Brake Vacuum

[vanst]

I have added power disk brakes to my 55 Chevy 409/425 Project. Could someone tell me where the vacuum was picked up for this in 425hp cars? Do I need to drill and tap the intake or pull it from the carb? I can't seem to locate a picture in the assembly guide or on line. Thanks Terry:D

[dq409]

What carbs are you using ?
If they are AFB or AVS style carbs use the carb base port on the rear carb,,,dq

[vanst]

Thanks Dq409, I'm using the original AFB's. However they way the engine "was" before I started had the beather 3/8 line from the oil fill tube to the front carb. The base of the rear carb had (2) 1/8 lines, one to the vacuum advance and one to the right hand exhaust heat riser. Have 409's ever used a hollow stud carb mount for the vacuum advance like early Corvettes? Do you know of a hose diagram anywhere I could referance, I've looked but can't locate one? Thanks Terry

[bobs409]

Terry,

I have my 400hp (single 4bbl) power brakes T'eed into the PCV hose at the rear of the carb.

BTW, Late in '63 on the 400hp 409's, they added a threaded hole to the intakes for power brakes but not sure if the 425 intake followed suit or not. In any case, you and I obviously don't have that threaded hole so tapping into the PCV hose is one option. Drilling a hole in the intake is another but I don't recommend that. I also have a vacuum gauge T'eed into this area and everything works great.



Bob


Oh yeh, that hollow stud was on some 348's. (not sure about 409's) Do you by chance have any assembly manuals? They show the hose routing in them.

[jim_ss409]

They say that adding 1" open spacers helps the power on these engines. You could consider adding a set and tapping in a fitting on the rear spacer.

[vanst]

Thanks for the info Bob, I do have a 64 Impala assembly guide but the information in the "options" section for brakes on a 425HP is not good. I,m just trying to find out from other guys with 425's and power brakes how the factory supplied all the vacuum sources. I thinks with the info you guys supplied I have enough to get the job done. Thanks again. Terry

[SS425HP]

Don't think you will find a 425 HP 409 with power brakes, nor any info on it. To my recollection, it wasn't done. I think this has been hashed out here, before. The brake booster prevents removing the driver side valve cover. Needed to adjust valve settings, which was done quite often back then. Don't think the 400 had them, either.

Fred

[bobs409]

Fred,

Why would they have added a threaded hole in the late '63 400 intake then? (unless my information is incorrect)

This needs further investigation. :D

[vanst]

In my car I installed an offset booster offered by http://www.ecihotrodbrakes.com/ made to correct this valve cover issue. It works the nuts (no not the 348nut). I posted a picture to this site last week which shows the booster which is offset over 2" and up 1". Thanks

[bobs409]

With my 66 Chevelle/409, it's so close but I am able to remove the cover. It takes just the right finess though. Mine even has the larger booster.

P.S., I just browsed through my 63 assembly manual and shop manual but I don't see any pics to help. (I hate trying to find something in those dang books! It seems you never find what you want. :mad: )

[CDNpontiac409guy]

Absolutely, Fred.... the 400 & 425 HP engines WERE AVAILABLE with powere brakes !:p I have an original 400HP Parisienne right here with L31 and power brakes right on the build sheet !

Vacuum taps into a T at the back of the rear carb on all 2X4 option cars, as well as 380/400 HP in 62 & 63. The 64 & 65 400HP intake has the provision on the intake.

[dq409]

Vanst,,,, That offset booster is cool !!!

I have room on my large booster to mount it with a half inch +- but have to move it to remove the Moon valve cover.
Not a big deal,,, only takes a few minutes to do but,,,,, that would be cool to have.
I`ll add it to my wish list !!!,,,dq

[SS425HP]

Well, I have never seen one. Not saying they didn't do it, but I sure have never seen it.

Fred