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Brakes soft

Tiny
BILL29211
  • MEMBER
  • 2002 DODGE CARAVAN
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 108,000 MILES
I replaced the rear cylinders and bled all the lines (several times) but the brakes are still soft and at times while pressure applied just fall to the floor after being somewhat stiff. Can this be the master cylinder and are there any tricks to changing one when you have abs?
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Monday, August 17th, 2009 AT 6:03 AM

9 Replies

Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Pump brakes does the peddle go up and if so most likely you have air in the system and have to bleed again
changing master cylinder will not help
if need to change master cylinder

Have to bench bleed new master cylinder until all air out before installing it in
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Monday, August 17th, 2009 AT 6:21 AM
Tiny
BILL29211
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  • 4 POSTS
Is there a specific pattern for bleeding? Should the van be running or not? Is there any bleeding that should be done where the lines go into the abs box?
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Monday, August 17th, 2009 AT 7:15 AM
Tiny
BILL29211
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  • 4 POSTS
Should we pump them and then hold them to the floor and then open each one? And repeat. Repeat. Repeat. Until all 4 are done?
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Monday, August 17th, 2009 AT 7:18 AM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Engine off, start farthest away from the master cylinder and work your way towards it. Does the pedal fall if you apply light pressure, but if you hit it hard it is ok?If so the master may be by-pasing internally, which would require another one. As said before you need to bench bleed it to get the air out before installing it. I prefer to open the bleeder, then slowly push down, close bleeder and let up slowly
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Monday, August 17th, 2009 AT 3:07 PM
Tiny
BILL29211
  • MEMBER
  • 4 POSTS
After bleeding you will get some o.K. Pressure. Without letting up, the pedal will sometimes fall all the way to the floor. Sometimes if you just lighten up and then press again it will then fall to the floor.
I ordered a master cylinder today and will have it tommorrow. Can you give me the low down on this replacement. The vehicle has abs.
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Monday, August 17th, 2009 AT 3:25 PM
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
THIS SHOULD COVER IT ALL

When performing bleeding procedure, ensure rear brakes shoes are properly adjusted.
Ensure master cylinder fluid level remains close to FULL mark.
Check master cylinder fluid level periodically while bleeding brake system.
Add DOT 3 brake fluid as required.

Manual Bleeding
Fill master cylinder (if necessary).
Reinstall master cylinder cap.
Install clear hose on left rear bleed screw.
Place other end of hose in clean transparent container of brake fluid.
Ensure end of clear hose is submerged in brake fluid.
Pump brake pedal 3-4 times.
Hold brake pedal down.
Open bleed screw at least one full turn.
Brake pedal will drop to the floor. Close bleed screw. Release brake pedal.
Repeat bleeding procedure until brake fluid flow is clear and free of bubbles.
Bleed remaining brakelines in proper sequence at each wheel.
Ensure bleed screws are tightened to specification.
BRAKELINE BLEEDING SEQUENCE
All Models LR, RF, RR, LF

BENCH BLEEDING MASTER CYLINDER
NOTE:Bleeder tubes must be installed on master cylinder when performing bleeding procedure.

Clamp master cylinder in soft-jaw vise at mounting flange on master cylinder.
Install Bleeder Tube (6920) in each outlet port on master cylinder with ends of bleeder tubes positioned in brake fluid reservoir on master cylinder. Fill master cylinder with brake fluid.
Ensure ends of bleeder tubes are submerged in brake fluid in in master cylinder reservoir.
Using wooden dowel, slowly depress pistons in master cylinder and then release, allowing pistons to return.
Repeat procedure until no bubbles exit from bleeder tubes.
Remove bleeder tubes and plug master cylinder outlets to keep fluid from draining

MASTER CYLINDER
Removal

CAUTION:Master cylinder is used to create a seal for holding vacuum in power brake booster. Vacuum in power brake booster must be released before removing master cylinder. Ensure area around master cylinder filler tube, master cylinder fluid reservoir and master cylinder-to-power brake booster are clean before servicing master cylinder. Area may be cleaned with brake parts cleaner.

Release vacuum from power brake booster by pumping brake pedal several times with engine off until brake pedal becomes firm.
Clean area around master cylinder filler tube and master cylinder fluid reservoir.
Remove master cylinder filler tube from master cylinder fluid reservoir by pushing filler tube downward and rotating filler tube.
Remove filler cap from master cylinder filler tube and install on master cylinder.
Disconnect electrical connector at brake fluid level sensor located on master cylinder fluid reservoir. Place shop towel under master cylinder to absorb brake fluid.
Disconnect brakelines from master cylinder.
Install plugs at brakeline outlets on master cylinder. Clean master cylinder-to-power brake booster area to prevent dirt particles from falling into power brake booster.
Remove master cylinder-to-power brake booster nuts, and slide master cylinder from power brake booster.
Remove master cylinder-to-power brake booster vacuum seal from groove on mounting flange of master cylinder by pulling vacuum seal from master cylinder.
DO NOT pry vacuum seal from master cylinder.
Installation
CAUTION:Master cylinder-to-power brake booster vacuum seal must always be replaced. DO NOT reuse vacuum seal.

Bench bleed master cylinder before installing. See above
Ensure NEW master cylinder-to-power brake booster vacuum seal is squarely installed in groove on mounting flange of master cylinder before installing master cylinder.
Ensure push rod in power brake booster aligns with piston in master cylinder.
Tighten master cylinder-to-power brake booster nuts and brakeline nuts to specification.

On models without ABS, bleed brake system. See BLEEDING BRAKE SYSTEM ABOVE .
On models with ABS, it is not necessary to bleed Hydraulic Control Unit (HCU), but base brake system must be bled. SEE BLEEDING BRAKE SYSTEM ABOVE

GOOD LUCK
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Monday, August 17th, 2009 AT 5:26 PM
Tiny
AANDRUS7
  • MEMBER
  • 2 POSTS
Had the exact same problem with my 2002 Dodge Grand Caravan. Replaced the master cylinder and bled all 4 wheels on 5 different occasions. Each time the brakes returned to normal but over a period of weeks the pedal gradually became softer with increased travel. Eventually it would go to the floor and have no stopping power. There were several rather mystifying points; first of all very little or no air seemed to be expelled with each bleed. Even when the pedal traveled near or to the floor, there was no red brake warning light and there was no ABS light or fault codes. The culprit was something relatively simple; the lower slide pin in the left front caliper mounting bracket was frozen. It had no in and out movement whatsoever. Normally you would think the end result would be abnormal brake pad wear, but the resulting improper movement of the caliper piston not correctly drawing the outboard brake pad into proper contact with the rotor can and will gradually produce a soft brake pedal. Definitely something worthwhile to check.
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Wednesday, April 26th, 2017 AT 3:51 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,638 POSTS
Hey,

Great addition to this thread! Please feel free to help out on the site whenever it can add information that will help.

Cheers, Ken
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Saturday, April 29th, 2017 AT 3:06 PM
Tiny
AANDRUS7
  • MEMBER
  • 2 POSTS
Thanks Ken,

Glad I was able to offer some useful input. This problem had my van out of commission all winter. It had all the earmarks of one of those ABS HCU's others were talking about, especially on the Dodge Forum website. Not to imply that this is THE answer but had I went with the scan tool bleed or HCU replacement, the problem still would have been there. I would not have even had a clue about something like this had I not looked on the Honda website for a neighbor who was experiencing the same problem with his Accord.
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Saturday, April 29th, 2017 AT 8:06 PM

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