[leeklm]

During my 68 strret/strip build, I researched line sizing and other various suggestions when installing rear disc brakes. I ended up going with the Ford Explorer calipers on my new 9".

I read several articles suggesting that disc calipers could use smaller brake line than drums, and many were installing 3/16 line all the way around. Since I had an entire roll of 3/16, that is what i used. From the start, braking on the car was ok, but not great. I bought a guage to test line pressures, which were on the low side of spec on the front. I did not have the proper line adapter to test the rear, but could tell it needed more rear brake.

Figured it would not hurt to save a few pounds so I talked to Wilwood and bought their recommended MC, and connected to a generic 4 wheel disc distribution block . Front line pressure was a little better with the wilwood, but no seat of the pants difference. Next step was to remove the block, connecting brake lines directly to the MC. Maybe a little better, but minimal.

This past wknd I replaced the 3/16 rear line with 1/4" from the MC to the T, leaving 3/16 to each wheel. Immediate improvement!! Braking is great, and can really feel the rear brakes doing something. I have 275/15 Nitto street tires and use a 10" racing slick, so always figured I could use more rear braking. If I was using a skinny rear street tire, I think I would now have to install an adjustable bias valve to slow the rear brakes down.

Anyway, I guess the lesson is to not assume rear discs can always use a smaller brake line!!!

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[ZeGermanHam]

Yep, the 1/4" line that runs from front to rear should be retained. It's my understanding (and I'm no expert) that disc brakes require more volume at the same PSI than drums.

[Geoff]

Discs require more pressure than drums, all else being equal. Considerably more pressure. A disc brake caliper is essentially a G clamp.
The drum brakes used on our Pontiacs are a duo-servo type where the brake shoes tend to get 'locked up' by the rotating drum, which assists in the braking action. Self assistance. Discs do not have this feature & relay on more line pressure.

[HWYSTR455]

Yeah, discovered this years ago, but this is something that needs to be repeated over time.

Volume is just as important as psi, and is controlled by caliper volumes, line sizes/volume (and length), and master cyl bore size. There's actually a formula for calculating it.

Secondary variables are, as examples, restrictions, pad take-up, and fluid (moisture, type, etc).

Following an OE type system is a 'safe' approach, any variation should be thought-through for potential impacts. I generally recommend line kits that are 'conversion' sets, based off the original design. A front to rear line generally is in the $65 range, and worth saving the time & headaches.

You can vary master cyl bore size to target a certain feel or modulation, but it's more used for 'fine tuning' than correcting any other factors. It is possible to end up 'outside the box' and not have properly functioning brakes.

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[punkin]

Which bore diameter MC did you get? Are you using power assist?

Thanks for sharing this information. This is good stuff.

[leeklm]

Here is the part... no power assist

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