vaccum brakes

684 Views 8 Replies 8 Participants Last post by [email protected], Jun 29, 2009

[email protected]

Discussion Starter · Jun 18, 2009

The cam i'm running is only producing about 6 inches of vaccum and i need 18 to run my booster. If i install a vaccum canister will this fix my brakes. Will my wife be able to drive it around safely in town without worrying about brake failure. Can you still stop the car without the booster? I know about the vaccum pumps but the performance catalog folks say the canister will be fine no pump needed but experience is where I will lean to so info is really appreciated. Dont want momma to crack up the toy or myself.

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SSedan64

· #2 · Jun 18, 2009

I haven't had good luck with cannisters/reservoirs. When running a large Dur. cam I usually go to a Manual master cylinder. Takes a little more leg effort but stops way better than trying to run a booster without enough vacuum.
Another option is Hydroboost.

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curtis73

· #3 · Jun 18, 2009

I think the better question is... why only 6? It takes a pretty massive cam or a bad tune to only make 6. Most brake boosters will work fine at 15in , and will work fine with 12in with a vac can, but 6 is pretty low for a streetable engine.

Post the specs: engine, cam, initial timing, compression, etc.

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greenhj

· #4 · Jun 18, 2009

my engine idles at 9" and i have the vac reserve canister as well.

I find a lot of vacuum (20+") is produced on overrun, and very light cruise so to my way of thinking, the reserve canister will help to store a lot more vac than the standard booster can hold.

Besides, at idle the car isnt probably going anywhere at any terrific speed so who cares how much vac there is, hopefully the brakes already applied and done its job.

I have no real issue with my brakes, factory issue disc/drum on a 3500lb car but i do admit to anticipating stops more whilst driving that car and leaving more room to the car in front (just in case it all turns to crap).

As said by SSedan64, both of those systems will alleviate your concerns if the lack of vacuum worries you.

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cobalt327

· #5 · Jun 18, 2009 (Edited)

[email protected] said:
If i install a vaccum canister will this fix my brakes.

It will provide adequate vacuum to let the booster work- but there's a "trick" to all this.

Tell the wifey to not "pump" the brakes. What she needs to learn to do, is apply the brakes and gradually increase the pressure as needed to stop safely- w/o pumping (applying then releasing repeatedly) the brakes. The pumping is what'll deplete the vacuum reservoir, and at idle (as when slowing for a traffic situation) there's insufficient vacuum to replenish the reservoir.

It's the same thing as when you kill the engine in a vehicle w/power brakes- you can stop very easily, as long as you apply and not release the brakes. If, on the other hand, you pump them on and off a few times, you're left w/stiff, non-power assisted brakes.

BTW, you CAN stop a vehicle w/o assist from the P/B booster- BUT stopping distance and brake control will suffer. A lot- especially a less-strong woman.

I would suggest that you both go to a safe, secluded parking lot, or other safe area (NOT on a roadway), and practice stopping using various techniques so that you know what to expect.

As well as stopping the vehicle w/o any power assist, as in a case where the engine might stall. Kill the ignition (and for Heavens sake, DO NOT switch the key to "LOCK"- just turn it as far as needed to shut off the engine, not lock the steering wheel!) and have her (and you, for that matter) practice stopping that way, just so you'll know how your car reacts.

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redride

· #6 · Jun 20, 2009

I have run into the same problem in a couple of pro street cars I have built including the one I have now. My current car has a 502 with a large roller ground on 107 along with a very small 7" booster (factory was 11") which this combo creates low vacuum for the brakes. I purchased a SSBC vacuum pump which worked great----BUT--- very loud and lots of vibaration when it would cycle on. I took it back off and put on a vacuum can that I had left over from another build and it works just fine. No problems with in town driving. A vacuum can is a very inexpensive way to solve your vacuum problem. Just my 2 cents worth.

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Frisco

· #7 · Jun 20, 2009

With the correct pedal ratio (6-1 or 7-1) and a manual master cylinder that is sized correctly, you will not need any power assist.

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Deez

· #8 · Jun 20, 2009

Forget power brakes. Forget power steering windows door locks and all of the other cushy power crap. If running a street brawelr that has little vacuum like you mention, why play with power brakes? Ever get on it and right away have to hit the skids? It will let you know where your heart is for sure. If your engine coimbo is right and that's all the vacuum you have you should not use that type brake system. JMO

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[email protected]

Discussion Starter · #9 · Jun 29, 2009

power brakes

To curtis73 its not poorly tuned, just tuned really good. I dont have the cam specs infront of me but I do know that the lift was 725 which doesnt tell much but yes it is large, On the dyno it turned 704 horse at 6300 but started running short on the petro, carb's not big enough. Its a street engine but just on the raggedy raggedy edge of it. 1200 rpm idle and so on. Good grocery getter! The braking is the next hurdle. I'll try the canister its cheap. Thanks everyone for the tips.

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