The Stovebolt Site Forums The Shop Area General Truck Talk Brake booster / vacuum question

I purchased and installed a brake booster on my '61 K10, and it has not been working right. As far as I can tell the booster holds vacuum, but the braking ability is not at all improved.

When I test the brakes at low speed they seem to work momentarily, but quickly revert to non-boosted behavior.

I have a 235 with the Rochester B carb. I'm using the 1/4" vacuum port from the base of the carb to run to the booster. I also installed an inline check valve to prevent vacuum loss. This valve is working correctly; I've tested it. Is it possible that I'm not drawing enough vacuum pressure from the small vacuum fitting on the carb? Any ideas on how to test and identify the source of problems?

http://www.sacred-cactus.com/g2/v/troy/61Chevy/PA010037.JPG.html

Thanks!

That,s too small of an opening. There should be a plug in the port going to 3-4 cyl,s. Remove it & install a fitting & 3/8 tubing & hose.

Hey Wrenchbender,

Could you elaborate on that a bit? I just installed a booster and was wondering where I was supposed to hook up the vacuum line. Where/what is this port you speak of?

I think that Wrenchbender Retired is referring to the port on side of the intake manifold below the carb. On my 46 that was used for the vacuum wipers.

I was talking to ECI today about the front disc brake kit and they were not sure that a 235 would generate enough vacuum for a booster.

I'd like to know for sure that the 3/8" hose from the intake port will do it before I order a booster.

By the way, what size booster diaphram are you using? Single or dual diapram?

Thanks

Hy guys, A booster [vacuum] works by applying vacuum to both sides of a diaphragm when it is in non apply mode. When you apply the brakes an atmosphere valve opens allowing filtered atmosheric pressure air to enter the apply side of the diaphragm, one side of the diaphragm now has pressure on it, the other side of the diaphragm has vacuum or less than zero pressure on it. The diaphragm with the pushrod which applies the master cylinder now moves very easily to the apply side. When you release the brake pedal the atmosphere valve closes and the engine vacuum restores both sides of the diaphragm to a balanced vacuum on both sides condition. As to whether or not a 235 can generate enough vacuum to support a booster, of course it can, hundreds of Chev. trucks powered by 235s are or were driving around with hydrovac power brakes, hope that helps.

46,

To be totally honest, I have no idea what size I'm using. All I know is I bought it out LMC for the year that I needed. It fits in the engine bay, so it can't be too wrong!! An educated guess says a single diaphragm booster is what I've got. All things being equal, (and I doubt there would be much real difference), I have a 230 in my truck, but once again I don't see how it wouldn't be able to create enough vacuum.

Ya gotta hook it up right off the intake manifold,

Does anyone out there happen to have some sort of pics that would illustrate this?? I've got a very visual-based mind...