Brake temperature sensor - advice?

[dtfastbear]

You might regonize my name from a long list of brake related, depressing posts with titles like - "Help! I'm boiling the brake fluid!"

Anyway, I'm still having some problems, but things are getting better. I've made it my personal mission to learn as much as I can about brake behavior of Carreras and what different mods (cool kit, different rotors/pads, bias valve, etc) and other influences (weight in the car, driving style, 2 driver car at DE events, etc.) have on brake temperatures and performance. There seems to be so much information that is either speculation, theoretical or just plain wrong out there that I'd like to see for myself what REALLY makes the brakes hot and what REALLY cools the brakes down.

Has anyone on the list ever fabricated (or purchased?) a brake temperature sensor/gauge? I imagine I'll have to use a thermocouple since the temps are so high, but any advice on a source for parts, sensor mounting, etc. would be greatly appreciated.

I promise to share my finding with the world, or at least this forum.

Thanks,

Dean

[911pcars]

Hi Dean,
Good project.

This is what I did. Took a short length of flat aluminum stock and drilled a hole on each end, then bent it 90 degrees. Attached one end to one of the caliper mount bolts. The other end uses a nut and bolt to clamp onto the tip of a thermocouple which, of course, connects to a temperature gauge. Make sure this doesn't interfere with the chassis/suspension as you turn lock-to-lock, then tie-wrap the thermocouple wire securely. I used a Fluke meter which has temperature measuring capabilities (but only up to around 500 deg. F). Actual caliper/rotor temperatures will exceed this in a race situation.

But actual caliper temperature measurement may not be necessary. While this setup won't measure actual brake rotor or brake caliper temperatures (that requires a more sophisticated setup), it will measure relative temperatures of different braking setups/components in real time. It's more convenient compared to using telltale paint or stick-on temp. measuring decals.

The tricky part of your testing will be the repeatability factor so you can attribute a positive change due to a change in a braking component and not variable vehicle speed, braking force, tire and road conditions, etc.

I did this to measure the effect of my "MPC" product to test temperature reduction for a water spray brake system. My initial conclusions at Willow Springs were inconclusive due to a broken thermocouple wire and couldn't repair it in time, but as it turns out the system proves to be effective.

Hope this gives you somewhere to begin,

Sherwood Lee
http://members.rennlist.org/911pcars
www.seinesystems.com

[cstreit]

Why not just use some of the temperature sensitive paint designed for this sort of thing?

If you're boiling fluid:

1. Make sure they're working right
2. Get higher temp fluid
3. Get some air in there (brake cooling kits)
4. Get bigger rotors. They are the heat sink.
5. Learn to not use them so much (my big problem)

[Bill Verburg]

The best thing to use is temperature indicating paint or strips. Either works well, they are both accurate and easily applied.

Thermal indicating paint/strips

The paint is also available from many of the race supply houses like Essex, or directly from the brake manufacturers, Brembo, Alcon, or AP

The use of such things is mostly an intellectual activity as there are only a finite # of possible things that you can do. In order I would suggest [list=1][*]ducting-3" minimum to hub w/ a blocking plate or TRE has a set up that uses the 993 scoops w/ a blocking plate[*]pads/fluid Pagid Orange for track use, Castrol SRF or Motul 600 or possibly GS610[*]930 size rotors w/ appropriate calipers[*]993tt rotors w/ appropriate calipres[/list=1]

[ChrisBennet]

Years ago I ran a thermocouple right to the back of the brakepad. The Carrera pistons have a cutaway in the face of the piston so the wire can slip right in there behind the brakepad. Clean the back of the brakepad and tape it down with aluminum duct tape. I ran it a multimeter that accepts type K thermocouples and has a min/max logging feature.
Do a search on Omega thermocouples and you'll find more info.
-Chris

[old_skul]

I agree with Chris on at least one point. My use of the brakes was what was causing them to overheat, so I changed my braking method, and my fade on the track went away.

I started off doing "limousine" braking - putting on the brakes long before a corner, and braking hard just before turning in. This heats up the brakes a LOT, and then heats them up some more.

After going through sets of pads, and eventually rotors, I decided to become a little more trusting of my car's ability to brake.

Now, as I approach a corner, I have moved my braking point to a more reasonable distance (shorter) to turn-in. And when I brake, I brake "in reverse" - meaning, I am very hard on the brakes when I first apply them, and I ease off as I approach turn-in. I'm not jabbing the brakes when I put them on, it's just that I smoothly apply 98% braking, trailing off as I turn in.

[dtfastbear]

Good stuff, guys! I've been poking around on the web and have found some small battery powered logging devices that will sample the thermocouple's output at specified intervals (like every second) and then you can download the results to a PC. That seems like it would be the hot setup (no pun intended!)

I'll check out Omega, Chris. Thanks for the tip.

Bill - you're right that choices are limited, and I do recognize that this is an information gathering exercise only. I'd really just like to know what effect things like different pads have on brake temps...

Like I said, once I get it all together, I'll report back on my findings.

Thanks, guys!

Dean

[Don Wohlfarth]

Bill V, you da man!
Performance Friction sold temp indicating paint but it's NLA. I found out that Omega made it specifically for them but it's NLA.
I saw some listed in Coleman's catalog and called but it's NLA.
They sold their last dozen bottles to Behling Circle Track Supply
#1 800 255 4117 but you'd better hurry.
I found Castrol SRF on one week special at OG Racing for less than $60 per liter.
Dean, understand your desire to get to the bottom of your boiling fluid issues.
You might be on to something with the small data logging devices. I think the biggest problem you'll have is the repeatability factor from driver to driver, day to day, and track to track, in trying to set up a base line for comparison before you start trying to find different temps for different pads, rotors, and calipers.
You should still be able to get a general idea of what is causing your boiling problems, or at the least find out what doesn't work. It's that repeatability factor that makes it tough on us that don't do this for a living.

[ChrisBennet]

For what it's worth, my "data logging" solved my "brake problem". My codriver was using the brakes in the paddock after his run resulting in the max temp (back of pad) being reached when the car was parked. Logging mulitmeters are expensive but ones that just except temp aren't too bad. Mine only records min and max. As a bonus once you have the meter all you need to do is buy a sharp temp probe ($50) and viola' you have a tire pyrometer.
-Chris

[TimT]

Instead of a thermocouple you could try an infrared pick up. Motec data logging has inputs for brake temps.

take apart one of those $80 instant read pyrometers (Raytech), and mount the pickup on the strut facing the disc ( or caliper) then mount the display on the dash somewhere.

[911pcars]

Tim,
I like your suggestion. Any links available to this hardware?

Sherwood

[dtfastbear]

I see you point, Don. My methods won't be completely scientific - at best I can try a different set of pads from one session to another, or try different braking techniques from one session to another to try to get some back to back comparisons. From day to day or track to track, the comparisons won't be as useful.

One thing I am wondering about is how long the heat stays in the brakes. My wife and I both drive the car, so I'm wondering how much it cools down between sessions, for instance. And would doing two cool down laps instead of one make a big difference? And would driving slowly through the pits for 5 minutes make much of a difference over parking the car...

I've found some interesting devices at Omega - now I have to find the one that will work the best for the least money. At the rate I'm going through brake pads and such, it might be worth $200 for an instrument if I think I'll find anything worth while...

Thanks for the input, Don!

Dean

[Don Wohlfarth]

Dean, your idea will work for trying to determine your problem. For comparison purposes it will be more difficult without a base line.
Cool down laps will make a big difference. Temps flow from a high body to a low body until no heat transfer takes place. A typical 100 degree day and brake rotors ~ 1000 degrees you have a large temp differential so the temp of the rotor will drop fairly quickly, just guessing to maybe 6-700 degrees, still damn hot but significantly lower than the 1000 they were just a couple minutes ago.
When you take tire temps you dash into the hot pit and take the temp immediately with no cool down. Even on a 100 degree day your tire shouldn't be but ~190-200 so you have no where near the temp differential that you would with your rotors but you want tire temps as soon as possible because of cooling.
Driving thru the pits for 5 min will allow more of that amibent 100 accross the rotor versus parking the car. When you park the car put your hand down near the wheel and you can feel the heat radiating into the air raising the ambient to 110-115. Moving 100 degree air accross the rotor will cool in faster than that 110-115 degrees when it's parked.
With 2 drivers in a car the 1st driver gets the brakes hot. If the 2nd driver is going out immediately (back to back sessions) driver 2 would be more likely to have boiling problems because the brakes have not cooled down so he is starting his session from a higher temp than driver 1. If you have a severe boiling problem driver 1 should run around the pits for a couple minutes to cool the brakes as much as possible. With back to back sessions this means 2nd driver may be late getting out and should use caution after a couple laps and be aware of a brake fadding issue. Ugly situation, have no other suggestions.

[dtfastbear]

Here's the tool I want to use to measure and capture temperatures on the brakes:

http://www.omega.com/Temperature/pdf/HH305_306.pdf

I'd just need the right thermocouples and an easy way to mount the sensors. Then I could capture two different readings (front and rear?, left and right?) and then download them and see the temp profile over the course of a full day of driving.

Now I just need to find the $185 to pony up to buy the device!

Thanks again for all the advice, guys.

Dean

[Early_S_Man]

Dean,

There is nothing wrong with the Omega HH305 or HH306 approach, but the HH610 is available in a four-channel model, and all four calipers could be equipped with an $11 - $15 aircraftspark plug washer-style Type-K thermocouple under the lower M12 mounting bolt.

Have you considered a lower-cost, single-channel system such as using a single thermocouple and a $59.88 closeout-priced Craftsman Professional 34-82356 Multimeter with PC interface and Windows software ... that can take Type-K thermocouples?

[Don Wohlfarth]

Warren, that sounds like hot set up. Would having the thermocouple under the mounting bolt be too far away to get accurate reading on the rotor/caliper? Be interesting to have a thermocouple under the top and bottom bolt to see what kind of difference you'd find.

[jluetjen]

A younger (and slower) teammate once asked Fangio how he went so fast. He pointed to the man's right foot and said "I use more of that and less of that (pointing at the man's left foot)"

I once used street pads on my ITB race car in the hope that they'd survive one session. They were down to bare metal by the end of the race. What were my fastest laps? The last few! A lifelong driving lesson was learned!

[Wil Ferch]

I may have mentioned this before...
Mark is "spot-on" for braking in reverse...brake hard in the beginning and let up slightly throughout your braking zone. This is still something I work on because it's so difficult to get right. Bonus, the car won't "bob" as you turn-in and begin to get onto the gas . In contrast to letting up after just being hardest on the brakes at the end of your braking zone.

Chris B..as usual...is correct about high heat soak when you park. As you do your cool-down lap, don't ever touch your brakes...and when you finally come to a stop...push the clutch down, turn off the motor, coast ...and re-engage the clutch on a dead motor very slowly to stop the car. You've stopped the last motion ( 1-2 mph) using the clutch friction surface and not the brakes.

Worked well for me on the notorious-for-brakes Watkins Glen circuit during DE's...and gave me time to dust off the car between runs... while all around me were bleeding brakes. *Then* they saw my dinky Carrera brakes and calipers! Icing on the cake !

---Wil Ferch

[dtfastbear]

Here's an update on my quest to disspell brake rumors and lore...

I purchased a datalogger and some thermocouples on eBay! The unit I bought is actually designed to take temperatures inside industrial ovens, so it is a rugged little beast.

Anyway, I attached a thermocouple to the brake pad mounting pin (just because it was convenient) and drove around for a while yesterday. It works! I was able to capture my brake temps, sampling 3 times per second, for an hour. Then, I just plug the unit into my laptop and can see a detailed graph of the temp over time.

I can record 6 temperatures simultaneously, so I figure I'll put one on each caliper, perhaps a second thermocouple at a different spot on one caliper, and then one to record ambient temperature. This should give me the flexibility to try things like a different shaped air scoop on one side versus the other, bias adjustments, different braking techniques, etc. and see the real effects of the changes.

I'll share my results once I get the whole system up and running. I'm running at Laguna the 13th and 14th of September - I hope to have it collecting meaningful data by then.

Dean

[BGCarrera32]

Dean, did you see my PM?

BG