Hard Brake Pedal
Thread Starter
Pro
Joined: Apr 2008
Posts: 586
Likes: 119
From: Saint Cloud, FL
Hard Brake Pedal
Here's the symptom(s): With foot on pedal and engine running pedal feels fine. If I shut off the engine with foot on pedal the pedal immediately goes hard. Also I seem to notice that sometimes the ABS does not make the self test noise in which case I have a hard brake pedal when driving. If the self-test occurs the pedal seems softer.
Any ideas?
1994 coupe
Any ideas?
1994 coupe
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
When shutting the engine off you should be able to get 3 soft pedals before it get hard, and a vacuum sound as you depress the pedal. If you don’t get that, the booster sounds like it has a leak or the check valve is bad.
The ABS check sounds like another problem.
The ABS check sounds like another problem.
Thread Starter
Pro
Joined: Apr 2008
Posts: 586
Likes: 119
From: Saint Cloud, FL
Hmmmm... I don't hear any of the typical leak noises from the pedal inside the car when engine is running. Must be more likely the check valve then.
I was told that original owner had replaced the booster and it was evidenced by a non-functioning cruise control (brake switch adjustment) and mal-functioning sports seats (from seat removal, air pump hose disconnected and lft/right harness swapped). OO was deceased at time of purchase.
I was told that original owner had replaced the booster and it was evidenced by a non-functioning cruise control (brake switch adjustment) and mal-functioning sports seats (from seat removal, air pump hose disconnected and lft/right harness swapped). OO was deceased at time of purchase.
Safety Car
Joined: Jul 2004
Posts: 3,845
Likes: 30
Here's the symptom(s): With foot on pedal and engine running pedal feels fine. If I shut off the engine with foot on pedal the pedal immediately goes hard. Also I seem to notice that sometimes the ABS does not make the self test noise in which case I have a hard brake pedal when driving. If the self-test occurs the pedal seems softer.
Any ideas?
1994 coupe
Any ideas?
1994 coupe
...sound like it could be the vacuum booster hose or CHECK VALVE.
Thread Starter
Pro
Joined: Apr 2008
Posts: 586
Likes: 119
From: Saint Cloud, FL
I found the check-valve (12521454) several places but it seems the grommet (14067550) has been discontinued. Do you suppose you can swap out just the valve? I'm assuming here it's just the valve, and they're cheap.
Safety Car
Joined: Jul 2004
Posts: 3,845
Likes: 30
...just pull out the valve CAREFULLY and then inspect the grommet for tears, etc...the valve can be replaced by itself.....
Racer
Joined: Mar 2008
Posts: 254
Likes: 0
From: Perth W.A
So i tried it with my 90 c4, well i only got 1 and a bit presses before it went hard!
and the only time i hear the vacuum sound is when the engine is running and i push the pedal!
I thought this to be strange as it's going against what other are saying should be the case!
So i tried my brakes in a 98 commodore and (with engine off) i got 1 press before pedal went hard, and vacuum noise when pressing it when engine on! (same as the vette)
also i tried a brand new ute and the same thing happenen!
So its seems that a hard pedal should result after 1 press with engine off! and the vacuum(hissing noise) is normal while engine on!
After saying this my c4 pedal needs to be pushed about 1/3 of it's travel before begining to brake! and even then it requires some effort to pull the car up! my guess is it needs bleeding!
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Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
I have been told this by another vette owner on here!
So i tried it with my 90 c4, well i only got 1 and a bit presses before it went hard!
and the only time i hear the vacuum sound is when the engine is running and i push the pedal!
I thought this to be strange as it's going against what other are saying should be the case!
So i tried my brakes in a 98 commodore and (with engine off) i got 1 press before pedal went hard, and vacuum noise when pressing it when engine on! (same as the vette)
also i tried a brand new ute and the same thing happenen!
So its seems that a hard pedal should result after 1 press with engine off! and the vacuum(hissing noise) is normal while engine on!
After saying this my c4 pedal needs to be pushed about 1/3 of it's travel before begining to brake! and even then it requires some effort to pull the car up! my guess is it needs bleeding!
So i tried it with my 90 c4, well i only got 1 and a bit presses before it went hard!
and the only time i hear the vacuum sound is when the engine is running and i push the pedal!
I thought this to be strange as it's going against what other are saying should be the case!
So i tried my brakes in a 98 commodore and (with engine off) i got 1 press before pedal went hard, and vacuum noise when pressing it when engine on! (same as the vette)
also i tried a brand new ute and the same thing happenen!
So its seems that a hard pedal should result after 1 press with engine off! and the vacuum(hissing noise) is normal while engine on!
After saying this my c4 pedal needs to be pushed about 1/3 of it's travel before begining to brake! and even then it requires some effort to pull the car up! my guess is it needs bleeding!
This feature was built into the brake systems for safety where if the engine died you would not loose you ability to stop the car immediately and would have a reserve of vacuum to give you 2-3 good pumps of braking. This is why there is a check valve to hold the vacuum in the booster. With every pump the pedal does get harder until you deplete the reserve vacuum at pump 4 or so depending on depth of pedal travel and other specific factors.
When the engine runs and you push the brake you can hear a whoosh or vacuum being released. However there is a difference in sound between a normal sound of a booster and one with a vacuum leak from the diaphragm.
If you are experiencing something much different perhaps there is a problem.
Racer
Joined: Mar 2008
Posts: 254
Likes: 0
From: Perth W.A
pcolt94: Okay i have never really got into the braking side of things, i have preferred to have a professional take care of these things! not knowing what i am doing is not that safe, and brakes are very important!
The only reason i have begun to investigate the vettes brakes, is because they don't feel good at all and i know they should be better, so it got me interested in comparing them with other car's brake systems!
And as you say that the 3x pedal thing, before it loses vacuum is normal, well i have found that every system i have checked with concern to engine off and the amount of times the pedal can be depressed, is 1 and a bit! I have checked the vette, a 10 year old car and a new car! all the same!
So if it is common knowledge between members on this forum that it should be 3 presses, then i'm stumped!
I'm not saying that they are all wrong, but maybe, just maybe their cars have a stuffed check valve/booster?
My pedal with engine on is definately not hard, it feels ok just doesn't pull the car up very quickly unless a descent amount of pedal effort is used!
The only reason i have begun to investigate the vettes brakes, is because they don't feel good at all and i know they should be better, so it got me interested in comparing them with other car's brake systems!
And as you say that the 3x pedal thing, before it loses vacuum is normal, well i have found that every system i have checked with concern to engine off and the amount of times the pedal can be depressed, is 1 and a bit! I have checked the vette, a 10 year old car and a new car! all the same!
So if it is common knowledge between members on this forum that it should be 3 presses, then i'm stumped!
I'm not saying that they are all wrong, but maybe, just maybe their cars have a stuffed check valve/booster?
My pedal with engine on is definately not hard, it feels ok just doesn't pull the car up very quickly unless a descent amount of pedal effort is used!
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
Phantom, If you depress the pedal as far as it will go with the engine off.......then you may get less pumps.
Others may just pump it a bit and get three pumps. but if you are pumping iron at that gym and then pushing that pedal....that may explain the difference.
I'm just guessing.
Others may just pump it a bit and get three pumps. but if you are pumping iron at that gym and then pushing that pedal....that may explain the difference.
I'm just guessing.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
If you don’t know by now than C4s have brake issues. Getting good braking and stopping power can be a problem. After replacing many things in my own car and upgrading the brake system seems like the pad material is a bigger factor than other cars. Last pad I went with was the Hawk HPS which did not work out as I expected although others like them. I ended up with (month ago) Brembo pads which really work well for me. I can really stop quick get rubber squeal and activate the ABS.
If you want to bleed the brakes fine or even replace the fluid. But air in a system will really give you a sponge feel. It never helped me because I never had air. My solution was to find the right or better pads.
Racer
Joined: Mar 2008
Posts: 254
Likes: 0
From: Perth W.A
jhammons01: LOL yes i am talking about full depresses of the pedal!
pcolt97: yes i have come to learn that the brakes aren't as good as had expected(especially for a sports car)
I too think the pedal and rod adjustment seems fine! and it doesn't seem spongy, i am guessing the Previous owner used cheapish pads and/or just haven't bedded in properly!
In Australia on my other cars i use Bendix!, they seem to be a good pad, not too cheap, not too $$$$
I will try to source some to fit the vette brakes!
thanks for your help
pcolt97: yes i have come to learn that the brakes aren't as good as had expected(especially for a sports car)
I too think the pedal and rod adjustment seems fine! and it doesn't seem spongy, i am guessing the Previous owner used cheapish pads and/or just haven't bedded in properly!
In Australia on my other cars i use Bendix!, they seem to be a good pad, not too cheap, not too $$$$
I will try to source some to fit the vette brakes!
thanks for your help
Melting Slicks
Joined: Jul 1999
Posts: 3,214
Likes: 101
From: Decatur, Alabama
Hard pedal and hissing from the brake pedal area is FOR SURE signs of a bad booster. But to go a little further, taking away the hissing part, how do identify a bad master cylinder vs booster. I have heard othat pump the brakes with motor off, hold down pedal then start engine, if booster is good then pedal should THEN depress further as your foot is still holding pressure. Also, anyone have a pic they can post of the booster valve your talking about replacing (and the discontinued grommet)? thx!
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
What's "ute"?
There is a rod adjustment that needs to be made when replacing the booster. If out of adjustment you end up with what you describe.
Racer
Joined: Sep 2002
Posts: 337
Likes: 2
From: New Orleans La
Hard brake pedal/very little brakes!
I jumped in my 93 C4 and to my surprise I could hardly come to a stop.
I had to press very hard to get it to slow to a stop.
Is this a booster problem?
Thanks
Herb
I had to press very hard to get it to slow to a stop.
Is this a booster problem?
Thanks
Herb
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
For a '93, and if it happened over night......there is a ABS computer reset technique that I would look at primarily.
I don't know how to do it as I have an '84....but there are many threads on the topic.
ABS Codes....or something like that.
I don't know how to do it as I have an '84....but there are many threads on the topic.
ABS Codes....or something like that.
