vacuum brakes...

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joshua dewitt

joshua dewitt

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73 dart swinger, built small block with a split pattern cam, and air gap intake with 2 inch carb spacer. timing advanced, runs pretty good, idles with 16ish in.of vacuum. gut wen but into gear and step on brake car will not idle well, and then dies, I still may have a converter going out, but realized that I need 22+ inches to run the brakes....
I just ordered a remove vacuum pump kit form summit, and the polished vacuum reservoir canister, and installing in the trunk to solely the power brakes, will run a hard line under the inside the sub frame connector down drivers side to a braided stainless hoses to the booster. plug off the manifold port. I have ran a canister before, but not he pump, anyone used one? tighter? was trying to keep some storage vacuum so pump didn't run all the time..., noise isn't an issue due to the noise of the exhaust , and Mallory fuel pump running.
 
This may be a mistake.

Many guys on here will tell you that you don't NEED a booster if the brakes are otherwise in good shape. That is, drums not oversize, good lining, and so on.

But putting the vacuum system in the trunk MAY be a mistake......are you putting the vacuum can up front? "That vacuum" and by that what we really mean is AIR has to flow down that tube. The "pulse" if you will flow is quite a bit of air upon brake application when you are trying to push it through several feet of X/X size tube.

I myself have found that even with my diminished legs......I can no longer walk very far......I don't need a booster. In my case I'm running the later 73/ 74 Duster brakes, and a Versailles 9" rear axle, with disc. Factory master with residual valves punctured. I have no trouble getting it "whoaed"
 
^^^^^^ Xs2.

There are several threads on how to achieve excellent braking by changing Master cylinder bore size, and even changing wheel cyl size.

Remember, power brakes don't improve your brakes ability, it's only ONE of the ways to supplement your leg power.
 
it will stop fine, before cam swap. but have NO VACUUM guys... the master stops fine, not a pedal issue, I have a big cam... didn't want to change over to manual brakes...
it have disc brakes, ford rear axle with 7/8" bore wheel cylinders. and everything new!!!! car is a total resto... just new cam doesn't make enough vacuum at idle for power brakes anymore... , also had to install a kill switch for the ignition coil so I can gent cylinders spinning for cranking, then light it up like a full race car.... too much cylinder pressure wen warm.. like I said built motor, advanced cam.. hauls' ***...
 
OK, so if you are not willing to convert to manual..........

and the engine does not produce enough vacuum..........

then "something else."

Either a vacuum pump or a hydroboost.

All I'm saying is, if you run the pump clear back to the trunk it may or may not work well. Are you aware of anyone else who did this successfully? I don't know. I'd at least want the vacuum can up front.
 
my plan was pump in the trunk, canister in engine bay, both running on check valves, I know of old street rods have done this for years. but not stopping higher speed stuff..
and if doesn't work I will go to manual larger master cylinder and ditch the power brakes...
 
I can't believe 16 in of vacuum isn't enough. My Dart with Disc/drum and power brakes works fine @15 inches of vacuum. You sure the diaphragm isn't ruptured in your booster?
 
Should be fine with the tank (Reservoir) up front because once the vacuum pulls the booster diaphram it doesn't need any more flow.

But you can only use the brakes every 15 minutes. JK:D

It should work fine, but if I was able to get it I'd rather have hydroboost.
 
SGBARRACUDA said:
I can't believe 16 in of vacuum isn't enough. My Dart with Disc/drum and power brakes works fine @15 inches of vacuum. You sure the diaphragm isn't ruptured in your booster?
Click to expand...

I was thinking that exact same thing.
 
My power brakes worked just fine with the 292/509 cam, and 11.2 Scr. It idled at under 10 inches.How often do you need power assist at idle? As soon as the car is moving, the rpms are climbing, and the vacuum is rising. Then the booster stores the vacuum. It stores enough for most situations, including multiple applications. Ima thinking, from your symptoms, the diaphragm is ruptured. The stalling on application kindof gives it away.16inches is plenty.Even stock teeners barely pull 22 in gear at idle.
I think you need to do some detective work.

And Josh,I think somebody is feeding you misinformation, or your gauge is. A big-cammed engine will not idle at 16 inches in the first place. And if an engine idles at 16,it certainly will not need to be spun up before lighting.I tell you what, why don't you tell us a little more about your engine;like cam specs and exact cylinder pressure and exact compression ratio.And I mean exact.Timing specs would be nice too; such as initial timing, power timing, and at what rpm it is all in by.If your combo is really pulling 16, you should not be having a problem. But if it is idling at 8 inches, and the booster is leaking, well then you have issues all right.
 
well I haven't driven the car yet, been a complete resto, it is possible the booted may have an issues, I don't hear any air leaks, and with a quick spray no signs of vacuum leaks. the brakes just don't like it. when I have more time since getting my house ready to move everything is on hold... right now the car is movable, under own power not right yet but getting there. piss the neighbors off every time I fire it up to play with it. hehehehhe... dynomax ultra flows 2.5" and 3" open header dumps under car... going to plug off all vacuum ports and recheck idle vacuum when I get a chance, I have the pump and reservoir now came in today, but now I have to make wifey happy and live in and get house ready, "sellers market I've been told" and time to flip.. and pay the bills off, Credit cards to summit and jegs...hehehhehehe....thanks all for the info...
 
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