Brake warning light, what gives?

[UTKarmann_Ghia]

I rebuilt my front calipers a few weeks ago, installed new pads and bled my system. Pedal felt a little soft for a bit, but has gotten back to about normal now. Just to be sure I got all of the air out, I bled the front calipers again. As soon as I finished I took the car out and the pedal felt just a little stiffer, great. But now the stinking brake warning light is coming on.

Anybody know what gives with this? I checked the manual and it says the light comes on for 1) parking brake and 2) hydrolic problem. Really clear that one is. It's not a big problem as the brakes are working great, but man I'd like to figure out why it's coming on now.

[nostatic]

I think it also can come on in an over-voltage situation were the VR and/or alternator is not up to snuff.

[UTKarmann_Ghia]

Thanks for the thought. I checked my voltage last month, but I can check it again. Seems a bit strange tho that I bled the brakes and THEN it comes on.

Do you happen to know what the light keys off of? I should mention that it's on constantly, like the parking brake is on.

[AFJuvat]

It can also come on if there is an (engine) oil pressure problem. As well as a faulty contact switch in the reat of the handbrake lever.

Verify that you have good brake pressure and that you aren't leaking from somewhere (reservoir grommets and brake light switches immediately come to mind).

AFJuvat

[notmytarga]

After I rebuilt my calipers my brake light has been on like you describe. Occasionally it would be off but would come back with brake use. I read in the results of a search here that it is because of a master cylinder part that gets shifted in the process of redoing the brakes. If I remember correctly it is a plastic piece between the rear and front portions of the master cylinder that shifts when the pressure in one circuit is different that the other - and is sensed by the electrical warning switch screwed into the MC. How IS this reset??

I know that it took a while to get my S caliper pistons to stop retreating into the cylinders and during this time the front pressure was low. The solution to that problem is to pump them out against the old brake pads then force the new/thicker pads in.

For now mine is "fixed" by disconnectiong the electrical connection attached to the master cylinder behind the drivers front wheel.
I feel that I can tell if there is a brake issue without the need for a warning light - especially since I have gone over the system recently.

Eventually I will rebuild the MC - which is fine otherwise - to remove this gremlin. Unless someone can tell us how to reset that MC pressure equilibration indicator non-invasively!!

[Joerg]

Hi,

this is translated from Marks-webpage www.heckschleuder.de (TechTips):

Following will cause a light up of the brake light:

1) level announcement brake fluid container (if existing/year of construction-available)
2.) loss of a brake circuit
3.) tightened handbrake
4.) lining remainder thickness of wear contacts (if existing/year of construction-available)
5.) malfunctioning of the oil pressure switch (if existing/year of construction-available)

Diagnostic routine brake warning lamp 911 SC:

Flare continues to shine after starting the engine?

Yes: The oil pressure control light shines despite normal announcement of the oil pressure instrument likewise?

if yes: renew Oil pressure switch, and/or examine the wiring !

if no: The warning lamp shines after tightening the emergency brake somewhat brighter?

if no: Renew the switches at the hand brake handle, and/or examine wiring!

if yes: clamp battery for one minute, clamp to put back (chip-reset)!

The lamp is on after attaching the battery further?

if yes : replace Display unit, and/or wiring examine!

if no: The light will appear after breaking...replace both oil-pressure-switches, use new fluid.

-
Regards
Jörg

[Mike Feinstein]

Are you using pad sensors? If so, one may be shorted...if not, and they're tied off, one may be shorted. Just a thought.

[johnsjmc]

I,m not sure of the brake pressure differential switch design installed on your car but a common design has a switch that needs to be centered to keep the light off. If you bled alot from the front without bleeding the rear the switch is off center and indicates a low pressure situation as you describe.To reset to off you bleed a slight amount of fluid from the rear(or opposite )end while watching the light .Doing so will move the piston in the switch towards the other end and you stop when the light goes off.Alternately if the light comes back on you may have to bleed a little from the front again as the switch may have moved over center towards the other end.

[UTKarmann_Ghia]

Sounds good John, I'll have to give it a shot next weekend. I did bleed alot from the front brakes as I rebuilt the calipers a few weeks ago. I'll probably rebuild the rears next summer Kinda makes sense what you're saying. That may simulate a failure in the front or back systems causing the light to come on.

[UTKarmann_Ghia]

Last weekend I bled the rears as was suggested and the light didnt go off. Also, it's now been over a month since I rebuilt my front calipers and replaced my pads and I STILL dont have the firm pedal I had before this work. I was told that in a fairly short amount of time that they would settle in themselves and the pedal would firm up. Now, I hear a "click" when I release the pedal and it's about half way up. I'm beginning to wonder if something is now wrong with my brakes.

I did have my 17 year old push the pedal to bleed them, could that have hurt the master cylinder? I told him to be careful and not push the pedal to the floor, but who knows.

Does any of this seem familiar to anyone?

Do I need to take out my pads and fit them in tighter, even after a month of driving and several hundred miles?

?

[vash]

i know, i know. early s man told me the switch needs to be reset. the reset button is on the pressure sender switch attached to the master cylinder. it is in the middle of the switch under the tiny rubber boot. it really isnt a button, but more of a tiny plastic plunger that needs to be pressed back in this if for the internally grounded switch, one wire to it.. i read somewhere the older switches (with two wires going to it, one for ground) is reset by disconnecting the neg battery cable.

that be my guess....

cliff

[cstreit]

Loss of pressure and/or when the pedal goes to a certain point (like when you're bleeding or redoing calipers) sets it on.

On the SC I think all you need to do is disconnect then re-connect the battery to reset it. On earlier cars you need to reset the switch manually as unfixed sez above.

[UTKarmann_Ghia]

Man, you guys ROCK! I'll try it this weekend when I have a few minutes. I dont know what I'd do without this board...and I dont wanna find out. Cheers to you brothers, thanks again!

[vash]

let us know if it works.

[Early_S_Man]

Non-boosted brake systems have the 'centered-pin' switch ...

SCs and other vacuum-boosted brake system have two VW-style SPDT pessure-sensitive switches mounted on the master cylinder pressure ports. The switches get gunked-up by rubber wear products, corrosion, etc. over time and have to be replaced. Same exact ATe switch was used on all VW Beetles from '67 thru '79!

[UTKarmann_Ghia]

Warren, is there some sortof diagram on pelican that shows the switch you're talking about?

Is it common that after caliper rebuilds and bleeding that these all of the sudden go bad? Could these be why my pedal is not firm again?

[Early_S_Man]

Matt,

When you bleed the brakes you excercise the cups and seals over the entire length of the master cylinder bore ... thus, particle buildup may be dislodged and disturbed from its' normal resting place that lies undisturbed in normal use of the brakes. It only takes a few milliseconds difference in the operating speed of the two switches to activate the warning lamp!

Here is the pic of the master cylinder and switches from Pelican's catalog:

[UTKarmann_Ghia]

Oh, you're talking about the brake light switches? I didnt know there were 2 of them and I didnt know that the time delay between them acts as a switch to the brake warning light. Is that what you're saying?

But why would these switches also give me a soft pedal, or would they?

[Early_S_Man]

Matt,

Yes, the brake switches act as a trigger for the brake warning lamp via the Black wire. See circuits below ...

I don't think the switches are related to a soft-pedal condition.

[UTKarmann_Ghia]

Well, I talked with a local mechanic. I told him what was going on and that I also heard a clicking near my brake pedal when it comes back up. Never heard this before and the pedal has never traveled that far before either, even though my brakes feel pretty good. Well, he said it sounds like I may have ruptured a seal in my master cylinder which is logical since I had my 17 year old pumping the brakes for me when I was bleeding them.

Does anybody know if you can buy a rebuild kit for our master cylinders or do you have to buy a rebuilt one?

Grrrrr, I hate it when I break something when I'm trying to fix something!