i'm with mark and jerry
most mopars had big front drums and big rear drums
we swap to disk on the front and do not consider doing anything about the rear.
modern car
big disks on the front, piddling little disks on the rear
less modern car big disks on the front tiny drums on the rear
Updated mopar: medium disks on the front and 11 inch duo servo ditch finder drums at the back, that originally balanced (poorly) with drums on the front, but in no way are balanced with disks, coupled to a master cylinder sized large, to account for the assistance a servo would give
the drums were balanced front to rear via shoe area and the bore of the wheel cylinder, and the line pressure was set by the size of the master cylinder bore and hence the surface area of its piston. that serface area is pie r squared Pi x r*2 increase bore and surface area goes up by a power of 2
disks on the front throws all of that out of the window.
disc calipers need a higher line pressure to truly work and this is the problem
disc calipers involve applying your peddle force to a huge piston where a cylinders pistons are small
the wheel cylinders use the principal of leverage, cylinder at one end acting by levering out longish shoes a disk caliper doesn't
with the drum disk combo what you get is the rears nearly locked at the point where the front discs are nearly starting to work.
i.e you are using only part of the capacity of your front disks and can't use anymore of that capcity because the rears will lock.
makes going to front disks a waste of money you leave a large % of that braking capacity unused.. you want to be using 100% of that capacity
you can sling in a brake bias but it is really just a switch that keeps the already too high line pressure to the rear at a set point and allows the fronts to work eventually.. i.e its only useful in an emergency stop for it to work properly the brakes already need to be much closer in balance front to rear.
happy none assisted brakes
1) disks on the front as big as you can fit
2) the smallest drums that fit your axle at the rear
3) the narrowest drums that fit your axle at the rear
4) the smallest bore wheel cylinders that fit your backing plate at the rear
5) a master cylinder for disks. The narrower it is, the more progressive the braking and the longer the peddle travel. it will approach exceedingly firm slowly. rather than within 2mm off the top. It should never feel like the brake pads are made of polished wood.....! moving from 1 1/8 inch bore to 1 inch bore master cylinder increases the brake line pressure by about 26% but increases the brake peddle travel only a bit, same foot force on peddle produces 25% more shove on the pads and shoes. Perfect to take up what you feel you lost by removing the servo
6) if you reduce the bore of the master cylinder you probably don't need to worry about the peddle ratio i.e the distance of the push rod from the peddle pivot. re engineering this is a PITA
the point is if you get the lot balanced front to rear properly, the front disks actually work properly, the rear never locks up so the car doesn't try to do a right angle turn in an emergency stop, and you have removed servo clutter and more things to go wrong from up front.
my car is 1.4 tonnes it has 10.5 inch disks on the front and 9 inch drums on the rear manual brakes it stops
a dodge charger is 400KG more
surely with the big B body discs on the front 10 inch narrow drums on the rear, the small bore wheel cylinders and a 1 inch master cylinder
all should stop pretty well
master cylinders.
looks like servo cars had bigger master cylinders than manual as you would expect as the serve assistance needed to be taken into account . you can get a 15/16 master but it needs to be modified to fit the pushrod retainer and is designed for 4 wheel disks hence if used with drums at the rear you need late model wheel cylinders that work without a residual pressure valve in the Master
- mopar master cylinders.png (681.16 KiB) Viewed 1699 times
Ram Man on brakes
http://therammaninc.com/files/categorie ... -19746.pdf
Dave
