Brakes seem to require alot of foot pressure

[dlafont]

I've been having a problem since I upgraded my brakes in the front and back.

I put Baer sportstrack 12" in the front and PBR 11" disks in the back.

I have blead all 4 corners and the pedal is very very firm so there appears to be no air in the system. I also have a vacuum booster upgrade with an appropriate master cylinder. I have also done the proportioning valve modification that Baer recommends for the Disk-Disk setup.

I have also verified that the brakes do work on all 4 corners.

The problem I am having is that it seems I have to press really hard on the pedal to get any braking power. Do I need to upgrade the master cylinder for the new Baer brakes? Or could the master cylinder be shot? What else could it be?

Thanks,

Don

 

[charlief1]

Since you now have vacuum brakes what kind of vacuum does it have at idle? If you don't have enough then the pedal will be very hard.

 

[dlafont]

Since you now have vacuum brakes what kind of vacuum does it have at idle? If you don't have enough then the pedal will be very hard.

Seems good. Looks like around 6 - 8 psi judging from the fuel pressure change when I unplug the vacuum line on the regulator.

Also verified vacuum is making it to the booster fine. No leaks.

 

[Roger]

6-8 inches of vavuum is not enough. If memory serves me correctly, 16 inches is about minimum.

Why not consider 84 & 85 GN hydroboost? They are on most new diesel powered vehicles.

 

[Mark E.]

What is the bore of the master cylinder?

When I did my brake upgrades I found an 1 3/8" master, thinking that was the ticket. Bigger is not always better. I also have to put extra effort. I am going to try a 1 1/8" one of these days.

 

[dlafont]

6-8 inches of vavuum is not enough. If memory serves me correctly, 16 inches is about minimum.

Why not consider 84 & 85 GN hydroboost? They are on most new diesel powered vehicles.

6 - 8 psi works out to 12 - 16 inches so it might be boarderline.

I thought about hydroboost but i believe they should still work not too bad.

I really think something is wrong as I really have to press hard on them to even keep it from rolling forward while in park.

 

[TurboBuRick]

Sounds like no power assist. Did you pull vacuum on the booster and see if it's holding?

 

[dlafont]

Sounds like no power assist. Did you pull vacuum on the booster and see if it's holding?

I just checked and the booster seems to hold the vacuum fine. I pulled off the line before the check valve and vacuum held in the booster. Looks like the diaphram is fine in the booster.

 

[dlafont]

What is the bore of the master cylinder?

When I did my brake upgrades I found an 1 3/8" master, thinking that was the ticket. Bigger is not always better. I also have to put extra effort. I am going to try a 1 1/8" one of these days.

I'm not sure what the bore of the old master was but I just bought a master today with a 1" bore and I'm going to try that.

 

[gn4u2c]

I have the same fronts and 11 rear from ed miller and my car will put you through the windshield if your not ready. I still have the powermaster so what do i know. I would put a gauge on your system to see what kind of vacuum you got and install a vac canister if your below 15psi at idle. Should solve your problems. make sure you check valve is good, no vac leaks anywhere on the motor ? booster has a good diaphragm?

 

[davidf]

This is probably irrelivent but where are you getting your vacumn source from? Did you tee off of something or did you get the vac block setup for vac brakes.

 

[dlafont]

So... I put in my new master with a 1" bore and it seems to improve things.. I will need to take it out and see but I spent most of my day tuning with my FAST XFI.

 

[dlafont]

So... Here is my status..

I bought this new 1" bore master cylinder... (Couldn't believe how cheap it was.. Only $150):

I took it out for a test drive today and the brakes seem to work reasonably well now.. I still have a feeling that they could do better.. I believe I can get more out of them if I had more vacuum like some of you have suggested. Currently I get about 6psi differential between atmosphere and vacuum and that works out to only around 12 inches of vacuum. I am looking to add a vacuum pump that should get it up to the recommended 16 - 21 inches of vacuum needed for the typical booster.

I believe that should do the trick.

Thanks for your help guys.

Don

 

[POWERBRAKEBOB]

Hydroboost

All cars that came with 4 whl disc brakes have HUGE vacuum boosters, Hydroboosts, or electric brake boosters such as the Lincoln LSC. 4 whl discs need DOUBLE the line pressure to make them work. Drum brakes LOCK UP at 600 psi, that's why they use prop valves to reduce the disc brake pressure (ususally 1100psi) to prevent the drums from locking up. Discs average 1600psi to lock. You must change the drum brake prop valve to a 4 disc type. The vacuum booster will never stop the car. That's why Buick NEVER used it on a turbocharged car. The Regal Vacuum booster used a 24mm piston, about 15/16". The Power master uses a 1.250" piston. we use a 1.125" piston with a Hydroboost. A vacuum booster, with very low vacuum has no power. You multiply the square inches of diaphragm area, times the inches of vacuum available to determine the output of a vacuum booster. No vacuum, no power. Put a large master on it, and it can't push it to high pressure. A pressure guage would read out at 450psi with this combo.The Hydroboost has so much power, with NO vacuum, you can feel the calipers expand. About 2000psi. It WILL stop the car, safely, and will outlast the life of the car.

 

[charlief1]

Hate to tell you thins Bob, but Buick did use vacuum boosters on turbo cars. Look at the early very ones that started in the 60's.

 

[turbo nasty]

Hate to tell you thins Bob, but Buick did use vacuum boosters on turbo cars. Look at the early very ones that started in the 60's.

To Add to that the 89 Turbo T/A with the Buick turbo v6 had vacum brakes from the factory!

 

[POWERBRAKEBOB]

Vacuum

IF you had more vacuum? My point exactly. Your car is not stopping, right? You are having problems? Even with Baer (Corvette) calipers? Check the brake pressure with a guage. It needs to have over 1100 psi available. Front and rear. This is stock operating pressure. My guess is you only have 700-800 with this combo. The Hydroboost can continue pushing the guage to 2000PSI. Buick put Hydroboosts or Powermasters on all their turbo cars, for the same reason. Vacuum problems. The few cars made in the 60's with turbos, had drum brakes, which can lock up even without a vacuum booster. Disc brakes require High Pressure to work. 4 wheel discs, even more.
GM has always had to grind their cams to get vacuum for the power brakes as a priority, instead of power. The L-88 Corvettes had 7" of vacuum, but because of it's speed it required power brakes. GM was afraid to sell this car to the public, BECAUSE the power brakes would not work in traffic. The race cars had to DOWNSHIFT to get enough vacuum to make the turns at 160. Buick would not accept liability for inadequate brakes for the same reasons. Therefore NO vacuum boosters on cars this fast, and this heavy.

 

[The_Six]

I was thinking of getting that same master Jegs has it listed for $89 but then I found out that was the crome cast one not the polished.
Right Stuff DBMC56C Right Stuff Brake Booster and Master Cylinder Kit