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  #1 (permalink)  
Old 07-13-2009, 11:56 PM
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Mysterious Brake problem

This is no hotrod question but I'm desperate!
My 18 year old daughter's car is a 96 accord. It has 245K and runs great except for one major problem. Occasionally when driving slow the brake pedal goes to the floor. When this happens there is usually one wheel that has brakes, the drivers front. But the pedal goes to the floor before anything happens and the car does not stop. DANGEROUS! It happens maybe every other day of driving.

Now let me give you some history.
This started after I replaced the master cylinder a year ago because it was leaking. Since then I have replaced the master cylinder a second time. Then replaced the abs system, then last weekend the master cylinder a third time.
Yes, I bought each of the master cylinders from different manufacturers.
I am certain there is no air in the system after the installations.
There is no fluid leaking anywhere.

Because it only happens when rpm's are low it almost has to be speed related.
Could it be the booster? What could cause the system to lose pressure temporarily other than the MC? Caliper?

Desperate here! Please help!

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Old 07-14-2009, 06:29 PM
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I doubt it is the booster, they are usually a solid connection with a diaphragm in the middle. I would say master cylinder but you have changed it 3 times. I would bleed the whole system again and see if you get any air. I am guessing you are not using any fluid. How is the pedal when it doesnt go to the floor. Is it solid.I would also check all the calipers mounts to be sure they are tight. Those have a strange brake line arrangement. A bad connection somewhere could be sucking air into the system somewhere.
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Old 07-14-2009, 08:16 PM
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When the brakes work they work great. Should I start replacing the rubber lines the calipers?
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Old 07-14-2009, 08:32 PM
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Did you bleed the abs system? To bleed it.Find the abs relay.Find the two big copper colored female pins on the socket.Use a jumper to run the pump for not over 15 seconds.(The key may have to be on)
You will see an 8mm or 10mm bleeder on top of the abs pump.It looks just like a brake bleeder.
You can put a hose on it.I just use a rag.It will be under pressure so watch your face.
You will see the fluid in the pump going down.Refill as necessary.

Repeat,run pump.stop,open bleeder,close bleeder,run pump.You are done when there are no more air bubbles.The fluid will be clear.




For clean up.I have found a water hose does the best to clean up.
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Old 07-14-2009, 08:33 PM
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Yes, we bled it after we replaced it.
Keep the questions coming! I know I missed something
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Old 07-14-2009, 08:51 PM
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I would really try bleeding the abs again.It does not take long at all.
I run the pump,open bleeder,close bleeder run pump,etc. For about 12 times.I clean ever thing up.Then I get the car up to about 20MPH in a safe area and lock up the brakes to make sure the abs is working(a grass field is great).And I drive it back in the shop and bleed the pump a couple of more cycles.
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Old 07-14-2009, 10:19 PM
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Quote:
Originally Posted by redlightning
I would really try bleeding the abs again.It does not take long at all.
I run the pump,open bleeder,close bleeder run pump,etc. For about 12 times.I clean ever thing up.Then I get the car up to about 20MPH in a safe area and lock up the brakes to make sure the abs is working(a grass field is great).And I drive it back in the shop and bleed the pump a couple of more cycles.
We bled it twice, replaced it, bled it the new one. Each time we did it according to the Honda Service Manual specs.
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Old 07-14-2009, 10:20 PM
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Quote:
Originally Posted by redlightning
Did you bleed the abs system? To bleed it.Find the abs relay.Find the two big copper colored female pins on the socket.Use a jumper to run the pump for not over 15 seconds.(The key may have to be on)
You will see an 8mm or 10mm bleeder on top of the abs pump.It looks just like a brake bleeder.
You can put a hose on it.I just use a rag.It will be under pressure so watch your face.
You will see the fluid in the pump going down.Refill as necessary.

Repeat,run pump.stop,open bleeder,close bleeder,run pump.You are done when there are no more air bubbles.The fluid will be clear.




For clean up.I have found a water hose does the best to clean up.
These are excellent directions but we have done this several times.
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Old 07-31-2009, 06:49 PM
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is there a proportioning valve somewhere?
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Old 07-31-2009, 09:36 PM
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When the pedal goes down can you pump it up?

If not, something is leaking. Either the MC or a valve in the ABS ( I don't know ABS's tho)
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Old 08-01-2009, 07:46 AM
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Are all of your vacuum lines attached and not leaking?
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