I'm adding more data logging and I was wondering if there is a way to find brake pressure on an e36 and turn it into an analog signal (like 0-5v or something)?

I think there is a brake pressure switch which does this on the e46 but I can't find anything on the e36. 

There are two ways you can do it. There is no BMW sensor that I could find. There is actually a sensor in the brake booster but I could not find a way to tap into it without messing up the stock electronics.

The better way is to plumb a brake pressure sensor into your brake lines. I have this now.

Before that I used to measure brake pedal angle. Find yourself a 10Kohm linear potentiometer (a horizontal slider like you see on an audio mixing board). Make sure it's linear and not logarithmic. Then run one end to the 5V reference from your data logger and the other end to ground. The center tap is what you measure.

I glued mine to a bit of Aluminum channel from Home Depot then attached it to the steering column casing with a hose clamp. I then ran a bit of coat hanger down to a tiny bracket on the pedal (also attached with a hose clamp). This will give you a variable voltage as you press the brake pedal.

If you want you can simulate pressure by applying some math to that channel in the PC software. But just having a relative trace of pedal movement is quite useful.

You could also do it with a string potentiometer but those are very expensive...

Thanks Peter! Does the e36 throttle position sensor work for data logging? My mechanic was suspecting that it is a 3 position sensor. Off, mid, flat.

Who sells brake pressure sensors?

I got my brake pressure sensor from Race-Technology.com.

Assuming you are using a high impedance data logger (like the DL1) then you can log almost anything without upsetting it.

The BMW TPS is a 3 wire sensor and is easy to tap into. If you can find it near the DME then that would be best. It's a rats nest. But if you Google around for the engine DME oin-put you should be able to find it.

I picked it up under the hood. There is a black plastic trough that runs along the top of the motor (near the fuel injectors). There is a nice loose pile of wires in it and it's fairly easy to trace which one is the center tap on the TPS.

Nearly set. Where did you get the fittings (T?) to plumb in the sensor and where did you put the sensor? Not obvious to my mechanic. Thanks for all the help. This is going to be great.

Oh, looks like you just need 1/8" npt fittings. I can get this from pegasus.

I think it was a standard brake line fitting... You can get any brand sensor. You only need a relative trace. I don't think you care if it is 357.5psi or 769.8psi.

I did a quick search and found this hydraulic pressure sender. Be reminded that the pressure in the hydraulic system can reach 1200psi. So, the sensor must be good to above that reading. On brake system with one MC, the pressure is the same in all calipers, unless a fixed or adjustable valve is installed. When using twin masters, then the pressure will be independent between masters. Many racecars builders will use mwchanical gauges to monitor the pressure in each system (front, rear).

http://directory.oemoffhighway.com/product/71408/Kavlico_Hydraulic_Pressure_Sensors

Thanks Lee! I ended up buying the racepak sensor Peter has. From the outside it looks like all of those sensors are built by the same people, at least they all look the same. I bet there aren't more than two OEMs for the actual sensor.

I'll post when I find out how the system works (traqmate + traqdataII + rpm, brake & throttle sensors).

Step 1 is to set up the data system.
Step 2 is to get someone who knows how to drive to take it out for a lap.
Step 3 is to take it out and do your best.
Step 4 is to understand where real driver is doing differently than you.
Step 5 is to go out on the track and do it.

Step 5 is always the tricky stop. I'm imagining someone at Ferrari saying: "now Luca, this is what Kimi is doing. Brake here, turn here, on the gas there. Do you think you could try?"