Engaging 6x6 under Braking

Issues pertaining to the TGB/C30X series engine and driveline issues
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roobar_and_custard
Australia
Posts: 78
Joined: Fri Sep 07, 2012 7:18 am
Location: Melbourne, Australia

Engaging 6x6 under Braking

Post by roobar_and_custard » Sun Jun 08, 2014 12:25 pm

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.

Uli-RT
Germany
Posts: 59
Joined: Wed May 16, 2012 7:27 am
Location: Baden-Württemberg

Re: Engaging 6x6 under Braking

Post by Uli-RT » Wed Jun 11, 2014 3:22 pm

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

roobar_and_custard
Australia
Posts: 78
Joined: Fri Sep 07, 2012 7:18 am
Location: Melbourne, Australia

Re: Engaging 6x6 under Braking

Post by roobar_and_custard » Wed Jun 11, 2014 6:57 pm

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.. :shock: and sometimes being pointed in the right direction saves hours of frustration.

Thanks. :D
Ian.
Attachments
Brake Pedal Parts List.jpg
Brake Pedal Parts List.jpg (64.79 KiB) Viewed 1427 times
Brake Warning Devices.jpg
Brake Warning Devices.jpg (86.54 KiB) Viewed 1427 times
Wiring Diagram for Front Wheel Drive.jpg
Wiring Diagram for Front Wheel Drive.jpg (82.65 KiB) Viewed 1427 times
Brake Hydraulic Parts.jpg
Brake Hydraulic Parts.jpg (54.22 KiB) Viewed 1427 times

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