Brake booster vacuum line?

[BlissfullyCrusin]

Fair warning, I may be completely off in my assumptions below..

I upgraded my carbs from the stock Solex to Weber IDF 40s for my engine. I believe the intake manifold is supposed to have a bung or something that the brake booster vacuum line attaches to? The new intake manifolds I received don't have these attachments. Do I need to find a machine shop to add them?

If this really is the case, could someone explain how the air intake can assist the car in braking? I just can't wrap my head around that...

[tristessa]

I upgraded my carbs from the stock Solex to Weber IDF 40s for my engine. I believe the intake manifold is supposed to have a bung or something that the brake booster vacuum line attaches to? The new intake manifolds I received don't have these attachments. Do I need to find a machine shop to add them?

You need manifold vacuum to the brake booster, otherwise you've got no power to your power brakes. Machine shop would be the easy way to do it, but it's not necessary if you're somewhat mechanically inclined. Drill the manifolds to .. well, whatever size is suggested on the package of the pipe tap (NPT thread) you'll need to buy. 1/4" NPT should be fine, 3/8" NPT might be overkill. Tapping the runners for cylinders #1 and #3 should be good enough, tapping all four might be overkill (but certainly wouldn't hurt)

Anyway, drill & tap both manifolds (however many holes and whatever size you decide on), install hose-barb nipples into the holes you just made. If you only tapped 1 & 3, run hose from the nipples to a tee and connect the brake booster hose to the tee as well. If you tapped all four, tee them together as 1/2 and 3/4, then run hose from those tees into a third tee and connect the brake booster to that one. In either case, don't forget the check valve.

If this really is the case, could someone explain how the air intake can assist the car in braking? I just can't wrap my head around that...

I'll leave that to Colin, he's got a better mind for explaining the inner workings than I do .. at least at this time of evening.

[chitwnvw]

I'm stealing adventurewagens pic -

John at aircooled.net told me to only tap the number 3 cylinder, which is what I did and it seems to work just fine.

[vwlover77]

The example is a traditional front-engine car, but the principles are the same....

http://auto.howstuffworks.com/power-brake.htm

[BlissfullyCrusin]

Thanks for all the responses!!

Tritessa - you say: "In either case, don't forget the check valve. "

Don't forget what? To attach a hose to it? I'm pretty sure all the vacuum hoses are still attached to the brake booster, so I can trace/replace those lines I think.


Chit - thanks for the pic! That helps a lot.

vwlover - Duh. I LOVE howstuffworks.com...should've checked there. Thanks!

[Amskeptic]

John at aircooled.net told me to only tap the number 3 cylinder, which is what I did and it seems to work just fine.

Do not tap to one cylinder only. The pulsing of one cylinder's intake stroke only is tough on the delicate actuating valve inside the booster, and any leak in the hoses from the engine to the booster will kill that cylinder in short order with only a slight loss of power as your clue.

The factory engineers tapped 1 and 3 because they are opposing cylinders with intake strokes separated by 360*. This serves as a decent enough pulse damper and gives you faster recharge of the booster. Colin