Brake line size

[impstocker]

With my 1965 Impala I/SA 396/325 build, I ran 3/16 brake line to the back brakes which are drums. Up front I have disc plus have a Adjustable proportional for the line going to the back. It seems the car originally had 3/16 line to the back because the T fitting in back is for a 3/16 line.

Would I need a 1/4 line instead?

Thanks for any help

Will Lamprecht

[Eman]

3/16 should work fine, I used it on my Camaro. The adj proportioning valve might work better on the frt section to stop the frt.s from locking. You just have to experiment and see how your car works.

[FireSale]

Prop valve goes in the line to the back brakes. It regulates pressure back there and keeps the rear from locking up before the front. Locking the rear first can spin the car. Because of weight transfer to the front of the car during braking, the front set must carry most of the stopping power for stability. Stunt drivers spin cars by pulling the emergency brake which locks the rear brakes only. The car nose dives and the rear tires break free.

Dale

[Eman]

Street cars and stunt cars are slightly different than dedicated drag cars. Locking the backs is bad and every car reacts differently especially after brake systems have been modified. Drag cars have skinny tires with high pressure and a small contact patch in the frt with large sticky low pressure tires on the back. That changes how the braking reacts along with the changes in weight bias and suspension modifications.
Try it the way you have it and adjust from there.

should have a residual valve in the back with drum brakes, and the adjustable proportional valve in the front.
3/16 should be fine.

The front tires will lock before the back because the amount of rubber contact on the track. It takes more brake force to lock the rear tires up because of this, the only time the front adjustable valve is used is on hard stops, this just restricts flow to the front calipers on a hard brake condition.

The residual valve in the rear line helps the rear brakes apply the same time as the front so you have even braking.

Before I installed brakes on my firebird, I called and talked to different manufactures. Strange and Mark Williams directed me to using the components above in the same manner.

Willwood, Aerospace told me to use the valve in the back and no residual valve. They were wrong

I can hold my car to 4000 on the starting line and kill almost 10 mph at the cones without tire smoke in complete control. I'm using Strange lightweight front brakes and rear 9" drums. The car runs 10.60's at 123. weighs 3550.

[69Cobra]

Very good info Todd. What changes if you have 4 wheel disc?

Take out the residual valve in rear line. I would call to confirm that along with what to do with the adjustable valve in the front. I'm sure it stays

[FireSale]

I have the adjustable valve in the back line of a disk/disk installation, but it's a Sportsman street car. Stops fine.

Dale

[Run to Rund]

My '66 A body with 115" wheelbase came with a 1/4" line to the rear. That size is working fine for me.

[117X]

My G Body has 1/4" to the front and 3/16" to the rear. It has Aerospace disks on all four corners and stops decent. When I first purchased the car the residual valve, which was located in the factory proportioning valve, was still there. It caused severe drag on the rear brakes. Since removing it the brakes release better but not as well as I'd like. When the car sits I do need to pump the brakes up a bit because there is no residual valve. Another oddity I noticed is, if I want to coast down the lanes and let the brake off gently it doesn't want to move. If I apply firm pressure and quickly let off the brake pedal it rolls right away. Has anyone ever noticed that with their system?


Todd, that is impressive you can hold at 4000; I can barely hold 3000. By the way, thanks again for you help at Cecil!