internal brake fluid leak?

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Elessee

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I've previously replaced the brake pump motor relay with a junkyard swap.
The old one's contacts were destroyed .. burned.. and had a tendancy to lock together and run the pump constantly and drain the battery.. (It runs with ignition-OFF)
That relay was the cause of a Mark 7 recall in 1989 or '90. It is under a lot of stress, switches high current, and doesn't last forever. Brand new relays are available at Ford for $52. These relays include an internal snubber circuit, a diode and resistor, for extra support.

I checked the "new" one tonight, and it's contacts are burned away like the old one. I suspect it is being overworked due to a fluid leak, described below.

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I just did a round trip 1000 mile nightime drive down Highway 5 through California to San Diego. This particular road is mostly flat, straight, has little traffic and allows +80MPH for hundreds of miles on end..

I didn't touch the brake pedal. But, every 25 minutes or so, the "Brake" and "Check Brakes" light lit, and stayed lit for around 65 seconds.. (I timed it) Bright RED and amber warnings .. at night.. very annoying.

There are / were no braking abnormalities or problems before, during or after the lamp is extinguished or in normal city driving.. nothing. There are no external fluid leaks, but I suspect there is an internal one.

Possible scenario:
A leaking valve in the master cylinder or ABS valve block slowly releases some of the 2,500 PSI in the accumulator. The system notices the pressure loss.
The pump goes on. Lamps go on. The pressure rises and the pump and lamps switch off.
This too-frequent on-off is killing the pump relay.
-----

So.. How do I pinpoint and fix an internal valve leak / pressure loss? First thing I'll do is completely purge and replace the brake fluid (tomorrow)...
I hope that does the trick.. If not.. well.. any suggestions are appreciated.
 
OldSchool1 said:
If you've checked all of the wet connections in the brake system and see no leakage, then your accumulator is going south.
Click to expand...


I've considered the accumulator... follow my line of thought and see if it makes sense or not..

As I understand it, the accumulator's interior is divided by an elastic (neoprene?) membrane. There's a gas (nitrogen?) on one side of the membrane. Brake fluid is pumped into the other side, which compresses the gas, and so stores extra hydraulic energy... enough high pressure fluid to provide several brake-pump cycles. The membrane keeps gas and fluid separated.

It's a simple thing.. no valves.. nothing but a steel ball with a membrane.

Now, what can go wrong with an accumulator?

Well, fluid / pressure could leak externally past a bad O-ring or similar.. But I have no external leakage.

Or, the membrane could have a crack, and fluid would seep into the gas area. Eventually the gas would be completely displaced by fluid and the whole ball would fill with fluid. No "elastic" hydraulic reserve pressure would be available.

Similarly, the gas could escape.. perhaps even through microscopic pores in the steel ball. If the gas escaped or somehow was lost, little or no reserve hydraulic pressure could build up. And, after just one brake stroke brake pressure approaches zero psi, and warning lamps light up.

This is not happening either, since I can pump the brakes several times as is normal... after which sometimes the pump turns on, but sometimes not..

An external fluid leak can be "bandaged" by adding more brake fluid. I'm not losing fluid.
An internal accumulator problem, like gas-loss or a broken membrane is a one-way street.. nothing can help that.. Normal levels of reserve pressure could not exist.

The only place in the system where reserve pressure can exist is in the accumulator. Far as I can see, that's the accumulator's only task.. and it seems to be doing it's job.

I'm losing accumulated pressure without touching the brakes.. something is allowing pressure to leak down. Then, the system pumps up and recovers normal operation.
-------

Another thought just occurred to me. I'm wondering whether or not if I'm actually losing brake pressure..
Could it be that a defective relay is sometimes stuck ON and the pump is running too much.. and over-presssurizing the system.. and overpressure is the reason the warning lamps light up?
 
Elessee said:
Another thought just occurred to me. I'm wondering whether or not if I'm actually losing brake pressure..
Could it be that a defective relay is sometimes stuck ON and the pump is running too much.. and over-presssurizing the system.. and overpressure is the reason the warning lamps light up?
Click to expand...

---------

I just realized that the only real symptom is warning lamps lighting up periodically (about every 30 minutes) without touching the brakes. I only assumed that the pump was running while the warning lamps are lit.. only assumed that the system pressure was low.
Otherwise, the brakes seemed OK and normal as far as brake strokes and stopping power.

------
Lets assume there is some small amount of normal internal leakage past valves or whatever. The system's sealing ability is not perfect.
So, while driving the pump goes on once in a while.
We drivers don't notice it. Pump goes on, the system recovers pressure within an acceptable range, the computer shuts off the pump, and all is well.

-------
Enter a bad pump relay.

System pressure drops to the pump-UP level. The relay activates the pump. System pressure rises to it's normal "high". But the bad relay is stuck ON.

The pump continues to pump. After about 20 minutes the pump-temperature sensor overheats and the pump shuts down to cool itself off.. At some point the computer spits out it's ERROR and the warning lights go on.

Since power to the relay is cut off, road vibration finally loosens the pump relay's contacts, and they separate. Meanwhile, the pump cools (Note that system pressure is adequate (high) and the brakes act normally while all this is happening.)

30 minutes later the same sequence of events recurrs.. i.e. Without braking, the system leaks down, the pump goes on and stays on too long. Pump over heats, and shuts down.. a fault is detected.. the warning lamps light up.. the pump cools off.. Rinse and repeat.

----
Fifty-two freakin bucks or not, I'm gonna spring for a new relay tomorrow.. the Ford guy had one on the shelf a couple months ago.. i hope it's still there.
 
Finally.

I've found someone more verbose than I am :)

You so nailed the answer that I cannot add to it.

I ~can~ change your mind about your accumulator assesment though as soon as I can locate Art's pictures and assessment of our accumulators.

In a nut shell, the gas ~can~ go into the fluid and the fluid ~can~ occupy the top of the accumulator (especially if the fluid is bad and compressable). At this point, the accumulator becomes more of an expansion tank than an accumulator.

The next time that anyone says that their brake fluid level is "variable" or "varies", consider the failed accumulator.
 
Last edited:
Other ideas

1, If it is losing the pressure, I would suspect a bad check valve. I would think it would be in the pump??? I tried looking it up in my Ford service manual but no luck.

2, Do you drive with both feet or do you use the right foot for gas and brake?
If you drive with both feet, do you always leave you left foot on the brake pedal?

3, Piston/bore/seals worn in master
 
OldSchool1 said:
Finally.

I've found someone more verbose than I am :)
You so nailed the answer that I cannot add to it.
I ~can~ change your mind about your accumulator assesment though as soon as I can locate Art's pictures and assessment of our accumulators.
In a nut shell, the gas ~can~ go into the fluid and the fluid ~can~ occupy the top of the accumulator (especially if the fluid is bad and compressable). At this point, the accumulator becomes more of an expansion tank than an accumulator.
The next time that anyone says that their brake fluid level is "variable" or "varies", consider the failed accumulator.
Click to expand...


Verbose is the word..
I figure a very few people are interested in mundane topics like weird brake problems (as opposed to sexy stuff like fancy wheels) and those few people might like things spelled out in detail.. But i have no legitimate excuses for talking too much..

Anyway, if my thinking is correct, a failed accumulator boils down to one thing: There can be little or no reserve brake fluid pressure if the accumulator has failed.
Accumulator failure means you couldn't pump the brakes more than once or twice before you experience a loss of power braking ability.

My car didn't have that symptom. Braking was normal while the warning lamps were ON and OFF. So, I don't think the accumulator has a problem.

I bought the new relay.. $52 :eek: ..ordered it and got it the next day.. installed it and have driven about 30 miles. So far no warning lamps.

Also, the pump hasn't yet been running when the engine shuts off.. something that was common previously. (It's mild vibration can sometimes be felt through the steering column.)
BTW, I'd open the hood and a light rap on the relay (mounted on the firewall) would (more often than not) shut the pump off, one indication that the relay's contacts were sticking ON.
(I believe this was the reason for the MK7 recall in the late '80s. The battery would run down and, of course, no brake pump/pressure while the overheated pump cooled off.
And some other stuff doesn't work properly with a low voltage battery (like the air spring system. IIRC, it needs to be fed around 11.5 VDC minimum or it starts to get confused.))

I'm driving to Vegas on Sunday... 8 solid hours. That will be the test of whether or not the new relay fixed whatever caused the warning lamps to light periodically.

-------------
Hey Ricks90billblass...
I am wondering if even in a brand new car, some small amount of the 2,500 PSI escapes over time (without hitting the brake pedal). I've worked with some hydraulic systems and I know that no seal is perfect. So, can it be that a brake system on a car with hundreds of thousands of miles is expected to lose a bit of pressure? If so, the pump should re-start once in a while to replace whatever pressure was lost.. and this might best be considered normal behavior, rather than something that needs fixing..

Bad check valve perhaps.. bad something.
There's a whole block of valves (the ABS valve block) mounted on the master cylinder. I've read up on it but can't say I know how it all works. I suppose that any leak in any sealing component could cause a leak-down / loss of pressure.
But to reiterate, I didn't experience a loss of pressure. All I know is the lamps lit. Why they lit is the mystery. Might it be overpressure from a constantly running pump? Did the computer detect a pump shutdown due to overheating? I dunno..

And I don't know why it's relevant but i was taught to drive an automatic with one foot. I think i was taught properly since it eliminates the chance of dragging the brakes..
---------

Enough verbosity for one day!
Thanks for the input.. I'll report back with whatever results there be..
 
Relay(ed)

Never enough verbosity for a Lincoln Mark VII owner :)

Elessee said:
... Also, the pump hasn't yet been running when the engine shuts off.. something that was common previously. (It's mild vibration can sometimes be felt through the steering column.)
BTW, I'd open the hood and a light rap on the relay (mounted on the firewall) would (more often than not) shut the pump off, one indication that the relay's contacts were sticking ON.
Click to expand...
Maybe I missed it earlier but that is a DEFINATE sign of a closed loop or ... a bad relay.
Elessee said:
... (I believe this was the reason for the MK7 recall in the late '80s. The battery would run down and, of course, no brake pump/pressure while the overheated pump cooled off.
Click to expand...
The primary recall was our pre 1990 ignition switches. See my signature.
Elessee said:
And some other stuff doesn't work properly with a low voltage battery (like the air spring system. IIRC, it needs to be fed around 11.5 VDC minimum or it starts to get confused.))
Click to expand...
ANY electrical conditions below 12 volts in our system will cause bad juju. You really should have base battery voltage (plus about 1.5 volts coming from the alternator) before even considering troupble shooting the others.
 
OldSchool1 said:
Maybe I missed it earlier but that is a DEFINATE sign of a closed loop or ... a bad relay.

The primary recall was our pre 1990 ignition switches. See my signature.
Click to expand...

I just drove to Vegas and back (1,000 miles) and the warning lamps didn't go on even once, (except as is normal on engine startups) so I'm pretty sure the whole problem was a bad relay.

The recall I referred to is on this page:
http://www.allworldauto.com/recalls/NHTSA_86V109000_1985_LINCOLN_MARK_VII_recall_10257.html

Here's the page info:

NHTSA Campaign Number: 86V109000
Vehicle/Equipment Make: LINCOLN
Vehicle/Eqipment Model: MARK VII
Model Year: 1985
Mfg Campaign Number:
Mfg Component Desc: SERVICE BRAKES, HYDRAULIC:pOWER ASSIST:HYDRAULIC
Mfg Involved in Recall: FORD MOTOR COMPANY
Manufacture Dates: 08-01-84 through 02-01-86
Type of Report: (V) Vehicle
Potential # of Units Affected: 38,000
Date Owner Notified by Mfg: 08-11-86
Recall Initiated By: ODI
Mfg Responsible for Recall: FORD MOTOR COMPANY
Report Recieved Date: 08-08-86
Record Creation Date: 08-13-86


Defect Summary: UNDER CERTAIN CONDITIONS, CONTACTS IN BRAKE SYSTEM RELAY COULD REMAIN CLOSED, CAUSING THE BRAKE PUMP MOTOR TO RUN CONTINUOUSLY, CAUSING IT TO OVERHEAT AND EVENTUALLY FAIL. CONSEQUENCE OF DEFECT: SHOULD THE BRAKE SUPPLY MOTOR FAIL, THE POWER ASSIST TO THE FRONT BRAKES WILL BE LOST, AND AFTER ABOUT 10 TO 15 NORMAL BRAKE STOPS, LOSS OF REAR BRAKE FUNCTION WILL RESULT, CAUSING INCREASED STOPPING DISTANCE. HOWEVER, THE INSTRUMENT BRAKE WARNING LIGHT WILL ILLUMINATE PRIOR TO REDUCED BRAKING CAPABILITY AND IF WARNING IS NOT HEEDED, AN ACCIDENT MAY OCCUR.

Consequence Summary:
Corrective Summary: REPLACE PUMP MOTOR RELAYS.

----------

So, what did they do about that defective relay? My guess is they only installed a slightly better relay in subsequent year/models.. the one that has a "snubber" circuit. Cut one open and you'll see the circuit. (I'm guessing that prior years had no snubber.)

A snubber circuit is a fat diode and a resistor across the points. To a degree, the snubber smoothes the sudden high current switching and helps reduce the heavy sparking, and supposedly protects the relay's contacts.

But it seems that these relays still go bad on a car that's 20+ years old. I see no reason to suspect a deeper problem.. except perhaps that they used a pump that draws more current than a reaonably sized and priced pump-relay can handle.

I'll open and check mine in a few months and see if there's appreciable contact erosion.
 
VERY VERY VERY cool post!

Thanks for the FACTS and also your indepth comments on the relay. Wow. I got about seven of these to replace.

Tahnk you!
 
I doubt anyone around here provides more helpful information than you do, OldSchool1.. So, thank you, too.
-------

There's one thing that puzzles me about that recall-explanation:
"...RELAY COULD REMAIN CLOSED, CAUSING THE BRAKE PUMP MOTOR TO RUN CONTINUOUSLY, CAUSING IT TO OVERHEAT AND EVENTUALLY FAIL..."

???
According to the manuals, the brake pump/motor on my 1988 Mk7 has protection against it damaging itself.

Page 12-32-96
Test D
Antilock Warning Lamp And Break Warning Lamp On And/Or Pump Motor Runs More Than 60 Seconds
(various test proceedures.. and)
"NOTE: If pump motor is allowed to run continuously for approximately 20 minutes, a thermal safety switch (inside motor) will shut off motor. A 2-10 minute cool-down period is typical before normal operation can resume."

-----
So, i wonder if that protective, internal thermal switch was added after the recall.. and if the earlier stock 1984/5/6 brake pump motors do not have the thermal safety switch.
If so, perhaps Ford's thinking was that the system was now protected, and maybe the original, problematic relays continued to be used in later years, while the pump motors (and controllers) are slightly different....

-------
To summarize the experience and draw conclusions...

The pump-relay contacts sticking closed seems to run the pump continuously, eventually tripping the motor's thermal switch. The controller sees this fault and both Brake and Anti-Lock lamps will light up. The pump motor is overheated and it's shut down temporarily.

Meanwhile brake fluid pressure does seem to be high/normal.

However, if you actually need to use the brakes a couple of times, be aware that there is no pump to pump the pressure back up for a period of some minutes (2-10).. so be real careful if those warning lamps are lit up...

Given time, the pump thermal switch cools. The controller senses that the pump is back online and, if needed, the pump will re-pressurize the system. (And here is where the relay's eroded contacts get another opportunity to stick closed, and to repeat the faulty cycle.)
 
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