IT18F brake pressure

[PD Mech Steve]

Have a CAT IT18F with worn out brakes. Wondering what if any residual brake pressure is acceptable after releasing pedal? I have a constant 30 Lbs.

 

[Mark250]

you haven't given a serial number but I will take a guess as they are similar
If the machine has done a lot of hours or worked hard I wouldn't worry too much about the residual pressure readings
the brake pistons are open to tank return via the brake foot valve and as such have no residual pressure. However as the hydraulic tank is sealed the brake pistons have hydraulic tank pressure imposed on them which will apply a very light brake application, As the differential housing is pressurised it tends to counter act this effect to a small degree
in other words check your hydraulic tank is not building up too much pressure by either being over full, reducing the tank air space or the hydraulic system is over heating causing a similar issue
also check your axle relief vent is keeping the axle housing pressurised
to confirm remove your hydraulic fill cap and recheck your pressures
it is also possible that the foot valve is not returning properly due to dirt build up or other mechanical reasons





Mark

 

[John C.]

Just a comment or question. I've never seen a axle vent that was meant to hold pressure in the axle. Dirt under the heel end of the brake pedal is spot on.

 

[Mark250]

Just a comment or question. I've never seen a axle vent that was meant to hold pressure in the axle. Dirt under the heel end of the brake pedal is spot on.

hi john.the F series with inboard brakes have a small relief valve that looks like a zerk fitting

 

[John C.]

I'll have to look for that next time I look at one of those machines.

Thanks

 

[kshansen]

hi john.the F series with inboard brakes have a small relief valve that looks like a zerk fittingView attachment 176695

I was trying to find some information on those myself. I do recall seeing them on some axle housings of loaders but could not recall where. I seem to recall they are marked with the relief pressure.

Also I have seen them used in some applications as a grease release valve to prevent excessive greasing pressure forcing out seals.

 

[PD Mech Steve]

Thanks guys for your input. However I have run with tank cap removed and still have pressure at brakes. In addition since this post was made, I have determined that the pressure increases with engine rpm's. I have isolated the source of this oil to either the accumulator charge valve or the main hyd pump case drain. These 2 are tied together at the tank. The return line from the brake valve Tee's into the return line at the accumulator charge valve. Once I removed the return line from the brake valve, I no longer had the pressure going to the brakes but still had the 30+ lbs at the accum. return. So basically a back feed from either accum. or main pump case drain. The consensus is that 30 lbs is't anything to worry about but it obviously is as the brakes drag at 30 and with increased engine RPM pressure rises to 50 at roughly 1/4 throttle and at that point wheels are locked up.