How much vacuum for vacuum brakes?

[smokin87]

I made the switch to vacuum brakes and they're not working great.

How much vacuum is needed to effectively operate vacuum brakes? I have a big lumpy aftermarket cam in my car. I'm not sure exactly what cam it is because it was in the car when I got it.

My car is pulling about 14-15 inches of vacuum at idle. I want to know if thats enough. I've seen that Powerbrakebob says you need 20" and SSBC brakes says 16". How much vacuum are some of your cars creating? That is for those of you guys with good vacuum brakes.

What would the pedal feel like if my problem was not enough vacuum? hard or soft etc?

My pedal doesn't get firm until its pretty close to the floor. That probably means theres still some air in the lines right? I just gravity bled it so I'll work on that. I also have new performance brake pads/shoes on order from Cotton so I'll see what that does for me too.

Thanks for any input!

Andy

 

[BlackMetal]

I would think if the problem was low vacuum, the pedal would feel hard, because you're not getting any assist. You're saying the pedal is soft, which is more like air in the system.

 

[jdpolzin]

Thats the main reason I'm not fond of vacuum brakes on a TR. My old motor had a larger cam in it and the vacuum brakes didnt work well at all. Go with Hydroboos and be done with it!

 

[smokin87]

hydroboost

I knew I would get some responses telling me to go hydroboost, and I just might do that as a last resort. I would prefer to get my newly installed (free-junkyard) vacuum system working though. So I'm going to do some trouble shooting first.

I'm not at all excited about the prospect of plumbimg a hydroboost system!

 

[BlackMetal]

I'm not at all excited about the prospect of plumbimg a hydroboost system!

I'm not either but I finally ordered the parts, I'll let you know if it's bad or not.

Until then, bleed your brakes and see how it goes.

14-15 vacuum is still fairly decent.

 

[jdpolzin]

I knew I would get some responses telling me to go hydroboost, and I just might do that as a last resort. I would prefer to get my newly installed (free-junkyard) vacuum system working though. So I'm going to do some trouble shooting first.

I'm not at all excited about the prospect of plumbimg a hydroboost system!

You guys are really over thinking the hydroboost. It's so easy. Seriously, extremely easy.

 

[BlackMetal]

You guys are really over thinking the hydroboost. It's so easy. Seriously, extremely easy.

Maybe we're all less talented than you. I'll be the judge of how easy it is.

Picked up my master cylinder today. Didn't include and bench bleeding fittings, awesome! Lines from Rock Auto should be here Monday. Hydroboost unit should be at the store Monday or Tuesday.

 

[TurboBuRick]

You guys are really over thinking the hydroboost. It's so easy. Seriously, extremely easy.

X2, it's not hard at all.


A couple other thing that may help, get rebuild kits for the front calipers with new rubber o-ring and slide bushings. That helps more than you would think.
Also adjust the back brakes so they drag slightly on the drum. That will raise the pedal. Make sure you have all the air out of the system.

 

[POWERBRAKEBOB]

Hydroboost conversion

It's so easy! Vacuum boosters are rated to operate at 20" of vacuum. Their power drops to 1/2 at 15" vacuum. Their power drops off to equal manual brakes at or below 11" because of the pedal ratio. The hydroboost makes the car handle and drive completely different, and puts the FUN back into the car! Guys here report holding 22lbs of boost with their foot on the brake! As the RPM's come up, the P/S pump spins faster, holding the Hydrobost on HARDER. You can take a turn at high speeds with complete confidence, using just a toe touch. The brakes also run cooler, because the cars stops in a shorter distance. Our new units come with a 1 year warranty, and bolt right on.