Mark IV ABS hydraulics

Brakepads, discs, handbrake. The brakes are crucial for your Volvo 480. Use this category to learn all you need to know!

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Ben Harris
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Post by Ben Harris » Sat Dec 18, 2004 5:17 pm

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.

Image
1998-2003 ... 1981 Austin Mini City
2003-2005 ... 1989 Volvo 480 ES (B18E)
2004-2006 ... 1994 Volvo 480 ES (B20F)
2006-2008 ... 1995 Mitsuibshi FTO GPX
2008-2008 ... 1994 Volvo 480 Turbo Auto (with RichMod)
2009-Onwards ... 1991 MK1 Eunos Roadster
2013-Onwards ... 1997 Subaru Impreza Turbo 2000 (Wagon)

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Ben Harris
480 Is my middle name
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Post by Ben Harris » Sat Dec 18, 2004 5:20 pm

... 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.
1998-2003 ... 1981 Austin Mini City
2003-2005 ... 1989 Volvo 480 ES (B18E)
2004-2006 ... 1994 Volvo 480 ES (B20F)
2006-2008 ... 1995 Mitsuibshi FTO GPX
2008-2008 ... 1994 Volvo 480 Turbo Auto (with RichMod)
2009-Onwards ... 1991 MK1 Eunos Roadster
2013-Onwards ... 1997 Subaru Impreza Turbo 2000 (Wagon)

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rpruen
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Post by rpruen » Sun Dec 19, 2004 12:18 pm

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
Car Status: Squashed :(
Now have 765 GLE 2.8 V6

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alfonzobonzo
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Post by alfonzobonzo » Sun Dec 19, 2004 6:37 pm

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.
Alfonz.

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