Very odd brake/alternator anomoly
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From: Boulder, CO
Very odd brake/alternator anomoly
After a really hard pull through 2nd or 3rd gear and a quick jump on the breaks my pedal is very hard. Like I've got no power break assist at all. After about 1-2 seconds the break pedal will depress and I'll get normal break operation.
Needless to say it's very scary when you are going 90mph and the break pedal refuses to operate for that 1-2 seconds.
I think the problem is that my car is draining all the power out of the alternator and it is not switching over fast enough to deliver proper power to the power break system.
I'm going to have the amperage measured from the altetrnator to see if it is low. The voltage is 14v as read by the PFC.
Is this a problem experienced by anyone else?
Is there anything I can do short of replacing the alternator?
Thanks!
Needless to say it's very scary when you are going 90mph and the break pedal refuses to operate for that 1-2 seconds.
I think the problem is that my car is draining all the power out of the alternator and it is not switching over fast enough to deliver proper power to the power break system.
I'm going to have the amperage measured from the altetrnator to see if it is low. The voltage is 14v as read by the PFC.
Is this a problem experienced by anyone else?
Is there anything I can do short of replacing the alternator?
Thanks!
Super Snuggles
Joined: Feb 2001
Posts: 10,091
Likes: 34
From: Redmond, WA
Let's see... you spelled "brake" properly in the thread title, but then proceeded to misspell it as "break" six times in your post... are you worthy of help? 
Just FYI, the "power" brake system does not rely on the vehicle's charging system at all. It uses engine vacuum (which is why there's a big vacuum hose leading from the brake booster to the upper intake manifold) to assist (hence the term "power") in depressing the brake pedal. That's it.
If you're having trouble with your brakes, and you've already ruled out air in the brake fluid, replace the large vacuum line mentioned above which passes across the top of the firewall. It has a one-way check valve in it that is intended to keep positive pressure (when the engine is under boost... exactly the situation you describe) out of the brake booster, which would (obviously) interfere with the proper operation of the brakes...
You're probably lucky the valve hasn't failed altogether. This is a known issue, and complete loss of the brakes can result. Personally, I wouldn't have been running the car up to 90 mph if I knew that there was a problem with the braking system...
Just FYI, the "power" brake system does not rely on the vehicle's charging system at all. It uses engine vacuum (which is why there's a big vacuum hose leading from the brake booster to the upper intake manifold) to assist (hence the term "power") in depressing the brake pedal. That's it.
If you're having trouble with your brakes, and you've already ruled out air in the brake fluid, replace the large vacuum line mentioned above which passes across the top of the firewall. It has a one-way check valve in it that is intended to keep positive pressure (when the engine is under boost... exactly the situation you describe) out of the brake booster, which would (obviously) interfere with the proper operation of the brakes...
You're probably lucky the valve hasn't failed altogether. This is a known issue, and complete loss of the brakes can result. Personally, I wouldn't have been running the car up to 90 mph if I knew that there was a problem with the braking system...
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From: Boulder, CO
aright wise guy, thanks for the help. Spelling usually falls into details I'm less concerned with.
I've been nervous about it so I was doing testing on a safe space where I could gear down if need be.
I'll investigate the check line. Thanks again!
I've been nervous about it so I was doing testing on a safe space where I could gear down if need be.
I'll investigate the check line. Thanks again!
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From: Dallas
Originally posted by jimlab
This is a known issue, and complete loss of the brakes can result.
This is a known issue, and complete loss of the brakes can result.
If the check valve failed you'd loose the vacuum in the booster and make brake application difficult. If you were on boost you could actually have the assist fighting you but that would end the instant you let off the gas and the bov vents the boost.
So where does this story of complete brake failure come from
Only was I see it possible is for the check valve to fail, fill the brake booster with pressurized air and then the check valve would have to somehow fail again and seal shut the vac line; in effect placing an inflated rubber bladder between you and the brake system which very well probably couldn't be overcome. I don't see it possible for the valve to fail that way; failing open and then instantly failing shut while the car is under boost.
built my own engine
Joined: Dec 2002
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From: Buckhead, Atlanta
check valve is to store max vaccum and help your brakes work a little better, it's not catastrophic if the valve fails, you juts have brake problems at certain RPM/driving conditions
it's mostly to keep oil/gas out of the booster
it's mostly to keep oil/gas out of the booster
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Thread Starter
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From: Boulder, CO
hmm. DamonB - yea, it sounds like the check valve is bad because the BOV does not vent immediatley and then I get normal brake (look ma, I spelled it right!) pressure back.
It only occurs when I jump from my gas to the brake very quickily. It is like the brake pedal is fighting me at that time. I'll see if that is the case. Thanks
It only occurs when I jump from my gas to the brake very quickily. It is like the brake pedal is fighting me at that time. I'll see if that is the case. Thanks
Super Snuggles
Joined: Feb 2001
Posts: 10,091
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From: Redmond, WA
Originally posted by DamonB
So where does this story of complete brake failure come from
So where does this story of complete brake failure come from
3.1 Recalls
There have been three recall notices put out on the 3rd Generation RX-7s,
two pertaining to engine fires, and one concerning brake booster failure.
You will want to make sure that the car in question has had these recalls
done. If they have not been performed, you will want to take the car to a
Mazda dealership where they will be performed free of charge. If you don't
know whether the recalls have been applied to a car, you can call the Mazda
Customer Service line at (800) 222-5500 with the vehicle's VIN, and they
can tell you.
3.1.1 Coolant recall
The coolant recall involved the replacement of some cooling system parts
with stronger/more heat resistant materials and lowering the pressure of
the cooling system from 1.3 bar to .9 bar. The parts replaced were the
water pump seal, the water level sensor, the upper radiator hose, the
filler cap, the filler cap body, the thermostat gasket, the water hose
leading to the throttle body, and the water hose leading to the coolant
separator tank.
3.1.2 Fuel line recall
The fuel line recall involved replacing the fuel lines under the intake
manifold with lines made from a more heat resistant material, and adding
a fan control unit that runs the cooling fans if the coolant gets too
hot, even if the car is turned off.
3.1.3 Brake recall
The brake recall involves the replacement of a vacuum check valve and
hose leading to the brake booster. The original unit may stick when
oily and cold, preventing power assist under braking.
There have been three recall notices put out on the 3rd Generation RX-7s,
two pertaining to engine fires, and one concerning brake booster failure.
You will want to make sure that the car in question has had these recalls
done. If they have not been performed, you will want to take the car to a
Mazda dealership where they will be performed free of charge. If you don't
know whether the recalls have been applied to a car, you can call the Mazda
Customer Service line at (800) 222-5500 with the vehicle's VIN, and they
can tell you.
3.1.1 Coolant recall
The coolant recall involved the replacement of some cooling system parts
with stronger/more heat resistant materials and lowering the pressure of
the cooling system from 1.3 bar to .9 bar. The parts replaced were the
water pump seal, the water level sensor, the upper radiator hose, the
filler cap, the filler cap body, the thermostat gasket, the water hose
leading to the throttle body, and the water hose leading to the coolant
separator tank.
3.1.2 Fuel line recall
The fuel line recall involved replacing the fuel lines under the intake
manifold with lines made from a more heat resistant material, and adding
a fan control unit that runs the cooling fans if the coolant gets too
hot, even if the car is turned off.
3.1.3 Brake recall
The brake recall involves the replacement of a vacuum check valve and
hose leading to the brake booster. The original unit may stick when
oily and cold, preventing power assist under braking.
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From: Dallas
Originally posted by jimlab
Checked the 3rd Gen. FAQ lately?
Checked the 3rd Gen. FAQ lately?
Loosing the booster is merely a loss of power assist, the brakes still work if you press hard.
Brake failure means no matter what you ain't stopping.
So the recall is for brake booster failure, not brake failure.
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From: Dallas
Originally posted by 93BlackFD
it's mostly to keep oil/gas out of the booster
it's mostly to keep oil/gas out of the booster
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