[71firebird400]

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.

[Bill Eveland]

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?

[pngoat]

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.

[george kujanski]

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

[71firebird400]

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. 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.

[scottk]

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)

[pngoat]

71firebird400:

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

[vinnyragu]

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/

[71firebird400]

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!

[dssco]

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.

[scottk]

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.

[engineer]

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.

[sts]

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.

[vinnyragu]

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.

[scottk]

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.

[71firebird400]

"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!

[Thumpin455_GTO]

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.

[Thumpin455_GTO]

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..

[scottk]

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.

[dssco]

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.