I Need Some Brake Help ASAP

[mikester]

So, Ive been redoing the brakes on my 81 Malibu. This all started with the DOT 5 brake fluid fiasco.
Back when I bled the brakes with the DOT 5 in it I never liked the way the pedal felt. It wasnt spongy but it didnt feel like it was totally bled. The pedal seemed soft and low. I assumed it was just a characteristic of the silicone fluid.
Just before I started working on the coupe I finished up the brake system on the 83 wagon. Bleeding the system didnt take that long and the pedals high and firm.
Now that Ive bled the coupe I see a huge difference in the way it feels when you step on the brake. Night and day.
I put in a new Delco master, new Raybestos calipers, new proportioning valve, new rubber lines and new wheel cylinders. All the SS hard lines were flushed out with denatured alcohol and brake cleaner and blown out with air. I bench bled the master and bled the system 2 different ways. First with a Mightyvac suction bleeder and then the old fashioned way. Lines are clear. No air. None !
I still have a soft low pedal. Exactly like I had with the old fluid. Completely different than the wagon. Im stumped.

The only thing Im thinking "might" be the problem is the booster. The 81 came with a large diameter single diaphragm booster when I bought it. At the time I thought a double diaphragm smaller diameter would be better. Instead of buying one from a place like rockauto I bought a generic booster from Pirate Jacks Brakes. The sales guy said it would work with no issues. Now Im wondering. Could it be the booster ? Maybe the rod that goes into the master is too short ?
I looked on rockautos site and theres different part numbers for each year. I would have thought the masters and boosters would all be the same for g body cars up to 1988.
What should I do at this point ? I mean the only thing I havent replaced over the past few days is that booster. Could it be the issue ? And if I replace it should I buy the correct part number for the year/model ? What the heck cold be the difference from 81 to 83 ? Its the only two things in the entire system that have different part numbers.
What do you guys think ?

 

[pontiacgp]

here is some good info on the DOT5

"
DOT 5
DOT 5 brake fluid is also known as "silicone" brake fluid. It was designed for the US Army, who has requested permission to stop using it.

Advantages:

It does not eat paint or skin.

It does not absorb water (BUT!!! See more on this under disadvantages, below.)

It has a higher boiling point than DOT 3 and DOT 4.

It is compatible with all rubber formulations.

It is a good choice for Concours cars which are rarely driven and/or never driven hard.

Disadvantages:

It does NOT mix with DOT3 or DOT 4 or DOT 5.1. Most reported problems with DOT 5 are probably due to some degree of mixing with other fluid types. A residue of the former non-compatible fluid is sufficient to cause serious issues. The best way to convert to DOT 5 is to totally rebuild the hydraulic system. Additionally, the same advice applies if switching from Dot 5 to any of the other fluids.

Since DOT 5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can cause localized corrosion in the hydraulics.

Careful bleeding is required to get all of the air out of the system. It is hard to you without introducing bubbles and thus results in soft pedal feel. These small bubbles will form large bubbles over time. It may be necessary to do a series of bleeds.

DOT 5 is less compressible (often creating a slightly softer pedal). It is not recommended for racing application.
It is hard to pour without introducing bubbles and thus results in soft pedal feel,

It is not recommended by the brake manufacturer, especially for ABS brakes.

It is about twice as expensive as DOT 4 fluid.

So silicone fluid aerates easily. Harley-Davison, one of the sole current OEM users of silicone fluid, warns buyers to let the fluid sit at least an hour before using it. If shaken on the way home, it will aerate enough to look like a freshly poured soft drink. Silicone fluid is also slightly more compressible than glycol fluid, does not change color to tip the user to its moisture content, and worst of all, neither accepts or disperses moisture, making systems using it more corrosion prone, and requiring much more frequent fluid changes. Silicone brake fluid also lacks glycol fluid's naturally occurring lubricity, making it incompatible with the mechanical valving in some anti-lock braking systems. "

 

[TURNA]

If the booster was bad the pedal would be rock hard.

Drain that crap out and find some good old DOT 3 non synthetic!!!!!!

 

[fleming442]

...and flush all the mung out thoroughly.

 

[mikester]

I guess I should have explained this better.
I just replaced EVERYTHING in the 81 except the hard SS lines because of the DOT 5 fluid. All new parts except the booster. Lines were totally flushed. At this point its not a problem with the brake fluid.
The DOT 5 thing started when I had to buy another proportioning valve for the wagon. Classic Tubes website says their valves are not compatible with the DOT 5. Spoke to their techs. They told me the issues so I replaced everything in the 81. The wagon had DOT 3 from day one.

So now back to the current problem. Why would the pedal be low and soft ? Master was bled. Systems been bled. No air at all. The only thing I can think of is maybe the rod that goes into the back of the master from the booster isnt right.
Maybe someone else has an idea ?

 

[pontiacgp]

If the rod was too short the pedal would sit low and be noticeable. As you are probably aware the rear brakes give you your pedal travel so if the shoes are sitting too far from the drum you'll have a low pedal. Did you get a good flow of brake fluid from the rear and when you bled the brakes did you start with the furthest brake from the master and work your way in?

 

[mikester]

If the rod was too short the pedal would sit low and be noticeable. As you are probably aware the rear brakes give you your pedal travel so if the shoes are sitting too far from the drum you'll have a low pedal. Did you get a good flow of brake fluid from the rear and when you bled the brakes did you start with the furthest brake from the master and work your way in?

Rear brakes are adjusted right. Ive got the shoes almost tight to the drums when you slide them on. As far as flow from the bleeders the fluid was coming out in a steady stream front and rear.
Bleeding started with the master on the bench, right rear first, left rear, right front, left front. Not the first time Ive bled brakes.
Like I said in my first post. Im stumped.
I need to find out whats causing this though.
Strange since the pedal in the wagon is totally different.

 

[69hurstolds]

The pushrod lengths MAY be different on your Pirate Jack's booster (never even heard of that company). IIRC, most G-body pushrods aren't adjustable. Or if they are, I've never attempted it. But they COULD be different lengths. Do you still have the old booster? If so, measure the depth from the mounting base for the MC to the tip of the push rod and then without disconnecting the brake lines, you may be able to remove the MC and measure the tip depth on the current booster and compare.

Then I'd bleed the lines again! I know that sounds counter-productive, but if air has pocketed somewhere, you may still have some trapped. I bled the piss out of my truck's brake lines, got a steady non-bubbly stream. Good. But there was just a little bit of what I figured was some sponginess. It may have been in my head, though. I came back the next day and did one more flush for peace of mind and the rear right had more bubbles coming out. After that last bleed, the pedal feel was right where it used to be. This was with DOT3/4 fluid though. Weird, because I used Valvoline "DOT 3 & 4" (says so on the bottle, wtf?? Make up your mind, Valvoline. Why not just say DOT 4?) brake fluid for full disclosure. My truck does have ABS system which was properly bled.

Seeing if any spaghetti sticks on the walls here.

 

[mikester]

BTW, when I took everything off the 81 I took the proportioning valve apart. I guess moisture pooled there since the car wasnt driven. The spring in the valve was covered in rusty mung. No wonder a lot of people/companies stopped using DOT 5.

 

[pontiacgp]

The rear brakes are adjusted with the drum installed and should have a light interference when rotating the drum.