Brakes don't work well
 

Hi, my '71 Firebird has manual discs on the front and drums on the rear. So far I've replaced the front and rear pads, along with the rear wheel cylinders, and master cylinder. Right now the car does NOT want to stop. I mean, most people would think something was terribly wrong if they drove my car. The tires will lock up, but it takes way too much force. I made sure to get the manual master cylinder (7/8" bore). The rotors looked new when I took them out. 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.

How was the brake fluid pressure coming out of the front bleeders? the flex hoses could be getting blocked. And how old are the calipers?

I agree that it could be the flex lines. They tend to deteriorate from the inside. When pressure is applied, the line tends to close off or expand greatly and limit or block the pressure form getting to the wheel cylinders. I had the problem you describe with my 65 goat. I have manual drum brakes. I replaced all the flex lines and the problem went away. Hope this helps. Good luck.

Which tires lock up? If you can lock up the tires, your brakes are working. If the force required to lock them up is too high, power discs would help that, as long as the master cylinder is sized correctly for the discs and the proportioning valve is set correctly.

If the flex lines are expanding under pressure, that'll rob the cylinders of the needed volume.

George

When I bled the front brakes the fluid came out of the bleeders about equal on both sides; which led me to believe that the hoses were fine. Perhaps, they're both partially blocked.... Either way it won't hurt to get some new hoses. I have not replaced the calipers since I bought the car (9 months ago) but they don't seem to leak. I know that there is no way this car stopped like this back in '71; so there must be something I'm missing. I'm not sure what wheels skid when I slam on the brakes; I'll check that next time I'm out with the car. You have to understand I'm probably pushing down on that pedal with 200+lbs of force. :eek: Thanks for the help!



One more thing- do you think high performance pads would make a big difference on this car? My parents put ceramic pads on their minivan and it made quite a difference.

Pad make a huge difference. DO NOT use parts-store OEM metallics with manual brakes if they did not come with them from the factory.

You can also get a $40 brake pressure gauge from summitracing to check the pressure at the bleeders. You should get about 600psi on that car @100lbs pedal load with manual brakes. If less, suspect a restriction somewhere, and check that the metering valve stem moves outward while braking.
http://www.babcox.com/editorial/bf/bf50014.htm (about 3/4 down)

71firebird400:

Post back when you find the problem. Be interested to know what it was.

Did you replace your caliper Bushings? They should move freely. Also, jack up the car and have someone push on the brake pedal while you are spinning the wheels. How do they work? Rear brakes. Check your backing plates. On the BOSSES where the shoes ride. Are they GROOVED? If so, Replace them.. I agree with buying Name brand Semi metalic pads. But remember, They Dont work well when cold. Takes a few Applications to warm them up. Dan/

Once again; thanks for ALL the advice. Dan and Scott ; I'll start checking things one by one that you've listed in your posts. Today I was messing around on the driveway and when I skid the front wheels lock up first. This was probably from 10-15 mph to stop, and the rear were not locking up.

I have not replace the brake caliper bushings. I think my next step might be replacing the pads, then hoses, then calipers. Thanks again!

Hello '71 bird 400, just some ideas, when you change pads rough up your rotors a little, a sanding disc on a drill works well. I would not use semi-met's on this car because they generate more heat (they have to be hot to work well). I don't think GM ever used them on birds until 76 with power discs. When you get your new pads on seat 'em in good, run her up to about 70 and slow down quickly to about 45. Do this about four or five times. Also make sure your rear brakes are correctly adjusted, that old girl will be hard to shut down if only the front binders are working! Hope this helps.

Block or disc sanding the rotors is a good idea. You could also have them turned if you trust them to do an excellent job.
The pads transmit material to the discs, and the new pads should have a fresh surface to transmit material to.

The rotor surface is supposed to have transmitted pad material to it, so the pads slide against like material, rather than the actual metal. When changing pad types, it is a MUST to have a fresh disc surface. otherwise it is just a good idea.

just use a green scotchbrite pad on the rotors and pads to remove any glaze, no need for a drill, you don't want swirl marks from a drill on the rotors either. no metallic pads on manual brakes, Did you crimp pads on calipers as well as lube the o rings and pins. Are the wheel bearings well lubed? check proportioning valve for action. it should move the pin.

You should listen to the majority on the surface condition of the rotors. Scruffed up isn'tan option; rather, it's mandatory, and this is common knowledge that even helper automotive technicians. Take a look at any technical manual about this issue. Not that it isn't an issue that should be addressed if the condition exists, but lack of grease in the bearings wouldn't cause the problem. In fact, it would aid in the braking because it's already slowing down the car, according the the logic that is applied.

It might be sticking calipers, but I would start with the master cylinder and brake rod. You THINK THAT IT'S IN THE CORRECT HOLE? I don't know which hole it needs to be in but if it were my car, I'd find out and KNOW THAT IT'S IN THE CORRECT HOLE!

And maybe it's the porporting valve. I don't like to throw money at a problem as a way to troublehsooot it. In this case, however, I would start with a different master cylinder. You can start with calipers, hoses, and work your way back with the hit-or-miss process, but if you keep us posted as you work your way back to the master cylinder, I'll take a major gamble and feel confidant that I can say "I told you so" as you work your way to the brake rod/master cylnder.

A question to engineer: Not suggesting metallic pads, but why would you not use metallic pads on manual drums? Please explain the differences of the hydralic values, whereby the hydralic value differs between manual and power. Maybe I have overlooked something, but I don't see where the hydralic value differes at the caliper. In other words, x-pounds of pressure at the caliper is x-pounds, regardless to whether the force is manual pressure or assisted pressure.

What did you find out? After reading the one where you Locked up the fronts and not the backs, I have to ask if you adjusted the shoes? If the shoes are not adjusted they wont work correctly. And I do not agree on not buying Semi metallic brake pads. They are FAR superior to organic. Any race shop wil tell you that. Dan. Dont forget to jack up the car and spin the wheels, Have someone hit the brakes.

Manual brakes which came factory with metallic pads or shoes also would normally come with a smaller bore master cylinder than their non heavy duty counterparts, to generate the extra line pressure needed... which means a lower pedal. Or they would simply come ONLY with power brakes. Most semi mets will require higher line pressure. The friction properties are not the same, and so are not well suited to a manual brake application, though they do reduce fade.

"I'll take a major gamble and feel confidant that I can say "I told you so" as you work your way to the brake rod/master cylnder"

My first post mentions that I've already replaced the master cylinder with a new, correct, one. Oh, and I'M POSITIVE THAT THE ROD IS IN THE RIGHT HOLE. Sorry about being unclear before. Yesterday I checked to make sure the proportioning valve was operating (the rod was coming out when you hit the brakes, and went back in when you let off). I also watched the brake lines as my friend hit the brakes; no evident bulging or expanding.

ScottK- what pads would you recommend?

Once again, thanks for all the help!

I would replace the hoses, its good insurance and wont hurt. They arent very expensive either.

Then I would make sure the rear brakes are working, first visually with the drum off, dont push the pedal down completely or you will trash the wheel cylinders. Move the pedal just enough to see the shoes move.

After ensuring they move, I would adjust the rear shoes so there is a slight drag when you spin the drum by hand. Keep the factory type rear adjusters in place. Back the car up five or six times and hit the brakes, that is how they adjust.

The pushrod does go in the top hole, you are correct about that.

As far as pads, I have had good luck with all types in manual brake vehicles. Some stop better than others, some produce more dust. it wounds to me like the fronts are working ok, the rears arent working much if at all, and the front could still use some attention.

Either rebuilding or replacing the front calipers would be the last step for me if I did everything mentioned above.

sts is correct about a non directional surface on the rotors. Scuffing across the rotor rather than around it is standard procedure in a competent shop. A preped contact area will work much better than a glazed rotor. I scuff them even after turning on a brake lathe, usually with an angle grinder and sanding pad, but a drill would work just as well. Keep it moving and you wont mess up the rotor. Just a bit of cross hatch is all you need, you dont need to remachine it with the drill..

The pads I recommend for manual brakes, regardless of whtever other problm you may have been having, is the stock, organic pads. Once you have your brakes working sufficiently with those, you can tune to your own needs. Only tune one thing at a time, to find the pros and cons. Go total stock first.

As a side note, many bench lathes will include a 4" 120grit disc sander to create a non-directional finish on the rotor. The lathe will create somewhat of an 'LP' finish, if anyone remenbers vinyl. The sanding disc helps to correct that.
If you look at most any new rotor, or most any engine part finish, it will include a cross hatch or 'non-directional' finish.
I was taught using a 36grit 2" sander followed by a 120grit 2" sander. Neither will make up for a poor lathe finish. There is a technique to using the 2" sander. When finished properly, it has the appearence of using a block sander, very similar to the appearence of a new (non directional finish) rotor.

I like Raybestos in the red box, I think RPG-D52?. I don't like metallics because they can sometimes be hard on rotors and they generate so much heat. On some applications you don't have a choice, or if you're racin'. Metallics become common in the late 70's, early 80's when they started down-sizing the brakes on little front wheel drive cr*pboxes to cut weight and still needed the brakes to work. I had a '72 bird with the same manual brakes and I remember them working pretty good, they were not luxerious but kept me from gettin' killed a few times. Good luck on your quest and amen to the swirly pattern sanded into the rotor.

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.

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.

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.

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.

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.

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

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

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.

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.

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.

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

-Brake Booster
-Power Master Cylinder

Thanks.

try mpbrakes they got a booster and master for 125.00

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.

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.http://images.google.com/images?q=tb...ges/20-131.jpg

The corvette style will also work http://images.google.com/images?q=tb...d5/e3/0f_2.JPG

The drum/drum master looks like this http://images.google.com/images?q=tb...ges/120021.jpg

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.

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.

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.
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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.
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.

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.

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.

ScottK- the pedal feels normal; it doesn't drop excessively or feel spongy. I think I might invest in the pressure gauge as I too feel that by going with power brakes it will just "mask" the problem rather than solve it.

Yes, using a power booster would only be masking the problem. It's hard pedal, not a graidiant solid mush as brakes are supposed to be.

I mentioned it back at the begining and I think that other people have mentioned it. Have you checked the tension on the brake rod? You haven't mentioned the results of this test, I'm not a mindreader, so I can only guess that you haven't tried this troubleshoot.

It needs zero lash, meaning almost/slightly flopping around. If there is enough pressure on the rod, it causes the m/c cups to cover the residgual port, a hole that allows the fluid to bleed off pressure when you let off the brakes. Covering the residgual port will give symptoms as you describe.

If you have actually loosened the rod until it slightly flops around, and it doesn't solve the problem, you can rule out this as a problem. But unless you actually loosen up the rod until it flops around, you cannot be positive that this isn't the problem. In the many years of being a proffesional mechanic, the biggest problem I have seen with professionals and amatures is that they do not troubleshoot with a go/no-go. You cannot say that's okay. You have to actually test setting it up with before change and after change. If you don't use that approach always, you're pissing in the wind, something that a lot of professional mechanics do because they will not take the time to verify correct operation of components.

Maybe an idiot would have a problem with setting the rod so that it flops around, but you show an abundance of common sense, so you probabally understand the definition of zero loas plus slop. If the rod is set at zero lash with slop, it cannot fall out. If you haven't tried it, you cannot rule it out as not causing the problem. Loosen the rod until it flops around and test the brakes. If it doesn't slove it, set it back where it was. If it solves the problem, and you cannot stand the thought of the rod flopping around, tighten it up some until the point just before it causes the hard pedal.

an excellent point- especially with power brakes.

I just ran downstairs and checked the linkage between the pedal and master cylinder; from just looking and feeling it; it felt somewhat "tight" (no slop). Perhaps this is the root of all these problems (I would be overjoyed!). It 11 pm here so I don't want to jump to any conclusions; but I'm definetly taking a closer look tomorrow. If it were in fact to tight how would I go about loosening it? Thanks!

Good News! I adjusted the brake pedal to have a little bit of slop and took the car out for a test drive. After about 3-4 blocks I noticed the brakes really starting to get stronger; now the car will skid the rear wheels (although the left locks up before the right; but thats another issue I'll have to work out). Overall the brakes improved quite a bit; now I want to bleed the system one last time and possible replace the front calipers; the reason being that with the brakes improved so much I notice things I couldn't before (the car wanders just a slight amount under heavy stopping). I would like to say THANK YOU to STS, Scarebird, ScottK, and anyone else who contributed! It's amazing that you guys stuck with it over the past months getting this thing figured out.

Mark

good to hear! one of my customers may have had the same issue...