964 Newbie: Question on Brake Booster Pressure
#1
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964 Newbie: Question on Brake Booster Pressure
Good morning all. I've had my 1991 964 C4 Cabrio for about two months now. Had some small bugs initially as the car and I got to know each other, but it's been running like a champ since resolving a vacuum leak that caused some stalling and hesitation.
Last Friday morning I had to do an emergency stop that engaged the ABS. Everything worked perfectly afterward, and the car was fine until today (Monday) when the "Brake" and "Differential" lights have come on and stay lit. The owner's manual says its a situation of low brake booster pressure and to wait for pressure to build up - but does not specify how long to wait.
I don't see any evidence of leaks or anything in the front trunk area. Any ideas? Brake fluid is about 1/8th of an inch from the "Min" level - could it be something as simple as adding a bit of DOT4? Running the engine and pumping the brakes a few times?
Thanks!
Last Friday morning I had to do an emergency stop that engaged the ABS. Everything worked perfectly afterward, and the car was fine until today (Monday) when the "Brake" and "Differential" lights have come on and stay lit. The owner's manual says its a situation of low brake booster pressure and to wait for pressure to build up - but does not specify how long to wait.
"If the brake pressure, interlock and central warning lights come on after starting the engine, you should not drive off until the pressure necessary for the brake booster and interlock control system has built up, and the warning light goes out."
Of course I read all of this AFTER I drove the car around for a 15 minutes and everything seems to be fine - no soft pedal or anything - but the lights never extinguished. I would think that would be adequate time for the pressure to build.I don't see any evidence of leaks or anything in the front trunk area. Any ideas? Brake fluid is about 1/8th of an inch from the "Min" level - could it be something as simple as adding a bit of DOT4? Running the engine and pumping the brakes a few times?
Thanks!
#2
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Yes, it could be that simple. Low fluid level will trigger an alert. No need to pump the pedal after adding fluid. The sensor is in the cap of the brake fluid resevoir. Although if the fluid did get to low you may need to flush the booster pump and accumulator.
Do you hear the booster pump running when you turn the key on?
Do you hear the booster pump running when you turn the key on?
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Thanks! Hey Rocket Bob, Nashua, eh! I'm right up the road in Amherst, we should connect some time! I'm an NCR-PCA member, but don't make too many events as my schedule has not allowed it. I am working on a 944 to run DE and Auto-x - hopefully next season.
#5
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Well the problem seems to have fixed itself. Went out again and no more lights. I'm going to go ahead and add some brake fluid just in case, but so far so good.
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Reservior topped up. Noticed that the lights do tend to stay on longer than the others. I wonder if it was a case of me driving off before they went out. If I wait an extra 5 seconds, they seem to go out and I'm good to go.
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#8
IHI KING!
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My ABS light takes a while to go out too. I have gotten used to it. Typically, the lights go out before I leave the parking space or garage. I have never timed it but I would say it takes 10-20 seconds.
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I thought a light or two is supposed to stay on until you hit 3K revs.
#10
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sound like your pump is good I would flush and bleed the entire system. Start bleeding with the bomb first.by turning the key on and opening the bleeder valve.(only a couple of seconds)
I do have these parts if you need them but I don't think you will.
Elliot
I do have these parts if you need them but I don't think you will.
Elliot
#11
Three Wheelin'
If the hydraulic system is working as intended the booster pump should stop after something like 20 seconds after an overnight stop. If it takes longer it's a sure sign that the primary hydraulic circuit needs bleeding.
My car took almost a minute and a half for the pump to stop before the hydraulic bleed. Now it's 20 secxonds.
Regards
Dave