Thread: Low Power brake booster vacum

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hi techinspector1 glade to see you're still kicking.

I know what the article abour residual valves says in MP but you have to read alot more than one article and get the big picture. My blown 32 has no residual valves runs a cool 550 h.p. has 18 in. LIVE vac. and the master is even under the floor and the brakes are perfect. Hum! Oh whoa is me. Why does my car stop so well? could it be because I have read the book on brake systems. I don't mean to be a smarty pants Mr. Techinspector But I do know brakes and MP is the best in the business and with their tech information in their book you can't go wrong. You just got to read it all not just part of it.

Originally Posted by lt1s10

hi techinspector1 glade to see you're still kicking.

and same to you Mike!!!!

Originally Posted by techinspector1

and same to you Mike!!!!

hope you'll be around more often.

How can I tell if I have the correct master and proportining valve ? neither one have numbers on them and I can only take the persons word for it that I purchased from. Are there any visable differences.
I had someone push on the brakes and I opened the rear bleeders and brake flouid came out, so I know fluid is making it to the wheel cyclinders. I'm not sure what you mean by the proportioning valve is not centered ?

most all of them center themselves now , but when ford first came out you had to bleed the brakes from front to rear, and center the valve. if you have fluid coming out all 4 wheels, then thats not the problem. sounds like to me your booster is bad or to small..

Thanks for the help, I'll get a larger booster.

Originally Posted by DennyW
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And yes, they should redo their thinking. I don't want 10 lbs fighting my rear shoe springs creating a brake drag.[/FONT]

Denny is right. Master Power Brake has it wrong. If you've ever changed your brake shoes, you know how strong those brake return springs are!! 10 psi in the wheel cylinder isn't going to move those springs!! You should also notice that the brake shoes are always pulled solidly against the round pin at the top of the backing plate. There is never a gap here when you have your foot off the prake pedal. Even if there was enough brake line pressure to hold the shoes off this pin, how would the brake system be "smart enough" to know how much gap there should be, and yet not cause the brakes to drag? Master Power Brake has it WRONG!!

Jim, That's a beautiful engine compartment, and you've shown us some really good pictures! Since you have a Corvette style m/c, did you plumb the front brakes to the m/c port toward the front of the car? Did you notice that the front reservoir in the m/c is larger than the rear? The larger reservoir is always for the front brakes, because disc brakes draw fluid from the reservoir as the pads wear. Drum brakes don't need such a large reservoir because the wheel cylinders always return to the same position, regardless of the wear on the brake shoes. There is a balance spring inside the m/c that compensates for the front/rear brake line pressure, and if you have the brake lines reversed, you won't have any rear brakes.

I don't even have power brakes on my truck, and it stops fine. A bigger power booster won't solve your problem!!

Rot Rod Roy Thanks for the compliment on the engine compartment. I spent a lot of time on it. To awnser your question. Yes I ran all new brake lines and yes the front lines come from the front reservior to the proportining valve and the two out lines on the front of the proportioning valve go to the front disc's, The front reservor is not larger than the rear. You can see in the pictures iI sent .
The rear comes from the back of the proportioning valve in 1/4 brake line to the back, braided flex line to a tee and than to 3/8 brake line to the wheel cyclenders. In going to recheck for kinks to the rear brakes and recheck my assembly of the brake shoes and springs. I have installed may rear brake shoes but it does not mean I did not make a mistake. I sent a few more pictures of the master and prop valve. I also encludes a picture of the engine compartment. Any and all input is welcome.

Jim, the centering of the proportioning valve that It1s10 mentioned is for the brake warning light, that you don't have connected. That's the terminal in the middle of your proportioning valve. Check to see if you have a connection to ground at this terminal. If you have a ground connection here, your warning sensor has been activated, and the internal piston will need to be re-centered to turn off the warning sensor. Since you have such a drastic difference in your front-to-rear brakes, this has probably been activated. To centralize this valve, you'll need to create a difference in the pressures between the front and the rear brake circuits that is the opposite of what caused the activation of this valve. If this is necessary, watch your ohm meter or test light while you bleed the front brakes until the switch turns off. Now try your wheel-spinning brake test again.

This type of proportioning valve is non-adjustable. Are you sure it's calibrated properly for your brake system? What do the people say where you bought it? Have they tried to help you solve your problem? Your major problem is the balance of the brakes between the front and rear brake circuits. That's what the proportioning valve is supposed to do! Any changes to the size of your booster won't fix that.

Your rear brakes must not be seized up, or the rear brakes would not release when you take your foot off the pedal, so they must not be getting sufficient pressure. The craftsmanship of your car is so nice, I can't imagine a pinched or crushed brake line, and this would also cause your rear brakes to drag when you take your foot off the pedal. (The rear brakes do release promptly when you take your foot off the pedal, don't they?) This points to a bad m/c or a bad proportioning valve.

Is there another port on the bottom of the proportioning valve with a plug in it? The proportioning valves I'm familiar with have the rear brake line connected to the bottom of the valve, rather than the back, like yours.

By the way, your front reservoir IS larger than the rear reservoir. Look at the bulges in the sides of the casting around the front reservoir.

Roy, I'm not sure what you mean buy is the proportioning valve calibrated for my brake system ??. I cannot ask the people I bought the brake system from because I bought the booster and master from Eklers and the Proportioning valve from Fatrodder on ebay, I probably should have bought a complete setup.
I rechecked all my brake lines (Checked good) and rechecked my rear brakes to make sure I assembled correctly All tooked good.
I checked to see if the warning sensor had be activated with my ohm meter and it was not activated. I tested it when I rebleed the brake system again.
Just a note: If you look at the Picture of the engine compartment you will see the vacum canister with a guage on it. When I stop the engine the vacum will hold at 17 for 20 minutes.

Update, I finally resolved my brake problem. I went with a 9 inch power brake booster, and removed the extra vacum canister. The brake pedel is when it should be and the car stops on a dime. Thanks to everyone that gave input to help resolve my problem.