My 72' 350 now has a bigger camshaft in it after a total rebuild. When coming to a stop, you press the brake pedal & the brakes work ok at first. But then when you get to the stop the brake pedal is hard like there is no vacuum left in the brake booster. If you raise the idle a bit the brake pedal feels ok again. I've checked for a vacuum leak & there doesn't seem to be one anywhere. Has anyone had to use some kind of vacuum pump when running a bigger camshaft?

 

Maybe you need a new brake booster?

 

Maybe but it worked ok before the rebuild.

 

Well, what was the idle vacuum level before the cam swap and now? You might need a vacuum reservoir canister or an aux vacuum pump.

 

That is exactly why the W31 did not have power brakes. Not enough vacuum, because of too much cam. A vacuum canister may help, otherwise it is hydroboost brakes for you.

 

Hydroboost definitely isn't cheap. The vacuum canister, is there one specifically for brakes or is it just one of the "round ball" types?

 

Actually i just found one on the CompCams website. Will give it a try & hope to avoid the cost of Hydroboost.

http://www.compperformancegroupstore...&Category_Code=

 

If you don't mind me asking, what is your current idle rpm and at what rpm does it get enough vacuum?

 

456 gears will take care of that problem.

 

In park it idles around 800 - 900 rpm. In gear/at a stop it idles around 600 rpm. If I touch the gas a bit (when in gear) & bring it up to above 800 rpm the brakes work fine.

 

What's your timing set to? With the torque converter you mentioned it should not drop that many rpms from park to drive.

 

Had the same problem on a '72 Supreme.

My manifold vacuum was only 14", I added a vacuum canister and it solved my problem.

I just got a black steel one from summit - did the trick!

I now run 20 - 25" of vacuum.
IMG_20130712_110802_964_zpsee72c716.jpg

IMG_20130712_110824_908_zpsfc6c11c5.jpg

 

I've got the same drop running a stock TC... I've bought a Hughes 2500 stall but haven't had time to install it yet.