Tech Editor's Desk Projects, papers, writings, thoughts, musings of our technical editor Joe Padavano. To begin with, he will be making threads and can approve posts to it if he wishes. This can be changed in the future if it does not work out well.

Need a brake genious

Old June 11th, 2012, 06:00 AM
  #1  
Registered User
Thread Starter
 
Join Date: Jan 2010
Location: Brookeville, MD.
Posts: 70
Need a brake genious

Been working with a friend on his 1970 W31 (manual DISC front, rear drums). He replaced every component of the brake system. All new lines, calipers, wheel cylinders, shoes, pads, distribution block and master cylinder. Bled the brakes in the proper order yesterday, and bled the master cylinder last. Wound up with a pedal that went down to the floor, but the front calipers were engaged. Got the car moving, calipers eventually loosened up. But petal still went to the floor with the brake light coming on. NO leaks anywhere. So we took off the master cylinder and put on another one that had been rebuilt (purchased at NAPA). Bench bled it, and installed it. We still have a pedal that goes to the floor, however, if you pump it 5 or 6 times it will firm up. Let it sit for 15 seconds and its back to the floor. My guess is we have 2 bad master cylinders (what are the odds), but before purchasing a third one, would welcome any opinions. Thanks!
mbrae5 is offline  
Old June 11th, 2012, 07:26 AM
  #2  
1974 DELTA 88
 
AZ455's Avatar
 
Join Date: Jun 2011
Location: Yavapai County, Arizona
Posts: 569
Did you bench bleed the master cylinder first? I would start there, then bleed the rest of the brake system.

The fact that it firms up when you pump it sounds like air in the lines.

Edit: Sorry, missed the part about you bench bleeding the 2nd MC you got. Either way, you mentioned you bled the MC last. You need to start the bleeding process at the master cylinder, then move on to the wheels, starting with the wheel farthest from the MC.

Last edited by AZ455; June 11th, 2012 at 07:34 AM.
AZ455 is offline  
Old June 11th, 2012, 07:51 AM
  #3  
Registered User
 
Join Date: Sep 2010
Location: Shorewood, Il.
Posts: 3,057
There was another thread with exactly the same problem, just recently.
Turns out, the calipers were on the wrong sides - bleeders should be UP!!
Rickman48 is offline  
Old June 11th, 2012, 07:59 AM
  #4  
Moderator
 
oldcutlass's Avatar
 
Join Date: Oct 2009
Location: Poteau, Ok
Posts: 31,923
If your drum brakes are not adjusted properly you will have a similar problem. When you bleed the brakes, have your buddy sit in the car, put enough pressure on the pedal to push it all the way to the floor when you loosen bleeder. He needs to hold it there until you retighten bleeder, and then raise the pedal. Pump up the brake again and repeat until you get a solid stream of brake fluid with no air bubbles. Recheck master cylinder for fluid level after each wheel.
oldcutlass is online now  
Old June 11th, 2012, 09:30 AM
  #5  
Old(s) Fart
 
joe_padavano's Avatar
 
Join Date: Mar 2007
Location: Northern VA
Posts: 31,741
It doesn't take a "genious", or even a genius, to diagnose this one.

Originally Posted by mbrae5 View Post
Bled the brakes in the proper order yesterday, and bled the master cylinder last.
So the answer is NO, you did not bleed the brakes in the proper order. Bench bleed the M/C FIRST, then the rest. Be aware that you may have pushed the differential pressure switch piston all the way to one side, so you may have THAT problem to deal with now.
joe_padavano is offline  
Old June 11th, 2012, 09:42 AM
  #6  
Registered User
 
Intragration's Avatar
 
Join Date: Aug 2011
Location: Northlake, IL
Posts: 622
You've gotta be really thorough with the bleeding. Starting with bench bleeding, you need to do it for a long time, making sure to go ALL the way in numerous times, shorter strokes, and different speeds. It sometimes takes me 20 minutes to get it bled properly. There's a lot of air in there that needs to be coaxed out. It gets a completely different feel when you're all done. As for the lines, I also keep going for a little bit once the bubbles stop, just to make sure. Keep the master topped off too, if it goes dry you need to take it off and bench bleed again.
Intragration is offline  
Old June 11th, 2012, 10:00 AM
  #7  
Registered User
 
Join Date: Dec 2011
Posts: 7,286
Sounds to me like major air in the line to the rear brakes. Re-bleed the rears, run at least 1/2 Qt thru. long after bubbles stop appearing.

And, make sure the adjusters were set so that the rear shoes are just barely smaller than the drum, with the slightest drag perhaps when brakes are off. That slight drag will wear away on the first drive. Generally, adjusters way out of whack will lead to a 1 or 2 pump before full brakes condition, not 5 or 6.
Octania is offline  
Old June 11th, 2012, 06:34 PM
  #8  
Registered User
 
Join Date: May 2012
Posts: 856
my .03, i dont pump the pedal,i push down one pump at a time. dont want to aerate the fluid.
oldolds88 is online now  
Old June 12th, 2012, 04:34 AM
  #9  
Registered User
Thread Starter
 
Join Date: Jan 2010
Location: Brookeville, MD.
Posts: 70
Thanks for all the feedback. We checked last night and the calipers are on the wrong sides, so we will switch those out, and bleed the brakes again.

And thanks for the spelling lesson Joe. Obviously I am no genius...
mbrae5 is offline  
Old June 12th, 2012, 09:10 AM
  #10  
Old(s) Fart
 
joe_padavano's Avatar
 
Join Date: Mar 2007
Location: Northern VA
Posts: 31,741
Originally Posted by mbrae5 View Post
Thanks for all the feedback. We checked last night and the calipers are on the wrong sides, so we will switch those out, and bleed the brakes again.
For future reference, the bleeder screw always needs to be at the highest point when the caliper is installed, or you'll never get the air out.
joe_padavano is offline  
Old June 12th, 2012, 06:54 PM
  #11  
Registered User
 
Join Date: Sep 2010
Location: Shorewood, Il.
Posts: 3,057
Win #2?
See # 3 -
Rickman48 is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
delmontcrusier
General Discussion
57
February 23rd, 2019 03:44 PM
Mocephus
Eighty-Eight
11
November 28th, 2016 08:30 AM
Maverick
Brakes/Hydraulic Systems
6
June 26th, 2013 08:21 AM
Del70
General Discussion
1
August 2nd, 2011 04:40 PM
jon69olds
Wheels and Tires
1
February 11th, 2011 11:57 AM


Thread Tools
Search this Thread
Quick Reply: Need a brake genious


Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.