Making Vacuum Brakes feel good!

[slant 6]

About a year ago I converted to vaccuum brakes. I heard so many good reasons why I should do it! I don't want to start a conflict about the PM versus Vaccuum, I just want to know if anyone has some tips on how to make the pedal feel better than my brother in laws 72 Chevy Pickup! (seriously!)

Ever since day one of this conversion I've been dissatified. I had a guy who is supposed to be a TR guru in my neck of the woods do it...I actually paid....I was lazy and had a job at the time, what can I say...

The pedal feel under quick braking or emergency braking has a initial hard feel and slight delay feel to it. I much preferred the PM feel to be honest with you. Also, when sitting at a light for more than a couple of minutes, I start to lose a little vaccuum and the pedal starts to fall unless I pump it up.

I've replaced the front calipers and new pads. Rebuilt the rear brakes, turned the drums etc. No air in the lines.

Are there high quality Master Cylinders out there or any other ideas? There's no way this should feel like this. Thanks!

Craig
Slant 6
87GN

 

[Glen]

slant 6 said

Making Vacuum Brakes feel good!

Try taking them to dinner and give positive reinforcement.

If you were to lose vacuum, the pedal gets hard. The fact that the pedal sinks leads me to think bad master cylinder or air still trapped in system. I prefer new, but they are rather expensive unless you can get a new cast iron M/C like Wagner, they tend to be cheaper than the new aluminum ones. I've never liked the feel of the vacuum brakes.

 

[captrob]

You are dealing with junkyard parts...

I didn't like the feel, so I bough a new larger b-body master cylinder(12 inch brakes). Still felt funny so I got another jy booster. It felt horrible, so I took it back and got another. Now I have the feel I want. Each jy booster gave a completely different feel to the brakes. Unless you go new, it's gonna be a crap shoot!
HTH, CaptRob

 

[FlyinGN]

sound like maybe you are losing vacuum.. Look at the vacuum line from the booster to the intake. Make sure no leaks are present. Maybe th ebooster itself is bad. Mine are fine and have been for years. I love the vacuum brakes..

 

[turbo nasty]

Sounds like a leaky booster. Hook up a vac pump/gauge and see if it holds. Handheld mitevac pump should suffice

 

[TurboBob]

Be sure the vaccuum source is NOT the PCV hose, that's a horrible place to get brake vaccuum. You need the right adapter for the top of the throttle body.

Bob

 

[slant 6]

Making Vacuum Brakes Feel Goooood!

I think taking them out to dinner may be the best answer! Or maybe if I buy them a 4 million dollar ring?

I'm not taking vacuum off of the pcv. I'll hook up a vacuum guage when I get a chance. I noticed that I can turn the hose fairly easy on the vacuum block. I'll tighten that first. It takes a few minutes sitting in one place for the pedal to fall. I have a cast iron MC.

I noticed someone going to a bigger brake system. I'll look into that thread. Perhaps that will make a difference.....depending on cost. I'm considering putting my PM back on. Felt more like a modern brake system than this setup.

Thanks all, for the help! It make take a couple of weeks to get around to it, but I'll post back any findings.

 

[turbofish38]

I had the same problems. Number one cause was a marginal booster. Lucked out and found a fresh aftermarket rebuilt on a car at U-Pull-It. I run the smallest aluminum bodied M/C for a G-body and its got a 24mm bore. The larger the piston the lower the pressure through the lines. Upgraded to braided stainless hoses and even though its not the hot set up for drag racing I run the hardest compound pads and shoes I could find. When my brakes get hot I can lock them up by modulating the amount of pressure my foot puts on the pedal which means I have locked them up accidently a few times running through the traps. I also have excellent stopping distances in bumper to bumper traffic. Pedal feel is almost like a manual set up with very little pedal travel which makes panic stopping a little scary but if you drive your car a lot you get used to it.

Eric Fisher

 

[FlyinGN]

cast iron master cylinder? Thars yur problem. Thats an aftermarket master cylinder.. The factory ones were aluminum. Much better then the aftermarket ones. Id get a good quality NEW aluminum master cylinder. Id bet ya (if ya have NO vacuum leaks) that that will make all the difference in the world..

 

[Glen]

Wagner makes a NEW master cylinder in cast iron and they are half the price of an aluminum one. I've been using one for years now with no problems.

 

[John Larkin]

I have the same crappy pedal. Stops fine, never scary but it is mushy. I'm starting to wonder if a proportioning valve swap from a vacuum brake car should also be included in a vacuum brake swap. It's possible that the stock prop valve is designed for use with the PM only. I'm going to try and locate one and swap it in. What's one more bleed?

 

[FlyinGN]

okay I did not know that. I was always under the ASSumption that the cast ones did not work as well as the aluminum ones..

Originally posted by Glen
Wagner makes a NEW master cylinder in cast iron and they are half the price of an aluminum one. I've been using one for years now with no problems.

 

[turbofish38]

Early(78-81) G-bodies used cast iron master cylinders and as far as function they work the same as the aluminum ones. Proportioning valves are the same between vacuum and PM.

Eric Fisher