Not enough vacuum

[Old Biker Trash]

I've dropped a crate 360 into a 65 Belvedere Wagon and added "The Right Stuff" disc brake conversion on the front. Motor dyno sheet says tested and ran 15.0 at 900 rpm and 20.0 1800 rpm. This is definitely enough to run brakes. BUT when I take a reading at the manifold, I was only getting 9-10 at 1000 rpm. I am not doubting the dyno sheet, Carolina Machine Engines has a good rep and the motor runs flawless. I bled the brakes 4-5 times so not doubting that but the vacuum just isn't there. Have the 3/8 hose from rear of manifold to booster and from carb to pvc. Don't really see or hear a leak??? Any thoughts, I know there is a lot more knowledge that me out here so I'm open to ideas.

 

[67belvedere/225]

what is your complaint, the brake pedal is too hard.?
is there a check valve missing on the brake booster or line?
if the pedal is good and hard with the engine off, then the problem is ether a defective booster, or low vacuum.
what does the manufacture recommend for minimum vacuum to make it operate

 

[Old Biker Trash]

what is your complaint, the brake pedal is too hard.?
is there a check valve missing on the brake booster or line?
if the pedal is good and hard with the engine off, then the problem is ether a defective booster, or low vacuum.
what does the manufacture recommend for minimum vacuum to make it operate

Brake pedal is what I think is soft. I can nail it at 10-15 miles mpr and it basically slows and stops, at 30-40, nail it , its better and can almost lock the tires in front . . . but they don't. I have a valve on the rear line to adjust. The manufacturer says 14 lbs min. and dyno says its there

 

[Yatzee]

I've dropped a crate 360 into a 65 Belvedere Wagon and added "The Right Stuff" disc brake conversion on the front. Motor dyno sheet says tested and ran 15.0 at 900 rpm and 20.0 1800 rpm. This is definitely enough to run brakes. BUT when I take a reading at the manifold, I was only getting 9-10 at 1000 rpm. I am not doubting the dyno sheet, Carolina Machine Engines has a good rep and the motor runs flawless. I bled the brakes 4-5 times so not doubting that but the vacuum just isn't there. Have the 3/8 hose from rear of manifold to booster and from carb to pvc. Don't really see or hear a leak??? Any thoughts, I know there is a lot more knowledge that me out here so I'm open to ideas.

View attachment 595763

It has been proven that for reliable power brakes the booster must have no less than 18 inches of vacuum. That's "reliable" under all conditions. I feel your pain as I was in the same position but at only 12 to 15 inches of vacuum with my Wilwood system upgrade I really couldn't drive the car. I mounted a 15/16 master but there was no difference. With no cost to me I tried a larger diameter booster, double diaphram booster and a different pedal ratio. I even tried a vacuum pump but it could not maintain the vacuum volume I needed even with a reserve tank and check valves. In your case I think the PCV is actually dropping your vacuum level to an unuseable volume. My car had power steering already so I thought, why not install a hydro-boost system that uses hydraulics rather than vacuum. Never looked back! Braking is superb at all rpm's and definitely outdoes any vacuum system. If your an owner that wishes to keep his car ultra original you'll have to resolve this issue by finding a way to maintain a higher volume of vacuum.

 

[Jackpot50]

It has been proven that for reliable power brakes the booster must have no less than 18 inches of vacuum. That's "reliable" under all conditions. I feel your pain as I was in the same position but at only 12 to 15 inches of vacuum with my Wilwood system upgrade I really couldn't drive the car. I mounted a 15/16 master but there was no difference. With no cost to me I tried a larger diameter booster, double diaphram booster and a different pedal ratio. I even tried a vacuum pump but it could not maintain the vacuum volume I needed even with a reserve tank and check valves. In your case I think the PCV is actually dropping your vacuum level to an unuseable volume. My car had power steering already so I thought, why not install a hydro-boost system that uses hydraulics rather than vacuum. Never looked back! Braking is superb at all rpm's and definitely outdoes any vacuum system. If your an owner that wishes to keep his car ultra original you'll have to resolve this issue by finding a way to maintain a higher volume of vacuum.

HydroBooster only way to go!

 

[Frank Mopar]

Make sure your rear brakes are adjusted up.

 

[Fran Blacker]

Do you have access to a second vacuum gauge? That would help confirm what your gauge says.

 

[Old Biker Trash]

It has been proven that for reliable power brakes the booster must have no less than 18 inches of vacuum. That's "reliable" under all conditions. I feel your pain as I was in the same position but at only 12 to 15 inches of vacuum with my Wilwood system upgrade I really couldn't drive the car. I mounted a 15/16 master but there was no difference. With no cost to me I tried a larger diameter booster, double diaphram booster and a different pedal ratio. I even tried a vacuum pump but it could not maintain the vacuum volume I needed even with a reserve tank and check valves. In your case I think the PCV is actually dropping your vacuum level to an unuseable volume. My car had power steering already so I thought, why not install a hydro-boost system that uses hydraulics rather than vacuum. Never looked back! Braking is superb at all rpm's and definitely outdoes any vacuum system. If your an owner that wishes to keep his car ultra original you'll have to resolve this issue by finding a way to maintain a higher volume of vacuum.

This isn't a PC car, just a fun car (I hope) to drive and enjoy. I will try the pcv valve first and that doesn't help - hydro-boost for sure as that seems to be the main reply to my question. - thanks

 

[Old Biker Trash]

HydroBooster only way to go!

If the pcv valve doesn't fix it, thats the way Ill go. - thanks

 

[Old Biker Trash]

Make sure your rear brakes are adjusted up.

I'll double check the rears (drum) and maybe I don't have the pressure valve adjusted correct. - thanks

 

[Old Biker Trash]

Do you have access to a second vacuum gauge? That would help confirm what your gauge says.

My gauge is fairly new, but I did notice that it doesn't seat at "0" when not attached. Will try this to.

 

[Old Biker Trash]

This is the gauge, is there a way to adjust this to 0 or is normal.

 

[Old Biker Trash]

My gauge is fairly new, but I did notice that it doesn't seat at "0" when not attached. Will try this to.

 

[coloradodave]

Borrow another gauge from Autozone or another parts store to confirm. Then advance the timing a little and see if the vacuum improves. I have 4 wheel power discs on my car and they operate fine with 12" of vacuum...

 

[67belvedere/225]

here is the thing , you need to figure out is that where the problem is
if it is the hydraulic part? is ok and adjusted properly. I find when I do brake jobs , that it needs a break in period of 2 drive cycles and then the pedal improves. and car stops properly. especially drum brake shoes , they take longer to bed in
you may be chasing the booster problem and it might not cure your condition.
pump the brake pedal when engine is off until it gets hard, how far does the pedal travel . if it is low you need to fix that
if not
keep pedal depressed then start engine and feel how much it goes down . if it moves a lot.then it s pulling enough vacuum.
if it stays hard and doesn't go down well maybe you need the hydraboost
maybe try and bed in the new brakes and see if any improvement . hard to say over the web

 

[rlem1977]

I'll double check the rears (drum) and maybe I don't have the pressure valve adjusted correct. - thanks

Better double check the price of a hydroboost, too. I have used some of the Right Stuff components. Biggest complaint is on vacuum boosters being defective. Might want to recheck your brake bleeding, make sure no air; and, as suggested, make sure your proportioning valve is adjusted correctly if you ar using an adjustable one.

 

[not so famous bob]

Better double check the price of a hydroboost, too. I have used some of the Right Stuff components. Biggest complaint is on vacuum boosters being defective. Might want to recheck your brake bleeding, make sure no air; and, as suggested, make sure your proportioning valve is adjusted correctly if you ar using an adjustable one.

I successfully used a vacuum canister w/ an air pump on a 600horse sbc . the power brakes worked great as long as u didn't keep pumping them. The check valve is very important, I had one on the vacuum pump in addition to the stock one in the stock master cyl.
drum. remember intake vacuum and engine crankcase vacuum are two diff. things !