Brake line sizes?

[shortbed70]

Ok I'm going to be pluming my brake lines soon but need to know what size line to buy to match up to the factory line on the rear and the factory t on the front? I know I need one union and two reducers comming off master. This is for my 65 chevy drum drum and I'm putting in an adjustable prop valve for the front.

[Captainfab]

The front lines are 3/16" and the rear line is 1/4" from the master to the hose on the differential. Then from the block on the hose they are 3/16" to each wheel cylinder. If you're running drum/drum you don't really need a proportioning valve. The original '67-'70 systems with the dual reserviors just used a distribution block. If you want to run an adjustable proportioning valve, it is most common to plumb them in the rear line.

[shortbed70]

Thanks captainfab I need to go buy some line after I get some lengths. Are you sure I need to put the valve on the back? I will be swapping to disc but not right away. The front line is going down to the original T fitting.

[Captainfab]

Normally an adjustable proportioning valve goes in the rear line so as to be able to reduce the pressure to the rear brakes. You want the front brakes to do the majority of the braking.

[Heater63]

Like Captainfab said, you won't need a proportioning valve until you put the disc conversion on the front. Disc system pressures and drum system pressures are quite different, thus the need to "proportion" them. The down and dirty method to set the valve (after all set up and bleed good) is to get out on the road at decent speed and perform hard stops, advancing the rear pressure until the rear tires try to lock up. Then back off the setting a little till the rears no longer are locking up.