Can Not Get Vacuum Brakes To Hold Boost!!!!!

[Dreamcar86]

Vacuum works fine. I have it on mine. My dad has it on his. Most of my friends have it. It plain works well and has been super reliable.
If you are having problems then here are a few suggestions (some are redundant):
check proper function of the booster (make sure there is no loud hissing when the pedal is pressed while engine is running. If you hear a loud continuous hiss while holding the pedal, then you have a hole in the diaphram and the booster should be replaced as this will be the spot where you will loose vacuum)
check proper function of the check valve
check vacuum source
make sure you have more than 10 inches of vacuum available (cams with a lot of duration and/or over lap will kill the vacuum)
make sure you dont have a misfire or a cylinder down on compression or a huge vacuum leak some where else (such as the climate control, cruise control or any of the other vacuum sources)
It should also be noted that there are 2 different boosters fitted to G bodies.
One is a single diaphram (large diameter, shallow housing depth)
The other is a dual diaphragm (small diameter, thick housing)
I always use the dual diaphram. The TTA's had a dual diaphram as well that was mechanically identical to the G body unit.
Anytime someone has a problem with the pedal loosing assist I strongly question many of the above items since it should work flawlessly. The TTA came stock with it (as is common knowledge) and utilized all of the same critical parts that a Buick would have (cam, intake, etc).
Many guys dont like it when the tune/running condition of their engine is questioned, but those things play a big part in your vacuum readings. Parts integrity is also crucial. Not that G body boosters go bad that often as I have never lost one personally, but it is mechanical and is possible. The one on my car is used from a salvage yard and has been on there for almost 5 years now.

I noticed that you said to use a check valve. If your vacuum source is the vacuum block on top of the plenum is the check valve necessary? If so, is there any special one to purchase? I have never ran one. What could happen if you do not run one?

Thanks in advance.

 

[POWERBRAKEBOB]

Hydroboost Vs Vacuum Vs Powermaster

I Was Watching The T.v. Show "pinks" Where They Race For Pink Slips (title To Your Car) Loser Gives Up His Car. When It Came Down To The Final There Was A G.n. On The Line. When He Staged, The Car Pushed Through The Lights, And He Redlighted. He Lost. Luckily, On This Show They Were Racing For $10,000. Prize Cash, And Not The Car. His Name Was I Think, John Nguyen. I Have Heard About So Many G.n.'s Red Lighting This Way. The H/b Holds Harder When The Pump Rpm's Come Up.

 

[Dreamcar86]

I Was Watching The T.v. Show "pinks" Where They Race For Pink Slips (title To Your Car) Loser Gives Up His Car. When It Came Down To The Final There Was A G.n. On The Line. When He Staged, The Car Pushed Through The Lights, And He Redlighted. He Lost. Luckily, On This Show They Were Racing For $10,000. Prize Cash, And Not The Car. His Name Was I Think, John Nguyen. I Have Heard About So Many G.n.'s Red Lighting This Way. The H/b Holds Harder When The Pump Rpm's Come Up.

That is one of our boys from Oklahoma City! By the way, that car is now on ebay if you would like it.

 

[TWISTER]

I Was Watching The T.v. Show "pinks" Where They Race For Pink Slips (title To Your Car) Loser Gives Up His Car. When It Came Down To The Final There Was A G.n. On The Line. When He Staged, The Car Pushed Through The Lights, And He Redlighted. He Lost. Luckily, On This Show They Were Racing For $10,000. Prize Cash, And Not The Car. His Name Was I Think, John Nguyen. I Have Heard About So Many G.n.'s Red Lighting This Way. The H/b Holds Harder When The Pump Rpm's Come Up.

He said he forgot to set the Trans brake. I dont think you will find many 10 sec cars leaving off the foot brake.

 

[POWERBRAKEBOB]

Hydroboost Vs Vacuum Vs Powermaster

These Cars Are Used Both For Street Use And Drag Racing. You Can't Set The Trans Brake When You Are Coming Down An Off Ramp At 70 Plus, Or Idling Along In Traffic. The Brake Issue Here Has Been One Of The Hottest Topics, Period. It's Not Just About Building Boost, Or Going The Fastest, But Is Also A Safety Issue. Your Car, Your Life, Other People's Lives. Etc. The Powermaster Has A 1.250" Master Piston, Almost Impossible To Push When The 12v Pump Shorts Out. The Vacuum Booster Was Not Designed To Work Under Manifold Pressure. Buick Did Not Want To Put A Vacuum Booster On Their Turbo Charged Cars For Reasons Of Safety And Liability. If The Vacuum Hose Or Check Valve Blow Off Their Car, They Are Liable For The Damages. The G.n. Is A Heavy, Full Framed Car. It Needs The Brake Pressure. The 83-85 T Types Came With A Hydroboost. No One Here That Owns One Of Those Cars Complains About The Brakes. No One. They Are 24 Years Old, And Still Work. Cars With F.i., Overdrives, Low Or No Vacuum And Are Heavy, Need Superior Stopping Power, Ie; Pressure. Drilling Holes In Rotors Does Not Raise The Line Pressure, And Line Pressure Is What Stops The Car. Bigger Rotors May Absorb More Heat, But Do Not Raise The Line Pressure. Bigger Wheel Cyls Do Raise The Pressure Against The Shoes. It Is Line Pressure Times The Square Inches Of Area Of The Caliper Area, And The Wheel Cyl Piston Area That Puts The Squeeze On That Slippery Rotor And Drum. They Don't Steer A 747 With A Tiller.

 

[QUIP'6']

i can hold 17 psi off my vacuum brakes. i got the s-10 cylinders and the larger bore master cylinder from advanced it works like a charm also when i stop hard and fast it will put you through the windshield if not careful

 

[Frank718]

i can hold 17 psi off my vacuum brakes. i got the s-10 cylinders and the larger bore master cylinder from advanced it works like a charm also when i stop hard and fast it will put you through the windshield if not careful

Maybe you can give me info on how to fix my brake system.I know I have a stock vacuum brake system.When I press the brakes I hear a hissing sound,but when I press it hard I don't here it no more. Now,in this thread the guy are saying to replace the propotion vaules and change the vacuum soure. So is it possible anyone can give me a step by step break down on how to make brakes hold to at least 10 lbAnd where can I get the parts. Right now I cannot launch with boost and the most I can hold is 1800 rpm.Thanks in advance.

 

[John Larkin]

Buy a new, not remanufactured, master cylinder from NAPA for a 1986 Olds Cutlass RWD with 307 engine. You may receive a cast iron one with the plastic reservior. That is fine; this is what I have also. A junkyard booster that actually holds vacuum is also needed. Take a MityVac with you with a large adapter cone and pull vacuum at the yard. It should hold indefinitely. You might even find one that when you pull the check valve out purges on the spot. Mine was like that so I knew it was a good one. Once you use these two critical and proper parts, you should have a solid pedal and be able to hold 10+ psi, maybe more. Also read this article:

Follow a Diagnostic Process When Curing a Low Brake Pedal, Bill Williams, Brake & Front End, June 2001

It is not literally applicable but halfway through step 5, pay attention to the quick take-up valve operation. That is the important information and completely applicable. Front brakes are important also.

 

[QUIP'6']

Maybe you can give me info on how to fix my brake system.I know I have a stock vacuum brake system.When I press the brakes I hear a hissing sound,but when I press it hard I don't here it no more. Now,in this thread the guy are saying to replace the propotion vaules and change the vacuum soure. So is it possible anyone can give me a step by step break down on how to make brakes hold to at least 10 lbAnd where can I get the parts. Right now I cannot launch with boost and the most I can hold is 1800 rpm.Thanks in advance.

frst off get rid of your cast iron proportioning valve i got this one on ebay
eBay Motors: GM STYLE DISC/DRUM PROPORTIONING COMBINATION VALVE (item 110066522481 end time Dec-16-06 07:01:02 PST) then get s-10 wheel cylinders for the rears and get a tta vacuum block for the vacuum brakes and a new check valve also make sure you get the larger bore master cylinder its 24mm and 36mm the other ones are ajust 24mm this way you get more holding power. http://www.partsamerica.com/ProductDetail.aspx?mfrcode=TRQ&mfrpartnumber=M39376&parttype=230&ptset=A then you have to bleed the piss out of them!!!! i then take the car out and ride the brakes hard to seat them just floor the gas and then apply brake hard to almost stop the car but yet it doesnt. i dont even have soft shoes on my car

 

[POWERBRAKEBOB]

Hydroboost Vs Vacuum Vs Powermaster

The Vacuum Leak When The Booster Is In The Released Position Indicates The Poppet Valve Is Knocked Out Of Place Or The Valve Body (plastic Part) Is Broken. This Can Happen During Installation Or The Pedal Was Not Changed To The Vacuum Pedal, Pushing The Rod To A Wrong Angle.

 

[Dreamcar86]

I'm getting vacuum from the pcv line,only place I saw to tap into.I completely flushed the fluid before the install.Trying to leave around 7-8psi,but it "pushes through the brakes",even trying to do a burnout.Never had this problem before the swap.
Enlighten me a little on the proportioning valve.I had to change it about 6 yrs ago (AC Delco) but can't remember much about it.
Thanks!!!

Brother, I have been down this road. DO NOT tap into the PCV line. Spend a little money and get the billet vacuum block that goes on top of the throttle body and that will help right from the start. After you do this report your findings and we can help you from there. There is no problem with vacuum brakes, however they do have to be set up properly. I know this one from experience.

 

[QUIP'6']

another trick to do is make sure there is no lip on your rear drum slid your drum on till it is real hard to get on. alot of people adjust brakes assume thats was far out on the drum they can go so they put it on and not knowing theres a huge lip on it so when they install them instead of bieng up against the drum its a 1/16 or so away from the drum. thats alot of wasted psi.

 

[GNVAIR]

Another great tip is to use the larger bore master cylinder. I use one for an 86Caprice wagon. You will need a G body reservoir for it to clear the hood. I used a ball joint pickle fork to remove the reservoirs. Unbelievable the difference the larger bore master cylinder makes!

 

[Dreamcar86]

Another great tip is to use the larger bore master cylinder. I use one for an 86Caprice wagon. You will need a G body reservoir for it to clear the hood. I used a ball joint pickle fork to remove the reservoirs. Unbelievable the difference the larger bore master cylinder makes!

This is a new for me. I have not heard of the larger bore master cylinders but I am liking the sounds of it already.

Thanks for the tip!

 

[Dreamcar86]

Another great tip is to use the larger bore master cylinder. I use one for an 86Caprice wagon. You will need a G body reservoir for it to clear the hood. I used a ball joint pickle fork to remove the reservoirs. Unbelievable the difference the larger bore master cylinder makes!

By the way, I forgot to ask you what brake booster do you use?

 

[GNVAIR]

I use the G body dual diaphram unit. Mine actually came off a V6 Regal, but it is identical to the one my father's Monte SS has.

 

[turbows6]

I am going to have to say now that a larger bore master will make things worse instead of better. Bigger pistons on the Master cylinder have more surface area to push against making it harder to build brake line pressure. Think of a hydraulic jack, tiny piston on the pump, big piston on the ram. Smaller master cylinder/ bigger wheel cylinders will give you more mechanical advantage.

 

[GNVAIR]

I am going to have to say now that a larger bore master will make things worse instead of better. Bigger pistons on the Master cylinder have more surface area to push against making it harder to build brake line pressure. Think of a hydraulic jack, tiny piston on the pump, big piston on the ram. Smaller master cylinder/ bigger wheel cylinders will give you more mechanical advantage.

Worked for me. Have you tried it?

 

[turbows6]

Yes, I have proven this in theory and practice on my dodge dart. It has wilwood disc brakes on all four corners and a wilwood master cylinder without power assist. I switched to a smaller piston master cylinder to make the car brake with less pedal effort.

For example to produce 1000 psi line pressure on a master cyl with a 1 1/8" bore diameter (ex. wilwood pn# 260-8556) would requre 994 pounds of pressure applied to the piston.

Area of a circle is PI x Radius squared (1.125"/2 Sq. x PI) = .994 Sq. in.

to produce 1000 psi line pressure on a master cyl with a 7/8" bore diameter (ex. wilwood pn# 260-9439) would require 601 pounds of pressure applied to the piston.

(7/8"/2 Sq. x PI) = .601 Sq. in.

Switching the 1 1/8" master for the 7/8" master therefore offered about a 39.5% reduction in pedal effort for equal brake line pressure, or you could also say that it resulted in over 65% more line pressure with equal pressure appled to the brake pedal.

The only downside you have is more pedal travel is needed, and you loose some of the pedals sensitivity.

Would have done in on my TTA, but it builds boost on the footbrake fine with completely stock vaccum brakes. Even with the Cpt-66

 

[Frank718]

By the way, I forgot to ask you what brake booster do you use?

I hade purchase the billet vacuum block and now I can hold up to about 2100 rpms. Before I could only hold up to 1800 rpms,so my next step is to get the S10 cylinders and flush the system.