Fastmax32168

I know I am not the only guy that has complained of a hard brake pedal on a late model C4. My 94 brakes have always been terrible, In spite of upgrades over time of new rotors, quality pads, stainless lines, J55 upgrade, and a new M cylinder. The brakes still sucked. They always felt like they had no boost even though the unit checked out and worked normally. I finally broke down and decided to let someone else work on my car (I hate doing that you know) by taking it to Corvette Masters in Orlando.
With the ability to read the ABS unit it turned out that there were 3 codes stored in my computer. Even though the light came on when you started the car, the ABS went through the self check and then the light went off, ( in other words it acted as it should) the 3 codes that were in it were somehow preventing my brakes from working normally. They cleared the codes, went through the diagnostics on the unit to insure it was OK, and voila! I have brakes now.
I know I have seen lots of guys complain about this, and I would have never suspected the solution could have been so simple. So if your brake pedal requires way too much effort to stop the car and there seems to be no reasonable solution to it, I would strongly reccomend you have someone look into the ABS units subconscious mind and perform the necessary brain surgery.
Thank you Corvette Masters!
Roy

92LRC

I've had a similar problem with my 92. I changed out the lines to Stainless and it's still hard. I was getting ready to take a look at the booster and maybe replace it but now I'm going to have to check the system for codes.

Thanks for the post.

corvettedan22

I dont think that will effect my 85

Da Mail Man

....interesting..i have an 88 and have been chasing crappy "fred flintstone" brakes for 2 years after multiple bleedings, flushings, m/c change-out, s/s flex lines, new pads, new rotors, and new ck valve, where the booster cks good and holds vacuum..........is there wa way to "clear" the codes on the 88 if it so applies?....

CentralCoaster

You may be on to something big here. Some members say it's fine, others say theirs are unbelievably bad.

Another guy with bad brakes pulled the fuse on his ABS and said it felt like a whole new car.



Pulling the fuse could be a quick check to see if it is the ABS, before going in for a scan.

CentralCoaster

Do your brakes feel stiff? Early brakes even with ABS haven't had many issues reported. Mine always had great bite. Did the ABS module change significantly at some point?

Da Mail Man

.......would not pulling the battery cable to exactly the same thing?...

CentralCoaster

And better yet, what are these codes, what caused them, and how do you prevent them from coming back?

Fastmax32168

I had tried that on the advice of Gordon Killebrew but all it did was make the light come on and stay on, it didnt fix the problem.
As best as I can read my copy the codes stored were:
C0063 Valve relay circuit malfunction
C0065 Adjuster circuit assembly malfunction
c0023? Low brake fluid.

Roy

Fastmax32168

You would think so but I have had the cable disconnected many times and it never made any difference.
Roy

steve40th

How did they pull the codes?

coupeguy2001

86E, new master, new front calipers, new booster, new front pads.
the brakes were always a sore spot with me, and I gradually figured that the booster was under engineered for the car.
I was planning on maybe stepping up to a dual piston caliper.
Now, I may play with the electronics a little to see if it's something else.
Come to think of it, my rear pads seem to last forever.
Maybe the ABS has sufficiently shut off the fluid to the rears, and that's why it is hard to stop, and the pads last a long time.
Sigh.......another area that The General kept a secret that I have to unlock.........

pcolt94

No. Unlike the PCM/ECM and CCM codes, when the battery cable is disconnected it will not clear the codes in the EBTCM. The brake computer (behind drivers seat) stores its own codes and you have to use the on board diagnostics going in to module 9 and use sub module 9.7 to clear the codes. Or use a tech 1 or tech 2 can do it to.

I believe this information is good for 92-94, possibly 95, and not sure about 96 since it is OBDII.

I’m not arguing with success, but a code is an indication of a fault or problem. The code can always be cleared but if the problem is not fixed, the code will be reset. The code is used to lead you to a problem area so the trouble can be repaired. So I don’t understand how clearing a code can make a brake system or for that mater, anything work better as if it was repaired.

I would need a real good technical explanation, that would be believable to me. Like the valves in the pump were restricting fluid flow with out the pump running. Pulling the fuse or power to it should disable any solenoid action in the ABS pump.

I happen to know the guys at Corvette Masters and they are a knowledgeable group also that helped me out once and have spoke with on several occasions. They use a tech 2 which they probably used to clear the codes.

I sure would like to hear the rest of the story if there is one.

CentralCoaster

Trust me the brake hardware is completely capable. I was driving around on untouched 50k mile stock parts and I was impressed. When I started putting on crap replacement pads, less impressed. The booster is fine if it works properly. Only fundamental difference between my brakes and yours is the ABS. A DRM bias spring will increase rear pressure too, this helps.

CentralCoaster

Damn dude how many computers you got in that thing? 1 is too many for me.

CentralCoaster

What the original post implies, is that the ABS will function differently with latent codes in the system. A "limp home" mode of sorts.

Fastmax32168

I worry about exactly that, George did tell me that they went through all of the diagnostics and couldnt find a problem. He also kept the car an extra day and drove it around trying to make sure they wouldnt reset.
I am not sure he had a technical explanation for it, I think if he did he would have given it to me. It was simply the last possible place to look for a problem given everything else I had done to the car.
I assume something was simply stuck the wrong direction inside of that thing. But you know what happens when you assume things.....
Roy

Wildride

Although I don't understand how clearing the codes without addressing the underlying problems would correct any "Hard Brake" symptoms, if it works; GREAT!

It isn't necessary to use a Tech-1 scanner to clear the codes on OBD-I cars. They can be cleared by using a U shaped piece of wire (paper clip) inserted into the "A" and "H" pins of the ALDL socket.

1. Turn the ignition "Off"

2. Ground pin "H" to pin "A"

3. Turn the ignition "ON"

4. Wait for the code to begin flashing.

5. Unground pin "H" from pin "A" for at least one second, then reground it. This must be done three (3) times within ten (10) seconds

6. Wait at least 15 seconds before turning the ignition "OFF". The verify that Code 12 is the only code being flashed. If not, the codes haven't been properly cleared and you must repeat the procedure.

The computer will also clear a code if it doesn't reappear after 100 engine on/off cycles.

pcolt94

The 94 has three. (as if he didn’t know). That is one reason I steer clear of a C5. I think they use 3 computers just to move the seats.

I am familiar with the limp home mode for the engine, but not for the brake system. If I should come across it reading the bible (FSM), I will sure tell all.

I have a vested interest in strange brake problems, for I fought one myself on my C4. It was just poor braking, replaced it all except the brake computer and booster which performed fine. Installed the J55 system and finally got good brakes but wish I could have made the original system work normal and safe. So I’m always interested in any new information that might shed light on the illusive brake problems of the early 90 C4s with ABS.

FASTMAX - Thanks for the reply and best of luck on your good brakes.

89 Bob L

Does this informationapply to older models such as an 89?