I am in the process of upgrading my '63 B500 from single circuit (reservoir) power brake system to a double circuit (reservoir) power brake system. The vehicle has dual rear wheel cylinders and drums on all four corners. After installing a Cardone 10-1393 dual master cylinder for a '72 F350, (as recommended on this forum) and replacing all the brake lines, I discovered that the original vacuum power booster will not hold vacuum. The pedal is hard and fades and does not push enough fluid to sufficiently apply the rear brakes. I pinched off the hose to the rear brakes and the pedal remained firm and did not fade, so the issue is in the rear brakes. I will adjust them as soon as I can get the lug nuts broken loose and the adjusters free-turning. Meanwhile, my search to replace the vacuum booster came up with a $500 price tag, IF it was available at all. So, my problems are:

-Not enough fluid reaching the rear wheel cylinders. I could adjust the shoes and install a residual check valve in the rear lines to hold a minimal pressure to the wheel cylinders.
-I don't want to spend $500 for a power brake booster.

my questions are:

-Is the Cardone M/C 10-1393, for the '72 F350 sufficient for the drum brakes on this F500?
-What would be a compatible vacuum booster for said M/C that would also fit my bus?
-Is there another master cylinder - booster combination that would work for this application?

Thanks,
Neal

 

Are you sure the vacuum booster is bad? If everything works when the rear brakes are pinched then the booster may be ok. A remanufactured booster to match that master cylinder lists for about $125.00, so I would go that route instead of trying to keep the original mismatched components.

A few other things come to mind:

1. It sounds like you have not had the rear wheels apart. Did you replace/rebuild the rear wheel cylinders? I have no idea but those cylinders may be huge and that could be problem, or they may just be leaking or stuck. If they are too big that could be a problem and a possible solution would be to see if a smaller cylinder would bolt to your backing plate, or beyond that maye using a different backing plate.

2. Did you replace the rear flex line? These are notorious for causing pedal feel problems. Also there is that axle vent "T" fitting below the flex line that could be clogged on one side or the other.

3. The problem could also be that you need to use a smaller guage brake line. You said that you replaced all the lines but didn't say if you used 3/16" or 1/4" line. 3/16" will accomodate a smaller cylinder bore than the 1/4" (or larger?) line that was probably originally on your bus and would probably give a lot better pedal response at the back of that long bus.

 

Excellent points, Orange. I have not had the rear wheels apart yet and have not rebuilt or replaced the wheel cylinders. I have a new flex line for the rear but have not replaced the old one yet as it looked fairly new. Those are things I will be doing next. I am sure the booster is bad - it was full of rusty brake fluid and water, and there was no difference with or without the vacuum hose attached. The new brake line is all 1/4". If I still have issues after replacing the booster and adjusting the rear shoes, I will look into replacing it with 3/16". I found the matching booster at Parts Geek for right around $100 including core and S+H. I'm hoping it will bolt right in and have the proper amount of travel etc.
Thanks,
Neal