Ok, now I'm a little confused. With the engine not running, its a straight shot from the pedal to the MC.
All the booster can do is decrease felt pedal pressure by helping you push the MC. It can't actually change the point where the pressure builds up, so it must be masking the feel.
But, I'm not sure exactly what we are seeing here.
I don't know how much you know about hydraulics, so if I am "talking down" forgive me, but I'm trying to bypass a lot of give and take by throwing in everything.
First, assume the brake system is perfect, no air, no weak hoses, no leaky MC.
For all intents and purposes you can consider the fluid in the system to be a steel rod.
Any movement of the MC, results in the same movement at the other end adjusted for the ratio.
Here is how it works:
None of these numbers are correct, because its actually the surface area, but don't mind that. The principle is the same.
If you have a 2 inch bore MC, and a 2 inch bore slave cylinder, then if you push the MC 2 inches with a pressure of 2 pounds, then the slave will move 2 inches and exert a force of 2 pounds.
If you have 1 inch MC, and the 2 inch slave, then a 2 inch push of 2 pounds will move the slave 1 inch with a force of 4 pounds.
It works exactly like a lever. This is how hydraulics works. Your 20 ton bottle jack has a large slave cylinder, the ram, and a tiny MC, the little rod worked by the handle.
Each time you push the rod a long distance, the ram moves only a tiny amount, but with great force.
If you have a 1 inch MC, and a 1000 inch slave, pushing the MC 1 inch with 1 pound of force, will push the slave with 1000 pounds of force but only move it 1 thousandth of an inch.
Remember, the fluid in a brake system does not compress. If you had all steel lines, and the brake cylinders were welded so they could not move, then you could stand on the brake pedal, and it would feel like it was welded too.
To apply the brakes on your truck, you first need fluid volume to move the cylinders out until the shoes or pads touch the moving parts.
Disks are simple clamping devices, so they need lots of force. This is why a disk brake piston is so large.
With a big piston and a small MC, you get a lot of force. But, very little movement because the MC does not put out enough volume with its small size to move the big piston.
But, thats OK, because disks don't retract much, so they don't have far to go.
Modern drums are self actuating.
They do not require as much pressure. When you press the pedal, the shoes move out until they touch the drum.
As soon as they do, the friction begins to try to rotate them. When they rotate slightly, it causes them to jam in the drum.
The more friction, the harder they jam. Thus they use the wheel's force against it to help with the braking.
So, those cylinders can be much smaller than the disks.
But, they retract a lot, and the pedal has to travel farther to move them out until the shoes touch.
This is why the rear adjustment is so important to pedal height.
Now, when you are using non-power brakes, you often have to go to a smaller bore MC so as to get more pressure at the brakes and cut down on pedal force. But, since you are moving less fluid per inch of travel, your pedal will move farther to extend the pistons far enough to make contact.
With a power booster, you can increase the size of the bore, to move more fluid. It means you have to apply more force to the MC to do the same amount of braking, but the pedal does not have to move as far.
But, you do not feel more force, because the booster is doing all the heavy lifting.
This is why, if you go to Rockauto, you will see that the really big bore MCs are for hydroboost units.
Lots of help.
Now, lets see what happens when the shoes and pads are in contact. At this point in theory, the pedal would quit moving.
But, the rubber hoses will expand some, the pad material will compress on the front, and the shoes on the back brakes are only touching slightly.
So, you still have pedal travel and this is why you can control braking, instead of them just locking up instantly.
As you continue to press harder, the braking force increases.
In your case, the booster must be fairly sensitive, so its masking the first part of the force when you press the pedal.
This should not be part of the problem.
The only way your pedal can move as far as it is, is either because something in the system is calling for a lot of fluid, or you have air in the system somewhere.
Air will compress, and let the pedal move as the bubble gets smaller and smaller under pressure.
I have a sneaking suspicion that the problem is in your antilock system............
Yeah, I know its gone, but that is still where the problem is if I am right.
Remember, the front disks take a lot of fluid, due to their size, but they don't actually draw that much, because they have to move very little.
Its the rear brakes that suck up the volume, because they have to move out a lot.
Adjusting the rears right up against the drums, barely touching will help, but there is something else.
Car makers have had this problem for a while. A small MC will work on the front, because there you need pressure, not volume.
But, you need a larger one for the rear since the pressure is not as great, but it needs more volume.
See the problem they get when you have both types on the car?
Some MC actually have two different bore sizes in them. One for the disk, and one for the drum.
But, others do that and/or another way.
They put a low pressure check valve on the rear drums. It lets the shoes retract a little way, then blocks the fluid so they stay right up next to the drums.
That way, you don't need much volume to move them back out.
If I am right, your abs system had one built in. Probably not working. With the abs out, you have no valve.
They sell them online, it is certainly worth a try. You have to get the pressure right, you don't want the rear brakes dragging, but most of them are adjustable.
I will check around.
Fart, this darn thing has run on forever.......again. Sorry about that.
Other than the brakes, how you been doing? As you can see, there is nothing wrong with my hands.........
. I could use any tips to help firm it up.
My bad
