need for a proportioning valve. We'll see.

I have the same style master cylinder as you, but I opted for the 7/8(.875) bore because I will not be running a booster. Smaller piston = more line pressure with the same amount of pedal input. I don't know if 7/8" is a good bore for a street application, or the pedal ratio in our trucks, but that's the bore I run on the rear system of my dirt race cars with a 1" bore on the front system to give me rear bias. So that's what I based my MC bore choice off of. I've read that anything larger than 1.00" is not good for a non-power setup.

From what I was able to find in my search, disc brakes take more fluid volume than drum brakes. So you would run a smaller line on a disc system to displace more MC volume to the disc calipers. Smaller line holds less fluid, so for the same displacement at the MC, you get more fluid out the other end of the line at the caliper. That reasoning led me to use 3/16" line. That's also the reasoning a drum brake MC won't work on disc brakes, it doesn't have enough stroke or displacement for the volume needs of a disc system.

I will be using "NiCopp" (a seamless line made of a copper nickel alloy specifically for brake systems) and single-flare 37 degree, or "AN" fittings (tube nuts and sleeves). You should be able to get the line at your local auto parts store. It comes in a coil, so you will have to straighten it, but it's not a big deal to do by hand. They also claim you don't need a bending tool, you just form bends where you need them with your hands. The fittings you will probably have to order from Summit or somebody. Your local hydraulic shop might be able to get you what you need also. I use the 37 degree fittings because they were made to be serviceable, and the flare is MUCH easier to make in my opinion. I've had plenty of double flares that leaked, I've never had a 37 leak. If you need a flaring tool, spend the $130 or whatever it is on the Ridgid ratcheting unit, it's worth the money. Speedway motors sells it, they don't list the brand name, but the price will be right in that range.

Sorry to write a novel. I just got done doing the research for my truck, so I thought I'd share. Also, here is a good resource I found from people who SPECIALIZE in brakes: http://www.mpbrakes.com/technical-su...-cylinders.cfm


Hope all that helps!

Re: 4-Wheel Disc Brake Line Bore
 

Thanks Portmod, that's definatley some good info to digest and think on

My plan is also to run no booster, just manual M/C but I was thinking with a 1" bore to match the corvettes manual disc setup

Also with a prop valve to control the rear bias
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Re: 4-Wheel Disc Brake Line Bore
 

Sounds like a plan to me!

Glad the info could help, good luck with your system!
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Re: 4-Wheel Disc Brake Line Bore
 

I definitely recommend that you pick up an adjustable prop valve so that you can fine tune the rear bias. Take a look in the suspension marketplace there are some vendors on here that have them for great prices. I got one last month but have been too lazy to install it yet. Just my 2¢.
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Re: 4-Wheel Disc Brake Line Bore
 

I agree, I'll probably need one, but I'm going to make it hard on myself and install one later on. I'm curious to see how staggering the piston area on the calipers works out.
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Re: 4-Wheel Disc Brake Line Bore
 

You will be fine with 3/16" line from the master/prop valve to each front caliper. Then run 1/4" from the master/prop valve to the 'tee' at the differential, and then 3/16" from the 'tee' to each rear caliper. This is what GM does on the factory disc/drum and also on the disc/disc systems.

Re: 4-Wheel Disc Brake Line Bore
 

Capt. Would you know if a 1" bore manual master would work well along with the line bore sizes you mentioned?

Planning on running:
Prop Valve you suggested:
- Wilwood Disc Brakes 260-11179 - Wilwood Brake Proportioning Valves
- http://www.summitracing.com/search/?...60-11179&dds=1


Also any suggestions on pre-bent vs bending lines: Just wondering if I bend my own whats the best line to go with.

Most people suggest with a quality flare/bending tool its not too hard to do.

I've read alot of mixed reviews on Poly Armor from the local parts stores: http://67-72chevytrucks.com/vboard/s...d.php?t=478219

Re: 4-Wheel Disc Brake Line Bore
 

I am going to call Wilwood and discuss the proper MC bore size for my application tomorrow.

Also I have reached the below layout currently and have a few questions:

On a Drum brake truck are the lines running from the T-fitting to each side 3/16" or 1/4" factory?


Rear Hardlines on the axle are the factory 1/4"?


Anyone have any information on Caliper Threads
- Cadillac Rear Calipers with e-brake?
- Stock front Calipers ECE supplies?
- I dont know what threads or details to be looking for

I am purchasing the Early Classic front disc brake kit and they supply new hardlines from the MC to Prop Valve to the front and rear t-fittings, the rest is all factory lines.

You can purchase a pre-bent line kit from POL that supplies these same lines but also provides the lines running to the rear of the truck.

Re: 4-Wheel Disc Brake Line Bore
 

Being cought up in my diagraming I see CaptainFab states 3/16" on the differential/axle

Still wondering about the factory line size from the front tee to each side, if that is already 3/16" then I shouldnt need to buy any replacement lines correct? ECE already has me covered for what I would need

Is there any need to run 3/16 Line to the rear while im at it or is 1/4 good to go
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Re: 4-Wheel Disc Brake Line Bore
 

Just spoke with Wilwood:

MC Recommendations: Biggest issue is how you like the pedal to feel

7/8 Bore: creates more pedal pressure to calipers
- A spongy feel to pedal
- More like a power brake feeling
- 2-3" Pedal travel before engaging

1" Bore: High and firm feel
- Most people want a more firm pedal
- 1" pedal travel before engaging

Line Recommendations: 3/16" Front to Rear for Discs
- 1/4" is for drum brake applications

Braided Lines for Stock D52's:
- 7/16"-20 Banjo Bolt Style

Re: 4-Wheel Disc Brake Line Bore
 

I am doing a simular setup right now. I am running the larger master cylinder but the same prop valve. The Wilwood adj prop valve has 3/16 size line in all ports. you can stay with that on the front just as your drawing shows. be sure to plug the extra FO port. On the rear I am using an adaptor to get the 1/4 line to the prop valve, that runs to the rear of the truck, when the steel line gets to the rear axle it changes to a rubber hose. That hose tees off to each side of the rear axle at the 3/16 size, steel lines out of the tee and over to the calipers where I am using the same hose that is on the front of the truck. So I have the same set up on the rear of the truck as what is on the front. calipers, pads, and hoses.