Brake lines from dual reservoir

[RivNut]

I installed a dual reservoir master cylinder on my '64 and bent and flared lines to work with the original distribution block and existing lines.  At the time I did this, I worked with the lines that a friend of mine ordered for me (he gets them at a discount and the parts aren't taxed.)  I didn't think much about it but it recently occurred to me that I may have a problem when I actually put the brakes to use.  The line coming from the front reservoir has a larger inside diameter than the line from the rear reservoir.  Will this create different pressures to the corresponding wheel cylinders based on a constant pedal pressure?  Should I be running lines with like dimensions from each reservoir?

 

Here's a picture of my conundrum.

 

 

 

[alini]

It depends on the design of the MC, if its set up for disk fronts it might already be designed to have higher pressure.  Some dual reservoir MCs have two seperate pistons in the bore and spring tension drives the second piston, this creates a pressure output change.  Remember many newer cars have more front brake than rear by design.  Since the first gens had a single output it was designed to have all four brakes applied evenly, which is fine.  As long as you dont have pull side to side, I wouldnt sweat the finer details.

[PWB]

Pascal has your back:

 

"Pascal's law or the principle of transmission of fluid-pressure (also Pascal's Principle) is a principle in fluid mechanics that states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations (initial differences) remain the same.The law was established by French mathematician Blaise Pascal."

 

 

 

[RivNut]

I followed the swap as outlined in the tech tips of the ROA's website.  I mounted a dual reservoir master cylinder for a '67 Buick with drum / drum brakes and I'm running the original drums on the car.  I have a Scarebird disk brake conversion set up which calls for disks, calipers and rotors from a '76 Buick.  I found a '76 Riviera in a salvage yard and took the booster, m/c, lines, distribution block, along with the disks, rotors, and calipers from that car.  When (if) I ever do the swap, the entire system will be a factory '76 system from the booster to the wheels.  So right now I'm just needing to know if I should have the same sized lines running from the drum / drum reservoir that I installed on the original booster.

 

Ed 

[alini]

line size doesnt affect pressure, it only affects volume.  So pushing the pedal will drive more fluid through the larger pipes...the pressure will be no different

[Guest Dale in Vancouver]

  Hi Ed. I've done exactly the same modification with my '64 and experienced no problems at all. Cheers,  Dale.

[Guest Kaber]

Ed,

 

I would happily check my set up for you, I used the same M/C as you. Sadly my son's car is in storage and it is inaccessible right now. It does seem like the advice given here is correct. The line size should have little bearing on brake performance.

 

T

[RivNut]

Kaber,

 

My car is inaccessible right now as well,  not because of storage but because my garage is cold enough to freeze the proverbial witches t***ty.

 

Ed

[64Rivvy]

Also as long as you install a proportioning valve, which it looks like you did, you should be able to adjust and account for any slight variations in pressure front to back.  

[RivNut]

No proportioning valve.  None from the factory so I didn't add one.  The article, which many have followed, on the website does not call for one.  Probably no need for one until/unless I do a disk brake swap.

 

Ed

[OldGerman]

Hi Ed,

 

did you follow the Manual of the master brake cylinder manufacturer, to which brake circle the front reservoir should be routed ?

I remember I did that wrong on my Chrysler 300 on conversion to a dual master cylinder.

I thought, the front cylinder excit operates the front brakes, but this was wrong in that case.

 

There were also different sizes for the brake lines of front and rear breaks.

 

Frank

[Chasander]

proportioning is achieved on a drum brake car w/ different sized wheel cylinders

[Seafoam65]

                Ed, your brakes will work fine with the lines the way they are now.......not to worry.

[RivNut]

Thanks guys.  I'll leave them as is for now.  I was just thinking that if I did want to change them so that they'd look the same, now would be the time to do it since the car is still sitting with the inner fenders over in the corner of the garage.  Here's another question.  Should I be able to find the proper sized lines with the correct fittings so that I don't have to install the two adapters at the master cylinder?

 

Thanks again.

 

Ed

[Riviera63]

Ed,

 

Yes you can. I followed Jim Cannons post on this thread: http://forums.aaca.org/topic/221099-63-riviera-dual-master-conversion-help/?hl=%2Bdual+%2Bmaster+%2Bcylinder#entry1145797 or search dual master cylinder if the link doesn't work and it is entitled: 63 Riviera Dual Master Conversion Help.....started by Kaber. Jim lists all of the parts you need from Inline Tube for the conversion including the fittings for the lines to the master cylinder that fit the 3/16" line. I did not order the master cylinder fittings as the shop that did mine just got them locally or made up the lines with the fittings themselves, I don't remember which. The picture I have isn't that great but my lines are both the 3/16".

 

Bill

 

 

Edited January 20, 2016 by Riviera63 (see edit history)

[RivNut]

I stopped by a local jobber's on the way home tonight to stock up on washer fluid and while I was there, I asked about brake lines.  The ones that you buy with already flared ends need some kind of union, but I can purchase unions with the correct threads for the diameter that I want.  If I buy a large length of line and the correct ends, I can custom fit them together and flare them. I can then bend them to whatever shape I need.  That will be much more aesthetically pleasing and give me the half inch more clearance that I'd like at the fender well.

 

Too cold in the garage to do anything this week, but I'll get to work on it in the next couple of weeks, take some pictures, and post them.

 

Ed

[96roadmaster]

I have the same master cylinder as you on my 64, except the front and rear lines are the same size on my car. In a full panic stop the rears grab a tiny bit sooner than the fronts. Not enough to lock them up or send the car oversteering or swapping ends, but I do notice the rears grab a fraction of a second sooner.

Doesn't bother me and I actually do prefer a slight rear bias, but most people prefer the more natural front bias.

I think you'll be fine either way.

[RivNut]

Lots of cars with drum / drum brakes will have the same tendency.  The weight shift in a full panic stop will lift weight from the rear so the back tires lose traction and start to lock up while the front of the car is taking on more weight, giving those tires more traction, and preventing them from breaking loose.  Ask me how I know.  Happened in my dad's '57 Buick on a long, lonely asphalt road in the middle of farm country.   One road sign, two fence posts, and one telephone pole later, I finally came to a stop.

[64Rivvy]

   No proportioning valve.  None from the factory so I didn't add one.  The article, which many have followed, on the website does not call for one.  Probably no need for one until/unless I do a disk brake swap.

 

 

Ed,

 

Sorry -  I should have paid closer attention.  I just assumed you were doing a disc swap.  Good luck and let us know how it turns out.  

[RivNut]

In this particular case, the switch to a dual reservoir master cylinder is a safety factor.  A loss of brakes on one end doesn't mean the same on the other end.