Brake Lights do not work

[red911]

Hello all,

My newly restored at home 1967 911 has a very spongy brake pedal. At first during the first 25 miles and brake pad bedding procedure, the right rear locked up. I took the advice of this group and found that I did not have the 1 mm distance from the brake pedal shaft to the master cylinder.

Then I lost my brake lights. I have attached a photo of the brake light switch. It has a dual master cylinder set up. The switch has continuity at approximately 2 cm, so it works fine. Also, no fluid comes out of the master cylinder, even when I push hard on my spongy pedal.

I would think that brake fluid would exit the hole where the brake switch threads in? Am I correct?

The brake pedal almost goes to the floor and I have bled and rebled the calipers. And yes, the bleeders are pointed up.

Any ideas?

Thanks in advance, Tom

[Xavier PJB]

Hi,

I would say the purge was not done properly and either you do have enough brake fluid or have air in the circuit. About your stop light, maybe silly tip, have you checked the fuse ? (I blown half a dozen of stop light fuse, before fixing it by putting a bigger fuse :-)

Cheers

[edmayo]

Dual circuit master cylinders used a mechanical brake light switch on the pedal assembly, that switch is the warning switch for loss of pressure in one circuit. When I put a dual circuit master cylinder on my 67 I used the original pressure switch by adding another banjo.

[red911]

Hi Brakekiller. I am thinking that there is air in the system, but after purging and purging, the pedal is still spongy. The brake light circuit works because I used a jumper wire with alligator clips and the brake lights came on, so the fuse is good. I did not bleed the master cylinder prior to installing. Any tips on trying to get the air out of the master brake cylinder while it is on the car? I think that is where the air is stuck. Should the warning switch hole with the switch out have fluid come out under pressure (and I put a lot of foot pressure on the pedal)?

Thank you Ed. I used a jumper and the brake lights lit, so the wires I have plugged into the warning switch is for the brake lights. I should either use a contact switch on the brake pedal inside the car, or a banjo to feed pressure from the brake lines to the larger brake switch. In the '66 911 I restored, I used a NAPA microswitch on the brake pedal. Since there are no additional wires in a single brake circuit system, I can just leave the warning switch there without any wires, and go to the microswitch, or a banjo.

Thanks Tom

[red911]

Hello all,

I went to this site to look at "histeris" or getting the brake caliper rubber seals to seat.

First, I bled each wheel, then, I took out the brake pad and replaced it with a piece of wood so the brake piston would push in. Then, I pushed out the piston and replaced the pad. I did each wheel one at a time, and each pad from the outside to the inside separately.

http://www.hillmanimages.com/912/030629-2937.html

The pedal is more solid, but still spongy.

Any more ideas, other than continuing to use the brakes?

Thanks Tom

[edmayo]

If you have both new pads and new or turned rotors it will take several hundred miles to seat in which should result in a firmer pedal.

[John912]

I would go back and check clearances at the brake pedal shaft. The conversion to dual master requires that you shorten the shaft. In any case, when I shortened mine I couldn't get a hard pedal so (after repeated bleeding with no results) I went back to adjust the clearance and it all worked fine.

Hello all,

My newly restored at home 1967 911 has a very spongy brake pedal. At first during the first 25 miles and brake pad bedding procedure, the right rear locked up. I took the advice of this group and found that I did not have the 1 mm distance from the brake pedal shaft to the master cylinder.

Then I lost my brake lights. I have attached a photo of the brake light switch. It has a dual master cylinder set up. The switch has continuity at approximately 2 cm, so it works fine. Also, no fluid comes out of the master cylinder, even when I push hard on my spongy pedal.

I would think that brake fluid would exit the hole where the brake switch threads in? Am I correct?

The brake pedal almost goes to the floor and I have bled and rebled the calipers. And yes, the bleeders are pointed up.

Any ideas?

Thanks in advance, Tom

[304065]

I don't think it's the shaft length, if the OP has 1mm clearance then he MUST have shortened the SWB shaft, as it's about 3/4" too long to begin with.

Here is the original single circuit - see it has one inlet and two outlets- one for the left front and one for the right front and rears, on which the brake light switch is mounted. Photos from http://classicandspeedparts.com/ where I bought my dual-circuit.


Here is the dual circuit below.



Notice that it does not have a brake light switch, it has a brake FAILURE switch. The brake LIGHT switch was mounted on the pedal cluster as you can see here.

http://www.early911sregistry.org/for...by-Bruce-Stone

I agree with Ed, either mount the pressure switch on a banjo fitting or convert to the later pedal cluster.

Ed is also correct that new stuff takes a while to feel right-- I have restored calipers, new rotors, new pads, new lines, new MC and new fluid and it still feels like the final laps of a 90 minute enduro. I have bled the system with a pressure bleeder and gotten all kinds of yellow preservative grease out of the master cylinder. It will get better or it will get taken apart!

[John912]

Sorry, I was responding to: The brake pedal almost goes to the floor and I have bled and rebled the calipers. And yes, the bleeders are pointed up.

Any ideas?

[304065]

Sorry, I was responding to: The brake pedal almost goes to the floor and I have bled and rebled the calipers. And yes, the bleeders are pointed up.

Any ideas?

I'm with you now.

Yes, I think there are air bubbles hiding in the pistons. After safely jacking and supporting the car so it doesn't fall on you and cause personal injury or property damage, remove the wheels, remove the hairpins, pins and brake pads, and retract each piston all the way into the bore so it doesn't go any further. A good, but whoppingly expensive, tool for this is the HAZET 4971-1 :



Anyway, this should push the air back there into the caliper where it can escape into the (upward pointing) bleeder valve.

Take care during this operation that you don't overflow the fluid reservoir. This will push fluid backwards into the reservoir. If you can't do this, it tells you that you truly haven't achieved the 1mm clearance and the piston in the MC is still depressed.

Now bleed normally.