Petza914

I cleaned my car getting it ready for the SITM trip on Friday and did some rinsing under the hood (I know - not the brightest idea). When I went to move it back into the garage, I got a flashing Brake Pressure warning light. I've never had this before and the brakes were redone during the build so I'm thinking I just got a connector wet as the brakes have also always been fine, fluid level is fine too and there's no fluid on the ground and has never been. I installed a new main ground strap today so I've done the battery disconnect / reconnect, but with just the key on (not starting the car), I still have the flashing warning light.

So need some advice - will starting and driving the car if nothings wrong cause the light to go away? Will some miles with some air moving around likely clear away the water and allow me to reset the warning with the dash button? If I truly do have a problem, will it be immediately apparent as soon as I go to brake the first few times? Any ideas on what easy to access connectors I could check for wetness that could trip this?

What's the consensus about driving it with the warning light on, as I don't really think I have a problem, just a warning light.

Thanks.

dr bob

Pete--

The brakes on your car are diagonal split rather than front-and-rear split. On the master cylinder there are two identical pressure switches, each a "single pole double throw" configuration. If pressure drops in one circuit but not the other as you press the pedal. the simple alarm-light logic gives you the warning. Since the warning is coincidental with the wash you did, it's probably water into one (or both) of the switches that's causing the symptom.

It might be tempting to see if it clears on its own as a wet switch dries out, but... My experience has been that it may clear for a while after it's dried out, but the corrosion caused by the water in there will eventually disable the switch and the light will come back.

What I'd do: Dry the switches out now, using a heat gun or similar, to get the water out before it starts corroding stuff inside. In pinch I'd go lightly with a little butane torch. Just warm enough to encourage the water out. If that doesn't work for you, replace the switches. They are easy thread-in switches, three wires connect to each one. You can find them at almost any parts place, but I recommend that you buy a matched pair of good switches regardless of the source. In a pinch, VW dealers carry the best switches (same ATE switches as Porsche OEM), albeit at a steeper price.

Ping Dave & Jeannie, and they can throw a pair in the trailer for you if they haven't left already.

Robbrizzle

I've had a bad pressure switch (there are two) cause that. I can't recall the precise time for the battery reset you've tried but 5 mins to be on the safe side should do it.

hacker-pschorr

When I bought my 80 they were both leaking causing the warning.

EDIT - also posted below. For some reason I thought I mentioned this in the initial post:

FYI for anyone who runs into issues with these switches. The switches could have a very minor leak, so minor the leaking fluid stays pooled up in the rubber boot and nothing external is visible. That is until the leak gets worse and suddenly the pedal goes to the floor and you have no brakes.

safulop

Isn't WD-40 supposed to drive out water?

Petza914

Thanks everyone. I'll take a look at bit later tonight and see what I see. I can do a 2nd battery disconnect after as I haven't put everything back together yet, like the Sharkwoofer.

dr bob

Of course... Don't totally discount the idea that there really is a pressure/braking imbalance, and the switches are working exactly as designed.

Most warning systems are fairly robust, fail to a somewhat "safe" mode, etc. 'Fairly robust' is the key phrase here. The switches are a wildcard, in that there are cheap ones and better ones. Often, when a system works correctly and the light comes on, we immediately jump to the conclusion that the switches have failed. May or may not be the corect conclusion. There's always that wild chance that the warning is appropriate.

Petza914

Checked it out and it looks like the fiont-most master cylinder pressure switch is probably the culprit for the warning light. Boot was very wet inside and the wires and connectors were green. Dried everything out and used some Deoxit D5 on it, put things back together, but still have the light. Did a battery disconnect/reconnect, waiting about 10 minutes before reconnecting, and still have the light. What I wasn't able to do tonight was start or drive the car (since the kids rooms are right about the garage) to see if that would clear the light, but I'll try that before heading out in the morning. By the condition of the connector, I'm not too concerned about the light being on. I also haven't driven the car since washing it so I have a nice light coating of rust on the rotors. After applying the brakes the first time, I'll take a look to see if all 4 have been wiped clean or if 2 of them (one front and one rear) look like they're not being applied, which would lead me to believe I might have a pressure issue and I'll have to come up with a plan B, which would probably be to head up in the 997 and park in the 2 cylinders short & wrong engine configuration section but at least get to meet everyone and deliver the parts that have been committed to.

Chris Lockhart

Good luck with it Pete. Hope you have a blast at SITM.

Imo000

Take it out for a good test drive and if the brakes feel fine, keep driving to the SITM. Figure out the warning system problem when you come back, probably an electrical issue.

hacker-pschorr

FYI for anyone who runs into issues with these switches. The switches could have a very minor leak, so minor the leaking fluid stays pooled up in the rubber boot and nothing external is visible. That is until the leak gets worse and suddenly the pedal goes to the floor and you have no brakes.

Petza914

That's exactly what I did. Looks like the switches were ruined by water. Brakes are fine and Stan took a look for me - thanks Mr. Merlin. I'll get some new switches on order.

Thanks.

Imo000

Only if it wasn't a split system by since t it is a split system, you will have brakes for the other two wheels. It's a diagonal setup so this makes it a safer setup.

hacker-pschorr

That's a nice theory on the bar napkin, but in reality it doesn't work that way. Sure you have some brakes but to imply it's no big deal, keep driving the car is not the best advice.

This happened to my 80 last year. The pedal suddenly went to the floor and the car didn't stop as it normally should. For that brief moment it felt like there were no brakes at all.
Thankfully we were just around the corner from home on country roads so I was able to slowly and safely nurse it home. Even with the split system, I still had to use the parking brake to bring it to a complete stop at intersections.

Granted, it appears a leak is not Petza's issue, but for anyone else who gets the flashing brake warning light on an early car, don't take it lightly until it's fixed or properly diagnosed.