ot farm truck brakes

im still sorting out the brakes on this 1957 chevy 4400, nearly everything is new, brakes are adjusted correctly maybe even a little tight, i have good brakes, but its on the second stroke of the pedal, im down to either a wrong master cylinder which is also new, or a problem with the hydroboost, now the manual says to add one ounce of "bendix vacuum cylinder oil" to the hydroboost unit at the lubrication plug every 10,000 miles or 6 months, since this truck was parked for 46 years it probably needs some lol .this is a new one on me, what is the oil, or its modern equivelent? and where should it be added?

did you bleed the bleeder on top of the hydroboost? Sometimes that bleeder screw gets overlooked.

good brakes on second stroke of pedal usually is air in system or brakes out of adjustment

A bad booster will make the brakes weak but won't make you pump them up. You have air in the system. If you can't get the system to bleed normally, you may need to reverse-bleed them by pumping fluid backwards from the wheel cylinders. I have a Phoenix Systems kit for this purpose.

And are you bleeding from the furthest point first, and working your way in?

(ie. right rear, left rear, right front, left front)

If your pedal is hard on the second application, I doubt it's air. It sounds like a clearance issue which doesn't have to be at the shoe/drum area. Are the shoes fully around the anchor at the top in the rear? If not, an e-brake cable(s) are hanging up. Did you measure the piston depth where the pushrod goes on the new master cylinder. Don't over adjust, just make sure it's the same.

Bleed the brakes - completely and properly. Air in the system is the ONLY thing that can make you need to pump them. Especially on a truck this old, brake systems are incredibly simple. This is NOT rocket science. Bleed the brakes!!!!

pedal is hard, and doesnt go down when i hold the brakes on, truck stops normaly just on the 2nd stroke, of the pedal,like itsjust not moving enough fluid, but where? the brakes are fully seated on the anchors i pulled the wheel ends back down and checked,the rear has dual wheel cylinders and i counted each click on there adjustment to make sure the shoes were the same on both,each wheel cylinder has its own adjustment wheel, all the shoes are adjusted to slightly rub the drums, the e brake is on the driveshaft, behind the transmission , when bleeding i can get no air out of the system anywhere, including the 2 bleeders on the hybroboost , i even picked the rear of the truck up off the ground about 4 feet, to try to make any trapped air get out, never got any out, the master cylinder is under the drivers floor, and the number does cross to the new one that i bought, this thing is making me crazy! this restoration could wrap up this weekend if i can get the brakes working, ive been working on this truck for 2 years and the owner [ whio actually bought this truck new] is into it for considerable money, but i cant send it back with brakes like this, i hope this makes somebody think of something, its probably something simple and stupid, but i cant figure out what it can be

I have worked on truck JUICE brakes for a lot of years and the best way to get them bleed is with a power bleeder . and once your dead sure that all the air is out of the system then the next thing is the adjustment and IF you have to STROKE the pedal to get brakes they are still to loose so tighten them up a bit more . Myself i plum hate JUICE BRAKES on anything over a 3/4 ton .

I had a 2 ton International with that problem. You will probably need a pressure brake bleeder to get all the air out of the line. I built my own with a plastic hand weed sprayer. and a piece of steel and gasket to clamp over the master cylinder. Worked real well and solved the problem. Try Utube for examples of home made bleeders

You need to go make some hard stops to wear the shoes into the drum then readjust. Just a few high spots will cause your problem. When I put new brakes in my C65 several years ago it took nearly 1000 miles of hauling grain before they mated well enough that I could adjust them tight enough to do away with the second pedal stroke. If your pedal is hard, even if it takes a few strokes you have no air in the system. If you have air in the system your pedal will be spongy no matter how much you pump it. Never heard of the vacuum cylinder oil so I cant help you there.

A few things come to mind. Before we start, I too hate hydroboost!

First, it's already been mentioned, the shoe to drum fit. If the lining isn't radiused the same as the ID of the drum, the shoes will flex causing low pedal, but also spongy pedal. Since you have good pedal on the second pump, I don't think this is the real problem.

Also there could still be some air. If you don't have a reverse bleeder, you can make one with a new, clean oil pump can (might run some brake cleaner through it first, just to be sure) and a short piece of hose. Pump the can until you get solid flow, put the hose on the wheel cylinder bleeders, and pump backward through the system. Helps to have someone watch the master cylinder to see if air comes out.

Another suspect is the master cylinder. Not sure, but worth doing some research, I suspect the standard master cyl bore is smaller than the cyl used with hydroboost. Maybe the wrong master cylinder.

Had a similar problem on an old IH truck I had. Turned out to be air in the wheel cyliners. They were at an angle that left a small amount of air above the bleeder. I tried all the things said here and nothing worked. Finally took a feeler gauge and slid it in the cylinder to open the rubber a bit and let the air out and no more problems.

One other tip..

If you pump them up until you have good pedal, then release the pedal, watch the master cyl reservoir. If there is an ongoing fountain of fluid coming up out of the hole in the bottom of the reservoir, then there is still air in the system.