New Disc Brakes but soft pedal - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Suspension - Brakes - Steering
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 04-09-2011, 07:59 AM
Registered User
 
Join Date: Feb 2010
Location: janesville,wi
Posts: 38
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
New Disc Brakes but soft pedal

I am finally getting aroud to test driving my car after a 3 year resto. I installed a 4-wheel disc brake conversion. The front and master is Classic Performance, and the rear is Right Stuff. It is a power system.
The problem I have always had is the brakes are soft. when I push the pedal it goes almost 3/4 of the way to the floor before the car stops. I have talked to both companies and they have run out of ideas. I have increased the pedal throw as far as I can. I installed a new 1 1/8 bore master. reverse bled all teh lines to be sure there is no air in the lines. The only thing I can think is to put a 2 psi residual valve in the rear lines.
What do you guys think?
Front and rear calipers are single piston. 11 in. booster, 15-18 inches vac from engine. 3/16 lines go to the front calipers. 1/4 lines goes to the split at the rear.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 04-09-2011, 10:04 AM
ogre's Avatar
the 'Duracell Project'
 
Last photo:
Join Date: Nov 2009
Location: Motown
Posts: 1,535
Wiki Edits: 0

Thanks: 0
Thanked 164 Times in 138 Posts
usually residual valves are for when you have the mc mounted low.
since you've tried everything else, i would add them.
minimize use of flex lines.
also check to see that all your bleed screws are on top.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 04-09-2011, 10:09 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 60
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 598 Times in 547 Posts
You may need to change the pedal ratio. Or is that what you mean when you said you've increased the pedal throw?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 04-09-2011, 10:56 AM
Maxwell007's Avatar
Member
 
Last photo:
Join Date: Jul 2005
Location: California
Posts: 41
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I agree with Ogre. Check the bleeder screw locations first.
What kind of rear calipers do you have? If they are the GM type with an integrated parking brake, there is a trick to adjusting these. I have seen these type calipers cause the same symptoms you are describing.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 04-09-2011, 06:47 PM
Registered User
 
Join Date: Feb 2010
Location: janesville,wi
Posts: 38
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Yeah they are the calipers with the e- brake. They are a pain in the a** to set and bleed. While I am thinking about it does anyone know a caliper I can put in their place? I don't have the e-brake hooked up anymore anyways.

Yeah they had me check the pedal ratio and they said it was spot on. what would you recommend it be I will check it tomorrow. I don't remember what it was.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 04-09-2011, 09:42 PM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 60
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 598 Times in 547 Posts
Quote:
Originally Posted by ducrider123
Yeah they are the calipers with the e- brake. They are a pain in the a** to set and bleed. While I am thinking about it does anyone know a caliper I can put in their place? I don't have the e-brake hooked up anymore anyways.

Yeah they had me check the pedal ratio and they said it was spot on. what would you recommend it be I will check it tomorrow. I don't remember what it was.
3.5:1 to 4.5:1 for power brakes is in the area you want to be.

Here's a good place to do a little reading.
http://www.mpbrakes.com/technical-su...igurations.cfm
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 06-20-2011, 10:31 AM
Registered User
 
Join Date: Jun 2011
Location: NY
Posts: 2
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Hey, I know this thread is a little old, but I just came across it on google. I've been having the same symptoms on my '78 T/A with stock disc/drum setup. I've replaced almost everything with OEM parts (calipers, drums, pads, M/C, lines, booster), and have the same problem. It takes about 3/4 of the pedal's travel to get any real braking power. The pedal should be stock (I'm not the original owner, so I can't really confirm that), so I never considered the ratio.

Did you ever figure out what was going on with yours?

Thanks,
Jim
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 06-25-2011, 09:48 PM
Registered User
 
Join Date: Feb 2010
Location: janesville,wi
Posts: 38
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
My major problem was the seal on the back of the booster to the master was cracked. I still have a lil soft pedal but it's better for a low vac engine.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 06-27-2011, 11:34 AM
Registered User
 
Join Date: Jun 2011
Location: NY
Posts: 2
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by ducrider123
My major problem was the seal on the back of the booster to the master was cracked. I still have a lil soft pedal but it's better for a low vac engine.
Very interesting, I have fairly low vac as well. Would that cause a soft pedal? I was always under the impression that lower vac would result in a harder pedal because there would be less power assist - is that not the case?

Thanks again for the reply, and I'm glad you sort of resolved your issues.

Jim
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 06-27-2011, 08:25 PM
Registered User
 
Join Date: Feb 2010
Location: janesville,wi
Posts: 38
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I don't think hooking up the booster gave me more brakes. I did a lot of things at once so I am not sure what the fix was. I installed a larger master 1 1/8" Increased the lever throow as much as I can. The other problem I think I have is the rear disc calipers are e-brake calipers and they don't seem to stay tight to the rotor as I would like.

As for you do you have a new prop valve? any residual valves?
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 06-28-2011, 10:59 AM
ogre's Avatar
the 'Duracell Project'
 
Last photo:
Join Date: Nov 2009
Location: Motown
Posts: 1,535
Wiki Edits: 0

Thanks: 0
Thanked 164 Times in 138 Posts
Quote:
Originally Posted by ducrider123
The other problem I think I have is the rear disc calipers are e-brake calipers and they don't seem to stay tight to the rotor as I would like.
installation of a residual pressure valve should fix this.
this is why they are recommended.

for low vacumn applications, i'd use a hydroboost
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 06-28-2011, 01:03 PM
Registered User
 
Join Date: Feb 2010
Location: janesville,wi
Posts: 38
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
are you talking a 2 lb for the rear disc brakes? or for the guy with the drum brakes?
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 07-04-2011, 11:06 PM
Registered User
 
Last photo:
Join Date: Jul 2010
Location: evansville
Posts: 28
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
This is not really haing so much to do with your problem so much as just my experiences.I use vett type masters on most disk conversions.If the system has rear drum I do a 10lb residual even if master is not low.Also never overlook pushrod adj. (had that one bite personally) to make sure replenish port is uncovering when pedal released.
Reply With Quote Quick reply to this message

Recent Suspension - Brakes - Steering posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last 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 for yourself.
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.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

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
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
brake pedal hard then soft but hardly any brakes Wildwestshow Suspension - Brakes - Steering 1 12-24-2010 08:18 PM
Soft Brakes... S10xGN Suspension - Brakes - Steering 13 08-24-2009 02:06 AM
Will a Brake Master Cyl. Designed for Disc/Drum be Adequate for 4-Wheel Disc Brakes? mrwumper Suspension - Brakes - Steering 3 04-16-2009 10:38 AM
79 malibu soft brakes mikes68493 Suspension - Brakes - Steering 5 06-12-2007 09:37 PM
soft brake pedal jum Suspension - Brakes - Steering 5 03-05-2006 08:14 PM


All times are GMT -6. The time now is 08:48 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.