Hard brake pedal solution, finally!!
Race Director
Joined: Jun 2004
Posts: 13,960
Likes: 707
From: WI
94 auto. A little while after doing the "C5 Brake-Upgrade", my brakes were amazing. Have been for a couple of years now, but over the winter, I installed an LT4 Hotcam.
After being down for a couple of months, I get it running, and now my pedal is hard as a rock.
I started reading this thread a little at a time. Now I finally finished it and I'm going to attempt the "Code Clearing" and "ABS Stimulation" techniques described above. (It only took 4 years and 350+ posts to start seeing affirmative answers that seem to be the cure for more than one person. (Hopefully, I will be on that list, too.)
Tomorrow, (Saturday), I'll give it a good thrashing and relay the results back here.
After being down for a couple of months, I get it running, and now my pedal is hard as a rock.
I started reading this thread a little at a time. Now I finally finished it and I'm going to attempt the "Code Clearing" and "ABS Stimulation" techniques described above. (It only took 4 years and 350+ posts to start seeing affirmative answers that seem to be the cure for more than one person. (Hopefully, I will be on that list, too.)
Tomorrow, (Saturday), I'll give it a good thrashing and relay the results back here.
Re exercising the ABS, I still think braking improvement from that would be caused by rebedding the pads. Someone could test this by bedding the pads THEN exercising the ABS.
Question, what year did the "Electro/mechanical module" start (post 353)? Mine has nothing that pushes back against my foot for braking.
Burning Brakes
Joined: Aug 2010
Posts: 951
Likes: 3
From: Placerville CA
Just an update: my brakes still require a lot of pressure to reach lockup/ABS activation, so based on some posts here and with high hopes I pulled the fuse for the ABS/ASR systems. Result: no difference at all. Only a "service ASR" light on the display.
Maybe it's just the nature of this beast.
Maybe it's just the nature of this beast.
7th Gear
Joined: Feb 2006
Posts: 7
Likes: 1
From: Richmond TX
another c4 brake issue....
I am sorry if this problem has been previously addressed and if so please point me in the right direction. My 1991 now has the best brakes it has ever had...but....pedal drops to the floor. New rotors, pads, ss lines, booster, now on 3rd oem master. The brake was high and hard until m/c replacement. I finally got power brakes and they work great...except for the pedal issue. This car has been bled, power bled, gravity bled and bled again. I have done everything I know and my mechanic is losing his hair over this. Any suggestions are appreciated.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
I myself would look at this as a new problem from square 1.
Did you bench bleed the master before you installed it?
If not, it may be impossible to clear it while you are trying to bleed the system.
If you did bench bleed, then the master could be bad. I would repalce the master, bench bleed and go from there.
Generally, if the master is OK and it was bench bleed, air in the system would probably give it a soft pedal but usually would not go to the floor.
Did you bench bleed the master before you installed it?
If not, it may be impossible to clear it while you are trying to bleed the system.
If you did bench bleed, then the master could be bad. I would repalce the master, bench bleed and go from there.
Generally, if the master is OK and it was bench bleed, air in the system would probably give it a soft pedal but usually would not go to the floor.
Last edited by pcolt94; Apr 8, 2012 at 12:19 PM.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Im wondering if GM didnt have a high defect rate with these master cylinders....Ive spoe to another member at length today who is very adept with these cars.
What solved his spongy problem (he tried everythign too) was to install a M/C off an LS1 Camaro. One fitting has to be changed, the well in the hood will need a very slight shaving to clear the reservoir. Said to double check the rod length as the rod is just a slight tad longer than the Vettes, may need a slight shimming (20 thou?)
Said it fixed his problem completely.
SO, going on that Im assuming these seals may have a high defect rate and may be bypassing internally giving a crappy pedal feel?
Wonder if I wasted coin on speedbleeders today. Ill try anything at this point.
What solved his spongy problem (he tried everythign too) was to install a M/C off an LS1 Camaro. One fitting has to be changed, the well in the hood will need a very slight shaving to clear the reservoir. Said to double check the rod length as the rod is just a slight tad longer than the Vettes, may need a slight shimming (20 thou?)
Said it fixed his problem completely.
SO, going on that Im assuming these seals may have a high defect rate and may be bypassing internally giving a crappy pedal feel?
Wonder if I wasted coin on speedbleeders today. Ill try anything at this point.
Spongy brakes on C4's mostly occur because of the master cylinder design. The MC bleeder is not at the very top of the cylinder and air can stay at the highest point. Also, bleeding brakes by opening slave cylinders and squirting fluid out is not the best technique because air attempts to go to the highest point in the brake system and it resists moving along with the brake fluid and out the bleeder. A better way to bleed brakes is to connect a hose to the bleeder, open the bleeder and pull a vacuum at the filler on the MC, this way brake fluid moves from the lowest point to the highest point and air bubbles will want to move along with the fluid to the highest point!
Also, the ABS unit has a pump that pulses brake line pressure to the wheels when one or more wheel sensors indicate that a wheel has stopped rotating. Early C4's had all the wheels pulsed, I believe later C4's only had the stopped wheel pulsed which is the best ABS system.
Pro
Joined: Jan 2004
Posts: 707
Likes: 0
From: Syracuse Utah
Has anyone just removed that huge chunk of metal called the ABS? Probably weights about 35 pounds. Possibly safer too. I hate it when you have to hit the brakes hard and all the sudden the abs kicks in and the car lunges forward and you just about have a cow trying to stop.
Burning Brakes
Joined: Aug 2010
Posts: 951
Likes: 3
From: Placerville CA
Has anyone just removed that huge chunk of metal called the ABS? Probably weights about 35 pounds. Possibly safer too. I hate it when you have to hit the brakes hard and all the sudden the abs kicks in and the car lunges forward and you just about have a cow trying to stop.
But in a car? On the road? You've got to be kidding. It's always better to have steerable -- albeit reduced -- braking than to be sliding out of control into the thing you are braking for.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Is this intended as a joke? There are a very few occasions when you can have more control of a vehicle without ABS, and they are mostly limited to 1) on a motorcycle; and 2) when that motorcycle is on dirt. Sometimes you want to lock up the rear wheel to get it to slide out for faster cornering.
But in a car? On the road? You've got to be kidding. It's always better to have steerable -- albeit reduced -- braking than to be sliding out of control into the thing you are braking for.
But in a car? On the road? You've got to be kidding. It's always better to have steerable -- albeit reduced -- braking than to be sliding out of control into the thing you are braking for.
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Pro
Joined: Jan 2004
Posts: 707
Likes: 0
From: Syracuse Utah
Is this intended as a joke? There are a very few occasions when you can have more control of a vehicle without ABS, and they are mostly limited to 1) on a motorcycle; and 2) when that motorcycle is on dirt. Sometimes you want to lock up the rear wheel to get it to slide out for faster cornering.
But in a car? On the road? You've got to be kidding. It's always better to have steerable -- albeit reduced -- braking than to be sliding out of control into the thing you are braking for.
But in a car? On the road? You've got to be kidding. It's always better to have steerable -- albeit reduced -- braking than to be sliding out of control into the thing you are braking for.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
On the Corvette ABS the two front wheels are independent. The rear wheels are pulsed together on the early years and later on were independent. I don't know when the change was made.
I have heard that non-ABS cars are better in snow because the locked up tires act as snow plows. Maybe you could disable the ABS in the winter?
I have heard that non-ABS cars are better in snow because the locked up tires act as snow plows. Maybe you could disable the ABS in the winter?
Race Director
Joined: Jun 2004
Posts: 13,960
Likes: 707
From: WI
It's removed on mine, search my threads as I made one about it.
When the tire skids in ABS or through a slide you lose a considerable (30%) amount of braking. If you're into the ABS you are actually hurting your stopping distance.
Weight was around 20 lbs. See the weight sticky in gen.
When the tire skids in ABS or through a slide you lose a considerable (30%) amount of braking. If you're into the ABS you are actually hurting your stopping distance.
Weight was around 20 lbs. See the weight sticky in gen.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Does anyone know if and where the GM or delco part number is located on a master cylinder. I am starting to think the problem with the high pedal pressure on mine is all master cylinder related. The difference between a 92 MC and a 91 is 25% if I got a 92 MC when the 91 was replaced it would explain a bunch. I got a NAPA rebuilt and they do list 2 different part #s but if mis boxed would explain a lot.
Pro
Joined: Feb 2012
Posts: 668
Likes: 21
I got a head ache. I just read all of this because my 92 has the hard petal syndrome too. The only thing I learned was a new to me thing " speed bleeders". Now go ahead a teach me how to fix the bleepen hard petal. It's the only thing I don't like about the car. I really don't feel to safe with it. My 79 vette stops better.
Drifting
Joined: Sep 2005
Posts: 1,867
Likes: 3
From: Pasadena Maryland
I started a thread on Brakes and got a link to this thread.
Just wanted to know if anyone used a pressure gage on the caliper?
I did yesterday and saw 900 PSI engine off, booster vacuum used up and 1400 with the engine running. Might not have got all the air out, but pedal felt good.
I cannot get the anti-locks to activate on dry road. at a 10 MPH roll I can jump on the brakes and roll 2 or 3 feet before it stops.
93 Coupe(Ruby) with standard brakes, 12" front rotors.
Just wanted to know if anyone used a pressure gage on the caliper?
I did yesterday and saw 900 PSI engine off, booster vacuum used up and 1400 with the engine running. Might not have got all the air out, but pedal felt good.
I cannot get the anti-locks to activate on dry road. at a 10 MPH roll I can jump on the brakes and roll 2 or 3 feet before it stops.
93 Coupe(Ruby) with standard brakes, 12" front rotors.
Racer
Joined: Feb 2012
Posts: 319
Likes: 0
From: Daytona Beach Florida
I have the same problem... I put 3 quarts through it while vacuum bleeding and can't get them to lock up... I now believe its the rear brakes that are not pulling/stopping there fair share... Don't get me wrong the car does stop well... But not what I would expect...
I read the link posted and I'm starting to believe the issue may be in the ABS unit diverting pressure...
Did you test pressure on the rear brakes??
I read the link posted and I'm starting to believe the issue may be in the ABS unit diverting pressure...
Did you test pressure on the rear brakes??
Drifting
Joined: Sep 2005
Posts: 1,867
Likes: 3
From: Pasadena Maryland
No, I did not. You have to remove the Parking Brake cable and that has a procedure for the self adjuster. They do work though, my neighbor sat in the car and pushed on the brake pedal with the engine off and all 4 rotors would lock and release just fine.
I read that too, I have a TECH1 scanner and will check that out?
I also read that when you bleed the brakes you have to bleed the line that feeds the ABS unit. The line is not under pressure, it just feeds fluid into the unit. So if there is air in that line, it will get pushed through the ABS unit. But I don't think that is my issue.
I read that too, I have a TECH1 scanner and will check that out?
I also read that when you bleed the brakes you have to bleed the line that feeds the ABS unit. The line is not under pressure, it just feeds fluid into the unit. So if there is air in that line, it will get pushed through the ABS unit. But I don't think that is my issue.
Last edited by kalister1; Jun 18, 2012 at 11:22 AM.
Racer
Joined: Feb 2012
Posts: 319
Likes: 0
From: Daytona Beach Florida
No, I did not. You have to remove the Parking Brake cable and that has a procedure for the self adjuster. They do work though, my neighbor sat in the car and pushed on the brake pedal with the engine off and all 4 rotors would lock and release just fine.
I read that too, I have a TECH1 scanner and will check that out?
I also read that when you bleed the brakes you have to bleed the line that feeds the ABS unit. The line is not under pressure, it just feeds fluid into the unit. So if there is air in that line, it will get pushed through the ABS unit. But I don't think that is my issue.
I read that too, I have a TECH1 scanner and will check that out?
I also read that when you bleed the brakes you have to bleed the line that feeds the ABS unit. The line is not under pressure, it just feeds fluid into the unit. So if there is air in that line, it will get pushed through the ABS unit. But I don't think that is my issue.
Seeing the above mentioned action and knowing On the front the abs cycles the wheels left and right and the rear on there separate circuit(no left and right on the rear).. I leads me to believe there has to be an issue with the rear circuit... I leaning toward valve on the rear circuit isn't closing all the way and diverting some of the pressure to the rear wheels... That would explain in my belief why the rear brakes do not lock up and why the rear brakes don't lock and release when I do a panic stop on loose pavement...