Hard pedal with engine off; soft after starting - Chevelle Tech
Chevelle Tech join team chevelle as a supporting member  
Chevelle Parts at SS396.com      
GROUND UP & SS396.com         
Official Sponsor of Team Chevelle
     

Auto Insurance

Chevelles.com is the premier Chevrolet Chevelle Forum on the internet. Registered Users do not see the above ads.
Brakes, Suspension & Steering Conversion questions & more.

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old Mar 25th, 12, 1:41 PM
larrygk larrygk is offline
Tech Team
Larry
 
Join Date: Jun 2011
Location: San Diego
Posts: 459
Default Hard pedal with engine off; soft after starting

Hey guys before I dive into the obvious vacuum test wanted to get any suggestions on this.
Situation: With engine off, the pedal is very firm with little travel. Once engine is turned on pedal goes down dramatically and of course triggers the Brake Warning light on the dash.

What was done previous to resto: the completely stock power brake system was not touched while taking the car apart. Nothing was taken apart except of course removing the vacuum line from the booster and plugging up the hole to protect it while painting, etc. Brakes were bled and new shoes in rear were installed. Front pads were fine.

I will check the vacuum line which is new and appears to be fine, but if it is any hint the engine runs perfectly which of course supplies vacuum to other places (e.g. distributor).
__________________
Larry
San Diego, CA
1969 SS396
All Numbers Matching
L35 TH400 3.07
Factory Air, am/fm Stereo, PS, PB Disc/Drums
Factory SS Package
Dover White, Black Interior, Bench Seat
Restored to show condition-SOLD
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2  
Old Mar 25th, 12, 2:04 PM
65 Skylark 65 Skylark is offline
Tech Team
Bill
 
Join Date: Aug 2011
Location: Southern WI
Posts: 793
Default Re: Hard pedal with engine off; soft after starting

That's pretty much they way they're supposed to work with the exception of the pedal going down that far. Sounds like you still have air in the lines and need to bleed them again.
__________________
Bill
_____________________________________________
'65 Buick Skylark,
355 sbc, 10.2 comp, Trick Flow 195 heads, RPM Air gap, Holley 3310, Bullet 224/230 .483/.485, Hedmans, 200-4R, 10" 2,800, 4.10 12 bolt.....and factory a/c
http://s1085.photobucket.com/albums/...t=Buick007.jpg
Reply With Quote Quick reply to this message
  #3  
Old Mar 25th, 12, 3:10 PM
pnugene pnugene is online now
Team Member
Randy
 
Join Date: Aug 2008
Location: Central Alabama
Posts: 2,807
Default Re: Hard pedal with engine off; soft after starting

Quote:
Originally Posted by 65 Skylark View Post
That's pretty much they way they're supposed to work with the exception of the pedal going down that far. Sounds like you still have air in the lines and need to bleed them again.
I agree you have air in the lines, but you may also have a bad vacuum check valve on the booster or possibly a ruptured booster diaphragm.
__________________
Randy
TC # 5401
67 Project SS Clone

Son, that there pedal on the right, that's
the loud pedal. You stand on that, and
the Rat's gonna Roar.
Reply With Quote Quick reply to this message
  #4  
Old Mar 25th, 12, 3:16 PM
larrygk larrygk is offline
Tech Team
Larry
 
Join Date: Jun 2011
Location: San Diego
Posts: 459
Default Re: Hard pedal with engine off; soft after starting

Thanks Bill and Randy. Will go for the bleed first and hopefully the other 2 components are fine.
One of the most baffling things in a resto, for me anyway,is with certain components and assemblies that worked great before the project, and you did not have to touch them during the resto, all of the sudden, they don't work fine.
__________________
Larry
San Diego, CA
1969 SS396
All Numbers Matching
L35 TH400 3.07
Factory Air, am/fm Stereo, PS, PB Disc/Drums
Factory SS Package
Dover White, Black Interior, Bench Seat
Restored to show condition-SOLD
Reply With Quote Quick reply to this message
  #5  
Old Mar 25th, 12, 3:27 PM
Gary56 Gary56 is offline
Tech Team
Gary
 
Join Date: Dec 2011
Location: Central Oregon
Posts: 342
Default Re: Hard pedal with engine off; soft after starting

Quote:
Originally Posted by larrygk View Post
Thanks Bill and Randy. Will go for the bleed first and hopefully the other 2 components are fine.
One of the most baffling things in a resto, for me anyway,is with certain components and assemblies that worked great before the project, and you did not have to touch them during the resto, all of the sudden, they don't work fine.
First time you have anything work fine the last time you used it, next time not? You've been lucky if so. I don't believe anything on the vac part of the system will trigger your brake light to come on. Got to be a hydraulic issue, air in the line, big external leak, or leaking cup inside the master cylinder. jmo
Reply With Quote Quick reply to this message
  #6  
Old Mar 25th, 12, 3:32 PM
larrygk larrygk is offline
Tech Team
Larry
 
Join Date: Jun 2011
Location: San Diego
Posts: 459
Default Re: Hard pedal with engine off; soft after starting

Gary- Thanks. You may have been clear on this but if not, the brake warning light only comes on when I press the pedal while engine running, in Park. Yeah I agree it most likely is air in the lines. I guess that months of non-use can do that.
__________________
Larry
San Diego, CA
1969 SS396
All Numbers Matching
L35 TH400 3.07
Factory Air, am/fm Stereo, PS, PB Disc/Drums
Factory SS Package
Dover White, Black Interior, Bench Seat
Restored to show condition-SOLD
Reply With Quote Quick reply to this message
  #7  
Old Mar 25th, 12, 11:48 PM
Gary56 Gary56 is offline
Tech Team
Gary
 
Join Date: Dec 2011
Location: Central Oregon
Posts: 342
Default Re: Hard pedal with engine off; soft after starting

Quote:
Originally Posted by larrygk View Post
Gary- Thanks. You may have been clear on this but if not, the brake warning light only comes on when I press the pedal while engine running, in Park. Yeah I agree it most likely is air in the lines. I guess that months of non-use can do that.
You were clear, maybe I was not. There are two only things that I know of that will trigger the dash light. The switch on the emergency brake pedal, and the proportioning valve located below your master cylinder. The proportioning valve has a spool, for lack of a better term, in it with a ground post between the flanges of the spool. If there's a pressure difference between the front and rear brake lines, the spool moves one way or the other, completes the circuit to ground, and the dash light comes on. That pressure difference can originate in the master cylinder itself or anywhere down the lines. No connection to the vacuum booster at all. I suspect it's just to hard for you to overcome the springs in the booster and master cylinder to activate the switch in the proportioning valve with the engine off (no vacuum assist). BTW, did you adjust the brake shoes when you changed them? If the fronts are properly adjusted or disc, and the rears are not anywhere near tight enough, that will probably do it. jmo
Reply With Quote Quick reply to this message
  #8  
Old Mar 26th, 12, 12:44 PM
larrygk larrygk is offline
Tech Team
Larry
 
Join Date: Jun 2011
Location: San Diego
Posts: 459
Default Re: Hard pedal with engine off; soft after starting

Thanks Gary. Appreciate the detail. As far as the brake shoes, I will recheck the new ones we installed as well as adjustment. All these brake related items were "done" when I first got the car to get it road-worthy but that was about a year ago so no surprise that things are not the same. Also thanks for the reminder on the E-brake activation of the light. I tested that the other day and no light so I will check the switch/connection.
Larry
__________________
Larry
San Diego, CA
1969 SS396
All Numbers Matching
L35 TH400 3.07
Factory Air, am/fm Stereo, PS, PB Disc/Drums
Factory SS Package
Dover White, Black Interior, Bench Seat
Restored to show condition-SOLD
Reply With Quote Quick reply to this message
  #9  
Old Mar 26th, 12, 3:07 PM
JWagner JWagner is online now
Gold Member
 
Join Date: Sep 1998
Location: Tucson, AZ, USA
Posts: 7,698
Default Re: Hard pedal with engine off; soft after starting

What Gary said about adjusting the rear bake shoes. Double check that.
Reply With Quote Quick reply to this message
  #10  
Old Mar 26th, 12, 3:12 PM
larrygk larrygk is offline
Tech Team
Larry
 
Join Date: Jun 2011
Location: San Diego
Posts: 459
Default Re: Hard pedal with engine off; soft after starting

Thanks. Been a while since I adjusted shoes. When you turn the tire by hand how much resistance is about right? Right now they turn with shoe scraping noise for sure but it is not difficult to turn them.
__________________
Larry
San Diego, CA
1969 SS396
All Numbers Matching
L35 TH400 3.07
Factory Air, am/fm Stereo, PS, PB Disc/Drums
Factory SS Package
Dover White, Black Interior, Bench Seat
Restored to show condition-SOLD
Reply With Quote Quick reply to this message
  #11  
Old Mar 26th, 12, 4:21 PM
Gary56 Gary56 is offline
Tech Team
Gary
 
Join Date: Dec 2011
Location: Central Oregon
Posts: 342
Default Re: Hard pedal with engine off; soft after starting

I usually adjust them untill I can't turn the wheel, then back them off a couple of clicks. One way to sort of test for adjustment is to pump the brake pedal. If it gets higher and firmer with every pump, that's probably it. If the pedal starts out high, and slowly sinks to the floor, that indicates a leak which can be inside the master cylinder or external down the line. A low spongy pedal indicates air in the system. No biggie. You'll get it figured out.
Reply With Quote Quick reply to this message
  #12  
Old Mar 26th, 12, 5:52 PM
larrygk larrygk is offline
Tech Team
Larry
 
Join Date: Jun 2011
Location: San Diego
Posts: 459
Default Re: Hard pedal with engine off; soft after starting

Yeah it needs to be bled. I adjusted the shoes and in fact they needed it! Brand new, but loose. Started her up and pedal is better but still triggers light. It does not sink to the floor but goes about 2/3's down and stops firmly. So bleeding is next. My gut says it is not the booster or MC but that is the guess for now based on when I got the car.
Also I did order a new booster vacuum check valve to be sure. I thought a check valve only lets (in this case) air in one way, thus the term "check". I blew through the existing one both ways and it freely lets air in both ways.
__________________
Larry
San Diego, CA
1969 SS396
All Numbers Matching
L35 TH400 3.07
Factory Air, am/fm Stereo, PS, PB Disc/Drums
Factory SS Package
Dover White, Black Interior, Bench Seat
Restored to show condition-SOLD
Reply With Quote Quick reply to this message
  #13  
Old Mar 26th, 12, 10:38 PM
pnugene pnugene is online now
Team Member
Randy
 
Join Date: Aug 2008
Location: Central Alabama
Posts: 2,807
Default Re: Hard pedal with engine off; soft after starting

Quote:
Originally Posted by larrygk View Post
Yeah it needs to be bled. I adjusted the shoes and in fact they needed it! Brand new, but loose. Started her up and pedal is better but still triggers light. It does not sink to the floor but goes about 2/3's down and stops firmly. So bleeding is next. My gut says it is not the booster or MC but that is the guess for now based on when I got the car.
Also I did order a new booster vacuum check valve to be sure. I thought a check valve only lets (in this case) air in one way, thus the term "check". I blew through the existing one both ways and it freely lets air in both ways.
This explains the hard pedal when engine isn't running. The check valve should hold vacuum in the booster for a couple presses on the brake before the pedal becomes firm. Sounds like you're getting there, bleed your brakes and replace the check valve, and see how it works out.
__________________
Randy
TC # 5401
67 Project SS Clone

Son, that there pedal on the right, that's
the loud pedal. You stand on that, and
the Rat's gonna Roar.
Reply With Quote Quick reply to this message
  #14  
Old Mar 28th, 12, 12:53 AM
larrygk larrygk is offline
Tech Team
Larry
 
Join Date: Jun 2011
Location: San Diego
Posts: 459
Default Re: Hard pedal with engine off; soft after starting

Yup. Bled first, new check valve. The car will now stop. Although bleeding did not expose any real "bubbles before clear fluid" scenario. Just kind of did it's thing. The culprit was the check valve. But go figure,,,,light never came on and pedal was not that soft before when I bought the car and drove it for a week before tearing it down. And it had the same bad check valve. The mysteries of life.....
Thanks guys for the assistance.
__________________
Larry
San Diego, CA
1969 SS396
All Numbers Matching
L35 TH400 3.07
Factory Air, am/fm Stereo, PS, PB Disc/Drums
Factory SS Package
Dover White, Black Interior, Bench Seat
Restored to show condition-SOLD
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply
Chevelle Tech > Mechanical > Brakes, Suspension & Steering      Current Topic: Hard pedal with engine off; soft after starting
Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Chevelle Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address. Note, you will be sent a confirmation request to this address.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 4:08 PM.


Is there a site like this for?    El Caminos Camaros Novas Impalas GTO Chevy Punch All Chevys

2009 Team Chevelle - AutoForums