PDA

View Full Version : Dual Diagonal Braking Question



astroracer
06-26-2013, 08:19 AM
Quoted from Wiki:
"Diagonal split systems were used initially on American Motors (https://www.pro-touring.com/wiki/American_Motors) automobiles in the 1967 production year. The right front and left rear are served by one actuating piston while the left front and the right rear are served, exclusively, by a second actuating piston (both pistons pressurize their respective coupled lines from a single foot pedal). If either circuit fails, the other, with at least one front wheel braking (the front brakes provide most of the speed reduction) remains intact to stop the mechanically-damaged vehicle. Just before 1970, diagonally split systems had become universal for automobiles sold in the United States. This system was developed with front wheel drive cars suspension design to maintain better control and stability during a system failure.
The diameter and length of the master cylinder has a significant effect on the performance of the brake system. A larger diameter master cylinder delivers more hydraulic fluid to the caliper pistons, yet requires more brake pedal force and less brake pedal stroke to achieve a given deceleration. A smaller diameter master cylinder has the opposite effect.
A master cylinder may also use differing diameters between the two sections to allow for increased fluid volume to one set of caliper pistons or the other."

I was totally floored by this when I read about it on another forum. How many of you know this is being done and have no clue about it? How many have plumbed their brake systems through OEM MC's and Prop valves and done them Front/Rear and not diagonal as designed? What kind of problems will this cause in performance, bleeding, and longevity?
With all of the suspension design I do I have never delved into the Brake design side of the system. I was fully unaware this is being done and most of the cars we drive have split systems...
Mark

sccacuda
06-26-2013, 10:57 AM
Can't comment on other makes, but Chrysler Corp. vehicles use a front/rear split for rear wheel and all wheel drive vehicles, and diagonal split on the front drivers. So Mopar guys don't panic! Good info for anyone thinking of using a front wheel drive master.

dontlifttoshift
06-26-2013, 01:05 PM
As far as I knew, only front wheel drive split the systems diagonally. It had everything to do with all of the weight being on the front of the car and they wanted to ensure that at least one front caliper was in action.

astroracer
06-26-2013, 02:26 PM
Makes sense. Still seems like it would cause problems during hard cornering/wet braking conditions... I will be going with standard front/rear split when I plumb the van. Thanks guys!
Mark

dontlifttoshift
06-26-2013, 05:29 PM
It would only be a problem if you lost pressure on one side of the split. If everything is sealed up, it functions normally. 1" piston is 1" piston, doesn't matter if it is the rear piston or front piston.

MonzaRacer
06-28-2013, 07:06 PM
Newer cars are diagonal split systems. Works better on FWD cars and less well on RWD cars.
Theory is it keeps car more stable if 1/2 of system fails.
ANOTHER BIG REASON IS THAT THE CURRENT CROP OF CARS AT LEAST BACK 20-25 YRS OR BETTER HAVENT GOT ENOUGH REAR BRAKES TO STOP ANY CURRENT CAR ON ROAD.
Where as older cars had at least 9 or 10 in drum brakes and the rears can actually stop you. Try stopping a 2500-3000 lb car with 7.750in rear drumsthat are barely 1 1/4ish wide. Aint gonna happen, safely.