'69 satellite 2 dr, drums front and rear. Under hard braking the rears lock up. The front brakes don't feel like they are working as hard as they should and the front of the car doesn't seem to dive much. I replaced the front shoes (premium Wagner), new wheel cylinders, and new wheel hoses but the problem is still there. I would love to change to discs but I'm a divorced dad paying child support on 4 kids so these stock drums will have to do for now. This is my 4th daily driver Mopar and all 4 have had this problem to one degree or another. It destroyed the front clip of my '70 Charger a few years ago during an emergency stop situation and I can not let it happen again! Surely this isn't normal. Or is it?

Duo-servo brakes. Almost impossible to modulate. First fix: Smaller rear wheel cyls.

Rick

Alot of Mopars have too much rear bias. Are they locking up on a full panic stop or medium braking or?? Are the front shoes good & tight?

They don't lock up under medium braking but it's pretty easy to do beyond that. It doesn't take a panic stop to slide the back tires. When I did the front shoes I adjusted them per the shop manual which had them pretty tight but not dragging.

Rick, any suggestions on what applications have smaller wheel cylinders that will fit? I have one leaking and will be changing them asap.

First thing is to take the drums off and check to be sure you are not leaking gear lube past the seals, that will make the rear lock up.
And check the condition of the shoes, I had some not long ago that the friction material was no longer attached to the shoe, bonding let go..
And dont forget to check the parking brake, to be sure it is completely releasing, check the top of the shoes, both should touch the anchor pin..

Brake fluid on the shoe will cause expansion of shoe material also, as mentioned, if you have a bad enough w/c leak it could have contaminated shoe now. Smaller W/C's will help, or you could get a narrower set of shoes to take away some of the stopping surface.

what is the condition of the drums?

The drums and shoes are in good condition with no brake fluid contamination yet and the axle seal is not leaking. For a smaller wheel cylinder I checked the first obvious choice - a '69 A body (Dart) but the mounting holes are closer together so will not bolt up. So where do I get smaller wheel cylinders? I need to replace the one that is leaking asap as this is the only drivable vehicle I have right now!

I'd say contact Ehrenberg for 7/8" ones but with you needing them asap if we knew what OE apps used a smaller bore but the prob is they (your parts house) may list it as a smaller bore but supersede you to a larger bore (bring a scale). wheel cyl kits are dirt cheap, only several dollars & might get a hone/kit & be up & running in no time assuming the bore/pistons are not in bad shape & I'd say you are OK. On the hone I'd get a dingleberry but they are $$$. A 3 stone one is cheap & use the fine stones w it

The other thing to consider here is brake drum SIZE

Have the front drums been turned "out" too much? This will cause the circle formed by the shoes to hit "only in the middle" of the now "too big" circle of the drums, and you won't have full shoe contact.

What happens THEN is, as the front shoes try to wear into this larger circle, the center area of the lining gets hardened and glazed, and no longer brakes as it should, so even IF the lining finally "wears into" the drum, what you then have is part of the lining is doing no work.

The other thing you haven't mentioned is things like tires and stance. Is the rear end all jacked up with air shocks / shackles? This can dramatically change the front/ rear weight bias

Are the shoes installed correctly? Primary shoe in the right position?

I'll pull the front drums off and examine the front shoes. The stance is stock, all suspension parts are stock incl the shocks. If anything, the car sits low in the rear and bottoms out easily with any passengers or a full tank of gas which brings up another issue of where to get good quality leaf springs but need to get the brakes lined out first. Rick didn't mention that he has any smaller w/c's in his reply but if he does and there's not a readily available choice, I'd just repl the leaking one with stock replacement right now until I got the smaller ones. They're not very expensive anyway. Esp compared to sheel metal/hospital bills/burial expences.

You're right. I replied 9" when they asked which size. I assumed the 10" ones would be the same size as B body 10". I'll do some more investigating. What's the diff between 10" A body and 10" B body backing plates?

This might help

The 7/8" W/C is Raybestos PN WC37236

Might want to heck and make sure your front brakes are properly adjusted. I seem to recall my 64 300 did not have self adjusting brakes in the front, just the back, but it's been about 20 years since then. Even if both ends have self adjusters the fronts might not be working properly (froze up, stretched cables, etc).

Since you are on a budget, some investigation could save you money.