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Brake pressure failure - air in caliper but no fluid loss
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East Coast Resident
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Dec 16, 2015, 4:02 PM
Post #1 of 24
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Brake pressure failure - air in caliper but no fluid loss
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I have a brake issue with my Dodge Caravan that I just can't wrap my head around. I am quite experienced with auto repair as I formaly worked in a auto salvage yard for 17 years and have always maintained my own vehicles. However, I am not an expert and I am at a loss.
The vehicle in question is a 2003 Dodge Grand Caravan sport. 3.8L AOD FWD with ABS and 4 wheel disc brakes.
The issue is that every 3 or 4 days the brake peddle gets spongy and goes to the floor. This has been going on now for about two months and all I need to do to temporarily correct the issue is bleed the left front brake caliper and that's it. It has air in it every time and the fluid is infused with air and has gone frothy. The only time I have to add fluid is after several bleedings. Where this air is coming from, I have no idea. Over the past year or so, due to age and milage, the van has had 4 new brake calipers with new pads, 4 new rotors, one new right rear flex line (brake hose, steel line hybrid type) and has had a complete brake fluid flush. I have pumped around 4L of new, dot 3 through the system and there's nothing but clean, clear brake fluid at all four corners and yet every 3 to 4 days the left front caliper develops a pocket of air that totally kills brake pressure. And the air is right there at the bleeder screw. Three pumps, one twist of the bleeder and it's gone and the peddle is high and hard. The brake peddle is perfect for the next day or two and then the pressure slowly decreases. In a bypassing master cylinder, repeated pumps can bring back the pressure but that doesn't work very well in my situation because I have air in the left front caliper every time. I have bled the entire system 3 times and I have lost track of how many times I have bled that left front caliper. My ABS unit is non-functional and has been defective long before this brake issue started, so I'm reluctant to blame it. I'm at a loss. Am I missing something? Is it at all possible for a breach in the front brake hose to pull in air upon release of the peddle and yet hold pressure when pressing the brake?
It's very puzzling. Please help. I need this van to last another year until I finish trade school.
(This post was edited by East Coast Resident on Dec 16, 2015, 4:28 PM)
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Tom Greenleaf
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Dec 16, 2015, 4:16 PM
Post #2 of 24
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Re: Brake pressure failure - air in caliper but no fluid loss
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Frothy fluid could be created by master cylinder but would think brakes would never have a true normal feel with bleeding out just one.
Is ABS light on? Get codes for that.
Still think there's a high chance master cylinder is the cause. Hard to tell as you said brake goes to floor but it almost cant have zero braking power just a little bit left as the master is really two separate pressure pumps in one unit. If any chance wrong fluid as in an oil has ever had a chance to get in this everything rubber could be bad and fail.
There's only a slight chance if you did it and knew it right away that oil would float and a chance you could suck it all out before ever touching brake pedal.
Clues to contamination if it's that at all would show bloated rubber filler cap seal pretty quickly almost always,
T
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kev2
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Dec 16, 2015, 4:29 PM
Post #3 of 24
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Re: Brake pressure failure - air in caliper but no fluid loss
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some thoughts-
there is no pulling to one side.
ANY evidence of fluid on leakage.
you are using correct DOT rated fluid.
check the rotor run out.
the flex hose give it a good inspection.
excess heat that side
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East Coast Resident
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Dec 16, 2015, 5:15 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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some thoughts-
there is no pulling to one side.
ANY evidence of fluid on leakage.
you are using correct DOT rated fluid.
check the rotor run out.
the flex hose give it a good inspection.
excess heat that side
Thanks for your input!
No, no pulling to the left, no abnormal heat on that corner, no sticking, no leaks, it's the correct dot rating, rotors and calipers are less than 8 months old and the fluid has all been flushed in an effort to correct this issue. 4 litres of brake fluid have been run through the system plus some small bottles, I have a hard time believing there's any air in there now. I've stood up on the Brake peddle to the point where I thought I'd bust a brake hose for sure, but no leaks and no fluid loss since this all started.
Just to clearify, this issue happened out of the blue. The 4 calipers, rotors and rear flex line had been replaced months before this issue even surfaced. One day in october, my wife came home and said that the brake peddle had gone spongy on her and I was sure that it was a brake hose but there was no leaks and the reservoir was still full. From that day on, I have not been able to correct the issue. I'm willing to replace the master cylinder because it's not a cost or labour issue, it's a matter of is it even the cause. I've bled that left front caliper every 3 to 4 days of vehicle use since October and once I crack that bleeder open just once, a tiny bit of air comes out, followed by a tiny bit of frothy brake fluid and then, clear fluid with no air. I even removed the caliper, emptied it, flushed with fresh fluid, reinstalled it, bled it and still no improvement. The air returns every 3 to 4 days. I thought that maybe, just maybe, there might have been some water contamination from when it was new and that the water was boiling during regular use. I'm really stretching the limits of possibility with that, I know.
I may just replace that left front brake hose and then go for the master cylinder but is it at all possible that now, after the 12 months or so that it's been non-functional, that the ABS unit is causing this issue with just that one brake caliper?
(This post was edited by East Coast Resident on Dec 16, 2015, 5:17 PM)
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Tom Greenleaf
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Dec 17, 2015, 3:40 AM
Post #5 of 24
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Re: Brake pressure failure - air in caliper but no fluid loss
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Dot 3 brake fluid or above #s wouldn't be a cause directly.
Said already a master cylinder COULD do this and reading outside the box bleeding out FL is the closest line so it could behave at least better for some time.
IDK - Google out what the guts of a master cyl. looks like inside. It's a machined bore with a specifically made shaft that holds rubber one way seals almost exactly the concept of an old "T" handle air pump...... push down the seal then seals. Push slow it doesn't. On return up in the air pump it lets air pass the seal. The master is similar as it lets fluid pass the seal when brake released. What can happen is under wild pressure it isn't sealing so even minute passage of brake fluid could foam up as there's some % however low of moisture in brake fluid that will alter it totally for it's temp and rubber friendly properties but also with some time the moisture will ruin parts along the way via corrosion. Dot 5 I believe is pure Silicone and not hygroscopic with the highest boiling point but any moisture will settle to the lowest points and need that product change out on a routine.
Seems you've ruled out or replace most other things just hope new was good.
It would be excellent to know for sure by plugging up where lines go to master but it wouldn't do the failure fast enough to be sure in this case and IMO. I doubt it's expensive so it's a highly likely item to cause this is possibly the best that can be known,
T
(PS: Doubt Maine allows remanufactured master cylinders (MA doesn't) but if they do go new. I don't think you could see or machine out the flaw I would bet this one has nor if a redone one had the same flaw so start new only please)
(This post was edited by Tom Greenleaf on Dec 17, 2015, 3:41 AM)
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Hammer Time
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Dec 17, 2015, 6:38 AM
Post #6 of 24
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Re: Brake pressure failure - air in caliper but no fluid loss
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I seriously doubt the master cylinder would cause this. Air rises to the top. It doesn't run down hill to the wheels.
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Tom Greenleaf
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Dec 17, 2015, 7:20 AM
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Re: Brake pressure failure - air in caliper but no fluid loss
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I can't know exactly what "foamy/frothy" air means for this and never really found that just carbonated bubbles to bleed out and stayed out once gone. If this thing is making "whipped cream" out of fluid or something now I wonder about contamination more?
There probably is more to this than any one thing now considering contamination?
T
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kev2
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Dec 17, 2015, 7:47 AM
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Re: Brake pressure failure - air in caliper but no fluid loss
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Some thoughts - You claim that all checks have been done - it is a DOT 3 requirement, the issue was there before new parts,
scan for ABS codes - yes even if light is off.
Then use scanner to do the ABS bleed procedure...
as mentioned rotor run out check..
guide pins free no corrosion.
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East Coast Resident
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Dec 17, 2015, 1:10 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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Some thoughts - You claim that all checks have been done - it is a DOT 3 requirement, the issue was there before new parts,
scan for ABS codes - yes even if light is off.
Then use scanner to do the ABS bleed procedure...
as mentioned rotor run out check..
guide pins free no corrosion.
I mentioned above that my ABS unit is non-functional. Trouble lights are lit. I scanned the ABS system for codes a years ago when it quit on me. The code was for a loss of power to the pump. I checked it out and power and grounds are available to all necessary wires at plug. The unit is defective and is $350 plus shipping and since it had not been effecting brake performance, I left it as is. The brake pressure was unaffected and working perfectly up until two months ago when the left front caliper started developing tiny pockets of air. The caliper is not sticking, pads are wearing equally on both sides and the fluid is fresh, clean DOT3.
I apologize to the more experiences technicians here, but I am not inexperienced. I have replaced many defective master cylinders due to bypassing issues and I am well aware of their internal structure. In the case of a bypassing master cylinder, swift and firm pumping will momentarily return brake pressure and in severe cases, the peddle will slowly drop to the floor in a fairly short period of time. In none of these cases will it introduce air at the brake caliper end of the line. I've even seen them leak into the brake booster, mine is not leaking.
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Hammer Time
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Dec 17, 2015, 1:16 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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The only time I've experienced this is in the older Corvettes. If the rotors were not turning true, the calipers would pump air into themselves but those were 4 piston calipers and a very uncommon design. I've never seen it happen to any other car.
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kev2
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Dec 17, 2015, 1:37 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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agree with colleague -- the exact reason* I mentioned run out 2 times. Not an overly difficult check- esp after all the work done.
I will look into the ABS issue- as the full brake bleed will use a scanner to operate ABS- so called unintended consequences of disabling.
* corvette was the ' memory' jogger.
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Hammer Time
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Dec 17, 2015, 1:48 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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Oh believe me. It is a fact. I've been in this business over 50 years and I resolved that issue for many corvette owners. The rotor had to be shimmed to less that .005" runout and the problem disappeared. It happened to me on 2 of my own vehicles but i blame it on the design of the caliper pistons.
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East Coast Resident
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Dec 17, 2015, 2:31 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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Hammer Time,
what were the vehicles you owned that had this issue and was there fluid leakage at the caliper seals. I took a look at mine today when I changed that brake hose and it still looks new. Still has the black paint and there's no leakage at all.
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kev2
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Dec 17, 2015, 2:33 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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HT and I are confirming the runout issue we have seen and dealt with.
taking my time to look at manual - what I see so far run out .0014in.
there are 2 non interchangeable calipers and rotors.... A TRW and Tevis system.. Do you have traction control?
Time permitting I will look at the ABS - A 4 channel system may yield a clue
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Hammer Time
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Dec 17, 2015, 2:35 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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They were both Corvettes and neither one exhibited any pulsation.
You have to remove the wheel and put the lug nuts back on the rotor and use a dial indicator. I used to use that metal based AC duct tap as shim material. Again, I have never seen this happen on anything but a Corvette.
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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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East Coast Resident
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Dec 17, 2015, 2:44 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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Ok, I've never worked on a corvette and that's probably why I've never seen it at all. I must say though, this van has had warped rotors before and they had never caused any issues like this.
(This post was edited by East Coast Resident on Dec 17, 2015, 2:47 PM)
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kev2
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Dec 17, 2015, 4:11 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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Two things I see-
the mentioned runout BUT it is looking like the ABS ( HCU) might be the issue... the internal valves that separate the channels, I'm Looking for a test that may help...
there were no models made without an ABS system so we cannot eliminate - change to a non ABS model. BUT I will look.
Have you looked at your trade (salvage?) as a source for parts?
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East Coast Resident
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Dec 17, 2015, 4:55 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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Yeah, I had a used ABS unit in my possession about 3 weeks ago but it was totally different when I compared both. Evidently, the yard had inventoried it incorrectly. Different electrical plug and line locations.
I have to tell you though, when I got a look at mine, I was not impressed with it's condition. I live on a rock out in the North Atlantic! St. John's, Newfoundland. Vehicles corrode extremely bad here and I give up rust proofing this van 5 years ago.
I had blamed the ABS unit initially but figured it was sitting there for about 10 months without causing any issues.
Do you really think the unit is causing small pockets of air in the caliper?
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East Coast Resident
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Dec 28, 2015, 8:30 PM
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Re: Brake pressure failure - air in caliper but no fluid loss
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OK, it was December 17th since we last discussed the break issue on my 2003 Grand Caravan. I hope everyone is having a great Christmas and I wish you a happy and safe New Year.
The news has been good I my end so far. I swapped out the left front brake hose back on December 19th and I'm happy to inform you that the brake peddle has been great ever since. The problem would typically reoccur after 3 or 4 days and thus far it's been good. I don't know if it was a fluke but the ABS unit is still not working, the brake warning lights are still lit but there is no more air developing at the bleeder screw. The brake peddle has been great ever since. Honestly, I'm still waiting for the peddle to drop.
On another note, A friend of mine who was a mechanic for years did hear about the leaking caliper issue and he suspected that was my issue. It happened to him on a vehicle that was not a Corvette. I forget what it was.
Here's hoping I never have an issue with this again, It drove me absolutely nuts!
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