Ok here is my problem. when my brakes are cold for about the first or 5 stops the break are EXTREMELY TOUCHY + they make a squeal. i
mean at slow speeds if i even tap them they lock up. after a few or so stops they are fine and act normal. the car has front disk andrear drum with semi metallic pads all the way around. i just got thecar and was checking the breaks and one of the pads in the back was cracked will this cause that? I was going to do a break job this weekend and put organic pads on because I do not like the soundthe semi metallic are making (which im told is normal). is my pads the problem or do I need to look at something else?????

thanks as always

Hot66ss

check for a brake fluid leak,or binding caliper on front. I don't think the pads are the problem.If the pads are saturated with fluid replace them.Is it a front wheel locking or rear? Tony

I would check the calipers very closely to make sure that there is no binding going on with the piston. If there is, then you'll have to rebuild them, or get rebuilts.

Also check your assemblies carefully to see if your backing plates, lines and everything looks in good order. Take a good look at the master cylinder and see if the rubber bladder under your cap is good.

I have had a similar problem with my F-Body and it turned out that a caliper seal was shot and somehow resulted in fluid contamination. The solution was to rebuild my calipers and completely flush all the brake lines. I also re-did the rear just because I was there and figured that I might as well do the whole thing. Besides, replacing all the fluid is a small price to pay for piece of mind and good stopping power. The fluid get's darker because it attacts water. It is supposed to be clear and is suggested to be completely flushed when it get's dark.

I realize that the semi metalic pads are slightly noisy, but they are better than straight organics. I use semi's and am quite pleased.

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The proud owner of a Canadian 64-SS with ZZ4 Power!
Team Chevelle Gold Member #37
Canadian Classic Chevelles & Beaumonts Member #350

I had a problem like this once. Check to see if your rotor's are "glazed". If you overheated the break's ( which it sound's like ) you're either gonna have to turn them or replace them. Check the thickness of the rotor's and drum's too, if they've been turned a couple of time's already chance's are they're getting close to minimum thickness and can't dissipate heat correctly.

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Nick P.
Team Chevelle Gold #36

Personally I don't believe in turning rotors. Turning rotors just makes them even thinner and more prone to warping. Rotors are cheap, just get new ones if that is the problem.

Everyone - Is it possible that his Brake Booster is overboosting?

and the reason it gets better after a few stops is the pads heat up?

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David Nafarrete
1965 406 6speed
(almost on the road again)

Which wheel or wheels are locking up? If more than one wheel is locking, both front for example, look for a problem that would affect both, usually the master cylinder.The piston could be sticking.

Good luck, we have been chasing this same problem on a 1993 F150 4X4 work truck since it was new, the brakes have been replaced at least 5 times in the last 75,000 miles. This truck is very hard on front brakes. Including rotors, calipers(once) drums and pads and a master cylinder. Still does it very often but not always (?), sometime's after it sits for several days or the weather is damp.

I think just the front lock. i knew the 2nd owner of the caqr who did the covershion on the breaks to disc and he said all the stuff is new (now about 2 years old). I was thinking of doing the breaks and then if that didnt clear it up, replace the booster. i was also thinking that there maybe a problem in the booster and after the engine worms up real, heats the booter it may cause the diraphram or what ever is causing it to swell up and then clear up. just a though

thanks guys

Hot66ss

It just occured to me... An obvious problem might be the proportioning valve. The previous owner said that everything is "new". Is the proportioning valve one of the adjustable ones ? If so, you may just have to adjust it. If Not, then it could be either defective or could be from a wrong type of car. These valves (original production ones) are designed for very specific applications and weight distributions.

It's a matter of balancing the braking pressure on the front & rear relative to the proportionate weight differential of the car. A 1966 SS with 396 has an effective weight distribution of 56/44. This means that 56% of 3841 lbs curb weight (2150 lbs)is on the front of the car and 44% on the rear which translates to 1691 lbs.

If you have a non-adjustable proportioning valve then you should seek to replace it with a Camaro or Firebird valve from the late 70's to 1981. These models of cars have very close weight distribution. Or buy an adjustable one and and work out the pressure differential by road testing.

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The proud owner of a Canadian 64-SS with ZZ4 Power!
Team Chevelle Gold Member #37
Canadian Classic Chevelles & Beaumonts Member #350

I have a non-adjustable valve. Even if it was the proportioning valve why would it only do it when the breaks are cool? also I might add I have noticed shrieks coming from the breaks when they are cold.

Thanks for all the help

Hot66ss

Some additional questions:

Are all the brakes binding when cold or just the fronts ?

The "upgrade" to disks, was is an after market kit or a collection of rebuilt parts ?

If it was a collection of parts, do you know what parts were used ? What was the donor vehicle that the parts would have come from ?

Was the booster & master replaced or just the master with the original booster ?

Were all the breaklines, front to back replaced with new lines ?

Is your brake fluid clear or is it darkening or already dark ?

Are there any grooves worn into the disks and/or drums ?

Where is the vaccum coming from for the booster ? Can you test to see how much vaccum you are getting cold & hot ?

This upgrade was a kit not just a pile of old stuff this guy had laying around. i think just the fronts are binding i cant reallly tell. its both a new master clynder and booster (now about 2 years old). I don't know if the break lines are new? the fluid is a dark color. the is a grove in one of the drums (dont know about the other i have not pulled it yet) but i will today. i am new at this and do not know how to test vacume. ok heres what i did i got the breaks to do the lock up thing them i went and pulled off the vacume line to the booster and drove it around a bit. if acted normal (except for no power breaks) no lock ups just good stops. i also just did it again this moring and pluged if off when they where cold no problem stoped fine no lockups. Does it sound like a bad booster to you guys? kind of does to me?

Thanks for all the help

Hot66ss

Mine does the same thing yours is doing. I have semi-metallic shoes (drum brakes all around) and in the humidity of Florida, the brake parts actually rust a little, causing the squeal. Once you apply your brakes a couple of times, the rust wears off and your set. Its that simple. Go ahead and check everything else posted here, though. Good luck!!

From what you described, there is less possibilities. I am inclined to go with a vaccum problem. Because this has been a problem for a while, you will have to make sure that any glazing is removed with emery paper and that all surfaces are clean and free of contaminants.

1) The vaccum that you are getting from the engine is too much. IE: Wrong Vaccum port or incorrect mounting.

2) Defective Brake Booster. That is a replacement item and you'll have to find one that will match up. If you know who made the kit, then you should have no problem.

3) As a good measure, I would bleed out the entire brake system and replace all the fluid with fresh clear fluid. This will result in better feel and firm things up a bit too. It's a two man job and it will take a couple of hours if you are using a hand pump.

4) To test the Vaccum, you will have to go out and get a Vac. Tester which can be hooked up to a hose running from your port on the manifold. If you have a Small block, your vaccum should be around 12 lbs. I could be wrong, best check.

Hope it helps.

Anyone Else... Can anyone else verify the vaccum ?

if the rust thing is correct why does it not do it when the vacume is pluged? why does it take so long to beed the breaks?

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The break bleeding takes so long because you have to clear all the lines of old fluid. So someone has to pour new fluid into the master while you are dumping the old fluid at each wheel. I have done this on a few cars and it's just a slow process and it goes better if you have a buddy to help.

Our 92 GMC Safari did the same thing. The first time you apply the brakes in the morning they would grab. Then they were OK until the next morning. Last week we had a complete brake job done as they were shot.( 110K miles ) All new shoes, new front rotors, turned rear drums, flushed the system with new fluid. All works great again.
My guess is the rotors/drums need surfacing and the shoes need replacing.

You said the fluid is dark. Should be more of a clear/tan fluid than dark. Needs to be flushed.

My guess to your question as to why they don't grab when the vacuum is plugged is that you now have less than manual brakes and can't apply enough initial pressure to make them grab. I'm surprized you can even get the car stopped. I don't recommend driving a power brake car without the power booster.

Good luck,

Bill


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Bill Taylor
Team Chevelle
Gold Member #73

Ok here is my plan of attack. I'm first going to flush all of my lines out and put in clear fluid. (think i should put dot5?) one person told me i should disconnect the lines to the mater cylinder then open the valves and blow out the crap with an air hose. he also said that the reason my fluid might be bad is because there is rust in the lines? after the air hose he said flush it out with alcohol then blow out the lines again with an air hose. does this sound ok to do?? anyway after flushing im going to take my drums and rotors off and have them turned i am also going to put on new pads should i go with semi metallic? i am going to take a look at the caliper and just clean it if it looks ok. i will also do the normal bearings etc. etc.


thanks for all of the help guys

Hot66ss