Single Chamber master to dual chamber quesitons?
 

Howdy folks.

For peace of mind, I am replacing the single chamber master cylinder on my 64 with a 67-70 dual MC and I just wanted to confirm some things.

My plan is to:
1. replace the old 1/4” line with a new 1/4” line running to the tee on the frame
2. running a new 3/16” from the master to the line going to the rear and plugging off the unused port on the passenger side tee that used to connect to the rear line.

My question is the front port on the master cylinder is a 1/2" fitting and the rear is 9/16”. I believe front ports are normally plumbed to the front brakes and rear to rear but would it make more sense to use the 9/16” port for the front 1/4" line?

I know it doesn’t much matter with 4-wheel drum but wanted to check with more experienced folks who have probably done this a few dozen times.

Re: Single Chamber master to dual chamber quesitons?
 

You need a proportioning valve. You will have to dial down the pressure going to the rear brakes.
The one in this picture is a Wilwood. You can see the dial at the rear. That will lower the pressure to the rear brakes, it also acts as your tee. You can hide this anywhere you want. You can also get a preset one without the dial.

Re: Single Chamber master to dual chamber quesitons?
 

You do not need a proportioning valve if going from single pot MC to dual pot MC with DRUM DRUM.

Also, on these early dual masters, FRONT port goes to front wheels, REAR port to rear wheels.

Re: Single Chamber master to dual chamber quesitons?
 

Came here to say this.

For drum/drum the "proportioning" is accomplished by the different wheel cylinder diameters front to rear.

I did this update on my '63 Grand Prix and did not use a prop valve.

K

Re: Single Chamber master to dual chamber quesitons?
 

That's a disc/drum master.

You can tell by the different reservoir size front vs rear.

K

Re: Single Chamber master to dual chamber quesitons?
 

Thanks the port plumbing is what I needed confirmed. :metal:

Re: Single Chamber master to dual chamber quesitons?
 

No problem. There are multiple threads on here (mine included) that confirm.

A good pic from Chevy:

https://67-72chevytrucks.com/vboard/...1&d=1517629947

Re: Single Chamber master to dual chamber quesitons?
 

I forgot about Drum/Drum. Everything I have is disc and I guess you just forget about drum brakes after a while. :D