[Bill Eveland]

Plan on replacing the calipers with the new hoses, chances are the bleeder screws won't come loose anyway. Unless the calipers have been replaced recently.
I use an on car lathe on a regular basis and its designed to put a non directional finish on the rotor. Before the on car lathe came out, when the rotor was on the brake lathe turning, I would use a piece of emery cloth on each side and move it from top to bottom of the rotor quickly to have a crosshatch finish.
At home you could also use emery cloth by hand and sand overlapping circles in the rotor to put on a finish that would work.

[vinnyragu]

While talking to the guys at work, One guy mentioned to check along your rear axle housing for your brake lines being crushed. Possibly at one time it was towed and this would happen. Dan.

[Pontiac Dave]

Manual Disc??? Is there such a thing? I thought all disc brakes came with a power booster. I might be wrong but, I think your problem is that the clevis pin is in the wrong hole. Try the lower hole, I think you are exserting to much force on your master causing it to lock up.

[sts]

No, you are not unclear before, and I understood what I read, but you aren't reading. One of the first suggestions was that it's not uncommon for new master cylinders to be bad out of the box. That's why I would go ahead and try another master cylinder. As far as the correct hole: You said that you think. . . . My experaince as a professional mechanic has been that when people say they think, that's what they are doing. When you scrape the frosting off, however, they never verified the yes or no goo/bad. They only thought about it. It's amazing how many people, including professionas, think something is good or bad and act without verifying.

Are the back shoes adjusted correctly? It doesn't take a lot of slack before it starts showing up as a low pedal problem

My opinion is that you are barking up the right tree. You are clear in your description, and something tells me that you followed effective troubleshooting protocall. If you belive a crushed brake line causes a spongy pedal, go ahead and replace all the steel lines with the hoses. That way, you can eliminate lines and hoses from the equasion. Next, replace the calipers and wheel cylinders. As I said, maybe, only maby, the hoses, but I don't see what else except for the master cylinder. And I know that off the shelf defective or wrong master cylinders are quite common.

If I were you, following the game plan you have done, I would try another master cylinder. Sure it's throwing money at it if it doesn't cure the problem, but if it does, you have a defective master cylinder, and if you have the receipt, you'll get a full refund for the defective part.

It doesn't matter to me becuse it's not my money. I'm just offering you my professional opinion. How do you think a brake shop would takle it? You think that they would go through all the shenagins that have been suggested? The fact is that they would hang a new master cylinder on the car. If it corrected the problem, they would sell it to you. If it didn't correct he problem, they would put the mastery cylinder back in stock and start looking elsewhere. As a shadetree mechanic, you don't have "those type of troubleshooting" tools.

You what you want. I'm only pointing out what seems to be the obvious reason for the no pedal, and suggesting the cheapest way to troubleshoot your problem. If you belive that some of the other suggestions are better choices, I won't be offended. All I ask is that if it's somethig other than the master cylinder, please make a new post and explain what was wrong because I'm always wishing to further my knowledge base.

[71firebird400]

Once again; I'd like to thank all you guys for putting in the effort to help me out. I think I'll check the rear drums one last time, and then my only option is to start replacing things. As much as I'd like to convince myself this is from bad brake lines I dont think it is. The car stops straight and the pedal is firm. If one line was blocked it would dart left or right. The chances of both being blocked, and still retaining a firm pedal are slim. Then again maybe the rear line is blocked; that would make more sense since only one line goes to both rear brakes. I'll make sure to post back when I get this thing solved. Thanks again.

[Pontiacpete]

Yes please because inquiring minds want to know...especially mine

[george kujanski]

I've read all the above and considering that the fronts lock up and the problem is stated that it does not want to stop, I'd say you are not getting stopping help from the rear drums.

Check to make sure that the mechanism and the self-adjusters are working, the shoes are at the proper initial adjustment, and finally that the proportioning valve is working correctly to get some pressure back there without totally relying on the fronts.

A previous post states that metallics get hotter; well, that's how brakes work. kinetic energy of the moving car gets converted to heat energy in the brakes. In order to stop, all of the kinetic energy in the car needs to get converted to heat...the same amount of energy gets dumped regardless of the type of brake pad being used.

If true, one explanation may be that one type of pad doesn't stop as effectively; i.e. more stopping distance, therefore more rotor revolutions and some of the total heat getting to the atmosphere due to more revolutions of the rotor (most front rotors are ventilated for that purpose).

George

[sts]

I doubt it's lines. Maybe, and just maybe, the rear hydralic hose that goes from the line to the rear might have a partial obstruction, and possibly the problem wouldn't show when bleeding the back brakes.

If the back shoes are adjusted properly, it seems as if you will have to play hit or miss, and start throwing money at the problem to troubleshoot. As I have said, the first place that I would throw money at is the master cylinder. If that didn't cure it, I would try a new rear hydralic hose. When I take a stance, I have the foundation on which to support my hunch. Otherwise, I'd keep it zipped, or say that I'm blindly guessing.

Despite the fact that the symptoms don't sound as if this is the problem, one thing that you might want to check--because it's free--is the tension on the master cylinder rod. There is not supposed to be any pressure on the master cylinder, zero lash. It's worth checking out becuause you don't have to get your wallet out.

[71firebird400]

Well right now I've got the rear brakes torn apart (manually adjusting them, sanding drums and pads, etc.) just "in case". It's going slow cause I have other things going on; but I won't forget to keep you guys updated if anything improves. Thanks again.

[71firebird400]

UPDATE-
Just got the car back from the shop- they turned the front rotors and took a quick look at everything else (it was at the shop for exhaust work). The car seems to be stopping better; but still does not stop well. Is it possible that as an earlier disc brake system it will never work as good as I want it to? Do you think adding a power booster would make a big difference? Thanks, once again, for your time.

Mark

[Pontiac Dave]

Originally Posted by 71firebird400

UPDATE-
Just got the car back from the shop- they turned the front rotors and took a quick look at everything else (it was at the shop for exhaust work). The car seems to be stopping better; but still does not stop well. Is it possible that as an earlier disc brake system it will never work as good as I want it to? Do you think adding a power booster would make a big difference? Thanks, once again, for your time.

Mark

Yes Mark......When you first told me that you have manual front disc brakes, I couldn't believe it. Now there are cars out there with the same set up and work okay, but I think you should be running a power booster on your car which would make a big difference. For about $200 or more you can convert over to power disc brakes. It's a small price to pay for your safety.

[71firebird400]

So if I were to convert to power brakes is this all I would need?

-Brake Booster
-Power Master Cylinder

Thanks.

[sandmanjoe]

try mpbrakes they got a booster and master for 125.00

[71firebird400]

Today I was checking out some second gens (Camaro's) at a local swap meet and noticed that all of their master cylinders had a larger front "bowl" (I don't know the actual word) than rear. These cars were all power disc/drum cars. The replacement master cylinder on my car has equal sized "bowls" for front and rear. Does know what the master cylinder is supposed to look like for a manual brake car? Thanks.

[scottk]

You might have got a drum master by mistake.

The proper disc/drum master for that car is the rectangular with a larger front bowl.

The corvette style will also work

The drum/drum master looks like this

All of these have a 1" bore for manual brake applications, but the stroke and fluid flow to the front brakes with the drum master is insufficient for stock disc brakes.

[Scarebird]

Scott, I do not agree with that. If the bore sizes and stroke are identical, the pressure will be the same. In a 2 reservoir MC, the pistons are separated by a spring to balance front and rear. Prior to 1981 , they were the same size bore. We have customers that our disc kits with 55-57 Pontiacs and their original single MC's with no issue, same with early 60's Buicks. The larger reservoir is for pad wear, as the disc piston is much bigger.

Now, 70 and later F-Birds as we know never came with front drum, only 67-69. NAPA says they both ran 1" master piston in manual flavor, 1-1/8" in power. Also, according to NAPA- all 1967 and later GM drum masters were 1", so pressure would be identical. I would try the lower hole for less leverage and more stroke per degree swing. It's free and quick to do.

[71firebird400]

Ok; I have the "corvette" style (Ironic since my dad just went through the brakes on his corvette) I think I'm going to try the lower hole as Scarebird suggests; but I will probably install a new master cylinder/brake booster this week.

[scottk]

71firebird400, skip to bottom
Scarebird, I have a question, are your 55-57 kits using the metric calipers, or the larger ones?
But sure if the bore and stroke are the same, and the spring rates are the same, the pressures should be identical.
I have no knowledge of the stoke of the fruit-jar masters, but the bore depth of the tandem drum master is shorter by almost 1", making for a potential of a much shorter stroke, depending on the length of the secondary piston in either unit. The best the tandem drum master can come up with as far as stroke would be 1/2 the difference in total bore length per circuit as the best the disc master can do.
If it cant deliver enough fluid to the front because the secondary piston bottoms out, the pressure will quit building in the front circuit. There were many different length secondary pistons, creating the possibility for some people to have problems, while others do not.
But it is a moot point, as he said he has a disc master anyway.
=========================================

Anyway, why change to the lower hole? I thought your problem was hard brakes? That will reduce your leverage and make them harder. Also, the pushrod angle will be incorrect, and although it may not actually bind or scissor, it will eventually ruin the master cylinder by pushing upwards against the piston instead of straight into it. The angle will also cause the leverage ratio to change through the swing of the pedal arc. The lower hole is for power brakes with a booster mounted at an angle.

1/24
At first I thought it was because I didnt have a booster, but this is pathetic. For the record; I made sure to put the brake rod into the upper hole on the pedal (I believe this is the correct one). The pedal is firm, so I'm pretty sure theres no air in the lines. The car stops straight, so all the brakes are working. What do you think could be causing my problems? Should I put new lines on? Thanks.
5/18
they turned the front rotors and took a quick look at everything else (it was at the shop for exhaust work). The car seems to be stopping better; but still does not stop well.

The pedal is firm, how far down does it go? Mine stops sufficiently with manual disc brakes, though it cannot compare to power brakes. Do Not put the rod in the lower hole with manual brakes.
Have you checked the pressures at the brakes yet? You can get a gauge from summit for $40. If the pressures are insufficient, changing to power brakes might just cover up the problem.

[Scarebird]

Originally Posted by scottk

71firebird400, skip to bottom
Scarebird, I have a question, are your 55-57 kits using the metric calipers, or the larger ones?
But sure if the bore and stroke are the same, and the spring rates are the same, the pressures should be identical.
I have no knowledge of the stoke of the fruit-jar masters, but the bore depth of the tandem drum master is shorter by almost 1", making for a potential of a much shorter stroke, depending on the length of the secondary piston in either unit. The best the tandem drum master can come up with as far as stroke would be 1/2 the difference in total bore length per circuit as the best the disc master can do.
If it cant deliver enough fluid to the front because the secondary piston bottoms out, the pressure will quit building in the front circuit. There were many different length secondary pistons, creating the possibility for some people to have problems, while others do not.
But it is a moot point, as he said he has a disc master anyway.
=========================================

Scott, having half the stroke in a dual master would make sense, as you are doubled up on pistons. That aslo solves a question I have myself, essential whether a dual piston master woul work on a OEM single booster- by your logic that answer would be no, as the booster stroke is twice as much, and would be too sensitive to use.

Our 55-57 Pontiac setup uses 2.9 inch pistons- previously 70-76 Firebird now 90-02 Astro AWD.

[scottk]

Scarebird, I don't know that that's true. The total stroke to activate all 4 wheels should be the same. My logic saying 1/2 the difference may be flawed. The point really was that the total stroke between the two different tandem masters may be different since the master itself is shorter.