I'm going to be swapping in a dual circuit master cylinder on my 56 Chevy. I have completely rebuilt the front brakes, kept em stock drums with the exception of installing a self adjuster kit and tapered roller bearings. Going to be redoing the rears soon too. My question is, with the dual master, do I need to install a proportioning (combination) valve in the brake circuit? I have seen them with and without them, and I was wondering with a stock 4 wheel drum system if a valve was necessary. What do the HAMB experts think? Valve or no valve? Also, should I run larger or smaller brake lines, or keep the same size? (I'm going to replace all the metal and rubber lines in the name of safety)
no you don't need a proportioning valve with a drum/drum system. One thing you might want to do, is check to see that the dual cylinder is actually working like it should. After you get it all working, open up a bleeder valve on the front and push the pedal...it should activate the rear brakes, and not bottom out on the floor. Then close the bleeder and open a rear bleeder, it should activate the front brakes. Dual master cylinders have more travel than singles. If you don't change the pedal ratio when you install a dual cylinder, the pedal will bottom out before the cylinder, and the dual cylinder won't give you any advantage over a single cylinder.
A proportioning valve applies hydraulic pressure to the front and rear systems at varying RATES. When you mash the pedal with a Prop valve in the system the rear brakes apply FIRST to help keep the car pointed straight ahead, but the pressure rises FASTER in the front brakes because that is where most of the stopping power comes from. I built a tub with exactally the same setup as you built - dual MC with drum / drum - no proportioning valve. Everything worked great - no problrms - until one day on my way to work - a 30 mile freeway commute - I got caught up in a contest of speed with a guy on a Ninja bike. At one point I drove deep into a corner at a very high rate of speed and stabbed the brake pedal quickly to whoa the car down. That tub swapped ends on me so quick I did'nt even have a chance to react and found myself spinning up over a curb pinwheeling between utility poles. So, yeah, it will work fine as long as you don't have to do any panic stops and as long as you don't do any slalom racing. Otherwise, get a prop valve.
As far as different sized lines I feel it makes little difference in your case. The volume of the lines is small compared with the volume of the brake cylinders and once they are charged with fluid pressure will build rapidly in either case. Big multi-piston discs or large commercial drums would probably benefit from large diameter lines for high performance driving but for a tri-five p***enger car - naw.
Yes, I have read about needing to adjust the pedal rod. It's threaded, so it shouldn't be too difficult. I haven't installed it yet; but I will within the next two weeks or so. I don't plan on doing any high speed driving or manuvering in this car, so it looks as though I should be able to get away without one. Hopefully I won't have to panic stop - much. One more thing, I have noticed on some cars at shows, that the brake lines coming from the master cylinder are bent into a spiral shape, like a curly fry. What is the purpose of this?
Like what Frenchtown said, but get the master cyl from somebody like stainless steel brakes and have the Prop valve sized to the master cylinder. The brake line size makes a difference, drum brakes need volume so make it a 1/4" to operate the wheel cylinders. In short, look how GM did their drum brakes - dual master cyl, prop valve and 1/4" lines. HP books has a good one on brakes and it is worth reading, it'll give all the info you need and why you need it. It is your brakes we are talking about here.
The purpose of a coil in the brake lines is to help eliminate hydraulic shock and elimiate vibration caused cracks. When you hit a brake pedal hard, like in a panic stop cuz grandma didn't see you and pulled out or that kid runs out chasing a ball, the pressures in the system go very high. This can actually cause a brake line to break from the shock. A coil in the line helps absorb this. If you want to see this phenomenon, have someone pounce on your brake pedal while you watch the master and lines, very common to see them move ever so slightly. It's one of those things that can cause a problem but not very often, but if it happens and you lose your brakes you might wish you had done it. Most builder's here probably don't do it and never have a problem, but it can happen. As far as brake line diameter goes, remember that you are not really moving much fluid, it has more to do with building pressure. Watch the master cylinder fluid level when you push the brake pedal, it really doesn't move much. Smaller line will generally build more pressure and have a firmer pedal feel. You can use 3/16" all the way around and you will not have any problems. Many OE's used 1/4" for drums and 3/16" for disc's but there are plenty of applications where 3/16" was used for drums also so you won't have any issues. The only thing I would say is in a 4 wheel drum application, use the same size all the way around. Many brake "Experts" have said not to change the line diameter as you could upset the balance of the brake system, but this is one of those things that is more theoretical than experienced in the real world.
It serves two purposes: First, It acts as a vibration damper, especially between something that is rigidly mounted and something that vibrates or moves. Short lines rigidly connected at both ends tend to work-harden and get brittle which can lead to fracture. Steel gas lines are often made with loops for the same reason. Now that you know the reason don't they look even cooler?! Second, You can buy off-t******lf pre-made lines that are too long and loop to length, lol.
If I understand, your car's braking system is OEM stock as to drum sizes and widths, and wheel cylinder bore diameter...except for the subs***uted dual master cylinder. Are the bores in the dual master cylinders the same diameter? If so, (and ***uming NO huge front/rear tire size discrepancy) - no proportioning valve is necessary. Keep the brake lines OEM size. BTW, Rule #1 for hydraulics is, fluids are not compressible... Yeah, the various brake books are good investments... .
GuyW, you are exactly right about my brake system - totally stock save the master cylinder. And I am running stock sized tires on the stock rims on all 4 wheels. Thanks for the replies gang. As usual the HAMB keeps me going on my projects!
When we put discs and a dual master cylinder on my father's '64 Plymouth we used a proportioning valve on just the rears. This was so we could control the amount of braking going towards the rear. He got the Stainless Steel Brakes kit. It took a little while to get it dialed in. At first it was too far out and the rears would lock. So we just kept adjusting it until we got it correct. The lines were left stock and the new lines that came with the kit were the same diameter.
not to hijack the thread, in my case i have all re built drums the previous owner put a gm booster/mc combo from a 80's truck also he use the original prop valve i been told many times to take the pro valve out and to run, residual pressure valves? i believe 10lbs? is this right? or should i keep the set up i have now?
I did my '65 Belair using a master out of a '70 Impala. All I needed was the "T" which also came out of the '70. I had to do something minor to get the stop light switch to actuate since I added a vacuum booster to it. Other than that it dropped in. I'd say that a manual brake '67 Chevy or Chevelle master would be the ticket. Bob
Just to make sure, the two ports on the master cylinder; one port goes to the front brakes and one port goes to the rear brakes, is that right? I actually feel stupid asking this, but I know that if I don't, I'll screw something up. I picked up a master cylinder from a 68 Chevelle the other day.
No on a prop valve but you may need residual checks. Most dual M/C do NOT have checks built in. In early drum dual systems the check was in the combo/warning light valve . Later that valve also was a prop valve on disk/drum systems. Yep one line to the front and the other to the rear. As to line size either 3/16 or 1/4. Have seen some OEM systems that used both !!
Cool thanks. If I do manage to find check valves somewhere, where in the system should I install them?
Guys THIS very topic has been hashed and rehashed MANY TIMES and that's actually a GOOD thing because each and every time there is always some ****PY advice mixed in with the good. Do yourselves a BIG FAVOR go back and RE-READ EVRYTHING The Frenchtown Flyer has written - Greg actually knows this stuff - he goes so far as to give a personal example of just 1 scenario where it would have saved himself a lot of grief - those of us who are looking to learn (and I include myself in this) would be wise to heed The Frenchtown Flyers words . If you wanna prove (?) what you can "get away" with then by all means do what ever strikes your fancy. Me I KNOW first hand how SHARP Greg aka The Frenchtown Flyer is - when he talks - I'm gonna listen!!!!!!! You could do far worse than listening to his advice here.
I'll answer your origional question with a question.....what kind of brakes you want - adequate/marginal or optimized??
Make sure you know which line goes to which end of the car. It varies from unit to unit. check out this: http://www.mpbrakes.com/technical-support/configurations.cfm -Bigchief.
I know speedway has them, I got mine from wilwood along with the tandem master I'm running on my drum/drum 52 pontiac. All things equal the pedal response should improve with residual/check valves. I installed mine within a foot of the master 1 for the front and 1 for the back. s.
All I know is that you are gonna want to run all new lines, I know a guy. They call him Brake line Billy, best part is he works for beer.
Whatever you do.........stay away fromt he ****py anodized Aluminum Residuals. Buy the Br*** ones from someone like ECI!
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