Is there a difference between the brake brass distribution blocks, 4 wheel drum, and 4 wheel disc? They look the same externally, was wondering if it would make a difference or not. Thanks in advance
You use a 4 wheel drum pressure differential switch block for a 4 wheel disc conversion. There was never a factory 4 wheel disc option.
When you switch from drum to disc, you can use the original distribution block but should add a proportion valve to adjust bias to rear wheels to avoid lock up.
Thank you. Do I need a proportioning valve if I swapped to 4 wheel disc?
I’m having brake issues after the swap and the only thing “original” is the distribution block, thought that might be the culprit.
The distribution block has no effect on braking. Its purpose is to provide a place for the warning switch to sense differential pressure.
You likely need an adjustable proportioning valve to keep the rear wheels from locking up.
Thanks Royce. That is the issue, my brakes won’t lock up at all. I come to a rolling stop Is the best I can get. From maybe 60 MPH, it takes me 4-5 car lengths to stop, even if I mash the pedal to the floor, and that is a rolling stop, not a “screeching halt” like I would expect if I mashed the pedal.
SSBC front/rear disc conversion, matching master/brake booster, 20psi to the booster.
Vacuum bled, pump bled, and gravity bled. Pedal feels right, just doesn’t stop.
The fitting sizes are different drum vs. disc. We have a diagram that shows each port size on every year.
Thanks Don, my block looks like the one for drum brakes. Seems like the internals are different? I could swear when I bled the rear brakes, the rear bowl (front brakes on disc diagram) is where the fluid was drawn from, and by the drum brake diagram, it is connected correctly.
The biggest difference in a disc vs drum scenario is that discs take more volume and less pressure to activate than drum.
Thanks. The shop that put on the new master I don’t think installed the new dist block that came with the kit. I had to reorder the block, should be in today. Will post how it goes.
You may not have enough line pressure. A different diameter master cylinder may be needed. I assume you mean 20 inches of mercury at the booster right?
Here’s a nice article on line pressure vs master cylinder bore size:
Royce,
Correct, I meant 20 inches of vacuum! Thanks for the chart, I will scour over it and see what I’m missing! Thanks again bud!
Don, was the diagram on a different page ?
Saw them as I clicked on the pics thanks.
Don, you are onto something. I took off the old distribution block, and compared it to the new SSBC “disc brake” block. The holes in the disc brake block are larger. Do I need to replace the lines or are they large enough? And it looks like the front brake line ends are 3/8, but the new dist block sizes are 1/2 inch. I’m assuming I can just put on an adapter? Thanks in advance
I would assume the aftermarket system has substantially bigger pistons and moves more fluid volume. I would also assume they would include new proper sized lines with their kist. I always stick with original so I really do not know. I did purchase a 68 with power 4w discs last year and when used with a factory booster it did not stop as well as the OEM disc in front and drum in back set up. Kind of disappointing… To make matters worse you are limited on what wheels you can run.
Thanks Don,
I’m going to cut the lines, put on the 1/2 inch fittings, throw it back together and see what I get. From the looks of it, the lines are capable of moving the fluid, but the holes in the original dist block are too small, and the volume of fluid is limited there. I’m with you, disappointed so far in this brake system!
Im thinking Royce is on to something here. Did you verify you had the correct master cylinder bore yet? It sound like you bought the complete kit so assuming you got the right one that your setup needed? typically those kits are matched pretty well but you never know.
I used my drum distribution block with an adjustable proportioning valve for my conversion. However Im running front granada disc and stock rear drums. I ran the stock 68 replacement booster and disc/drum master
A lot of the aftermarket stuff is under engineered. I doubt the distribution block holes have anything to do with the problem. You need more pressure, not more volume. Find out what the master cylinder ID is, that will be key to fixing this.
If you suspect the distribution block you can easily bypass it with unions. Cutting and double flaring brake lines is a royal pain that you may or may not be capable of.