Hydraulic brake pressure

[Jon Weywadt]

Has any of you measured the pressure in the hydraulic brake lines and can tell me what the pressure is when for example the front wheels lock up?

Jan and I were toying with the idea to install a pressure transducer that would feed a signal to a set of high-mounted brake lights. They would then light with an intensity controlled by the pressure. (Or a light bar, where the number of lit LEDs depended on the pressure) 

We don't know what the range of such a transducer should be able to measure. Anyone got an idea of the max pressure?

[Oetker]

Looks a bit complex to achieve.
Its toying with the idea, right?
Maybe a idea to make it go in 2 steps.
Lets presume under normal braking some bulbs or leds light up.
For the second step you can make a small box with a metal ball.
If this ball has to climb you can mount it this way it wouldn't under normal braking and runs up with
heavy braking.
At the end of the box you make a switch or sensor that see the ball and send a signal to the
second set of lights.
With a box I mean something small of course.

[JV]

Looks a bit complex to achieve.
Its toying with the idea, right?
Maybe a idea to make it go in 2 steps.
Lets presume under normal braking some bulbs or leds light up.
For the second step you can make a small box with a metal ball.
If this ball has to climb you can mount it this way it wouldn't under normal braking and runs up with
heavy braking.
At the end of the box you make a switch or sensor that see the ball and send a signal to the
second set of lights.
With a box I mean something small of course.

There are some alarm systems that have this kind of sensor in order to prevent that the car is stolen by putting it on a car-ambulance without the alarm system warning.

[Oetker]

Yep, but I think they are to sensitive for the purpose
A magnetic ball would be best.
At the end you can place a reed switch.
No fancy electronics needed.
For the box you can take a cigar-tube.

[Jon Weywadt]

I came across a document that describes adjusting the reduction valve to the rear brakes. From the graphs of the various adjustment options, it was evident that the hydraulic pressure when measured at the master cylinder could be as high as 1280 psi (twelve hundred and eighty psi or apx. 88 BAR). I did not expect it to be that high, but it means that any sensor I place in the system must be able to handle 0-100 BAR.

Speaking about the reduction valve. Mine is very rusty and could probably do with a replacement. Are there any of you who have replaced the reduction valve? If so, where did you get it and did it have to be adjusted, or is it ordered with a preset reduction setting. If so how much reduction is needed? My guess is that it is less than on a front engine car, due to the extra weight on the rear weels in a Murena, but what value should I look for or set?

[Oetker]

I never came across a partnumber fot this valve or anything I can replace it with.
So i provide some info found, and you can make your own plan.

First of all, info is confusing.
According to the manual it is made by Teves but also by DBA (Bendix)
However I have a spare that shows ATE.


It starts working at 27 bar, wich is achieved by a spring in the device.

This is info from the Dutch manual.



Ther are people that have mounted a adjustable one so you can make your own setup.

[Jon Weywadt]

I never came across a partnumber fot this valve or anything I can replace it with.
So i provide some info found, an you can make your own plan.

First of all ,info is confusing.
According to the manual it is made by Teves but also by DBA (Bendix)
However I have a spare that shows ATE.
---
It starts working at 27 bar, wich is achieved by a spring in the device.

This is info from the Dutch manual.
---

Hi Oetker.
That is great information.With the dutch manuals pressure numbers it should be possible to find a replacement that works. I will check at the brake shop.
thanks. Jon.

[Oetker]

Maybe this is interesting.

http://www.facebook.com/notes/speed-master-racing/wilwood-brake-proportioning-valves/412520986437

[klumzer]

It starts working at 27 bar, wich is achieved by a spring in the device.

Oetker, what does "it starts working" mean? It starts reducing the pressure or it opens...
So what is the pressure in the rear brake lines up to 27 bar in the front? The same or zero?

[Oetker]

Till 27 bar the pressure in the system is the same.
Above 27 bar it starts regulating (limit) the pressure for the rear brakes.
It is for break balance front rear where rear gets less pressure compared to front above 27 bar.
It is to prevent blocking the rear witch can be very nice in cornering.
Kind of old stile ABS for the rear brakes.
a good example is this film I made where I tested the all new brakes.
Look where I gave full brakes, the rear almost doesn't block.

http://www.youtube.com/watch?v=p2jK1lhnwV4

[klumzer]

Thanks. That is what I suspected, but I could not test it because the car is in small pieces...

I have a friend who works for a hydraulics company. I try to ask him if they could test the valve on a bench. If it works correctly it would be worth overhauling it. If not I have to look for a replacement.

By the way. Where is the place in the video where you tested the brakes. It is very similar to that one where I bought my car in Holland. It was Dronten if I remember well...

[klumzer]

We tested the brake reducing valve today. We needed two pressure gauges, a manual hydraulic pump and a lot of adapters to connect them to the right in- and outlets. Although the valve is very rusty outside it works correctly as it should so it is worth overhauling it. A new paint and it will look as a new one.
At 35 bar the outlet was about 32 and at 70 bar it was about 50. Below 30 bar inlet pressure the outlet was the same.


Unfortunately I was in a hurry and forgot to take a camera with me. Sorry about it...