L70 Intermitant brake failure

[kmbrad]

Hi all

My L70 occasionally has 100% brake failure. It's not front or rear but the complete circuit.


The gauge drops to zero


My older Volvo loader has a compressor but this one doesn't seem to have one.

Looking through manual it appears to be this that powers the braking circuit.


Does anyone have any idea what the problem could be?

Cheers

 

[lantraxco]

Well, 100 bar would be roughly 1,450 psi, so hydraulic brakes... intermittent means probably a valve sticking open somewhere, just as a wild guess.

 

[Jim D]

I don't know Volvo... Like lantraxco says, it's a hydraulic pressure brake system. Different from air brakes. Hydraulic brake systems usually have a piston or bladder accumulator to keep a volume of pressurized oil to operate the brakes if the pump can't provide enough volume, i.e. when the engine is idling or when it is off. If the accumulator has failed, and if the pump is worn, you can see no pressure and have no brakes when the engine driven pump is idling and you use the brakes multiple times or when the engine is idling rolling down hill and you are using the brakes.

First check the brake accumulator; that the gas reservoir has pressurized gas. A worn pump will generate excess heat, from pressure loss without doing any mechanical work; a worn pump will be hotter than normal.

 

[Volvopro]

Full working pressure on that machine is approx 150 bar at the gauge in cab, you probably have a separate reservoir for the brake oil on that age machine (later models fed from hyd tank). Obviously check you have oil in the reservoir, from the oil tank the feed is direct to the pump then to the pressure unloading valve via the filter both of which IIRC are under the step. If you have intermittent loss of all pressure at the gauge the chances are that the problem is in your unloader valve (press reg) as the pump is pumping all the time the engine is running.

 

[Volvomad]

What age is it. I have never seen an L70 with that type door (4300) or an engine driven oil pump . Does the pressure drop fast or slow without using the brakes?

 

[Volvopro]

The earliest L machines had the door that way round then the cab changed a little later, it was always a nuisance to get the correct door lock.