vacuum brakes not holding any boost

[richardv6]

got a car that has vacuum setup but wont hold boost,got new tta checkvalve on the booster,i see that in gbody parts brake kit their is a inline checkvalve of sorts in picture i dont have this,can i get that from a local parts store and what do i ask for or even a part#,i alsodo not have a vacuum caister do i need or not?thanks

 

[Scooter3800]

Adjust up the back brakes first, then see if it gets better. Then I would also look into the S10 wheel cylinders for more holding power...

 

[1quick6]

The valve on the booster should be enough to hold vacuum in the reservoir. Like the above, I'm thinking your back brakes just aren't up to snuff.

 

[84BuickGNYorkPA]

How many inch pounds of vacuum do you have at idle?

Chuck

 

[Red Regal T]

Are you setting the parking brake also when at the line?

 

[richardv6]

brakes

i already have new rear shoes and a10 wheel cylinders,and leaving at only foot brake.also when i get into boost real hard and let off brake pedal kind of hard.thats why i think vacum is the issue. motor runs stong dont think engine vacuum is problem but will check it.

 

[richardv6]

brakes

i had this complete drivetrain in another body and just switched it over to this one to lighten up. it had factory brake setup and could hold 15lbs,everything is the same as it was other than a vacuum brake setup, it already had correct pedal installed. also bleed the s--t out of it.thats why i thought i may need another checkvalve on it like whats in gbodies kit, that is showed in their picture.

 

[grocerygetter]

I agree with the other question...how much vac are you seeing with that cam?

 

[Red Regal T]

I have a stock cam and my vacuum at idle is about 17-18". Try engaging your E-brake on launch or switch to hydro-boost. Of course your powermaster never depended on vacuum.

 

[autoguy]

Check your brake booster for a leak.

Idle the car. Shut it off. Then pull the fitting with the hose on it out of the booster slowly. Listen for a vacuum hiss as you remove it. No hiss = a vacuum leak. Possibley in your booster. Also with the car off you should have power assist for at least one brake application.

 

[GNRick]

I rode in a guy's GN once with vacuum brakes. I believe he couldn't hold any boost either. If I remember correctly, he had trouble doing a burn out. Sometimes you only hear the good things about an "upgrade". You don't find out about the negatives until you install it on YOUR car.

 

[aminga]

Just an idea here but I went from being able to hold boost to pushing the front wheels through the lights (Powermaster) but one of the axle seals were seeping rear end grease onto the shoes. New seals, cleaned up the pads and drums and it was right as rain again.

 

[turbo nasty]

Vac swap here and I can hold the same amount as with eth PM around 5-7 psi before rear wheels start spinning.

Heck of alot cheaper the the PM in my eyes. The accumulator., pump, switch...stupid expensive!!!!

They put vac brakes from teh factory on the TTA with a turbo buick motor in it...HMMMM.

If you are wanting to hold a bunch a boost on the line or lauch where the boost comes up. Real answer is turbo/convertor combo and a transbrake.

The ebrake lauches, bigger wheel cyliders are asking to bend the backing plates and have rear wheel lock ups in the rain and panic stops. Just MO

 

[GNVYUS 1]

You can't expect the vacuum brakes to hold the same as the Powermaster, the line pressures are not even close.

You'll need to make sure the rear shoes are adjusted, while in reverse hit the brakes hard to adjust the shoes. Then before you launch blip the gas in neutral and slam the brakes while the rpms are at their highest or just coming off that rpm (or if your boost gauge has vacuum reading). This means you're going to have as much vacuum as possible to hold the rear drums.

The rest depends on power of brakes vs engine tq, don't expect too much here. A lot of us go to the transbrake to launch.

 

[richardv6]

Brakes

Well i installed the so called missing valve, all it was is a filter and did not make any differance.checked vacuum to booster and getting 15 inch of vacuum.the booster is holding vacuum and rear shoes are tight.i am not expecting 15lbs just want to be able to hold some. Getting fed up i will be looking for pm setup i guess.i got a transbrake just did not want to have to depend on it all the time.thanks guys for your inputs.

 

[1quick6]

Well i installed the so called missing valve, all it was is a filter and did not make any differance.checked vacuum to booster and getting 15 inch of vacuum.the booster is holding vacuum and rear shoes are tight.i am not expecting 15lbs just want to be able to hold some. Getting fed up i will be looking for pm setup i guess.i got a transbrake just did not want to have to depend on it all the time.thanks guys for your inputs.

If you really are at wits end with vacuum brakes, have you considered hydroboost? I'm not going to start a debate, but it is something to keep as an option. Yes, it's another $250 at the parts store and you'd need a different pedal again, but ...

 

[Nick Micale]

You can't expect the vacuum brakes to hold the same as the Powermaster, the line pressures are not even close.

Unless you have the data where you tested this, I have experienced just the opposite. In fact, most owners say it stops better than the PN ever did.

Turbo Nasty summed it up properly, if the conversion is done properly, a vacuum booster will work as well, usually better, than the un-reliable PM POS.

I know of a half-dozen local GN's that have had their front end totaled when their PM decided to quit in traffic.

Basically, PM or vac, both are an ASSIST for the same braking system, so holding boost should be the same for each.

 

[GNVYUS 1]

Ok I'll play along, the Powermaster uses phenolic vanes to pump brake fluid up to 2600psi to charge the accumulator bowl.

Hydroboost is used on HUGE Trucks due to it's 2000psi line pressure potential.

So, how much psi does the vacuum booster produce?

Ok I'll help, with a 1 1/8th master cylinder bore and a foot pressure of 100lbs your pressure is pretty much 603psi.

Considering that most of us can't hold 3psi with vacuum brakes vs 10-15psi with the PM or Hydro there must be something else there right?

 

[87Turbo-TWE4]

Just my 2 cents, but I switched from the powermaster to hydroboost and never looked back. I also have stainless lines with Delco rotors and Delco ceramic pads. Not only does it stop on a dime but it picks it up too. And I also agree with the S-10 cylinders. It's my next upgrade.

 

[turbo nasty]

Hurry someone tell Jack Cotton that the VAC brakes on his car are crap and he has to take them off and go with Hydroboost otherwise he cant lauch and stop properly.

No way VAC brakes hooked to whatever size rotors, calipers, disk/drum/whatever could stop a 140 plus MPH car long less a stock GN....