Brake warning light

Tim Martin · 03-20-2001, 07:23 PM

I'm having problems with my friend the brake warning light. I was replacing my tach when i realized it wasn't hooked up, so i plugged it in only to find it blinks. Now it has NOTHING to do with the e-brake, as i've tested the hell out of that. Some people tell me there is a reset somewhere down in the MC itself. I can't find it. I've looked and looked. I have pictures. What am i overlooking?

http://talking-dog.com/tim/914

Rouser · Rouser's Garage

There should be a pressure sender on the MC itself, with 1 or 2 spades (signal, or signal & ground; depending whether it's an early or late model sender).

It should have one (signal) or both (signal & ground) wires connected, and a small reset pushbutton in the center of the sender. Sometimes they're easy to reach, but most of the time you have to lower the splash shield to get to it.

BTW: I went to your site (nice car) and was curious where you purchased the combo gauge conversion kit. Looks like something I might be interested in doing.

Tim Martin · 03-20-2001, 08:46 PM

The "misc" section of my website has images of the sender. I can't see any button, can you?

As for the 904-style gauge, the kit was from PP, but they don't sell them anymore. I will be documenting the kit soon so others can make their own if they have access to machine tools and a silkscreening shop.

check back in a week or two...

.tim

72_914 · 72_914's Garage

Forget about the combo gauge, those are some sweet a@# wheels! I would have never gussed what they where. Super nice everyone should check them out.

------------------
James
Cincinnati, OH
1972 1.7L 914

Rouser · Rouser's Garage

Sorry, dude; I looked all over your "misc" page and don't see any sender (let alone a MC) on the work bench.

I did click the buttons on the alarm key fob, but didn't hear your car bark outside.

Tim Martin · 03-20-2001, 09:17 PM

everything is going wrong today! I just realized that i copied over the "newer" html files with some old skanky ones. The new ones i did while i was at work, and my computer crashed today and i lost everything! I sure as hell hope we have a tape backup!

I'll be fixing that tomorrow to. Check the website in 12 hours or so I should have it back how it should be. There should be twice as much as is there right now.

efeinsmith · 03-21-2001, 03:44 AM

The pressure sensor is located between the the two brakeline connections, facing the driver's side of the car. It actually measures a difference in pressure between the front and rear circuit. If there is no button on the sensor, you might have to remove it to allow the shuttle piston to recenter.

Eric

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Or you might just not be seeing the button that is there. The button is covered by a rubber "nipple". Simply press in on that nipple, and that will press the button.

--DD

scg · 03-21-2001, 01:48 PM

. . . or it might not have anything at all to do with the m/c -- it could be a bad ground or other temporary short somewhere.

Before I started work on my car this winter, I'd be driving along, hit a bump, and the warning light would start to blink all on its own (and then stop on its own before I could get to the garage too). Sometimes it would just fry the fuse. Now I know why the PO had that fuse missing . . .

I can hardly wait to get the car back together and see if the problem is still there

scott

Tim Martin · 03-22-2001, 09:55 PM

So I fixed my website.

There are now pictures of the MC, and blow-ups of many of the images. Plus captions and a play-by-play of my engine rebuild.

fun fun.

http://talking-dog.com/tim/914

[This message has been edited by Tim Martin (edited 03-22-2001).]

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Hey, did you know that you don't have a reset button on your brake switch?

Sorry, I couldn't help it. Anyway, it looks as if you have the switch with no reset button. You can try pressing that center post, but I don't think it will do anything.

See if the switch is closed or open. When closed, it makes the brake warning light blink. Just put an ohmmeter or continuity tester on the two terminals. If they're open, the switch is not causing your blinking light--it's somewhere else in the circuit.

--DD

Tim Martin · 03-23-2001, 07:37 AM

Excellent. I'll test that tomorrow. If it's bad, i'll consider replacing it.

What makes it trip? High pressure on one side and low on the other? I am in the middle of replacing a brakeline in the back, but i haven't pressed on the peddle since I drained it so I would assume it's not tripped?

it's not well documented how that switch works.

efeinsmith · 03-23-2001, 08:44 AM

Tim, within the master cylinder is a piston that has each end exposed to one of the m/c circuits (front or rear). If everything is OK, the pressure on either side is equal and the piston does not move. If you has a leak, then one side would have lower pressure than the other and the piston would move toward the low pressure side. In the center of the piston is a groove that the tip of the switch rests on. When the piston shifts, the tip of the switch is pressed in and the switch makes. So to get the light off, the piston must recenter. Some m/c did that automatically and some required the switch to be removed to allow it to recenter (sorry, I don't remember m/c worked which way).