Strange noise on 964 C-4

Hey everyone! I am pleased to report my recent purchase of a 90 C-4. I am absolutely in love. When I come to a stop, I hear a humming noise and feel a vibration through the brake pedal. Is this normal? Does anyone know what this noise is? If I let the car sit for several days and then start it, the warning lights for the brake and interlock come on for approximately 20 seconds and then go out. Is this normal also? Any help would be greatly appreciated. Thanks!

I don't know anything about the brake problem, but my 964 had the same dashboard light problems when I bought it. Turns out that a weak battery and a bad ground cable were to blame. I changed them out and the problem hasn't occured since. This also cured a problem I was having with erratic idel speed after a warm restart.

The C4 uses a hydraulicly actuated brake booster. It is possible that you have a prblem with this pump.

Scroogie:

I can't hear your noise from here, so without any details, it's tough to tell what you're up against.

I just bought a '91 C4 recently with VERY low miles. I am NOT an expert on these cars, in fact I'm still waiting on a back order of the 7 volume service manuals to come in (may take weeks...maybe even months..who knows?), but I can tell you what I've learned over the last year while researching the car as well as my own experiences with my C4 and cars in general.

Here are some points:

1. The brake fluid is used for more than just the braking in a C4. I believe the same fluid is used with the hydraulics associated with the all wheel drive system. It's supposed to be changed every two years. The system is pressurized and apparently a Bosche Hammer ($$$ tool) is needed to assist in changing the fluid. Make sure the previous owner was doing this.

2. My car does not exhibit any of the warning systems you're describing (lights staying on). I'm suspecting that you're getting a fault code, and you need a mechanic with the Bosche Hammer to read the codes to determine whether or not the faults are being recorded. Haynes publishes a manual that describes how to read these codes without a "Hammer", but I'm uncertain how well their procedures work.

3. The fuel pump, if it was marginal, MAY be able to translate vibration into a feeling in the brake pedal, but I sort of doubt it. This is speculation on my part. The fuel pump and tank are located in the proximity of the pedals. Noise like that you're describing is not uncommon when a fuel pump is failing or the pickup filters are dirty.

How many miles are on the car?

How are extensive are the service records?

Did you have a PPI done before buying the car? Did the mechanics use the "Hammer" to read any stored codes?

I suppose that if the car has a fair amount of miles it may take more time to pressurize the hydraulics (or perhaps there's a leak of one form or another) hence leading to the lights that stay on and then go away (once again, an educated guess...take it for what it's worth).

Hope this helped in some way, but as far as my own C4 goes (and yours as well) I'm a novice too.

Good Luck,

Bill Wagner