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Brake Fade

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
I am having a brake problem with our 1990 Six speed. At this time I can not detect any leaks and the on board diagnostic systems has not flagged any problems.

Most of the time the brakes and brake pedal work great. However, while applying the brake it will suddenly fade down about an inch and you can feel the car not stopping. A quick double pump and they are fine again.

The master cylinder is at the appropriate level and the pads are within normal limits. The car has 140,000 plus miles and has never had a deep bleed of the whole system. It does not pull, vibrate, or make any noise. The e-brake works perfect.

The anti-lock mechanism makes all the normal noises in reverse and shows no signs of leakage. The problem has persisted now for several months. It seems no worse and no better.

Any ideas?
 

c4c5specialist

Technical Advisor
Joined
May 29, 2001
Messages
3,682
Location
New Haven, Ct. USA
Corvette
Nope, but someday.
Questions??

Hi there Chris,
My first question is what kind of brake pads are on the car??
You see, brake fade is not usually air in the system, as this will show itself at all times.
Brake fade, by definition, is the feeling of less than adequate stopping power, due to outgassing of brake pads, causing gas interference between the surface of the pads, and the rotors.
In regular terms, basically, when the pads get hot, they release gases, that under mild use, vent off, not creating any problems. However, under severe braking, the gases that are released, actually sit between the pad, and the rotor, therefore, you feel not as much braking power. When you release the brake pedal, you remove the pad from the rotor surface, and the gases ventilate. The slot that is put in the center of the pads help to release the gases, however, if there is a lower quality pad, that does not have the slots in the center, there could be part of the problem.
Also, if the pad is not as high of quality, it could also produce more gases under lower temperatures, which also could show as brake fade as well.
This is what I suggest first, check your pads, is there a slot in the center, and what color is the backing plate, where is sits against the caliper??
Please answer these questions, and then we can proceed.
Best to you, c4c5
 

69MyWay

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Messages
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Location
Auburndale, Florida
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1969 Killer Shark
Good place to start looking.

This item is on the agenda for the coming weekend. I will let you know what I see there.

The only concern I have is that it is doing the fading thing under regular braking.

I believe the pads are genuine G.M. but have many miles on them. They are still in spec (wear indicator). It won't hurt to put a new set on anyway.

Thanks again. I appreciate and value your input.
 

Viper 10

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Joined
May 5, 2001
Messages
89
Location
USA
Corvette
'85 Light Bronze C4, '96 Blue/White GTS Coupe
You might want to check your brake lines for wear. This sounds like it could be solved with replacing stock lines with stainless steel lines.

E-brake should not be an issue because it is on the rear rotor and is mechanical. Your problems are probably with the fronts that take 80% of the load. JMO :D

Good luck.

Brad
 

69MyWay

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Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
I would not doubt the soft lines are in bad shape. The car has a whole lot of miles on it now. They look pretty rough on the outside (dried and cracked).

In the past, bad hoses have caused my cars to pull under braking or lock up one or the other caliper. This thing stops straight and has no pull. I guess that would indicate both lines have equal wear.

Based on the two replys, I will replace the pads and either upgrade to braded SS line, or at the least replace with the OEM rubber lines. I will drain the system and replace the fluid. I will have to read up on the procedure first to avoid any damage to the ABS unit.

It that does not cure it, I am thinking the master cylinder might have something wrong.

Better get the old Visa card ready.
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Broke Brakes

I had the same problem about 2 weeks ago.note I had all the pads replaced 4 months ago. Bled system
(orig BROWN icky fluid) and it was still there, I wanted to change my master 115K miles (just on principal) and lo and behold a small leak on the rear of the master.. Bada bing no fade brakes.

my .02

Mike
 

69MyWay

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Jul 3, 2001
Messages
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Location
Auburndale, Florida
Corvette
1969 Killer Shark
master cylinder

Thanks Mike.

This weekend has not gone as planned. Just finished a retrofit 134 A/C on my sister in laws van to get her back to Texas on Monday. I also let my other Corvette project distract me. Who would have thought it to take all day to build a pair of exhaust tip hole fillers?

The more I think about it, I believe it has to be the master cylinder. I am going to reverse my repair order and start with that and work my way down. Of course, I will drain the fluid at this time. After 140K plus miles, it has to be getting a little tired.

Did you run into anything unusual considering the ABS system during the drain and fill?
 
A

ArtZR1991

Guest
Chris,

The good news it that it is almost a dead cinch to be the fluid, or more likely the cylinder or the pads. As the pads wear down, a lot more voulme of fluid goes to the calipers, and if one has a wear ridge on it, it is being forced to mobe beyond that. So whatever you do, do the pads as well, because you are going to need that anyway, and there is a good chance that is it. Sort of the same problem the master cylinder might have, but in the caliper. But the new pad will move the piston back up into a safe area.

Another trick from an old Jag owner. Some may disagree here, but on any high performance car, the rotors should never be "turned down" to smooth them for new pads. Jag recommends replacing them. The turning down removes a lot of metal, more than several sets of pads would, and warping is the inevitable result. The much better solution, since rotors can outlast several sets of pads, is to replace the pads, drive carefully for 300 mi or more, allowing the new mads to match up to the rotors. Good as new, and much more resistive to warping. I haven't allowed my rotors to be "turned" for 20 years, since I ruined a set on a 1979 BMW. I have done this on several Jags, the BMW aggain, my Cobra, and an earlier Vette. Just a suggestion. Most brake guys will agree, presuming they are not losing income from the turning, and provided the rotors are worn, but not damaged. From your description, yours are worn, and certainly not damaged.

Hope this helps.
 

Viper 10

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May 5, 2001
Messages
89
Location
USA
Corvette
'85 Light Bronze C4, '96 Blue/White GTS Coupe
Art:

Good advice when it applies to high performance rotors. I have seen OE rotors warp like crazy under aggressive driving, and Corvette rotors are notorious for it. So you might not have any choice in turning the rotors, unless you replace them. Racing rotors don't have this problem because they cool more efficiently and are made of harder materials (but you have to pay more for them too).

I might add that if you plan to use a set of high performance or racing pads, the manufacturer will recommend that you bed them correctly. This is basically going through a routine of stopping your car from various speeds, multiple times in order to heat them and harden (or cure) them. If this doesn't occur, you will eat your pads much more quickly than expected.

Be cautious of using a racing pad, because they traditionally perform very poorly when cold, and need to be brought to a certain operating temperature before they perform.

I hope that this helps. Good luck.

Brad
 

GiDvEtTe84

Well-known member
Joined
May 8, 2001
Messages
67
Location
Maurice, LA
Corvette
1984 Cross-fire Corvette Coupe
Sometimes master cylinders will bleed off internally. This will cause your pedal to fade and slowly lower to the floor. It is almost undetectable because there are no leaks. This happened to me. Just a thought. :)
 

69MyWay

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Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
fixed

I decided to go with the old shotgun approach.

Just finished replacing:
1. pads (old ones were only about 80% worn).
2. Master Cylinder
3. front rubber lines
4. Compete fluid drain and fill.

Roters are in spec, good surface, and rear brake hoses looked fine. Front hoses were showing exterior signes of wear and cracking.

Total price--$130.00

I went with a reman master cylinder (lifetime gurantee), Autozone brake pads (lifetime) and Napa hoses. Just used the DOT 3 fluid.

So far so good. She goes Autocrossing the end of this month. That will be the true test. By then they should be broken in.

Thanks for all the suggestions.

Chris
 

Ken

Gone but not forgotten
Joined
Jan 30, 2001
Messages
8,237
Location
Hermosa Beach, CA
Corvette
1987 Z51 Silver Coupe
Brake tip...

This may have nothing to do with your brake question Chris, but I heard this tip at our monthly club meeting this morning.

It came from a Popular Mechanics magazine I think he said, and it involved putting a 2x4 under the brake pedal when you change pads/bleed brakes. I guess you put the 2x4 under the pedal when you bleed the brakes to prevent it from over-extending the piston in the master cylinder so that it doesn't encounter areas it normally wouldn't contact; rough areas that could potentially damage the piston surface and cause loss of pressure.

I had never heard this before, but it seems to make sense. I just thought I'd pass it along. Maybe someone has heard of this and disagrees with it. I'd like to hear.
 

Tom Bryant

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Edgerton, Ohio, United States
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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Brakes

On a somewhat related subject. we always see ads for high performance rotors that have been cryo treated or harder metal ect and they have dimples, cross drilled holes or grooves to vent off the gases which I understand. My question is can these rotors be turned when necessary or will the cutting tool snag on the dimple, hole, or groove and break the tool?

Tom
 
G

GS796

Guest
Well, all of the above diagnoses are good, but from my experience when the pedal falls and then pumps back up it's the master cylinder leaking internally and needs to be replaced.
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
Master Cylinder

GS796,

I agree with you 100%. I am sure that was the root of the problem. However, it did not hurt to drain all the old fluid and replace the soft lines. They were showing excessive signs of cracking on the outside. I really did not need to replace the pads, I wrote it backwards in the last post. There was at least 80% remaining (20% wear).

The price was much cheaper than expected on the MC at the local parts store.

I did not turn the rotors as there has been no vibration in the pedal and the surface looks even, smooth, and they were in specs.

We will see though after she runs Solo II on the 29th.
 

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