I am getting started doing a dual master cylinder install. I bought a 1970 Chevy Nova master cylinder and have bench bled it. First question is there are two "ports" on the master cylinder I bought. One is smaller than the other. Which is used for front and which for the back? My other question is about brake lines. Should I try and buy pre-bent lines or bend my own? The current configuration has one line goes to the front driver side and another feeds the other three wheels. If i buy pre-bent lines it would be in this same config right? also, for those that have done this upgrade, any other tips? I am just learning auto work here so any tips help.
The front of the master, as if it were mounted on the firewall is for the front system. In other words, the chamber furthest away from the pedal is the front. In our trucks, if you mount it under the floor, remember to use a residual pressure valve, since the master is at or under the caliper hight. 10# valve for drums and 2# for discs. If you are mounting under the floor and using the stock pedal, Master Power Brakes makes an excellent brake mount that is very easy to install. Some people like a proportioning valve, some don't. Your MC may have one already, if not it is your choice. I don't run one, I have 4 w discs and it stops quite well...The only problem is I can't do a power brake...... As far as lines, get a decent tool and bend your own. It is a fairly simple process, buy several of the different lengths, some union blocks, and go at it. Take approximate measurements and put the lengths together to get about the right length per run. Always estimate a little long, because bends take more length than you may think. If it is a little long, a few more bends or a spiral will help take up some line. A good tool is essential! Good luck.
Brake tools Besides a good bending tool, you will also probably need a good flaring tool, one that will let you do the double flares you need for your brake lines. Not hard to use, with a little practice, and available at most auto parts stores, Harbor Freight, Eastwood, etc.
Ol Chebby, If you have drum brakes all around with the dual master under the floor with no residual valve, what will be the problem you see? I have this arrangement and have found that I cannot get the brakes to bleed sufficiently. One pump does not do the trick, it takes two. I was wondering if I can improve the bleeding by adding 10# valve you mention. Thanks, Gater
Guess I should have mentioned a little about my setup. I bought the adapter from classic parts and the master cylinder is for all drum brakes. I will also be installing in the original location. Residual pressure valve huh. Where would that go? Would I need just one, or one per line?
Hi Nate, I think I have them adjusted correctly cause I did it per your instructions. What is an arc problem? Gater BTW, Don't mean to hijack the thread but thought this was still on topic so it would help cochran out too.
Well ; There's a residual check valve in the master cylinder all ready , all masters made for drum brakes have them . it's a very low pressure vsalve but should suffice . " Arc " of the brake shoe , is the outer curvature of the shoe , where it fits against the inside of the brake drum ~ new shoes are rarely correct , back in the old days we had simple grinding machines that you used to radius the brake shoe to match the drum perfectly , it blew out choking clouds of asbestous dust I wonder why no one uses them anymore It takes a bit of driving for the shoes you buy these days , to ' bed in' , this means for the high spots to wear down until the shoe fits snugly against the brake drum from heel to toe . When I bought my '49 , it had all new brakes shoes but the DPO didn't adjust them properly so I had terrible brakes , the pedal went 1/4 to the floor and stopping at any speed over 30 made the pedal actually sink and touch the toe board being a Yankee farm boy I am far too cheap (er , thrifty) to replace new shoes just because my truck was dangerous to drive , so I drove it ever so cerefully and adjusted the brakes every day or two , or was it weekly ? in any case the shoes soon bedded in and the brake pedal stopped 1/4 the way down and was hard as a rock . You did remember there's TWO adjusters per wheel right ? that's the # 1 most common error , # 2 is , turning both adjusters the same way so one shoe per wheel is retracted .
Upon Re-Reading My Response I see I wasn't very clear : Take any old brake shoe and any old drum ~ place the brake shoe inside the drum and see if it touches in the center but not at the ends , or vice - versa ~ THAT'S an arc problem . If you take off your shoes and test fit them , you'll know right away but I'd look at the adjustment then for proper assembly too , for example : if the parkbrake cable is adjusted too tight , you'll never get the rear brakes into proper adjustment as the parkbrake pushbar will hold the shoes out away from the service brake cylinders....
The residual valve goes in each line..one for front, one for rear...They hold back enough pressure to keep the shoes in close proximity to the drum. They also keep all the fluid from draining back to the M.C. when mounted under the floor. Bleed the M.C. on the bench before you install it, makes things a whole lot easier.
well I bench bled the MC and have it installed under the truck. That was the easy part. Now I am running the brake lines. got the front drivers side done now I have to run the rest. I would assume it is best to do the lines as one piece and not split it into smaller sections using junctions... right? It is going to be pretty tough to do it in full sections but it looks like it CAN be done. Anyways, thanks all for the info
I never bleed on the bench when installing floor mounted MCs. Bench bleeding is great for firewall mounted MCs as they have a tendency to not sit level there. I have installed 5 or more frame mounted and bled all right there on the frame without a problem. It is just less messy to install them if they are not full of fluid. Check your frame, if it is level, bleed it there.
