I got a new booster to stick in there over the holidays. Sick of the hissing snakes! Looks to be fairly straight forward and it will be good to have reliable brakes again. I love a challenge as much as the next guy, but playing hide-n-seek with my brakes is a bit much!
I'm going to try to back the master cylinder off without taking the brake lines loose first for obvious reasons. I hate bleeding brakes in the snow!

 

That'll cut down on your blowby problem.

 

I actually think you are right on that. I'm pretty sure the vacuum pump vents into the crankcase, and with the booster leaking as much as it is I'm sure that's causing some blowby. At hot idle I am getting a small but steady smoke puff out my new vent.

 

I don't believe they are designed to vent into the motor.

I think the pump is leaking discharged vacuum into the block.

why would you want to presureize the inside of your motor?

 

That's exactly where the air that's being sucked into the leaky booster is coming out. The vacuum pump discharges into the timing case. Normally not much air comes out of the pump once the system is pumped down, but in the case of a leak there can be an lot of air moving through there.

 

Huh, maybe my lack of brakes after 2-3 pedal pumps and my excessive blowby are related...

 

Nope, not on your truck. The old diaphragm vacuum pumps don't vent to the crankcase like the rotaries on the intercooled trucks. Your blowby is from honest wear.

 

Hehe, well, she came by it honestly, no doubt there If I were a nice guy, I'd retire the old relic, but she runs so goood

 

That`s just ONE of the many reasons this site rocks! I never knew the vac pump vented inside the engine...till now, thanks!

 

times two

just don't seem right.

not in a million years would I thought it vented internally

I learn something new everytime I read this forum

rock on

 

It's a piece of cake. There is plenty of play in the lines to remove the master from the booster without breaking the lines loose at all. You have to use a box/open end wrench on the master cyl nuts but it should take less than an hour and you won't have to mess with brake hydraulics.

I did it in the driveway up her about 6 weeks ago. Snow and everything.

 

Probably done to help meet federal noise limits...
Either that or to make sure that any brake fluid fumes that may have leaked into the booster doesn't vent to open air.

 

It vents into the engine because it's lubricated by engine oil. The vent is also the oil return.

Normally it's not an issue, but when there is a leak in the vacuum system then a lot of air gets pumped into the crankcase.