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Just Some Dude in Jersey
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Discussion Starter #1
A guy with a Vette at a car show told me that he lost braking power after upgrading his cam shaft. I only recently learned that cam shaft upgrades lower your idle vacuum and that this affects all sorts of things. BUT BRAKING?

He said that he was told that because of the lower intake manifold vacuum, caused by the cam, this lowered the vacuum going to the brake booster, thereby, lowering the vacuum assist that it provides.

Is there truth to this, does this noticably affect our cars, and what can be done about it?
 

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Super Moderator
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13,245 Posts
It lessens the reserve capacity for sure.



One reason that race cars have no power brakes, is that they use large cams with lower idle vacuum.
Another reason is that they seldom run at idle anyway. At wide open throttle zero vacuum is produced, therefore power brake assist simply doesn't work.



For a street car with a big cam you can add a vacuum reservoir to the system. Plenty of room in the front of a GT.

Or you could press the brake pedal harder. The brakes work exactly the same, they just require more effort to apply. I have never felt the need to add a vacuum reservoir in any of my street cars. For race cars I don't use vacuum-assist brakes at all. It has a lot to do with your preferences, and your own leg strength.
 

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Opeler
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692 Posts
You can add a small brake vacuum pump, with a vacuum switch. Every time you need your brake vacuum replenished, the pump will kick in. Works great! I have one on my Opel and my Chevelle.

Wes
 

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Just Some Dude in Jersey
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13,983 Posts
Discussion Starter #5
You can add a small brake vacuum pump, Works great! I have one on my Opel and my Chevelle.

Wes
How spruced up is your engine? Or how little vacuum do you have at idle? Mine reads between 3-5 inches idling IN GEAR with my automatic. I have 10-12 inches of vac in neutral or park with a slightly improved 2.0L.

Was there a very noticable difference when you added the pump? Can you just turn it off and have the brake assist work normally? How much are these wonderous devices? Are there any drawbacks to having a vacuum pump?
 

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Opeler
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692 Posts
Mine is a 2.0L with combo cam and big valve head. I couldn't get more than one push on the brake pedal before I ran out of assist. There are a bunch of different pumps available. You will probably pay around $75 - $100 for a used one, and $150 -$200 for a new pump. Don't just buy a pump without the vacuum switch, or it will run all of the time. I have a Pierberg pump from a Saab, that is super quiet, and an RV pump on my Chevelle that is a big more stout, and louder. You just can't hear it over the hotrod engine.
Wes
 

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Super Moderator
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.....There are a bunch of different pumps available. You will probably pay around $75 - $100 for a used one, and $150 -$200 for a new pump. Don't just buy a pump without the vacuum switch, or it will run all of the time. I have a Pierberg pump from a Saab, that is super quiet, ....Wes
All I found were engine driven pumps. Did you add a pulley and mount one or did you use a different one? I was hoping for a simple electrical solution. The electric aftermarket pumps I'm finding are in the $500 range, a bit pricey IMHO.

Thanks,
Harold
 

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Opeler
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692 Posts
Harold,

If you search "brake vacuum pump", you will find several. They are electrical. Summit, Jegs, and Amazon all have them. I just now searched for them again, so currently, they are available.

Wes
 

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Super Moderator
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Harold,

If you search "brake vacuum pump", you will find several. They are electrical. Summit, Jegs, and Amazon all have them. I just now searched for them again, so currently, they are available.

Wes
Wes, Thanks for the quick reply, I forgot Amazon. :pat: All I saw were the nice expensive ones in Summit. Under $200 sounds a LOT more reasonable. :yup:

Harold
 
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