a brake problem

[bosworth]

I'm getting close to having my 52 B3B ready for the road,  I've been doing a little joy riding on our dead end road and  I'm not impressed with the stopping power of my setup.  What I have is a standard Master cylinder, standard front brakes and a jeep cherokee rear axle with 9" drum brakes.   I believe the problem is that the wheel cylinders on the Jeep axle have only 13/16" bores, while the bores of the front wheel cylinder and Master cylinder are 1 1/4" each.   What I think from my high school physics days is that the rear cylinders will only produce about 42% of the pressure developed by the front cylinders.  I believe that the original rear cylinder was 1 1/8" bore which would have produced 80%   If the heating of the drums is an indication,  i'm finding that after a few hard stops that the front drums are getting quite a bit hotter than the rear drums.  My question is what are my options for increasing my breaking power; front disk brakes, a different master cylinder with a smaller bore,  is it possible to find wheel cylinders for the jeep axle with larger bores?  I should mention that I drive a 48 Plymouth with a stock braking system, that works great,  so I think I'm making a fair comparison.

Your thoughts and experience are greatly appreciated

Bill

Edited November 27, 2017 by bosworth

[lonejacklarry]

My first thought, Bill, is I'm wondering if this is the first drum brake vehicle you've had or if it has been a long time since drum brakes.  The reason is that we are all spoiled with disc brakes, vehicles that start in seconds, and radial tires that don't weave and follow the cracks.

If you are used to drum brakes and this truck is inferior to others, then it is a different thing.  I can't argue with your math but as I remember, the front brakes have way more braking power than the rears and that is why they will heat up more and quicker.

If you can lock the brakes on dry pavement  (safely), then you are getting all the braking you need and have applied more braking than is necessary.

[P15-D24]

To Lonejacklarry's point can you lock up all four wheels? If not you probably new some brake service, starting with an inspection and probably a shoe adjustment.  

[bosworth]

thanks for your reply;

I have two other vehicles with drum brakes a 31 model A ford pickup (mechanical, not hydraulic) and a 48 plymouth, both stop well and will lock up the wheels in a panic stop.  I have replaced all of the components in the front and rear brakes and as far as I can tell, they are adjusted.  I have adjusted the brakes on my 48 plymouth with good results.  I  don't think the wheels will lock up on this truck, although it occurs to me, even with an imbalance in bore diameters between the front and rear, the front brakes should still be working as original. 

Bill

[torqczar]

jeep brakes are self energizing don't need much  wheel cylinder size ..    you need to find a smooth dirt road,   roll along about 10 mph    panic stop,  get out look at skid marks    on  all   4 tires? the fronts skid mark should   longer than rears   .. if  brakes lock on this test they should lock up on pavement    if not, air in system,  this truck has  a  mushy pedal. yes/ no. or   your not  on the brake pedal hard enough ..

[bosworth]

Thanks, the info about the self energizing jeep brakes is just what I needed to know,  I will go back and bleed the brake system again and do as you suggest.  I am a little paranoid  about the brakes,  making them go is great, but getting them to stop is a priority.  Now, to find a smooth dirt road......

thanks

Bill