ClubCJ - The CJ Lancer Club

hiya gang! got an open sorta topic, looking for factual, expert opinions if possible....

Lets say, we upgrade our front brakes to a RA/VRX kit. Awesome!
The front brakes now have more braking force the the ECU "thinks" it has.
This mechanical upgrade to torsional stopping power is great for partial stops, ie-Non ABS stops.
The pedal feels nicer/firmer, it has more bite.(more friction)

My concern is, that after upgrading the brakes/rotors on the front, the rears are left underbraked.
In an ABS/TCS event, the ECU has to compensate for(and make) decrease(s)/increases(s) in pressure "reactively" because of the changed mechanical increase in friction to the front wheels.
Greater than it was "learned" to have possible at the factory whence it was born.
Its expecting smaller brakes with "x" stopping power at "y" brake pressure on the front wheels.
Instead it finds "2x" stopping powers, and "y" pressures, and this don't compute.
It has to react to the changed situation, instead of being able to predict wheel slip pro-actively, thus, INCREASING stopping distance...

Is there any truth to this? am i a crazy person?
And more importantly, if i upgrade my front discs, should i also upgrade my rears to the same percentage of mechanical advantage to even out the brake bias, and allow the electronics to work normally?

Phew!! hope that all made sense to someone!

Just reset the ECU for any mechanical modifications. Pretty simple.

Bryan many of us have upgraded our front brakes only.

My understanding is each wheel has a sensor. If one stops more then another then the force is distributed differently to compensate.

Generally the front brakes do 85% of the stopping.

I would replace the front brakes only. If you get a good second hand set of rear VRX brakes then I would upgrade but I dont think they would make much differences.

Remember VRX and RA brakes are different. They both have 294mm discs but with different offsets. RA have bigger pads and twin piston calipers.

I have ripped this as the simplest way to understand ABS: to put it bluntly, it doesnt matter what brakes you use, its the speed off acceleration and deceleration of each individual wheel that matters to the ABS system.


There are four main components to an ABS system:

* Speed sensors
* Pump
* Valves
* Controller

­Speed Sensors
The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.

Valves
There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:

* In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
* In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
*In position three, the valve releases some of the pressure from the brake.

Pump
Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.

Controller
The controller is a computer in the car. It watches the speed sensors and controls the valves.

There are different variations and control algorithms for ABS systems.Thios is how one of the simpler systems works.

The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.

The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.

When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second.

Anti-Lock Brake Types

­Anti-lock braking systems use different schemes depending on the type of brakes in use. We will refer to them by the number of channels -- that is, how many valves that are individually controlled -- and the number of speed sensors.

­Four-channel, four-sensor ABS
This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

Three-channel, three-sensor ABS
This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle.

This sys­tem provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness.

­One-channel, one-sensor ABS
This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.

This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness.

This system is easy to identify. Usually there will be one brake line going through a T-fitting to both rear wheels. You can locate the speed sensor by looking for an electrical connection near the differential on the rear-axle housing.­


More: http://auto.howstuffworks.com/auto-parts/brakes/brake-types/anti-lock-brake.htm

thanks for taking the time on that tate, good post, good info!

i guess my main worry is the vehicle behaviour in a stability control intervention.
From what you say, the sensors are the key point, not the ecu-brake calibration from the factory.
Following on, assuming its accurate to CJ's, it monitors wheel speed and hydro. pressure independently of each other.
This makes, as i said, "reactive" braking wrong, and old school ABS thinking.
So if opposing corners of the car were to be braked to try to 'yaw' the car around to the intended line, it would still work normally, regardless of any brake mod, front OR rear then.....

If it didn't rely on the sensors then pad wear and tyre wear and varied road surfaces/conditions would ruin your ABS's and stability control's ability to function correctly, let alone mods.

Ie its fine

I would even guess the VRX and all the lower models share the same ABS system (mechanical and computerised).