I have looked through my manual but cannot find an accurate description of where the vacuum lines go. Presently I have the PCV and Power Brake both running to the "front" carb (and I think this is why i am having such poor braking issues). The manual explains that the "rear" carb should have PCV and Dist vacuum, but it does not mention power brake vacuum, so I am assuming this is the only line that runs off the "front" carb? I know I read this somewhere, but I want to confirm before I start moving things around. Note - this is a 64 dual quad set-up on a 62 Wildcat 401. Thanks
I have a "T" on lower back of the base on my front carb, for power brake booster and PCV. Distributor vacuum advance is connected to rear carb, passenger side/front base. No other vacuum being used.
I would like to take a look at mine. PCV is from front for sure. Chassis manual is pretty lame on these details! I remember trying to find same stuff for the 65. Lots of connections off front carb. I’m thinking not off the back one because it would mess with the idle bypass circuit.
What is your vacuum at idle? The port on the rear carb is "manifold" and not "ported". I have an 11 inch booster, and about 15 inches of vacuum at idle. (but my front carb secondaries throttle plates are not fully sealing). So, you should have full manifold vacuum at idle and on deceleration for the brake booster. And make sure you are using the "Air Needle Valve" . The large brass screw on front/center of rear carb for idle speed and not using a throttle link idle stop screw (as is typical on most carbs). The 2x4 is designed to only meter fuel/air through the idle circuit with all the throttle plates fully closed. Anything else will affect idle, especially at the 550-650 RPM that the nailhead should be set. You could block the PCV and vacuum advance and see if that affects your brakes. If you can locate a hand pump vacuum tester, you can test the booster. (I bought one for about $25) Pretty easy. Pull the check valve hose, connect and pump down to 20 inches and let it set for 5 minutes. Should be zero loss of vacuum. Then press the brake pedal and see that about 10 inches drop, if no drop or you lose all vacuum, bad booster. Pump to 20 inches and then press and hold the pedal, it should drop and hold remaining vacuum as long as you hold the pedal. If it continues to drop, bad booster.
Ok thanks guys, Michael I will try testing vacuum following your protocol. Ted, the brakes have gotten progressively worse since I added the dual quads. All brake parts are new. I had great pedal with the single 4 barrel. Once I installed the dual quads, braking was a little worse. Then I added a rebuilt 64 booster with a dual reservoir master, now if I am on any kind of an incline I have to stand on the brake pedal, and the brakes really don't come on until I am into the pedal pretty hard. I have adjusted the brakes and bled the lines multiple times. I have more $ into this now than had I just went with a disc brake system. ha.
Go to a 67 booster and master cylinder. I had a similar issue with my 64 with a single 4bbl. When on an incline or at fast idle I had to push extra hard on the brake and sometimes even put it in neutral. I thought it was a bad booster so I bought a reman 64 booster which didn't help. I put a reman 67 booster and master cylinder from NAPA and problem solved. My brakes feel like a modern car. The 67 booster is a couple of inches larger in diameter and may not clear a column shift car. I have a thread on here that tells how to do the swap.
When I converted to a dual reservoir master ('67), I couldn't get a good pedal to save my life with the original '62 booster (I believe very similar to '64). As Mark said, the diameter difference is significant. I then swapped in a '67 booster and have had great brakes ever since.
Mark and Andy, I appreciate you sharing your experiences. Given you both went through this before and solved your issues with a 67 set up, I think this is what I need to try next. I got my parts from Booster Dewey and I remember telling him that I knew some guys had specifically used 67 booster, he seemed to think the 64 was what I needed. I will call him and hopefully he will swap me out.
