Had a engine swap done. Car ran like crap but no problem with brakes. Had engine tune today and lifter set. Now no brakes. The guy who worked on car said lower vaccumm is causing this and is going to use larger fitting to get more vaccumm to brake booster. Is brake booster electric or does it work on vaccumm from block. Need answer fast. We blocked one side of PVC and seemed to help. Thank you in advance.

 

Using a larger fitting isn't going to get "more" vacuum to the brake booster. If blocking the PCV improves things, then are you running the PCV and the brake booster to the same port on the carb? If so, don't.

 

Either change ports to direct, constant non-ported vacuum or run a reservoir.

Ed

 

He blocked vent for more vaccumm. I guess it would suck air. The port that the line is attached too is very small. His idea is it is retricting the vaccumm. The brake booster is mateal except for the last 6 inches were it goes to small rubber hose, then to small port. What is constant non ported vaccumm?

 

What kind of carb do you have?

 

Ok, here the deal. When driving car, brakes are ok. At low speed or need to stop and go, seems brakes are weak. I think brake booster, mechanic said this is because put cam in. Had cam in and didnt do it, I think he is full of s#$t.

 

There's two types of vacuum on carbs, ported and full:

From this site:

http://www.centuryperformance.com/timing.asp

"Ported vacuum means the port is drawing vacuum "above" the throttle blades in the carburetor. This means that as RPM increases, vacuum increases and in turn, vacuum advance increases...... With our suggestion of using the vacuum connection to full manifold vacuum, the port will be drawing vacuum below the throttle blades. A good running street engine will have a measured vacuum at idle between 14"-20" of manifold vacuum. Now, this will give you a ton of advance at idle, but as load increases (vacuum drops) you will take timing away. "

If you're tapped into ported vacuum, you only get good vacuum under load. You need full vacuum to the brakes, like off the manifold or just under the carb. What manifold do you have?

Ed

 

OK, the engine has just been rebuilt. The car brakes were fine. I took the car to have rockers adjusted. He adjusted rockers, set timing an set carb. When I pick it up it sounded great but brakes were hard. The mechanic said it was not getting vac because the engine was running right and the cam. Cam is .50 lift, nothing radicle. He installed a vac canister. I didnt buy it, how could tightening rocker decrease vaccumm, should increase. It has a edlebrook intake. The was a hose going to intake off fitting but it was very small, proably 1/8 inch. But, everything was working fine before he had it for 3 hours. I think he might have cinked something or pull vaccume line off somewhere or bgroke wire. seems strange to me. Also notice a little brake fluid on front of booster.
he said he could not figure out. holley 650, edlebrook

 

Ok I will end this. I took car to my mechanic today, tired of the BS. Know I would spend cash, but it would be fixed finally. The fittings comming off the manifold were increased to 1/4 inch. The were about 1/8. Also rehooked the vents back in the valve covers. Installed a vaccum advance distributor to go along with carb. Also reran the lines going to the vac canister. Also hooked up the trans correctly. With the new accell distributor the car is brutal. Spins wheel effortlessly. Reminds me of a 71 camaro I had that I swaped out a 301 a put in a 400. That didnt have headers, hiflow cat, cam ect ect.