Thread: Low Power brake booster vacum

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Thats All The Vac You Need. Thats Good Vac. WHERE HAVE YOU GOT YOUR BOOSTER HOOKED ? cant have nothing tee'd into it.

Here's a few more pictures to give you an idea where I have the vacum line hooked to. As you can see it is at the base of the carb. In one of the pictures you can see a brass plug screwed into the intake manifold. Is where I have the 3/8 plug where the vacum line should be hooked up? I went to the auto parts store and they gave me vacum hose 11/32 that is made for power brake boosters.

start the motor and pull the hose off and put your finger on the end of it. if you have vac. then it hooked up right.

I removed the vacum hose while running and there is vacum. If I leave the hose off the idle goes up but the engine does not die. Does this mean I have another problem I should be looking for ?

Originally Posted by Jim Standley

I removed the vacum hose while running and there is vacum. If I leave the hose off the idle goes up but the engine does not die. Does this mean I have another problem I should be looking for ?

no thats pretty standard.

Well I found part of the problem, or a combo of problems.
1) The correct vacum line helped.
2) When I installed the master push rod that attaches to the brake pedal assy, I did not line the rod up so it pushed in at the correct angle. Once I corrected this the hard pedal became more free but still a little firm/mushy. I will rebleed the brakes and give it another try. I will let you know the out come. Thanks for all the help. have a great X-mas.

Jim, do you have a 10 lb. residual pressure valve in the line to the rear brakes? If not, you'll need to install one. That will firm-up the pedal. Also, you need to adjust the shoes out against the drum so that you can just turn the rear tires by hand and get maybe a quarter turn by pushing on the tire and letting go.

I have taken the time to read your whole story and maybe this will help. First of all a 7 inch power brake booster is rather small for your ride. A dual 8 inch recommended but you could even go with a nine inch dual if you wanted to. I would use nothing smaller than a 8inch dual. It looks like the master is mounted on the firewall and if so you dont need any residual valves anywhere on the system. The only time you need residuals is if you master is located under the floor and is below your calipers. Use the correct proportioning valve though. Disc front drum rear if that what you have. That is critical. Also make sure that you have no more than .008 to .012 clearance on the push rod at the master. Make sure that your master is for disc, drum and the bore size is 1 inch or better I have 4 way disc and mine requires a 1 1/8 bore master. I think that you shoould now have all the answers for any possible situation. A vacum pump isn't going to help anything unless you have all the basics done right first. I hope I didn't sound like a know it all in writing all this. But I have pulled my hair out many times till I finally got it right.

Posted by Roy:
"you dont need any residual valves anywhere on the system"

You'd better call Master Power Brakes and tell them they're doing it all wrong then.
http://www.mpbrakes.com/uploads/docu...dualvalves.pdf

have same one pump the brakes and open the rear bleeder, to see if any brake fluid comes out. if not you have a restriction somewhere. you shouldn't need a residual valves if the Master slenderer is above the wheel cylinders. sounds like your proportioning valve is not centered.

hi techinspector1 glade to see you're still kicking.

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.

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.