by Old Skool Mon Oct 30, 2017 8:59 am
I thought this thread had been well discussed many years ago??
DRUM BRAKES are MECHANICAL POWER BRAKES by operation!!!!!! This not a new reply again... LOL
Caliper pistons are ONLY operated by pressure applied TO THEM with no mechanical multiplication other than the actual pressure applied to the piston, regardless of power brakes or non power brakes. Power brakes systems typically with a LARGER piston size to slow them down a touch and not be so violent in operation HOWEVER the caliper piston still ONLY affected by line pressure alone.
THAT IS THE REASON of why the rear drum brakes CAN lock up BEFORE the disc brake will and the reason of WHY the flow to the drum brake circuit NEEDS to be slowed down. This IS CALLED BRAKE BIAS which also includes front and rear weights, tire sizes,, etc,etc... AGAIN explained in detail in the book "HOW TO MAKE YOUR CAR HANDLE" by Fred Puhn, (HPBOOKS--46)
The stock drum brake Econoline BRAKE BIAS controlled by different sized wheel cylinders in the back versus the rears.
Also stated sooooooooooo many times. A 10 lb valve CAN LOCK UP A DISC BRAKE CALIPER as it HAS NO RETURN SPRINGS as drum brakes do.
A 2 lb RESIDUAL VALVE (check valve) IS RECOMMENDED for a disc brake circuit in which the calipers or brake lines are ABOVE the master cylinder reservoir height as it can cause a drain back to the M/C. Believe it or not stated in numerous tech articles.
A proportioning valve does exactly as it says, it PROPORTIONS the brake fluid. So,, if a drum brake is a mechanical power brake by operation wouldn't it also make sense also that it can lock up before a disc brake caliper can lock up!!! and the reason of why its operation needs to be slowed down to match the front disc brake caliper. THUS A PROPORTIONING VALVE IS NEEDED. Whoever stated that it needs to slow down the disc brake and not the drum brake is WAY OFF BASE regardless of who is saying that!!!
SOME also saying to use a PRE SET proportioning valve of which CAN ONLY BE CLOSE to the vehicles particular BRAKE BIAS and would be LUCKY to properly adjust the BRAKE BIAS if AT ALL and the reason of why I ONLY use an ADJUSTABLE proportioning valve on my disc setups.
OLKSKOOL