Volvo 480 Club Europe

TRACS operation

The following example illustrates how the TRACS works when one of the driven front wheels starts to spin. In this example the front–right wheel is spinning.

When the TRACS function is actuated, there is no pressure prevailing in the master cylinder (1). The pressure needed to brake the wheel must therefore be supplied by the hydraulic pump (E). However, the pump pressurizes the entire brake system. Vehicles equipped with TRACS therefore have two additional valves (Ta and Tb) which ensure that pressure is not applied to the rear wheel brakes or to the master cylinder; one valve for the primary circuit and one for the secondary circuit.

These TRACS valves are actuated simultaneously with the pump when the TRACS function is in operation. The built–up pressure is then transmitted only to the front wheel brakes and is controlled with the inlet and outlet valves.

As the front–right wheel is spinning, the situation at this wheel remains unchanged, i.e. inlet valve (C1) open and outlet valve (D1) closed, but inlet valve C2 for the front–left wheel closes and no pressure is admitted. The value of the permitted pressure limiting valve and the master cylinder.

When the brakes are applied, and therefore the brake light switch is activated, the TRACS function is immediately disengaged and the system moves to standby mode in readiness for ABS operation if required by the prevailing conditions.

The TRACS function will also be stopped if the computed temperature of the brakes exceeds a given threshold value.

... and I think here's the answer (in red):

Removal of the Hydraulic Control Unit

Release:
1.The two feed hoses.
2.The six brake pipes. Mark the pipes!
Note! On TRACS versions all six apertures are on the side of the unit.
Plug all bores and apertures to prevent dust and other impurities entering the system.
Remove the Hydraulic Control Unit together with the pump. Unplug the grey pump connector from the relay.
Fitting is in reverse order to removal.

Ben Harris wrote:Below, is a picture of the MKIV ABS unit in my 480. I'm now not so convinced that it does have TRACS any more! - If it does, it certainly doesn't seem to be working any more, but didn't report any fault codes when I checked the diagnostics readout. VADIS mentions something about having a TRACS light on the dashboard, as well as the ABS light. Mine doesn't have this. Would any other 480 owners with TRACS like to comment?
Ben.

My ABS unit doesn't look like yours, all the pipes come out via the side, and there is an extra cable that disapears underneath (Maybe yours has it but its in a different place?).

TRACS does work as I found out this morning driving to work in the snow It does go grrrrrrrr but only quietly, a bit louder than the abs self test (when powered up) but not much. Maybe JT needs to change his brake fluid or something?

Richard

thats the same pipe configuration that i have, but with a TRACS controller is doesnt work at all. - no ABS - no TRACS

with the standard ABS controller it does

have changed back to my old ABS controller till i have sorted out whats what.