Just made decision for brake upgrade.

[roger1]

Thanks Dave.
I replaced all 3 rubber hoses a couple years ago but only driven the car a few thousand miles since then.

I bench bled the master holding in a vise using the plug and tube method. I think I did a very thorough job with it. I did many iterations of pumping with a rod. Even let it set for a while to settle and pumped it again to make sure no new bubbles would show up.

When I bled the brake system, I used a Motive power bleeding tank along with a Power Probe master cylinder adapter designed for masters with plastic reservoirs. I added valves so I could pre-bleed all the air out of the tubes before bleeding the brake system.
I used the proper sequence for each wheel location. At the front calipers, I didn't bolt them onto the rotors and secured the pistons with a c clamp so I could tilt the caliper back and forth some while bleeding to make sure no air would be trapped at the top bleeder location.
Again, I did multiple iterations of going to each wheel location and felt I bled very far past the last indication of air bubbles.

Going to your summation sentence "I think you have air somewhere in the system, a defective master, a worn out vacuum booster, or rear shoes not adjusted."

Air: I think unlikely considering the bleed job I did but I may try your suggestions with clamps if you think I still should.
I've also been told that if you have air in the system pumping the pedal will raise it up. It does not do that.

Defective master: Thought of that too. I may have to take it off and try your brass plug method. I have one and I know the other is available locally.
I do not have any fluid seeping out the cap or bottom seals at the master. I've had a few other new master cylinders that were bad from the get-go on this car in the past. Why are these so bad in this generation? If this one is bad, I may consider going to an old cast iron design or an aftermarket.

Worn out vacuum booster: Since I have a new b body unit on the way, that will be the first thing I try before doing anything else.

Rear shoes not adjusted: Definitely not that. They are adjusted as tight as they can be to be able to put the drums on. Double checked them.

 

[MC96]

Definately need a bigger bore master if you have too much pedal travel

 

[malibudave]

Most of the master cylinder produced today are cast and assembled in China. Some master cylinders are made in the states, but this is rare and does not guarantee a good product either. I don't think its the casting so much as it is the seals are below standard or the assembly process is below standard.

If you pump the pedal a few times, and the pedal becomes high and firm, I would assume there is not air anywhere in the system, especially if the pedal does not sink to the floor when pressure is kept on the pedal. Fluid should only return to the master cylinder after the pedal is released.

Going with a larger bore master cylinder will give you a higher pedal, but it will reduce the line pressure and brake caliper clamping force. If you can't lock up tires, then I would suspect the master cylinder isn't generating the pressure, if no air is in the system.

If you clamp the rubber brake lines, make sure the car is on when you test if the pedal is firm. It is best that the vacuum booster is working to test this. If you have movement in the pedal when the lines are clamped off, you have an issue with the master cylinder or booster.

With the booster, make sure the push rod coming out of the booster, behind the master cylinder is the correct length and that the "dimple" in the master cylinder piston is the same as your original master cylinder's piston "dimple" that came with the booster originally.

Here is an option for a newer 1.0" master cylinder. It is from a right hand drive S-10 and should work well with any GM booster.

http://www.maliburacing.com/forum/viewtopic.php?f=25&t=124945

Step bore master cylinder came on S10s through 1997 and should be the same master cylinder as a 1982 and up g-body (except for the reservoir). The 1998 and up S10, came with a 1.0" bore master cylinder. For left hand drive S10s (American), both outlets are 1/2-20 and came out on the passenger side of the master cylinder. For the 1998 and up right hand drive S10s (U.S. Post Office?) used a 1.0" bore master cylinder, but it put the outlets on the driver side, but the outlet sizes where the standard 1/2-20 (rear port/front brakes) and 9/16-18 (front port/rear brakes). These 1.0" bore master cylinders where used on the Blazer with the twin piston calipers. The twin piston front Blazer caliper had a piston volume of 5.14 square inches versus the 2.75" caliper of 5.94 square inches of volume. LS1 F-bodies also use a 1.0" bore master cylinder with their twin piston calipers that had a 4.9 square inches of piston volume.

If you go to a B-body booster, you might want to go with a B-body master cylinder also. Should give you plenty of volume and pressure with the larger bore B-body master cylinder and the larger diameter, twin diaphragm booster.

 

[MC96]

I think when switching to a B body master the lines need swapped around. Could be wrong

 

[roger1]

Thanks Dave.
Like I said, I'm going to install the new B body booster before I do anything else. Who knows, that may fix my issue. If not, I'll go from there to the other things.

Btw, a friend of mine I was discussing this with thought that I might want to try front pads with a higher friction coefficient. He had just talked to a tech at Hawk about an issue he was having and gave me his name and number. He said they have pads like their HPS 5.0 that have up to 3 times the friction of a standard type of semi-metallic with no trade offs with life, dust or noise. He said they can give a seat of the pants difference in a panic stop. Do you have any comments about that?

I received my B body booster today. Had time to degrease it twice and get 2 coats of SPI epoxy on it. I'll let that dry overnight and slightly sand just to remove the nibs and then shoot a couple of coats of semi-gloss 2 part urethane black.
After that, I'll put it out in the sun to speed the cure of the epoxy underneath.

 

[malibudave]

3 times the friction will come at a certain temperature. If the pad is cold, most likely the "street pad" will be better. As things heat up, the aftermarket pads will start to exceed a "street pad" friction performance. At what temperature that happens, its hard to say.

With the pads you have, you still should be able to lock up the tires.

 

[pagrunt]

For the 1998 and up right hand drive S10s (U.S. Post Office?)

Look under LLV (Long Life Vehicle)

 

[81msw79]

The blazer brakes have a larger rotor and a larger brake pad. Why would you would you choose to up grade all these parts to stipp use a small brake pad? I have done the blazer brakes on my 81 wagon. Ut is a mojor change compared to my 83 wagon with all new stock style stuff.

 

[roger1]

The blazer brakes have a larger rotor and a larger brake pad. Why would you would you choose to up grade all these parts to stipp use a small brake pad? I have done the blazer brakes on my 81 wagon. Ut is a mojor change compared to my 83 wagon with all new stock style stuff.

I didn't think the D154 pad size was an issue and that the Blazer upgrade was more about the larger caliper piston and a little larger rotor.
With what I've done, I've got a larger piston with the Wilwood caliper (albeit still not as large as the Blazer's) and I think the only advantage to a larger rotor is for less heat. Since I'm going to use my car as a cruiser and not anything aggressive, I didn't think a larger rotor would really help me.
I also kind of prefer the stock type wheel bearing setup versus the non-serviceable Blazer type.

I thought at the time I was making a logical decision to go the route I did. But I will continue to make changes until I'm happy with my braking and will continue to think about other options. I still believe there is an issue with something defective somewhere that I have and I think Dave spelled those out pretty well. If that pursuit doesn't yield results that satisfy me, I'll look at other options including the Blazer brakes or a kit from Wilwood or Baer that uses modified stock spindles.

 

[malibudave]

Remember piston count does not matter when speaking of clamping force. What is important is total piston area that matters with relation to clamping force. A single piston caliper with a larger piston area will have more clamping for than a 2, 4, or six piston caliper will less piston area. You can argue that the clamping forces are spread out over the pad with a 2, 4, or six piston caliper and reduce pad taper, but for a daily driver, a caliper with a larger piston area is usually better.

A 2.75" piston caliper has more clamping force than a twin piston caliper with 1.81" pistons.

A brake pad with more fiction material area will last longer than a pad with less friction material, but it should not have any additional benefit in braking performance.

Larger rotor diameter gives you greater leverage when braking, which makes it easier for the car to brake. Look at it like a breaker bar. a 12" breaker bar will give you more leverage than a 10.5" breaker bar and make it easier for you to tighten or loosen a nut or bolt. In most cases a larger rotor will absorb and dissipate heat better. Usually an increase in rotor diameter comes with an increase in weight, which is not always good for acceleration or braking.

LS1 F-body front calipers and all, as far as I know, Corvettes have a piston area of 4.9 square inches or less on the front calipers. The C5 twin piston calipers have smaller pistons than the LS1 F-body twin piston caliper. So technically, the LS1 F-body has more clamping force than the C5 corvette twin piston caliper, but both are made of aluminum and the F-body will most likely flex (clamshell) more because it is generating more clamping force. Aluminum is good for weight saving, but not so good at deflection/clam shelling. Also remember that a Corvette or LS1 Camaro caliper has to go over a 1.25" thick rotor versus a rotor that is around 1.0" in thickness (g-body or blazer rotor), so it will have an inclination of deflection/clam shelling more.

With a 1.0" bore master cylinder and the same brake pad friction material and all other things being equal, technically, a stock setup with the larger 2.75" caliper will give you the greatest clamping force (rotor torque) over a Blazer twin piston and a LS1 F-body setup. This is using the brake calculator found at pro-touring.com. With the the Wilwood 2.75" bore caliper, you will also have the lowest overall weight, the lowest rotational weight, and the lowest amount of money spent. The Wilwood 2.75" caliper actually weighs less than a stock 2.38" piston caliper. Next would be the Blazer and then the F-body for performance, overall weight, and rotational weight.

So what is the real issue with the g-body brakes? In my opinion is a combination of things. 1982 and up low drag calipers, along with a step bore master cylinder, small diameter vacuum booster, old rubber brake lines, and old brake fluid that hasn't been changed in a while. These things paired with 10.5" rotors and you have a variety of things that will produce lack luster performance in a stock system. We are talking 30 to 40 year old brake systems now that are old and worn out.