Low Vacuum Options - Chevelle Tech
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post #1 of 48 (permalink) Old Apr 22nd, 19, 12:22 AM Thread Starter
blm
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Brad
 
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Low Vacuum Options

I have a new 496 with a big cam. After driving my 69 ss I noticed the brakes are very firm. I am guessing this is due to low vacuum. Have not measured it yet but pretty is sure that is the culprit.
I also have the original brake booster and original master cylinder that I had both rebuilt and restored only a year ago and I am very interested in keeping them. So this kind of limits my options.
Have read testimonies from some that say all that was needed was a vacuum reservoir. Another option would be a vacuum pump in addition to a reservoir.
I have read several favorable reviews on hydroboost systems but am wanting to use my booster and master cylinder. So what is the best option?
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post #2 of 48 (permalink) Old Apr 22nd, 19, 1:48 AM
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Re: Low Vacuum Options

You might check your check valve. I get one and a half good assisted braking as long as I don't pump the brakes. The vacuum booster hold enough vacuum for one good assisted brake application on my car. I installed a vacuum reservoir tank and get 3 good assisted brake applications before the pedal gets hard to press. I have a 4 speed, so keeping the idle speed up also helps keep the vacuum up or recharge the vacuum in the reservoir.

It's not the best system, but once I learned how to drive with this handicap, it works for as much as I drive the car. If it were a daily driver I would look into a better system, most likely hydro boost.
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post #3 of 48 (permalink) Old Apr 22nd, 19, 6:15 AM
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Steve
 
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Re: Low Vacuum Options

I put a vacuum pump on mine, as I had a similar issue with the 454 I have in my car today (PO put in a monster cam of unknown size, but it has a ton of overlap and low vacuum.)

There was a thread here about vacuum pumps I made a few posts about mine in:

https://www.chevelles.com/forums/16-...cuum-pump.html

1972 Chevelle, 454, 2004r, 3.08
1981 Camaro Z28, 355, TH350, 3.73
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post #4 of 48 (permalink) Old Apr 22nd, 19, 6:59 AM
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Re: Low Vacuum Options

I went through all the band aids of misery with having a drag strip camshaft in a street car but eventually sold the car. The guy that bought the car was smart and changed the cam. It was a Pontiac 455 and had the factory RA4 041 308/320 he changed it to the factory 068 288/302. I was in awe when I drove the car with that smaller cam. It felt like he added 200 horses!!! Low end torque was insane! That big cam was sucking the life out of that motor!

Do yourself a favor and pull that cam and put a street cam in there. Besides having good brakes it will have off idle brute torque that will make street driving so much fun...
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post #5 of 48 (permalink) Old Apr 22nd, 19, 7:35 AM
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Re: Low Vacuum Options

A vac reservoir does not increase vacuum, it only prolongs the poor braking. An electric vac pump is probably the least intrusive fix, but the noise might drive you mad...
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post #6 of 48 (permalink) Old Apr 22nd, 19, 9:37 AM Thread Starter
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Re: Low Vacuum Options

Thanks for the responses guys, and thanks for the link Steve. The specs on my cam are 612/636 lift and 303/311 duration.
Think maybe the pump might be the most reasonable fix for me. In another thread this pump was recommended. Opinions?

https://www.summitracing.com/parts/hla-009286001

Then this pressure switch was recommended but several reviews mentioned quick failure of the switch although it was replaced under warranty. Is there another brand with good reliability?

https://www.summitracing.com/parts/sum-760155-1

So it was recommended that a reservoir be installed also with the switch threaded into a reservoir. In addition I understand a relay needs to be incorporated. I don't have the headlight mod as I have an AAW classic update kit which should have a spot to run wiring for the supply to a pump. So I am just familiarizing myself with this. Does the vacuum hose from the pump/reservoir just T into the vacuum line from the manifold to the brake booster?
Steve, I like the location of your pump. Before reading the link I was imagining mounting the pump and reservoir behind the battery so completely hidden but then the vacuum hose has to make its way to the opposite corner.
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post #7 of 48 (permalink) Old Apr 22nd, 19, 9:37 AM
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Re: Low Vacuum Options

My 454 has around 7 vacuum but with a reservoir brakes are fine.
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post #8 of 48 (permalink) Old Apr 22nd, 19, 9:42 AM Thread Starter
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Re: Low Vacuum Options

Quote:
Originally Posted by stanski View Post
My 454 has around 7 vacuum but with a reservoir brakes are fine.
Guess I could try just a reservoir first if am going to do one anyway to see how brakes respond. How do you have the reservoir installed? Is it just in line between the intake and the booster?
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post #9 of 48 (permalink) Old Apr 22nd, 19, 10:40 AM
 
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Re: Low Vacuum Options

I went with the CVR Vane style vac pump along with there res, for my 496 setup on 4 wheel wilwood disc setup, it will all be installed in the next week or so.....Hopefully its all its cut out to be lol
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post #10 of 48 (permalink) Old Apr 22nd, 19, 10:50 AM
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Re: Low Vacuum Options

I've heard good things about those pumps too - those look like factory style pumps. I just went with the CVR unit because it was all contained in one nice little package. As I mentioned in the other thread, you can hear the pump, especially in the garage where it echos. But when I'm out driving I don't notice it too much. I've been told the factory style pumps are even quieter - if my pump noise ever drives me over the edge, I would probably try one of those.

Yes, the line just T's into the vacuum line between the manifold and booster.

I did not use a reservoir on mine.

Also, with an impending engine swap in the future, depending how much vacuum the new engine/cam combo has, I may just pull the fuse and see how the car brakes on that engine's vacuum to see if I still need it or not.

Quote:
Originally Posted by blm View Post
Thanks for the responses guys, and thanks for the link Steve. The specs on my cam are 612/636 lift and 303/311 duration.
Think maybe the pump might be the most reasonable fix for me. In another thread this pump was recommended. Opinions?

https://www.summitracing.com/parts/hla-009286001

Then this pressure switch was recommended but several reviews mentioned quick failure of the switch although it was replaced under warranty. Is there another brand with good reliability?

https://www.summitracing.com/parts/sum-760155-1

So it was recommended that a reservoir be installed also with the switch threaded into a reservoir. In addition I understand a relay needs to be incorporated. I don't have the headlight mod as I have an AAW classic update kit which should have a spot to run wiring for the supply to a pump. So I am just familiarizing myself with this. Does the vacuum hose from the pump/reservoir just T into the vacuum line from the manifold to the brake booster?
Steve, I like the location of your pump. Before reading the link I was imagining mounting the pump and reservoir behind the battery so completely hidden but then the vacuum hose has to make its way to the opposite corner.

1972 Chevelle, 454, 2004r, 3.08
1981 Camaro Z28, 355, TH350, 3.73
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post #11 of 48 (permalink) Old Apr 22nd, 19, 10:59 AM
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Re: Low Vacuum Options

Hey Brad,

had the same issue back in my Camaro days and my current 70 SS is not much better on the Vacuum dept.

To me there are only two legit fixes.

1. A nice hydroboost boost system. I purchased one from Hydratech for my Camaro and it was pretty sweet, amazing stopping power.

2. Manual brakes. I currently have a Wilwood manual set up on the Chevelle and have zero complaints, nice and tidy looking and stops just fine, is it not the throw you through the windshield of a hydroboost, but will the car stop on a dime, yep...

I think the pumps and canisters are mere bandaids and not a fix....just my opinon.

Pat
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post #12 of 48 (permalink) Old Apr 22nd, 19, 5:14 PM Thread Starter
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Re: Low Vacuum Options

Well I measured my vacuum at idle. Was about 7 in hg. Think my old 396 (not a stock cam) was about 12 or 13 at idle and that was enough to satisfy the power brakes.
What I find strange about vacuum pumps,reservoirs and hydroboosts is everyone has different levels of success. I went through a bunch of reviews on reservoirs and almost every one the reservoir either fixed the issue or greatly helped and then others say the reservoir did nothing. Kinda same with the pump.
Thinking I might just try a reservoir first and see what happens. Can always add to that if it doesn't work out..
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post #13 of 48 (permalink) Old Apr 22nd, 19, 11:09 PM
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Re: Low Vacuum Options

Quote:
Originally Posted by blm View Post
Well I measured my vacuum at idle. Was about 7 in hg. Think my old 396 (not a stock cam) was about 12 or 13 at idle and that was enough to satisfy the power brakes.
What I find strange about vacuum pumps,reservoirs and hydroboosts is everyone has different levels of success. I went through a bunch of reviews on reservoirs and almost every one the reservoir either fixed the issue or greatly helped and then others say the reservoir did nothing. Kinda same with the pump.
Thinking I might just try a reservoir first and see what happens. Can always add to that if it doesn't work out..
The thing with the reservoir is that you have to operate the engine in a range where it builds vacuum. Then you will have a few good brake applications. If your idle vacuum is 7hg and you hit the brakes without "making vacuum" first, you will still have only 7hg for assist. You build the most vacuum while decelerating and then store that vacuum in the reservoir. It works better with a 4speed. If you have a loosey goosey torque converter, you'll build less vacuum.

Any other method is better and safer for sure. Especially for us older guys that really need the assist.

If you do try just a reservoir, learn to brake smoothly in one application. You don't want to be pumping the pedal because you'll run out of vacuum assist. Then it will be all leg muscles from there.
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post #14 of 48 (permalink) Old Apr 28th, 19, 9:23 AM Thread Starter
blm
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Re: Low Vacuum Options

Well here is where I am at. I bought and received the CVR reservoir in this link.
https://www.summitracing.com/parts/cvs-vpr700.
But don't think I am going to install it. The pic doesn't do that canister justice as that sucker is big. After thinking about it I believe a pump would do me better than a reservoir. Also isn't the original booster a reservoir?
Unless someone can talk me off the ledge believe I will return the CVR reservoir and acquire a pump. Which leads me to another question. What is the difference between these two pumps?
https://www.summitracing.com/parts/cvs-vp655
Or
https://www.summitracing.com/parts/cvs-vp665

I like the features that these pumps offer with pressure switch and relay incorporated in the pump.
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post #15 of 48 (permalink) Old Apr 28th, 19, 9:37 AM
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Re: Low Vacuum Options

Quote:
Originally Posted by blm View Post
Well here is where I am at. I bought and received the CVR reservoir in this link.
https://www.summitracing.com/parts/cvs-vpr700.
But don't think I am going to install it. The pic doesn't do that canister justice as that sucker is big. After thinking about it I believe a pump would do me better than a reservoir. Also isn't the original booster a reservoir?
Unless someone can talk me off the ledge believe I will return the CVR reservoir and acquire a pump. Which leads me to another question. What is the difference between these two pumps?
https://www.summitracing.com/parts/cvs-vp655
Or
https://www.summitracing.com/parts/cvs-vp665

I like the features that these pumps offer with pressure switch and relay incorporated in the pump.

If your going to spend that much on a canister and pump just spend the extra $$$ and go with the hydro-boost kit and you know you won't have to worry. I've had mixed results with the canister and pump route on past cars.
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