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Hi All,
I read regularly that the Volvo has a system where under heavy braking it engages drive to the front axle to avoid the rear wheels locking up.

However, what does this? I have read through the maintainence manuals, owners manuals and looked at the brake system diagrams and there is nothing there that could perform this function.

Am I missing something??

Help please.
Ian.

Hi Ian,

there is a pressure switch in the brakeline under the dashboard. Breaking hard it opens the Valve (right side back of the cabin) for the frontwheeldrive. The same happens if you press the red Button for the Frontwheels or if you use the low Gears.
Thats all.

So, if you drive without front driveshaft, you better should press the red Button for the Frontwheels, otherwise it would be very loud if you brake hard.

Regards
Uli

Interesting...
There must be differences in the system between varoius markets then, because there is no clear explanation on how this works.

In the parts manual there are 2 switches on the pedal - 20 and 23. 20 is the brake failure warning, turning on permanently if the pedal overtravels (manual reset). 23 is the brake light switch.

In the maintainence manuals, under brakes, is an explanation of the brake warnings, showing clearly there is no pressure switch in the circuit, only pressure difference, and does confirm the function of 23 above.

And then... in the gearbox section, there is reference to the front drive activation, with a schematic showing a brake switch, but no indication of where this switch is

So, I think the switch I'm looking for item 21 in the hydraulics system - which is named "brake light switch", when in fact it is a pressure switch that corelates to the unmentioned switch in the above.

Wow - sorry... that was a lot of waffle...

These Volvos are great trucks, but sometimes just too complicated.. and sometimes being pointed in the right direction saves hours of frustration.

Thanks.
Ian.