Adjustable Proportioning Valve With ABS

[spdingtkts]

Where would you install, pre ABS controller or after?

I am thinking before (being in between the master and the EBCU so that everything was working correctly.

What say you all?

 

[swall]

What kind of ABS? Full power actuator or add-on type system? All wheel or just the fronts and a single rear? Diagonally split braking circuits or front to back split?

 

[spdingtkts]

The car is an 01 Jetta.

The ABS system is an electronically controlled OEM system that controls all four wheels. Each wheel has its own speed sensor.

I believe the split is front to rear.

 

[swall]

Did the system with ABS originally have a proportioning valve (prop valve)? As I am sure you know, the function of the prop valve is to reduce pressure to the rear brakes and help prevent lockup. But, ABS already does this. If you add a prop valve to a system designed to work without one, you may affect the turn on/turn off time of the modulator for the rear brakes. This could mess up the braking action, particularily during a stop on gravel or heavy snow. The ABS logic is designed to turn off the ABS cycling as the car comes to the last few feet of the stop and let the brakes lock. The plowing action of the locked wheels on the gravel or snow then stops the car for the last couple of feet. If you reduce the pressure to the rear brakes with the prop valve, the ABS may continue to cycle the rear brakes for this final increment of stopping and the stopping distance could increase.

 

[spdingtkts]

Actually I was thinking about increasing the pressure to the rear brakes.

 

[BrianPetersen]

A proportioning valve installed in the line to the rear brakes is only capable of reducing pressure. It can't create pressure that isn't in the system to begin with. Installing a proportioning valve in the front is not a good plan, it will limit overall braking performance.

The ABS controller in that car already has Electronic Brake-force Distribution as standard. That car, as with most front-drives, has a diagonally-split braking system.

But ... why do you want to increase pressure to the rear brakes? What is the rationale for doing so?

 

[GregLocock]

Presumably because the brake balance before lockup needs to be adjusted?

Normally you set that up via the piston diameters.

Cheers

Greg Locock

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