I have a full set of rebuilt `40`s brakes to swap for the stock rod brakes on my `32 roadster, I am intending to use a Mustang drum/drum master cylinder.On the original system using a single pot resevoir the rear pipes are 1/4" and the fronts are 3/16" so i believe...is this for brake bias ie; make the rears operate slightly less efficiently than the fronts...if so, does the Mustang cylinder require similar pipes or is the master cylinder built with this bias built in? Thanks in advance.
The brake lines to the rear are larger to compensate for pressure drop when the fluid flows thru them. Doesn't really have anything to do with braking efficiency, but rather the balancing of total resistance to flow within the lines from front to rear. Too small lines, especially the rear ones, can cause sluggish release of the brakes when you take your foot off the pedal and the shoe return springs are the only source of pressure to make the fluid flow backward in the lines. You would have the same sort of flow resistance during application as well, but you have the master cylinder to create a much higher pressure differential to overcome the resistance, so you'd be much less likely to notice it. You'd be best off to use 1/4" lines to the rear, while the fronts could be 3/16 or 1/4, depending on whatever works with the front section of your master cylinder. To actually answer your original question, a difference in line diameter won't create a bias in braking effort toward one end of the car or the other. There's going to be a certain amount of rear bias at equal pressures if you use a late model rear end with self energizing drum brakes. If you're using an early Ford rear with hyd brakes, then the balance would be more equal since neither end would have self energizing brakes. I had a 40 sedan in the early 70's with rebuilt stock front brakes and a late chevy rear with drums. Can't remember what M/C it had, but the brake balance was fine without any extra trick parts.
You can use any size tubing on the rear 40 Ford brakes. I have two Ford systems using 3/16" tube on the rear,and one using 3/16" on the front. I think the 1/4" lines were just overkill for the era. One ton trucks,with 12" drums,use 3/16" tube.
The size of the lines makes NO diference whatever in the operation of the brakes using those sizes . Some of you guys really need to study up on hydralic systems operation.
Thanks for the replies , I was going off the info about the sizes in pipes from the Bishop/tardel book, and wondered why the difference.The front and rear brakes seem almost identical and I figured there must be some kind of system built in to prevent the rears being as good as the front and locking up.As the original system uses a single pot mc, I thought the larger diameter rear pipes might effect a different amount of force at the initial pressing of the pedal ie; bringing the fronts on line slightly before the rears. I probably overthought things as usual.....thanks again for the input.
Reefer, Unless your Mustang master cylinder is a dual master cylinder and that is what you are trying to accomplish I would contact Richard Lacy at earlyv8@aol.com, (626) 338-2282 for his bracket to mount a '40 Ford master cylinder using the original '32 brake and clutch pedals and then just duplicate the '40 system with all 1/4 inch lines and fittings. That way you know you can get all the fittings, the leverage of the brake pedal is correct and the diameter of the master cylinder piston is correct for the wheel cylinders. Charlie Stephens
The Jalopy Journal
