Brake pad warning sensors - opinions please

[Fab64]

Hi all,

I've just started getting a brake pad sensor warning on my 1984 Carrera, so I pulled the wheels on the driver's side to see what the pads look like. I've only had this car since last August, it's my first 911 since I sold my '72 911T nearly 30 years ago, so I'm not sure what the sensors should look like.

Here's the left front - it looks to me like there's still some meat on the pad, and the sensor hasn't reached the rotor yet:




Here's the left rear - the inner pad looks pretty thin, and the sensor seems to be hanging over the rotor. Is this what it looks like when it gets worn down? I haven't tried un-plugging this sensor to see if the light goes out.



I'd appreciate your thoughts, thanks.

[chrisbruck]

Yes, I'd say that inner rear one would trigger the light. Also note the uneven wear on the back pads. The outer piston may be sticking. Probably time to rebuild the calipers. Make sure to check the passenger side too and assess the wear characteristics on that side.

[Fab64]

Thanks for confirming! I did notice the inner pad on the rear looked thinner, but didn't consider why this might be. Guess I'll be ordering a couple of caliper rebuild kits from our host. And, yes, I'll check the passenger side as soon as I can get access to that side of the car. Thanks again!

[yelcab1]

The second pix is worn out.

[eastbay]

Originally Posted by Fab64

I'd appreciate your thoughts, thanks.

Stuck piston on left side, look at the pad build up on the pin.

[bkreigsr]

Not a maintenance area where you should be frugal.

Put new pads on and sleep better at night.

They are relatively cheap and easy to install.

[Fab64]

Thanks, guys - I appreciate your experienced eyes. I had quite a bit of work done at a local facility in September, just after I got the car, and they never mentioned the brakes at all! Really surprising, as they were very thorough in the other work they did.

In any case, here's what I plan to do:

Drain the brake system, and replace the four brake hoses (at least one is dated 1984! ).
Rebuild rear calipers (inspect the fronts).
Inspect all four rotors to see whether or not they're within spec. If not, they'll be replaced.
Replace all brake pads.
Re-fill system with new fluid, and bleed.

Thanks again, this forum is a life-saver.

[Mark Salvetti]

I wouldn't drain the fluid as a first step. Much less likely to get air trapped in the master cylinder if you don't drain it. Instead, you can use a 2x4 to lightly depress the brake pedal. Just a couple of inches. That should keep the master from draining while you replace the hoses. You might also use some tubing and a clamp over the end of the metal lines, or even a piece of a nitrile glove secured with a zip tie.

I also like to pre-fill the caliper with as much fluid as possible before I reattach the brake line.

Then bleed the system.

Mark

[HarryD]

Originally Posted by Mark Salvetti

I wouldn't drain the fluid as a first step. Much less likely to get air trapped in the master cylinder if you don't drain it. Instead, you can use a 2x4 to lightly depress the brake pedal. Just a couple of inches. That should keep the master from draining while you replace the hoses. You might also use some tubing and a clamp over the end of the metal lines, or even a piece of a nitrile glove secured with a zip tie.

I also like to pre-fill the caliper with as much fluid as possible before I reattach the brake line.

Then bleed the system.

Mark

This. No need to drain unless you enjoy pumping a lot of fluid to get all the air out. When I replaced my brake lines and frond caliper, I did the above. All the air was purged as part of a normal flush.

[Quicksilver]

Originally Posted by Fab64

. . .
Here's the left rear - the inner pad looks pretty thin, and the sensor seems to be hanging over the rotor. Is this what it looks like when it gets worn down? I haven't tried un-plugging this sensor to see if the light goes out.
. . .

BTW - Unplugging the sensor won't make the warning light go out. If any sensor is unplugged the light will come on.

[Fab64]

Originally Posted by HarryD

No need to drain unless you enjoy pumping a lot of fluid to get all the air out. When I replaced my brake lines and frond caliper, I did the above. All the air was purged as part of a normal flush.

My reason for draining was to get new fluid into the system. Unfortunately, I didn't receive any maintenance history records with this car. But based on the deferred maintenance I've seen so far, I'm guessing the existing fluid has likely been in there for a very long time. Is there a better way to do that?

[HarryD]

Originally Posted by Fab64

My reason for draining was to get new fluid into the system. Unfortunately, I didn't receive any maintenance history records with this car. But based on the deferred maintenance I've seen so far, I'm guessing the existing fluid has likely been in there for a very long time. Is there a better way to do that?

This is what I have been doing for over 20 years. I use a Motive Bleeder (pressure bleeder but you can use the pump-the-pedal method too).

1) I remove the old fluid from the master cylinder with a turkey baster and refill with fresh fluid. My reservoir has an overflow nipple, I block that off.

2) I jack up the rear left wheel, remove the tire and attach a small clear hose to the bleeder nut. The hose goes up and then down into a bottle. This is to prevent sucking air into the caliper.

3) I attach my dry motive bleeder to the reservoir and pump to 10 psi. I crack the bleeder screw and let the fluid flow out (about 180 ml) until clear. Close the bleeder screw.

4) Remove the hose and bottle.

5) Reinstall the wheel.

6) Disconnect the Motive bleeder and refill reservoir.

Repeat at step 2 for each caliper.

If you are going to manually pump the pedal and do this by yourself:

1) I remove the old fluid from the master cylinder with a turkey baster and refill with fresh fluid.

2) I jack up the rear left wheel, remove the tire and attach a small clear hose to the bleeder nut. The hose goes up and then down into a bottle. This is to prevent sucking air into the caliper.

3) Put some fluid in the collection bottle to submerge the open end.

4) Open the bleeder valve

5) Gently pump the pedal (do not go to the floor). After several strokes, look at the bottle. The level should have risen. See if the fluid is clear in the tube. Keep doing this until the fluid is clear in the tube. You may need to refill the reservoir so keep an eye on that as well.

6) once clear, tighten the bleeder screw, remove hose and bottle, reinstall wheel, refill reservoir and move to next wheel.

Repeat steps 2-6.

You should start with the farthest cylinder (right rear) and then move closer to master cylinder. Left Rear, Right Front, left front.

I need no more that 180 ml from the farthest cylinder to get fresh fluid to it. The others need less.

[brighton911]

It is a Big mistake to drain the system, you will introduce all kinds of headaches if you do. Harry D's procedure is sound and I suggest you follow it.

[GH85Carrera]

Just a standard flush is enough. I have flushed my brakes with new fluid every single spring for the last 27 years. I double check the pad wear and replace any pads even close to over 3/4 worn out. Pads are cheap, and so is fluid.

My last set of pads did not have the notch in them for the sensor. I just zip tied the sensor out of the way. I have zero worries about wearing my pads out as I inspect them before every autocross or track day. I have a new set in stock on the shelf all the time. I want my brakes to work at 100% of the time with no ABS, I want all the stopping power I can get and even braking is vital to that.

[Mark Salvetti]

Originally Posted by GH85Carrera

Just a standard flush is enough.

Right, we're not saying you should keep the old fluid, we're saying you need to flush it out without letting the system go dry. It can be really difficult to get all the air out.

It used to be possible to buy brake fluid that was yellow or blue. Just alternate colors every flush, and it was easy to tell when the old fluid was gone. It's harder now, but if you bleed with a clear tube, you should be able to see when the fresh fluid arrives. Just a very subtle color change (unless your old fluid is really dark).

You can also bleed using gravity, but it is much slower than HarryD's method. It can be better than pumping the brakes though. If you over-stroke the master cylinder it is possible to damage the seals. And you can gravity bleed by yourself. See this thread: Gravity Bleeding: How?

Mark

[Cloggie]

Agree with all of the above with regard to not draining the system....you can flush it all out and if you are really anal, like me, you flush until the new fluid comes out and then do some more to make sure all the old stuff and any moisture in the system is gone.

I personally use gravity bleeding as it is gentler and easier, plus since my car uses silicone Dot 5 which is more viscous and prone to bubbles (and hence a softer pedal) the slow fluid movement using the gravity bleeding tends to reduce that.

As for the sensors....leave them on/leave the system functioning. I check all this stuff all the time and have never had the light go on for my 911, but I would not to be driving without the comfort of knowing all my brakes are good.

D..

[Cajundaddy]

My brake maintenance procedure over the last 20 years:

-Replace the pads and rotors as needed with higher temp components (Porterfield RS4 or equivalent for street use)
-Replace any worn sensors and zip tie the damn things up out of the way because they are an annoying nuisance.
- Generously bleed and flush the brake lines introducing fresh brake fluid with a Motiv pressure bleeder but NEVER EVER drain the brake lines completely. It is a nightmare to eliminate all of the air especially if on an ABS car.
-Clean, inspect and lube all of the moving parts of the caliper assy for more even wear.

[GH85Carrera]

I assume you know the process. Start with the passenger side rear (furthest from the master cylinder) and replace fluid until new fluid is seen, and then just a bit more. Then move to the driver's side rear wheel. Passenger front and finish with the driver's front. Don't be cheap and buy a small bottle, get a larger bottle of fluid, and be 100% sure every bit of the old fluid is replaced with fresh.

I start by using a vacuum pump to empty the reservoir, and fill it with clean fluid and then start on the calipers.

[HarryD]

Originally Posted by GH85Carrera

Just a standard flush is enough. I have flushed my brakes with new fluid every single spring for the last 27 years. I double check the pad wear and replace any pads even close to over 3/4 worn out. Pads are cheap, and so is fluid.

My last set of pads did not have the notch in them for the sensor. I just zip tied the sensor out of the way. I have zero worries about wearing my pads out as I inspect them before every autocross or track day. I have a new set in stock on the shelf all the time. I want my brakes to work at 100% of the time with no ABS, I want all the stopping power I can get and even braking is vital to that.

Pretty close to my story except I replace pads at 40-50%.

They get inspected every track day or Autocross. Last year I did something like 18 events.

[HarryD]

Originally Posted by Mark Salvetti

Right, we're not saying you should keep the old fluid, we're saying you need to flush it out without letting the system go dry. It can be really difficult to get all the air out.

It used to be possible to buy brake fluid that was yellow or blue. Just alternate colors every flush, and it was easy to tell when the old fluid was gone. It's harder now, but if you bleed with a clear tube, you should be able to see when the fresh fluid arrives. Just a very subtle color change (unless your old fluid is really dark).

You can also bleed using gravity, but it is much slower than HarryD's method. It can be better than pumping the brakes though. If you over-stroke the master cylinder it is possible to damage the seals. And you can gravity bleed by yourself. See this thread: Gravity Bleeding: How?

Mark

As I noted in my post above, in the blue/gold days I found that 180 ml per cylinder was more than enough to completely do a color change in my early car. A 1 liter (quart) bottle is more than enough.

I suggest you only use DOT 4. I find ATE typ 200 plenty good for my needs. There are others out there.

I tried Gravity Bleeding but it is too slow and Zen like for my taste. I used to vacuum bleed but the Motive is clearly, for me, the best way. Sadly, the adapter for my 1970 bus does not work well so I do the one man pump.