I've been reading about brakes and master cylinder testing and I keep coming across this acronym. What is a LSPV?
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Think of LSPV as a primitive ABS system.
As additional weight is added to your truck the tendency is for the rear end to lock up, a properly adjusted LSPV compenstes for load by reducing line pressure to the rear brakes.
Have you ever tried a pull the handbrake stunt and locked your rear tires??? pretty hard to steer straight unless you release the brake.
On your 80 it sits on the rear axle and can be adjusted to accommodate a lifted suspension. It's also a bleed location you should be aware of in addition to the 4 wheels.
you will not find the LSPV on the rear axle of an 80 series landcruiser. It is fited to the vehcle chassis cross member and there is a operating arm that is attahced to the rear axle
"The most important point to understand about proportioning valves is when they work - only during panic braking.
On some late-model vehicles, the mechanical proportioning valve has been replaced by "electronic" brake proportioning through the ABS system. By sensing wheel speeds, the ABS system reduces pressure to the rear brakes as needed when the brakes are applied.