Hi all. My neighbor has a 12 E with the hydraulic boosted brakes. They work really well most of the time.  Recently he has noticed that they work great when the engine is at idle up to around 2/3 throttle. However, at wide open throttle, the brake pedal goes strait to the floor and no amount of pumping will wake them up.  Slow the engine down, brakes come back.  

I'm not sure what to think. Anyone have any thoughts?  


Bruce P

Hi Bruce,
we used to fit No14 grader brake boosters to No12E's at the Dealer--machines we did this to were also fitted with Vickers power steering units and usually hydraulic blade side shift also that were usually Vickers cylinders--Australian production machines later on came from the factory with all this added booster etc. from Cat of Australia.
As an aside we also fitted front drums and brakes to the tandems along with softer linings to increase braking efficiency and lower foot pedal pressure required by the Country Roads Board--we had a Tapley De-accelerator Meter and pedal pressure pad/gauge set up to do brake efficiency tests to be sure the units met CRB requirements as per the Tenders.

Suggest check for a clogged pump suction screen in the Hyd. tank or clogged filter maybe even a collapsed suction hose inner lining--Vickers filters on our units and I cannot recall if the filters by-passed all flow back to the tank or simply by-passed the clogged filter back into the system.
If it is cold in your area maybe a lighter grade oil could be needed if the clogged screen or filter is not evident.

All these written words are for what we worked with and USA units would be different BUT the hydraulic system is still basically the same with screens and filters.

Cheers,
Eddie B.

Thanks Eddie. I wondered about cold oil too, but the owner says it has been doing this all summer.  I’ll have him check the filter.  There must not be a positive mechanical connection from booster to the master cylinder? I would think that if the hydraulics failed you would want to still use the brakes, albeit non boosted.  

Thanks again for the ideas.  

BP. 

Does the blade side shift also loose power (pressure) at high engine speed? Thinking pump is cavitating like ERB mentioned. Not related to this problem but if you ever come across a 12 with 4 wheel brakes as ERB mentioned, they take a smaller wheel cylinder, because the master doesn't have enough capacity to handle 4 cylinders.

Hi Bruce,
the No14 brake booster unit is superimposed between the pedal rod and the Master Cylinder so if there is no hydraulic pump working at least you have manual brakes--fail safe.
I would be suspicious of the tank suction screen if the oil viscosity is not the issue--Maybe after checking the oil viscosity is correct run the unit with the pump outlet hose disconnected back into the Hyd. tank filler neck and see what happens to the flow rate at the higher engine Rpm's.
Cheers,
Eddie B.

oldbeek wrote:

Does the blade side shift also loose power (pressure) at high engine speed? Thinking pump is cavitating like ERB mentioned. Not related to this problem but if you ever come across a 12 with 4 wheel brakes as ERB mentioned, they take a smaller wheel cylinder, because the master doesn't have enough capacity to handle 4 cylinders.

This grader has brakes on all four. As far as I know the side shift works all the time.