A dual reservoir master cylinder is something I've always added to any project car I've ever built since they became standard on newer cars. Always thought they were a good idea, but never tested one out until yesterday. Running around town in my '39 Chev yesterday when I pulled off the freeway to stop for gas. Pedal felt strange as I rolled off the freeway ramp as it's always very firm, but felt softer on the top half of travel. Pulling into the pumps it felt even softer on top, but very firm on the second half. After getting the tank filled, I decided the wise thing was to head home and took the freeway so as to avoid anymore stops than necessary. Once I got home I checked the master, and found the rear reservoir nearly empty! So I began checking for where the fluid went, but everything looked dry. I jacked the rear up on stands and fired the engine. Put my foot on the brakes and put it in gear. The rear tires just idled along, and nothing seemed to be stopping them. Pulled my rear wheels and drums, and the driver's side wheel cylinder was blown out! Passenger side was damp also, but not wet yet. I was pretty happy I had converted it to a modern Corvette style dual master, as it could have been very bad had this happened with an old style single pot.
I converted from single to dual years ago. I considered it the best upgrade I ever did on the car. I got the dual master cylinder from Pete&Jakes. A direct bolt in job...............
Normally if the master is mounted flange side to the rear of the car the rear reservoir feeds the front brakes. ( larger reservoir is for the front) Good thing you had that type of system and realized there was an issue, safety is no accident.
That is seriously good proof as to why we change to a dual cylinder when we are building one. My first experience with a brake cylinder failing was in 1964 when I had the little Green 55 Nash Metropolitan rag top. I was headed up the street from the Honda Motorcycle shop where I was working that summer and got to a light a couple of blocks up the street and the light changed and I hit the brakes and no brakes, I had enough room to to to the right of the car ahead of me and make it around the corner, I caught a bumper bolt on a 50 Chevy sitting at the curb with my right rear quarter panel just enough to leave a little green paint on the bolt, (I went back and checked) but it didn't dent the quarter panel of my car, I eased it back to the bike shop using the hand brake and got it parked and checked an no fluid. I'd only had that car a couple of weeks then as I had blown up the flathead in my 51 Merc on the way home one evening and had to buy a car I didn't plan on buying. The original master cylinder in my 48 got changed for pretty much the same reason. I had rebuilt it a couple of times over the years and one day it failed but at least it failed when I wasn't in traffic and I just blew a stop sign on the way to my buddy's place. We took his truck to town and I bought a 68 C 10 master cylinder and we built a bracket to mount it where the single had been. That's still on the truck now.
Lucky and good catch . wether a dual or single mast cylinder , brake maintenance is key. I inspect my brakes every season all wheels off drums off , everything gets a look , grease , adjustment cleaning etc . flush the brake fluid every 2 years . I suck all the fluid out of the master , then open all 4 bleeders and let it drip for some time while keeping the master full . Then bleed with 2 people . a dual master cylinder is cheap insurance, but proper brake maintenance is key to ( hopefully) avoiding issues. all my old cars get a dual master , for the cost involved and work to install it ( most instances) it’s time and money well spent .
No amount of maintenance, or nostalgia, will ever make a single-reservoir brake master cylinder safe.
This rear axle was one I bought used for my '39 when I built it, so I had checked it just a couple years ago before using it. I didn't replace anything because the Exploder I pulled it out of had brand new brake shoes, and wheel cylinders were dry with soft rubber cups. So I just cleaned it up, and stuck it under the '39. It's been on numerous 200 mile trips, and a 1200 mile trip when I had just 500 miles on the build, so I had no reason to suspect anything. I got the new shoes, and to get things done quickly I bought two new wheel cylinders, even though I prefer to rebuild them. I checked all the threads on the lines, and mounting bolts, and discovered they must have had a dull tap when they threaded the mounting bolts as I had to run a tap through before the bolts would even begin to go in more than 1/2 turn. These Ford 8.8" brakes are a PITA compared to others I've done over the years, but eventually I won and got them together. Cleaned up and took it for a spin, and she's stopping better than it has in recent times. Now feeling how good it's stopping I think the driver's rear had been seeping and destroyed the brake shoes even before it finally blew out. I can really anchor it in a panic stop now, even without power assist. She's ready for the next trip this summer, which will be in a month and about 250 miles each way.
The Jalopy Journal
