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Spongy/creeping brake pedal with eingine running
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4cefed
Novice
Sep 28, 2013, 9:50 AM
Post #1 of 15
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Spongy/creeping brake pedal with eingine running
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Hello all. I've been building and racing all sorts of cars for almost 20 years so I have a fair amount of experience, however this is driving me insane:
2003 Dodge (Neon) SRT-4
2.4L Turbocharged and intercooled 4cyl.
4 wheel ABS disc power brakes, ~130k miles.
The brake pads and discs are all fairly recent, no stuck slider pins or pads worn at an angle. No leaking caliper seals. The car sat for a few months with a rotted front subframe. I replaced it and got it back on the road but the brake pedal can be pushed right to the floor. I almost remember it was a little spongy before but still stopped ok. I bled and bled the system both with a hand vacuum pump and with a partner pumping the brakes. No change. With the engine off, the pedal is rock hard even when "standing" right on it. As soon as you start the engine and get the booster helping the pedal goes right to the floor.
I broke a bleeder in the rear that I was unable to extract and replaced the caliper. After more bleeding and a total flush of all old brake fluid, still no firm pedal. I assumed the master must have finally started to go, I replaced the master after successfully bench bleeding it, bled whole system RL,FR,RR,FL as the book said to, and still no change.
I don't have access to the DRB III tool to activate the ABS system to ensure no air is trapped in the unit, so after much research, some mechanics who work in Chrysler dealers said sometimes they don't have time to use the tool to bleed like the manual says. They claim the ABS unit will "self Bleed" after repeated ABS stops in a dirt parking lot. I have done this numerous times while bleeding in between. I have never seen any bubbles come out and there is no change.
I next figured the old stock rubber hoses were flexing with the added help from the booster. I replaced all rubber hoses with braided stainless performance lines. All crush washers replaced and hoses installed correctly. Bled system, ABS stops, bled system. Still no change.
I have been reading and researching this problem on the SRT forums and regular Neon forums. Numerous people are having this exact problem, some have ABS and a lot of them don't. I've been finding exactly this scenario with other car makes and manufactures as well. I don't want to blame the ABS system, it works well, and I have no reason to suspect air in it. I tried once to bring it to a mechanic for bleeding but they claimed they "didn't have the technology" to remove my stuck bleeder valve and instead wanted me to replace all calipers, pads, and discs. Surprise surprise. I have no problem with bringing it back to someone to have it bled properly with the tool if someone thinks it will help. People with this problem have been through two three and four new master cylinders with no change. So WHAT IS THE PROBLEM THEN? A big thank-you in advance for some professional help here.
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Discretesignals
Ultimate Carjunky
/ Moderator
Sep 29, 2013, 8:12 AM
Post #2 of 15
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Re: Spongy/creeping brake pedal with eingine running
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ABS light on?
Have you tried using a pressure bleeder? If the ABS unit has ingested air for some reason, you'll need to bleed the unit.
You could have a defective master.
Why would Dodge spend time and money to have an ABS bleed function on their DRB and have a procedure in service information written up if any tech could go out and activate the ABS system by doing panic stops to bleed the system??
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Discretesignals
Ultimate Carjunky
/ Moderator
Sep 29, 2013, 5:18 PM
Post #5 of 15
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Re: Spongy/creeping brake pedal with eingine running
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If your replacement master isn't defective, you have all the air out of the system, and there are no leaks, the only thing left is the ABS hydraulic control unit. As HT stated, you could have a valve not sealing or some other internal problem inside the HCU.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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4cefed
Novice
Oct 2, 2013, 3:12 AM
Post #6 of 15
(5686 views)
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Re: Spongy/creeping brake pedal with eingine running
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If a valve is not sealing in the HCU, is this only the case with the ignition on? if I pulled the fuse for the ABS then started the car for the vacuum boost would that rule anything out?
Seriously, what are the odds I bought a defective master? It was new, not a rebuild. It's a HUGE PITA to get at in this car too.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Oct 2, 2013, 4:02 AM
Post #7 of 15
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Re: Spongy/creeping brake pedal with eingine running
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Can't be sure but I think something in your bleeding either bench bleeding went wrong between bench and install or somewhere. Not sure this vacuum bleeding with a helper pumping pedal was helping or causing a problem?
Defective part even new? I've have them but not in this manner just not machined properly for the pushrod mostly. This isn't all adding up. You may have to start all over,
T
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4cefed
Novice
Oct 2, 2013, 3:21 PM
Post #8 of 15
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Re: Spongy/creeping brake pedal with eingine running
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When I flushed the system I used the vacuum pump, but all other flushing attempts were the old fashioned way with a helper pumping.
So seriously, other than something changing in the ABS system when the ignition is on, the only thing this could really be is sill a bad master right?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Oct 2, 2013, 4:12 PM
Post #9 of 15
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Re: Spongy/creeping brake pedal with engine running
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Not sure what you did with a vacuum pump? I've started some for a second with a hand held pump and finished with pump, hold, bleed, tighten bleeder and repeat.
If this took a while between proper bench bleeding and getting lines on it in car you could have trapped air.
Bad cylinder. Suks - you could make up plugs and see if it holds or just get another but request another brand as it may if faulty be a whole batch. That was the case when it happened to me - pegged it right to which factory - all got pulled from the parts places.
Could also be barking up the wrong tree and not bleeding it properly or some other reason entirely??
T
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Hammer Time
Ultimate Carjunky
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Oct 2, 2013, 4:16 PM
Post #10 of 15
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Re: Spongy/creeping brake pedal with eingine running
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The system needs to be bled electronically using a scan tool. There is really no other way to get the air out of the ABS unit.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
/ Moderator
Oct 2, 2013, 4:45 PM
Post #11 of 15
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Re: Spongy/creeping brake pedal with eingine running
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Tom had a good one about capping the master to see if it holds hard. That would pretty much eliminate that.
Sometimes when calipers are retracted, during a brake job, by pushing the fluid back up into the master, trash in the caliper gets pushed into the ABS system causing valves to hang.
Just a tip for other that may be reading this: Open the bleeder screws when retracting pistons. I personally attach my vacuum bleeder to the screw and use a piston retractor, so fluid doesn't spill everywhere. I've seen the old RWAL Ford modulators get messed up by pushing fluid back up through them quite often.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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4cefed
Novice
Oct 3, 2013, 1:53 PM
Post #13 of 15
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Re: Spongy/creeping brake pedal with eingine running
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Tom had a good one about capping the master to see if it holds hard. That would pretty much eliminate that.
Sometimes when calipers are retracted, during a brake job, by pushing the fluid back up into the master, trash in the caliper gets pushed into the ABS system causing valves to hang.
Just a tip for other that may be reading this: Open the bleeder screws when retracting pistons. I personally attach my vacuum bleeder to the screw and use a piston retractor, so fluid doesn't spill everywhere. I've seen the old RWAL Ford modulators get messed up by pushing fluid back up through them quite often.
Capping the master would be a great test, but if I have to rip all that stuff out of the way, I would just as soon put in another master.
When the pedal sinks to the floor it's not progressive like it's air compressing. It feels like it's just bypassing,
Good tip about opening the bleeders before compressing the cylinder, I'll do that from now on.
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4cefed
Novice
Oct 13, 2013, 6:33 PM
Post #14 of 15
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Re: Spongy/creeping brake pedal with eingine running
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I did some more diagnosis, apparently leaving the car sit while you stew about it won't fix anything.
I pulled the ABS fuse and started the car, still had spongy pedal. I put the fuse back and clamped off the vacuum supply to the booster, firm pedal as expected.
Today I got another master and some flare plugs for the ports. I ripped the engine bay apart again and pulled the brake lines from the installed master. I capped those and started the car, so my amazement, firm pedal. So the master in the car (and probably the one before it) was good. I'm going to pull the calipers off the front tomorrow and see if anything doesn't look good. Maybe there is a frozen pin somewhere I didn't see the first time.
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Hammer Time
Ultimate Carjunky
/ Moderator
Oct 13, 2013, 6:48 PM
Post #15 of 15
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Re: Spongy/creeping brake pedal with eingine running
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So, i guess you are going to continue to ignore the required electronic bleeding sequence.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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