Soft brake pedal issue

Tiny
CHRSRAM44
  • MEMBER
  • 2002 LINCOLN TOWN CAR
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 180,000 MILES
I'm a ASE Certified Mechanic with 7 years of experience and am having a very stubborn some issue of not being able to get a firm pedal. This car had recently had a brake hose break and had been ran dry of brake fluid. After replacing the hose that had ruptured and making sure there weren't any leaks, I bled the system from LR, RR, FR, LR both vacuum and manually, I then proceeded to connect a Scan to to bleed the ABS system, after following the procedure I then began to bleed the system the same way as before manually and by vacuum going around 4 times to each caliper and to no luck the pedal still will sink to the floor and build pressure after a few pumps but then loose the pressure after releasing the pedal and pushing it again after about 2- 4 seconds. Before the brake hose had ruptured, the vehicle had a very firm pedal and did not require much for to stop it, which led me to believe the master cylinder and other calipers/brake hoses are completely fine and that I'm just dealing with stubborn air trapped in the system. This is a first for me and need to find out what is the best method to bleed stubborn air out of the system.
Monday, February 10th, 2020 AT 12:17 AM

2 Replies

Tiny
MOTOR MASTER
  • MECHANIC
  • 279 POSTS
Hello my name is Dave.

The best way I found to get stubborn air out of a system is to first get a few feet small vacuum or washer hose that will fit snugly over the bleeder. I then get a clear drink bottle and put just enough brake fluid in it to cover the tip of the hose.
Starting at the wheel furthest from the master cylinder ans working my way towards the master I first put my wrench on the bleeder, slide the hose over the bleeder then put the other end into the bottle making sure that the tip is and remains covered during the entire process while the bleeder is open.
Fill the master, open the bleeder and have an assistant rapidly pump the brakes until the bubbles stop, hold the pedal to the floor then tighten the bleeder. Repeat for each wheel. I do this with the ABS fuse removed to prevent it from activating.
If this procedure is unsuccessful then you have another issue, one that I have encountered that thew me off for a good while when I first encountered it is a failing brake hose that has not yet ruptured. The best way I have found to find it is to have someone pump the brakes until they get firm then look at all the hoses fora bubble in them.
Please keep us up to date on your progress and thank you for using 2CarPros!
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Monday, February 10th, 2020 AT 4:33 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
If I can chime in here, when you bleed the system do you see air ? If not it sounds like the master has gone bad which happens when a brake hose ruptures. This guide will help other to see how the bleed a brake master with a guide to help check other causes of a low brake pedal:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

and

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please run down these guides and report back.
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Monday, February 10th, 2020 AT 12:26 PM

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