After replacing rear brake lines brakes do not work properly

Tiny
JLLRACER55
  • MEMBER
  • 1998 CHEVROLET CAVALIER
  • 2.2L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 187,896 MILES
I am out to see if I can seek some help/answers as to why I cannot seem to restore brake ability/pressure to the system on my car after having to replace the brake line going to the rear of the vehicle. I have bled all 4 wheels as I normally would, the rear drivers side wheel seems to have pressure that comes and goes. Acts as if it has air, bleed the system and the pedal still goes to the floor. The brake light was on, after the first try of the above I thought I had air trapped in the ABS module so I bought an expensive scan tool to allow me to release the abs module to let fluid pump through the system, attempted to bleed again and still nothing. Help please!
Saturday, May 23rd, 2020 AT 3:00 PM

7 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
Your description sounds like it still has air trapped in it. Not uncommon when replacing a line as any high spots tend to hold air bubbles. The somewhat easy solution is to pressure bleed the system as the pressure forces the fluid through and it will pull out the air. However when you bled the system did you push the pedal down fully? If so that may have damaged the seals in the master cylinder and is now letting fluid bypass the piston(s) in the master. Does the pedal slowly go down or is it more like there is no resistance at all?
If the first one it's more likely an internal leak. The latter means it still has air in it. Some parts stores have pressure bleeders you can get as loaner tools. Then bleed the system using the scan tool in the correct order and see what you get.
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Thursday, February 25th, 2021 AT 9:47 AM
Tiny
JLLRACER55
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Steve, I appreciate your quick reply. I don't seem to be getting anywhere still. :( Not sure how great of a tool it is, I purchased a vacuum/brake bleeding tool from Harbor Freight but don't seem to be getting anywhere with it. I also purchased 2 new calipers for the front since the bleed screws ended up snapping off on me. The pedal just seems to go to the floor with little to now resistance behind it but yet it still sounds squishy like there is air in the line somewhere still or that something is letting air in while losing pressure (suspect possibly another line? Or your idea, the master cylinder went during all this mess). Is there a way to check a line for seepage beside the obvious of seeing a leak? I have done several other brake jobs requiring brake line work, but never fought the job this long, it just seems no matter how much I try to bleed the lines, no change in the pedal, usually it changes even if its gradual as the air is pushed out, appreciate any additional input.
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Thursday, February 25th, 2021 AT 9:47 AM
Tiny
STEVE W.
  • MECHANIC
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I would start by gravity bleeding the system. Start at the right rear then left rear then right front and left front. Keep topping the master up. Now see if you have any pedal, if not pull the master and see if it will bench bleed. With no pressure on the pedal it sounds like a failed master or something went crazy in the booster and it's not even moving the master cylinder. Had that happen in a Blazer I had here, the return spring in the master failed and the pedal felt like it wasn't even connected. The only thing you could hear was the air transfer in the booster as you moved the pedal.
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Thursday, February 25th, 2021 AT 9:47 AM
Tiny
JLLRACER55
  • MEMBER
  • 4 POSTS
I will try that process again, that is what I have done previously and still not noticing any difference what so ever. How the heck do you bleed the master with the ABS modulator attached right to it? Looking at it last night I couldn’t figure out how the 2 come apart unless there’s bolts on the underside I can’t see?
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Thursday, February 25th, 2021 AT 9:47 AM
Tiny
STEVE W.
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It unbolts from the ABS unit. There are two tubes with o-rings that go from the master cylinder to the ABS unit. But to do a bench bleed on it you don't need to remove it. You can do it right in the car if you are careful. You just need to make up four return lines to go from the ports into the reservoir. Connect those to the ABS outputs, then use the scan tool to rehome the ABS motors and bleed it that way. Then to keep from having an issue while you remove the lines, put a weight onto the brake pedal to hold the piston inside so it is past the transfer port, that will keep the fluid from just draining out.
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Thursday, February 25th, 2021 AT 9:47 AM
Tiny
JLLRACER55
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  • 4 POSTS
Is there a easy way to differentiate between a failed master cylinder vs. An issue with the abs modulator? As I remember the brake light being on before the rear brake line went out. Which to me comes on either if fluid is low or if a pressure issue is recognized somewhere in the system I assume? Just trying to narrow it down.I've replaced brake lines on at least 3 other vehicles and never had the pedal not begin to firm back up even when air is present in a line. I just am trying to determine how I can figure out if its ABS related or master cylinder. Also wondered if you knew if the master cylinder line connects were meant for a double flare connection or a bubble flare?
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Thursday, February 25th, 2021 AT 9:47 AM
Tiny
STEVE W.
  • MECHANIC
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With the key off the ABS solenoids are off and only the master cylinder is doing anything so if you have the key off and have pumped the pedal enough that the booster has no vacuum and you still have no pedal it's air or master cylinder. The light being on before the line failed likely means you had a leak and the level sensor lit it up.
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Thursday, February 25th, 2021 AT 9:47 AM

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