Symptoms Of A Weak Accumulator, But...?

ridindirrty

ridindirrty

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Hi guys, air-ride is sorted, on to the brakes and YES I have scoured every possible thread looking for answers already ;) . I have a symptom in my brake system that behaves like a weak accumulator but I don't think this is the issue. I've read posts referring to internal leaks and i'm wondering if this could be my problem. When the car is left for a few hours and then restarted, the ABS pump immediately turns on to build pressure in the system. We all know that this really ought not to be the case if everything is tight and holding pressure. Once charged though, it behaves pretty normally, the pump activating every 4th or 5th brake application which leads me to think that the accumulator is ok. It was replaced 6 or 7 months ago with a brand new unit.
Is there some sort of check valve that could be malfunctioning, letting pressure bleed out of the accumulator? Could air in a particular part of the system cause this behaviour?
The reason for the post is this: The car sat idle for 2 days and the pressure in the system was extrordinarily depleted. She seems to be taking longer to build up pressure after sitting for the last day or 2 leading me to believe that this sh*t is getting worse.
I've been preparing to do a system flush as i've noticed my pedal getting harder during stop and go driving in the extreme heat lately, making me think my brake fluid is boiling. Could this also have something to do with it?
 
On my car, the pump almost invariably runs for at least a few seconds after driving and engine shut-down for only an hour or so.

If i moved back and forth to get into a parking space, depressing the brake pedal several times before shutting down, accumulated pressure may have been depleted to the very edge of the "pump-goes-on" limit, and the pump may have to do a maximum pump-up when restarting.

It might run for 20+ seconds after being left overnight. It might run for only 10. There are driving / parking / braking / shut-down variables that leave less or more pressure in the system, and less or more pumping is required with the re-start.

I have actually timed pump activity but only rarely. (For the sake of this thread I just did it.. turned the ignition to RUN and, after being parked and untouched for 2 days, the pump ran for 18 seconds. Then i waited about an hour. Still haven't touched the brake pedal. Turned the key, hood open. The pump ran for 8 seconds.
Since the pump runs smooth and quiet, I put a finger on the accumulator or master cylinder to detect it running.)

--------------------

First of all, does your amber Check Brakes lamp light up when, engine off, the ignition is turned to RUN? If not, the bulb is likely burned out. Fix that before trying to diagnose anything else.
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Assuming the lamp is functional:
Does that lamp ever light while driving? If yes, pressure is, at that time, dangerously low to the point where Anti-lock braking is not available. This is cause for worry and further investigation. [{EDIT} That's not accurate. There seem to be a variety of reasons the amber lamp may light up. The pump might have overheated and shut down, and the computer senses it.. or some sensor or component isn't responding to the computer's inquiries, low brake fluid level, etc.]

If the lamp never lights up while driving, adequate brake pressure is being maintained. The amount of time the brake pump is running is relatively immaterial. The system is doing it's job of maintaining adequate pressure.

I always keep an eye on the amber lamp out of habit, due to prior brake troubles.. and I wait patiently.. and don't drive off until it goes out. While pedal action might seem harder or softer while driving under various conditions, that Amber lamp is the one important indicator of basic brake component health. If it lights up while driving, there is very likely a problem with a component.
---

If you put a new accumulator in there 6 months ago, I assume the fluid was replaced at that time. Six months is nothing for brake fluid in a healthy system.. but it could be contaminated.. might just need a flush to remove air in the line.. who knows..
A flush is relatively quick, easy and inexpensive to do, and it's hard to argue against it.
 
Elessee said:
On my car, the pump almost invariably runs for at least a few seconds after driving and engine shut-down for only an hour or so.
Click to expand...

Yeah, but i do remember a time when it wasn't like that. Pretty sure I could leave it for quite some time, restart and the pump wouldn't need to run.

Elessee said:
If i moved back and forth to get into a parking space, depressing the brake pedal several times before shutting down, accumulated pressure may have been depleted to the very edge of the "pump-goes-on" limit, and the pump may have to do a maximum pump-up when restarting.
Click to expand...

Hmmm...true, true.

Elessee said:
It might run for 20+ seconds after being left overnight. It might run for only 10. There are driving / parking / braking / shut-down variables that leave less or more pressure in the system, and less or more pumping is required with the re-start.
Click to expand...

The thing that really got my attention was this. Last weekend the car did not budge from Friday night to Monday Morning. When I fired it up...no ABS pump. Put my foot on the brake...right on the floor, hard as a rock. Gave it a good nudge and the pump ran and pressurized the system. This is new.

Elessee said:
First of all, does your amber Check Brakes lamp light up when, engine off, the ignition is turned to RUN? If not, the bulb is likely burned out. Fix that before trying to diagnose anything else.
Click to expand...

Lamp is good, I check it daily.

Elessee said:
Does that lamp ever light while driving?
Click to expand...

Never (not yet anyway)
It has in the past when i had a serious leak (since repaired)

Elessee said:
If you put a new accumulator in there 6 months ago, I assume the fluid was replaced at that time.
Click to expand...

Nope, just a bleed and top up.
Flush will come this weekend weather permitting. I hear much talk of switching to DOT4. I like the idea but I have concerns about it causing problems in the cold weather. Wouldn't want to stress out an already old system. Any thoughts:confused: ?
 
I agree with most of what El said.

Flush flush flush the system with new new new fluid! Compare pump up times and pedal throw.

You should be good for another 20,000 miles after that.

Try it and let us know how you make it.
 
Any thoughts? Not many.. Seems like a flush is first on the list.

I don't like the idea of mixing DOT3 and DOT4. They do have different chemistry and weren't intended to be mixed. Whatever high-temp advantage DOT4 provides might be negated by a small amount of residual (old-wet-contaminated?) DOT3.

And you're proposing the change based only on an unfounded suspicion... that the fluid is actually boiling. If it's really boiling under reasonably sane driving conditions, there's some kinda problem beyond fluid. A high-temp fluid might only hide the problem.
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If fluid is the problem, it'd be far more likely that it has a little water in it, or air, or is otherwise contaminated, imo. Being hygroscopic, glycol-based fluid (DOT 3, 4, etc.) absorbs water from the air. A small amount of water drastically lowers it's boiling point.
I've heard there are test strips available that can detect water in brake fluid..
But fluid is cheap... I'd go buy a couple fresh quarts (dump any and all opened bottles) and flush the system really well. Get someone to help with a wrench at the calipers.
 
night and day

Elessee said:
Any thoughts? Not many.. Seems like a flush is first on the list....
Click to expand...
For brake problems, I prefer to assure that original and correct situations are first applied BEFORE I go trouble shooting. If my interior lights dim, I begin troubleshooting at the battery and then over to the alternator and regulator and then maybe out to the other accesories on that terminal (and there's a LOT). My last spot would be the switch.

I can't trouble shoot my accumulator if I have dirty brake fluid.

(This was one of my 1984s right after bleeding the fronts and before doing the rear. I call this photo NIGHT AND DAY)
Dscf7505.sized.jpg
 
What A Difference

Elessee said:
I don't like the idea of mixing DOT3 and DOT4.
Click to expand...

Went with my gut and your reasoning and stuck with DOT3 although I went with Prestone Synthetic

Flushed a good 4 1/2 litres through the system (about a gallon). Expelled quite a bit of nasty brown crap and more than a little air. Pedal felt fantastic on the ride home (did the work in a buddy's driveway).
Nice progressive feel to the pedal and much smoother braking. Most definately did some good here:D .
Still haven't restarted since sitting overnight. Will report back on what happens.
 
ridindirrty said:
Went with my gut and your reasoning and stuck with DOT3 although I went with Prestone Synthetic

Flushed a good 4 1/2 litres through the system (about a gallon). Expelled quite a bit of nasty brown crap and more than a little air. Pedal felt fantastic on the ride home (did the work in a buddy's driveway).
Nice progressive feel to the pedal and much smoother braking. Most definately did some good here:D .
Still haven't restarted since sitting overnight. Will report back on what happens.
Click to expand...

BRAVO!!
 
Same Thing Again

Well, here's the scoop, pedal feel has improved a great deal, braking performance has vastly improved...but...why must there always be a but:( ,
as I mentioned before, the car sat for about a day and a half. Started the car, no ABS pump. I was pleased because I thought everything was just that much better, but alas no. Pedal was hard as a rock and on the floor. Gave the pedal a push, ABS pump kicks in and pressurizes the system. System seems to lose pretty much all pressure if it sits for much longer than a day. Yet once charged up it performs as it should. Pump engages around every third or fourth pedal application, pedal feels great although i do at times feel a little shudder over the pedal stroke almost like there is air in there. This is NOT the ABS, it's VERY faint but it is there.
Does this sound familiar to anybody out there?
 
"..I would almost immediately say bad pressure switch.."

and I would agree.. It seems like pressure is leaking down past the pressure switch's proper limits, but the switch does not sense it, and does not turn on the pump.

I have a manual in front of me.
"..don't know where it is.."

It's mounted to the side of the pump itself, in a threaded boss.
It has a 5-wire connector attached.
It is removed with a factory tool.. a socket that fits over it's body. But if i recall, it can be removed with either an uncommonly large socket or a slip-wrench if there's room to swing it.
-------

The switch should activate the pump when system pressure drops to between 1900 and 2200 PSI.
It should turn the pump off when pressure increases to between 2350 and 2800 PSI.

The pumping-up should take no more than 60 seconds. A pressure gauge needs to be installed in the circuit to test accurately.
-----
However, it seems that ALL pressure is being lost during a period of inactivity. While the switch may be failing to activate the pump, from where, through where or how is that pressure escaping?

Pressure in the accumulator must be leaking past whatever check valve keeps it in there.

I am wondering if fluid could be leaking backwards through a bad check valve, backwards through the vanes of the pump, and back up into the reservoir.
[If pressure leaked the other way, through the master cylinder, it would go to the wheels expanding the calipers, thus apply the brakes and whatever "leaking" would stop there, so I doubt this is happening]

Does the Pressure Warning Switch (PWS) also include a check valve? Could a defective PWS affect both pump activation and pressure holding?
----

i'll keep reading and thinking on this.. it'd be nice if it can all be blamed on the PWS... not too difficult to replace it..
 
Tell me if this test will positively, without a doubt, confirm that the pressure switch is faulty:

First pump the system up and shut down the engine.

Turn the ignition off, but then turn the key to RUN. (The brake pump probably will not run. If it does, let it reach high pressure and it'll then shut off.)

Leave the ignition switch in RUN. Stand around and wait. [EDIT] No need to wait for pressure to drop. Just depress the brake pedal a few times and either the pump will go on or all pressure will be depleted.
 
OldSchool1 said:
El.
I love to quote the shop manuala.

Good fine. Nice write up. Good test.
Click to expand...

Thanks .. but if i had read more carefully, I'd have noticed the instruction to always replace the pump relay whenever replacing the pressure switch. :(
Maybe there is no test that can prove either one or the other is at fault.
(Relay is on the firewall, very near the master cylinder.. $50 at Ford)
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I guess low-pressure is detected by the PWS, and the controller in the trunk senses that. The controller then instructs the brake relay to close, which actually powers the pump..
So, although the pump doesn't activate, the PWS may be good, and either the controller or the relay could be malfunctioning.

There's a list of codes here.. any malfunction codes should be stored in the controller. A STAR tester would be the tool to access those codes.
Codes 11 and 99 point to the controller. #61 points to the PWS circuit.
 
I May Disagree Here

Elessee said:
"..I would almost immediately say bad pressure switch.."

and I would agree.. It seems like pressure is leaking down past the pressure switch's proper limits, but the switch does not sense it, and does not turn on the pump.
Click to expand...

I know where you're coming from but here's why that idea sounds fishy to me. I spent a good 4 hours on the weekend flushing and bleeding the crap out of this thing (key on - engine off). That pump cycled on and off countless times, never missing a beat, moving 5 litres of fluid through that system. At no time did it fail to switch on at the appropriate time.

Elessee said:
The pumping-up should take no more than 60 seconds. A pressure gauge needs to be installed in the circuit to test accurately.
Click to expand...

It never does.

Elessee said:
Pressure in the accumulator must be leaking past whatever check valve keeps it in there.
Click to expand...

That was my first idea. But...
It almost feels like there's a big pocket of air in there that floats to the highest part of the system when it sits idle. If I depress the pedal as it pressurizes (and for the first bunch of pedal applications), there is a good portion of the stroke with no resistance and then WHAM...there's the resitance.) Over a few applications (light pumping) the pedal feel improves until pretty much normal. It's like it's working through that air pocket i'm talking about. Am I way of the mark here? It sure seems to me like the pressure switch and pump motor are doing what they're supposed to do (99.9% of the time).
 
ok.. the system does seem to be working properly, except for what appears to be a loss in pressure when the car sits idle.

I'm wondering if the master cylinder has an air pocket in it. That can cause the pedal to go to the floor. After a few strokes, the pedal gets firm.

And, after depressing the pedal a few times the pump also goes on. This pump-up could be normal. Pressure need not be completely drained.. There is no direct evidence that accumulated pressure is gone. We only know that pedal action is weird.. In fact, since the pump does not go on, evidence suggests that pressure is high.

(maybe try this.. next time pressure seems to be zero, open a rear brake bleeder screw. If fluid jets out you've got pressure pushing it out.)

Notice that the reservoir has two low pressure hoses. One feeds the pump and the other goes to the front of the master cylinder. So, zero pressure fluid feeds the master cylinder. There might be lots of air up there.


-------

I could'a sworn i saw information about bleeding the master cylinder (MS) in the manual. It said the MS was bled just like a wheel caliper and had a bleeder screw. It said to bleed the MS before bleeding the wheels..

But i looked in the manual for that info.. cant find it or the bleed screw location on the master cylinder. Can't find it under he hood either... dang..

Searching Google all i see is bench-bleeding .. meaning the MS is removed and on a bench. Need to keep searching..
 
Hmmmmm...

Elessee said:
I'm wondering if the master cylinder has an air pocket in it. That can cause the pedal to go to the floor. After a few strokes, the pedal gets firm.
Click to expand...

This makes sense to me and I'll tell you why. About a year ago I had to change the ABS pump out as mine had an internal leak. Had a hell of a time getting that thing out of there. For the life of me I couldn't get at the screws or maneuver that thing out without yanking the whole master. What I DID do to avoid cracking those 22 year old hard lines was separate the ABS box from the master, leaving it in the car with those lines undisturbed.
I did the pump re&re on the bench, put the master back in the car, bolted up the ABS unit, bled the brakes, job done.
From that day no more leaks but...
my brakes have never felt quite the same. They stop the car fine but there has always been this intermittent dead zone along the pedal stroke, first third or so where there is no resistance. Always felt to me like an air pocket but no amount of bleeding seemed to change anything. The car stopped fine so I lived with it. I was just happy that it wasn't hemmoraging anymore.
This brings me to Now. The condition seems to have been aggrivated somehow, manifesting itself in the way I have explained. Sometimes when the system is building pressure after sitting it's like I can hear air passing through the pump. You know what i mean? The sound changes. Imagine the sound of ANY fluid pump passing air bubbles.

Elessee said:
(maybe try this.. next time pressure seems to be zero, open a rear brake bleeder screw. If fluid jets out you've got pressure pushing it out.)
Click to expand...

I like this idea.

Elessee said:
I could'a sworn i saw information about bleeding the master cylinder (MS) in the manual. It said the MS was bled just like a wheel caliper and had a bleeder screw. It said to bleed the MS before bleeding the wheels..
Click to expand...

I so wish i could do this.
 
Another way air can get into the MS is if the reservoir ever ran dry, like during a brake bleed.

ok.. so i see one reference in the non-ABS brake section. The manual directs Mark7 people to this section for instructions on bleeding the front brakes.

it says words to the effect that "If the Master Cylinder (why have i been abbreviating this MS when it's MC? :confused: ) is known or suspected to have air in bore, it must be bled first.

-------------
To bleed master cylinder, loosen upper secondary outlet fitting about three-quarters of a turn.
Have assistant push brake pedal slowly down through full travel.
Close outlet fitting.
Release pedal slowly.
Wait 5 seconds and repeat till no more air bubbles are seen.

-------------

Now, there are 4 brake lines and 3 fittings under my master cylinder's front end. I assume the upper secondary is one of those fittings.

Since there's no way to attach a hose, and fluid will make a mess on the floor, i guess bubbles will be visible as they spurt out of the loose fitting?

I'm not even sure this applies to an ABS system.. but it does seem like there must be a way to bleed the MC without taking it off the car.
 
Elessee said:
I'm not even sure this applies to an ABS system.. but it does seem like there must be a way to bleed the MC without taking it off the car.
Click to expand...

It sure sounds like it. I guess you're referring to those four lines that come out of the Teves box. Well, from the passage you've written there it sure seems like having air in the master cylinder bore is definately a possibility.
I also remember when we did that brake work on my car I had :q:q:q:qloads of air bubbling up and out of the reservoir after re-assembly. We "bled" that until there were no more bubbles and then moved on to the wheels. Ring any bells?
Thanks for scouring your manuals for this info by the way...the effort is appreciated ;)
 
If it were me, at this point i'd feel confident enough to loosen those brake line fittings and try a bleed.

First relieve all brake pressure, and then loosen and bleed all three fittings one at a time. I dunno if anything will bleed from the rear brake line fitting(s) since rear lines are normally under high pressure.

I can't envision any potential damage from giving it a try..

There might be some chance of air entering the MC if there's no accumulator pressure and the rear (normally pressurized) line fittings are loosened, and the pedal is depressed.. the MC might suck air with pedal movement.. i dunno..

Of course all this is easy to say since i don't have to mess with it.. and it won't be me that has to bleed the wheels again..
 
I Don't Know That I Would Say That ;)

Elessee said:
If it were me, at this point i'd feel confident enough to loosen those brake line fittings and try a bleed.
Click to expand...

I don't know that I would say that. I'm afraid that if I reef on these old fittings I might demo a hard line. Have you seen the bends on these things?:(

Any idea what the deal is with that big hex head on the top of the master? How sweet would it be if that was the way to bleed that baby. Hmmm...you know, I have the exploded view of the whole master cylinder complex. I'll have to go have a look for myself. Pretty sure I actually posted it somewhere here way back when :rolleyes: .
 
found your post..

http://www.lincolnvscadillac.com/showthread.php?t=43511&highlight=exploded+view+cylinder

That hex bolt or whatever it is, isn't labeled. It sure is big, and exposed and inviting..

Unless that bolt was designed specifically as a bleeding point, I have my doubts that it would be the proper place to do it. It's being positioned "high" means nothing. Wheel bleed points are low.

And why wouldn't they just put a caliper type bleed-nipple at that spot?

Does the bolt seem to offer any bleed for the ABS valve block? I can't see it.
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The manual has more than a few illustrations.. i'll take a closer look at them.
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[EDIT] I just realized something. Those three brake line fittings cannot be the place to bleed the master cylinder.

During a wheel-caliper bleed, those same 4 brake lines are bled from their lower ends / connections, but the M-Cylinder is not bled.. Why would the results of letting the lines bleed from their upper ends, mid length, or lower ends be any different?

btw, glancing at these illustrations, there's at least one instance of a notation to "not unscrew this plug for any reason". That plug, also atop the cylinder body but hidden under the reservoir, is a large hex-head with a cavity. The cavity accepts the reservoir's "push-in stud" which protrudes from it's underside.
 
Elessee said:
Unless that bolt was designed specifically as a bleeding point, I have my doubts that it would be the proper place to do it. It's being positioned "high" means nothing. Wheel bleed points are low.
Click to expand...

You're probably right but wouldn't say it's being positioned high would necessarily mean nothing. The bleed points on the calipers are where they are because it's the absolute end of the line. An air pocket in the MC would rise to the top of the bore if allowed to settle so it makes sense to me for a bleed point to be precisely there. But considering the size of that hex head it isn't likely that would be it.

Elessee said:
During a wheel-caliper bleed, those same 4 brake lines are bled from their lower ends / connections, but the M-Cylinder is not bled.. Why would the results of letting the lines bleed from their upper ends, mid length, or lower ends be any different?
Click to expand...

You took the words right out of my mouth. When I was looking it over last night I came to precisely the same conclusion.

What to do, What to do:runaway:
 
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