I have read every thread I can find on the H.A.M.B about adjusting brakes and still don't get it, I guess. I am building a T racer with Model A ****** and rear end. '40 Ford juicers on the rear end... no front breaks as yet. Using a '39 (new) master cylinder. I have about 1/8th inch play at the peddle. I was told the shoe to hub clearance at rest is 20thou so I drilled holes in the hubs to get a wire gauge in to set them. Problem; the brake peddle immediately comes up hard against the master cylinder pressure. There is no give or "squish". It stops but feels like you are pushing on a cement wall. It feels like the shoes don't travel enough. Any suggestions? Is the 20 thou correct or should the shoes be further away from the drum?
My guess is yo've got the master cylinder pushrod adjusted too long. This is the rod between the actual pedal and the master. This is where you will adjust your pedal free-play.
Did you try taking the line off the master cyl. to see if you had presure there when you pushed on the pedal. I had a master cyl. where the fluid would just dribble out. The parts store replaced it & everything is good to go now.
I agree with 500 single you need to adjust the mc rod. Plus just having rear brakes your going to have a very different braking sensation that your daily driver. I would tighten the brake shoes (one at a time) until there is a heavy drag when you try turning the drum then back off until there is a light drag. This works for me.
Yes...more play at the peddle is needed, so the master cylinder can release the pressure. And .20 is too much clearance between the shoes and the drum, though I doubt that's the cause of your problem. Do what Biggeorge said...adjust the shoes to have light drag when you turn the drum by hand.
This is rather hard to trouble shoot as you have not given the details of the pedal ***embly that you used in you construction. If this is a home made pedal the pedal ratio become important as it relates to the force applied. First lets start with just adjusting things correctly. Jack up the axle of your car, place on jack stands so you can remove the wheels. If this is the initail install bleed the brake system to remove any air trapped. The first step is to adjust the free play in the master cylinder. This means disconnecting the pedal to master cylinder push rod and making sure that the master cylinder is fully open. Now move the pedal to align the holes of the pedal throw to the master cylinder push rod clevis or bearing end. There should be no travel on the pedal push rod inward at this time and the pedal ***embly should be in a neutral upward position state not hitting the floor board. At this junction reduce the length of the master cylinder push rod two complete adjustment turns or approximately 1/8" of free play before the pedal applies pressure to the master cylinder. This insures that the master cylinder is completely open and not blocking the return of fluid to the storage reservoir. To adjust 1940 brakes is a two part job. The first part requires you to make a stop stick that can be placed between the brake pedal and the seat cushion. This should be cut to a length that slightly depresses the brake pedal and holds the pedal with about 20lbs of brake pressure. You should just feel the brakeshoes drag on the drum when it is rotated. After appling the static pressure it is now time to adjust the brake shoes. This is done by loosening the two anchor bolts at the bottom of the backing plate. Back off the 11/16" nut so it is loose and the anchor pin will turn with a 5/16" wrench. If you carefully look at the anchor pins there is a dot bored in the edge of the tang for reference. This should be pointing upward, To adjust the anchor bolt and move the shoe closer to the drum surface, the anchor bolt is rotated outward away from the vertical center line of the backing plate until you can feel the shoe draging on the drum. At that time reverse the direction until the shoe does not drag, hold the pin in place and tighten the anchor pin nut up. Repeat this operation on the opposite shoe anchor pin. Now go to the two 3/4" bolt heads in the upper part of the backing plate, they also rotate outward away from the vertical center line of the backing plate and seat the shoes to the brake drum. After seating the shoes evenly reverse the rotation of the hex head cam to a point where the shoes no longer drag on the brake drum. At this point the shoes should be correctly adjusted. Remove the pedal stop, You should be able to rotate the drum and only hear a slight rubbing sound of the shoes. There should be no excessive drag. Now apply the brakes and recheck the pedal pressure and check to insure that the brake shoes are returning and not draging on the drum surface. You should have a firm solid pedal.
could it have something to do with the fact that you are using a master that is meant to push 4 wheel cylinders to only push two?? basically pushing twice as much fluid or half the pedal travel that is required.
The number of cylinders does not change the force, it's the size of the master cylinder and wheel cylinders that is the important thing here. And pedal ratio is important to.
MR 42, I don't know the fluid equations, I just know how things work in real life. my midget had front and rear brakes. to start it you shut off the front brakes and locked up the rears until the push truck got going fast enough that the engine wouldn't chug and be damaged. when you shut off the front brakes your pedal felt like a rock with no give, when you turned on the front brakes it felt like a normal brake pedal. the amount of fluid that has to be pushed makes a difference in the feel of the pedal, regardless of the effort.
pedal travel will increase with every additional wheel cylinder added! decrease with every one subtracted. that system is not going to feel "right" until all four wheel cylinders are being used, and all the brakes are "broken in" and adjusted properly.
Sound like the shoes are to far out.If you take the drums off look at shoes, the ends should be chamfered back depth of lining 1/8 and back on angle 3/4"both ends.Take a tape measure and adjust 1/4 less then drum.Center shoes.Put back on and see if any better.You can always adjust later.You can,t adjust the shoes with a wire gauge,they are for points.LOL
Yes the feel will change with number of cylinders, but the force will not change. So the question is does the brakes work? even though they feel odd. Are they to hard to push you need to change to smaller size of the master cylinder, or increase the size of the wheel cylinders.
Maybe I should have explained myself better when I suggested the pedal ratio as a possible cause. The OP said the brakes stopped but the pedal was "concrete wall" hard. He did not mention that the brakes would not release which is the usual result of an improper push rod adjustment that does not let the fluid release. He said he had adjusted (all be it in a different way than normal for Lockheed brakes) the brakes to .020" clearance which is probably about twice the usual, so it did not really sound like an adjustment problem. He mentioned he was using '40 brakes and a '39 master, they have always seemed to get along together, so I didn't think he needed to start re-engineering with different size wheel cyls or master. His description made it sound like the master was working, so I didn't think it was defective. That left the pedal mechanism as possible cause, the OP did not mention what he was using, so that bought up my question on the pedal ratio, as the wrong ratio would result in what he was describing.
I love this forum. There is somebody that knows something about everything. For example, if you want to know the STUPID way to put breaks together...I'm your guy! (LOL). I adjusted the shoes as suggested by you all, made sure the master cylinder was releasing all the way, bled it again and everything seems to work as it should. The brakes engage and release properly. The 'concrete wall' peddle problem it appears is one of leverage. The distance from the center of the peddle to the center of the pivot shaft is 10". The distance from the center of the pivot shaft to the actuator pin is 3.5". A bit much I guess. My problem now is to figure out how to get this down to around 6:1 without lifting the master cylinder (it's already up to the floor). Thanks for the help.
I can't see how it would align without a pic from above..but...just tossing out an idea.. You have a spare boss sticking out of the trans case. Drill and tap for a beefy pivot, then do a bell crank to change the pedal ratio. You would have to add a tab to the brake pedal, above the pedal pivot. Then the brake pedal would pull on the crank and the other end of the crank would push the master. Thunderbirdesq just did some sort of bell crank on his 34...I think.
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