Brake Pressure Sensor Mounting

[tapandrack]

Just thought I'd post a simple way I found to mount front and rear brake pressure sensors directly to Girling master cylinders. This application is on an 88 Reynard.

By using two Russell Brake Switch Banjo Bolt Fittings (1/8" NPT Fem. x 3/8" -24) and attaching them to the banjo fittings going into the master cylinders you avoid using the typical -3AN 'Tee' brake line connector splice and adding 4 potential fail points in your brake system. I used the Aim PRS-839 brake pressure sensor and it fit perfectly.

Bob

[DanW]

Nice and neat. How do you bleed the air out?

[tapandrack]

Dan,
Good question, there is very little space for air between the Russell banjo bolt fitting's side hole port and the bottom of the sensor that threads into the top of the fitting above the hole. I just did a brake fluid flush with a power vacuum bleeder as part of maintenance and any air came out with that. Then I firmed it all up with a couple of regular pressure bleeds at each wheel using the brake pedal. Pedal is rock solid now.
Bob

[S. Frebert]

Nice find! I've though about how to do this also. Didnt really feel comfortable adding more connections that could possibly fail. This is good.

[steve everard]

Looks like a great solution but I have limited height ie 1 inch to sway bar. Is the sensor height larger than that? 99 VD

[Eric Cruz]

Way cool, tapandrack. You're probably pretty good at clearing feed jams, too Just ordered some of those fittings - thanks for sharing the idea and the link. My AiM transducers are the older version - longer and smaller diameter, so I'll see if they fit the space in the FE. Then I'll need another 15 feet of -3 hose to replace the ones I've got the Tee fittings in.

Then I'll do the second car....

Best regards,
Eric

[tapandrack]

Hi Eric,
LOL! Yep, love my Dan Wesson 1911
Glad you found the suggestion helpful.

Hey Steve,
Yes the Aim sensor, Russell fitting and wire bending radius will require more than 1", probably more like a fat 2+"

Regards,
Bob

[provamo]

OK i am stupid.....

WHY do i want to know my brake line pressures?

[steve everard]

To teach a driver braking techniques

[tapandrack]

To confirm degree of brake bias and review braking application in data.

[2BWise]

OK i am stupid.....

WHY do i want to know my brake line pressures?

I'm kinda there with you. Honest question.....is there anything in brake pressure that you can't get with a longitudinal accelerometer? Also, don't most people set brake bias by feel/preference? The optimum brake bias for straight line performance is usually too much for trail braking, so in most cases do we just tune it to as much rear brake as we can stand?

[DFR Dave Freitas]

A lot has to do with initial hit pressure and the trail off as the car slows. With the sensors, or just one sensor, you can learn a lot about what the driver is doing vs what he thinks he's doing.

[Pi_guy]

I'm kinda there with you. Honest question.....is there anything in brake pressure that you can't get with a longitudinal accelerometer?
?

Had a driver adjusting himself going down the straight and he was pushing on the brake peddle a bit nothing you noticed anywhere else. But it was a bit of a drag.

[romoman]

I'm kinda there with you. Honest question.....is there anything in brake pressure that you can't get with a longitudinal accelerometer? Also, don't most people set brake bias by feel/preference? The optimum brake bias for straight line performance is usually too much for trail braking, so in most cases do we just tune it to as much rear brake as we can stand?

And remember best feel doesn't always mean fastest. This lets you see exactly what the bias is set to and reproduce results and always get back to the same baseline.

[phantomjock]

Often wondered if this:
Dual brake pressure gauge

and video would be useful? Would be able to correlate brake application, pressure and geographic positioning for driver feedback. Admittedly, fidelity may not be as good - but a reasonable price break and simple DA. Thoughts (before I go and spend money on an extra lipstick cam...

Cheers - Jim

[tapandrack]

I'm kinda there with you. Honest question.....is there anything in brake pressure that you can't get with a longitudinal accelerometer? Also, don't most people set brake bias by feel/preference? The optimum brake bias for straight line performance is usually too much for trail braking, so in most cases do we just tune it to as much rear brake as we can stand?

Hey Bill,
There are many on this forum who have much more experience than me on the subject of data analysis but from my experience brake pressure and throttle position are my two most relied upon sensors in post-run data analysis.

LongG can will measure relative increase or decrease in acceleration or deceleration forces but I've found it a bit of a dull tool for data analysis when it comes to knowing what I actually did on track.

LongG increases only due to throttle application but I still use a TPS to know and measure degree of throttle application.

LongG can decrease due to throttle lift, braking or combination of left foot braking and throttle transitions in a corner. So a brake pressure sensor on the front Master Cylinder is a minimum to determine what you are actually doing on the track relative to brake application.

Front and rear brake pressure sensors allow you to measure brake bias as a setting once you get it where you want it as a repeatable measurement.

Just my two cents. Now being fast, that's another story!

Regards,
Bob

[Steve Demeter]

Bob,

Just don't let the front / rear pressure settings become anymore than a starting point.

Brake bias needs to be tuned sometimes lap by lap depending on the conditions, tire condition and even the driver feeling more comfortable as they migrate toward more rear bias.

I set my starting point with the car on stands. by helper applies a c clamp to the pedal until I determine that the front is just locked. Then go and check the rear. adjust until the front is just locked and the rear is just not locked. Do that once a year.

Then fine tune on the track.

With driver adjustable bias so common there is no need for the sophisticated set ups that were used when one had to remove the bodywork and turn the handle attached to the bias bar by the pedal.

[2BWise]

Hey Bill,
combination of left foot braking and throttle transitions

That's a good point and something I overlooked. Especially with left foot braking there are situations where only brake pressure will give you the full story.

[tapandrack]

Bob,

I set my starting point with the car on stands. by helper applies a c clamp to the pedal until I determine that the front is just locked. Then go and check the rear. adjust until the front is just locked and the rear is just not locked. Do that once a year...

Steve,
Great point. That's what I did when I set up the brakes earlier this year only I used the 75 ft-lbs trick that Buc01 (post #5) suggested in this thread. http://www.apexspeed.com/forums/showthread.php?t=58250

Used a big honking welding C clamp on the brake pedal to adjust pedal pressure like you stated and a torque wrench and it worked perfectly!

Regards,
Bob

[Marshall Mauney]

OK i am stupid.....

WHY do i want to know my brake line pressures?

1) Brake Bias
2) Driving technique
3) Braking efficiency, i.e., brake force vs. deceleration.

Keep in mind that brake pressure is not perfectly correlated to deceleration. Aero load, reverse engine loading, track angle (i.e., uphill/downhill), and deceleration due to lateral tire scrubbing all are part of the equation, so you can't just assume that deceleration is the same thing as braking force.

As for setting your brake bias, while driving style is certainly part of the picture. the real goal is to maximize available braking prior to lock-up at both ends of the car. Having gauges to read the relative pressures not only allows you to see what's actually happening on track, it also allows you to pre-set the bias to a known baseline in the pits after doing major work. Imagine having to replace a master cylinder during a race weekend, and the benefit becomes obvious.