Mixing Brake Line Sizes?

[Dennis Detweiler]

Does it make any difference if some brake lines on the car are difference sizes? Does it matter to the function/feel of the master cylinder in this case?

My rear brake lines are 3/16 and the front is the original 1/4. I'm in the middle of replacing the original master cylinder with a dual reservoir Wilwood. I may have to add some 3/16 brake line extensions onto the original 1/4 lines or just replace all of the front lines. I have front disc brakes and shoes on the rear.

[Sharps40]

Chevy trucks have had 1/4 to 3/16 reduction at the rear axle for years.   In fact, you can find short lengths of hard line with fittings to make the transition at any auto parts store.  I just put the adapter line, 6" or so, on the input side of the rear axle rubber brake line and plumb 3/16 hard line to the rear cylinders.  

[Sharps40]

hang on

 

Edited June 14, 2019 by Sharps40

[Sharps40]

Should be this one.

 

https://shop.advanceautoparts.com/p/poly-armour-pvf-steel-brake-line-adapter-3-16-x-8-3-8-24-inverted-7-16-24-inverted-paa-r340/22190038-P

[Dennis Detweiler]

Thanks Sharps40

[Dave72dt]

You can probably do it with a single adapter fitting w/o line also.  If it's in a tight spot and you need line, you may want to try the cupro/nickel line instead of the poly armour.  Poly-armour line does not bend anywhere near as easily as the cupro nickel line.

[Dennis Detweiler]

I already have some cupro nickel ordered. Not sure if I want to replace both front lines or just add some to the old lines. The old lines seem to be in good condition, but I want to move both front lines (left and right)  back a little farther to put the flexible lines to each caliper behind the caliper instead of the original position in front of the caliper.  That position would be better located for more clearance in turning.

[sser2]

FSM specifies the length of front and rear shoe linings. For '38-39, front linings are 10 9/32 and rear linings are 7 11/16 for both front and rear axle. Using the recommended lining length is very important because these lengths, together with wheel cylinder front and rear diameters, determine the front-rear proportion of braking forces. If this proportion is incorrect, either braking efficiency will decrease, or, which is much more dangerous, rear wheels may lock before front wheels, causing loss of control during braking. In modern cars, there is a front-rear proportioning valve in the hydraulic system, but those old cars didn't have the proportioning valve, and proportioning was achieved by careful design of wheel cylinders and shoes.

[Plymouthy Adams]

don't be like the guy on the TV commercial....IF THE BRAKES DON'T STOP YOU...SOMETHING WILL