LSPV - What is it?
- Thread starter dekuiper
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Load sensing proportioning valve. Google is your friend 
This is "a valve that attaches an arm to the rear axle, so that a heavily loaded bed compressed the suspension, which applies more braking power to the rear brakes".
This is "a valve that attaches an arm to the rear axle, so that a heavily loaded bed compressed the suspension, which applies more braking power to the rear brakes".
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.
From Toyota Technical Information Services:
"The LSPV is used on Toyota models such as Truck, Van and Station
Wagons which may be used to carry a variety of loads. The heavier the
load, the greater the portion of braking is required of the rear brakes.
The LSPV allows higher pressure to the rear brakes to accomplish this.
The LSPV is attached to the body or frame above the left rear control
arm or axle housing. Load sensing is accomplished by suspending the
sensing spring between the vehicle body and the rear axle housing. The
load sensing spring movement caused by vehicle height changes due to
load, is transmitted to the proportioning valve.
As a vehicle is loaded, the leaf springs are compressed as the vehicle
body lowers. The load sensing spring provides a variable force pushing
the proportioning piston up as the vehicle is loaded. As the piston is
lifted, a higher brake hydraulic pressure is required to force the piston
down resulting in higher pressure at the rear wheels."
There is more technical information if you are interested.
-onur
"The LSPV is used on Toyota models such as Truck, Van and Station
Wagons which may be used to carry a variety of loads. The heavier the
load, the greater the portion of braking is required of the rear brakes.
The LSPV allows higher pressure to the rear brakes to accomplish this.
The LSPV is attached to the body or frame above the left rear control
arm or axle housing. Load sensing is accomplished by suspending the
sensing spring between the vehicle body and the rear axle housing. The
load sensing spring movement caused by vehicle height changes due to
load, is transmitted to the proportioning valve.
As a vehicle is loaded, the leaf springs are compressed as the vehicle
body lowers. The load sensing spring provides a variable force pushing
the proportioning piston up as the vehicle is loaded. As the piston is
lifted, a higher brake hydraulic pressure is required to force the piston
down resulting in higher pressure at the rear wheels."
There is more technical information if you are interested.
-onur
Squash
SILVER Star
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.
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.
Are you sure about that?
Your post seems to be the opposite of the post right before it. And I thought his contained a direct quote from Toyota.
LSPV
Unless my JDM is different 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 of the vehicle.
It is indeed a brake bleeding point and is often overlooked.
Cheers
Unless my JDM is different 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 of the vehicle.
It is indeed a brake bleeding point and is often overlooked.
Cheers
Squash
SILVER Star
Point taken about the FSM and Beno's post so maybe I require some schooling...Now
"The most important point to understand about proportioning valves is when they work - only during panic braking. This means that a vehicle could potentially go its whole life without ever using its proportioning valve. Think about the little old lady that drives to and from church and the grocery store. It is possible that she will never have the need to make a panic stop and therefore never activate her proportioning valve. The other half of that equation is all those who drive near her will probably get a chance to see if their proportioning valves work! "
Take your vehicle onto a dirt patch, drive 15-20mph and slam on your brakes. Get out and look at the four skid marks, your front tires should lock up first and most.
If your rear wheels lock up greater than your fronts you will most likely head into the rubarb some day soon.
Read this copy:
PROPORTIONING VALVE & BRAKE BALANCE
To reduce hydraulic pressure to the rear brakes so the rear brakes don't lock up when the brakes are applied, a "proportioning valve" is required. This valve helps compensate for the differences in weight distribution front-to-rear as well as the forward weight shift that occurs when the brakes are applied.
What we're really talking about here is "brake balance" or "brake bias," which is the difference in the amount of hydraulic pressure channeled to the front and rear brakes. The front brakes on most rear-wheel-drive vehicles normally handle about 60-70 percent of the brake load. But on front-wheel-drive cars and minivans, as well as RWD and 4WD pickups and SUVs, the percentage handled by the front brakes can be as much as 90 percent of the load.
Consequently, the front brakes need a higher percentage of the total hydraulic force that's applied to keep all four brakes properly balanced.
If the front-to-rear brake force isn't balanced correctly by the proportioning valve, the rear brakes will receive too much brake force, causing them to lock up and skid when the brakes are applied. The other reason for using a proportioning valve to reduce hydraulic pressure to the rear brakes has to do with the design of the brakes themselves. When hydraulic pressure is applied to the wheel cylinder inside a drum brake, the shoes are pushed outward against the drum. When the shoes make contact, the rotation of the drum tries to drag them along. But since the shoes are anchored in place, the drum pulls the shoes up tighter only against itself. Because of this, drum brakes that are "self-energizing" require little additional pedal effort once the brakes are applied. Disc brakes, on the other hand, are not self-energizing. It takes increased pedal effort to squeeze the pads against the rotor.
Some vehicles have load sensing proportioning valves that change rear brake metering to compensate for changes in vehicle loading and weight shifts that occur during braking. This type of proportioning valve has an adjustable linkage that connects to the rear suspension or axle. As the vehicle is loaded, ride height decreases and pressure to the rear brakes is increased. This type of proportioning valve can be found on many minivans, pickups and even some passenger cars.
Load sensing proportioning valves usually are adjustable, and must be adjusted correctly if they are to properly balance the rear brakes to the vehicle's load. The valve linkage is adjusted with the suspension at its normal height (wheels on the ground) and the vehicle unloaded. The adjustment bracket or linkage is then adjusted according to the vehicle manufacturer's instructions, which typically involves adjusting the linkage to a certain position or height.
Load-sensing proportioning valves are also calibrated to work with stock springs. Any suspension modifications that increase the load-carrying capability (installing helper springs, or overload or air-assist shocks, for example) may adversely affect the operation of this type of proportioning valve. Modifications that make the suspension stiffer reduce the amount of deflection in the suspension when the vehicle is loaded, which prevents the proportioning valve from increasing rear brake effort as much as it normally would. A defective proportioning valve, or one that is not properly adjusted, can also upset brake balance. If the rear brakes on a vehicle seem to be overly aggressive (too much pressure to the rear brakes), or the vehicle seems to take too long to stop (not enough pressure to the rear brakes), the problem may be a bad proportioning valve. Proportioning valves can be tested by installing a pair of hydraulic gauges (one on each side of the valve) to see if the valve reduces pressure as it should.
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.
"The most important point to understand about proportioning valves is when they work - only during panic braking. This means that a vehicle could potentially go its whole life without ever using its proportioning valve. Think about the little old lady that drives to and from church and the grocery store. It is possible that she will never have the need to make a panic stop and therefore never activate her proportioning valve. The other half of that equation is all those who drive near her will probably get a chance to see if their proportioning valves work! "
Take your vehicle onto a dirt patch, drive 15-20mph and slam on your brakes. Get out and look at the four skid marks, your front tires should lock up first and most.
If your rear wheels lock up greater than your fronts you will most likely head into the rubarb some day soon.
Read this copy:
PROPORTIONING VALVE & BRAKE BALANCE
To reduce hydraulic pressure to the rear brakes so the rear brakes don't lock up when the brakes are applied, a "proportioning valve" is required. This valve helps compensate for the differences in weight distribution front-to-rear as well as the forward weight shift that occurs when the brakes are applied.
What we're really talking about here is "brake balance" or "brake bias," which is the difference in the amount of hydraulic pressure channeled to the front and rear brakes. The front brakes on most rear-wheel-drive vehicles normally handle about 60-70 percent of the brake load. But on front-wheel-drive cars and minivans, as well as RWD and 4WD pickups and SUVs, the percentage handled by the front brakes can be as much as 90 percent of the load.
If the front-to-rear brake force isn't balanced correctly by the proportioning valve, the rear brakes will receive too much brake force, causing them to lock up and skid when the brakes are applied. The other reason for using a proportioning valve to reduce hydraulic pressure to the rear brakes has to do with the design of the brakes themselves. When hydraulic pressure is applied to the wheel cylinder inside a drum brake, the shoes are pushed outward against the drum. When the shoes make contact, the rotation of the drum tries to drag them along. But since the shoes are anchored in place, the drum pulls the shoes up tighter only against itself. Because of this, drum brakes that are "self-energizing" require little additional pedal effort once the brakes are applied. Disc brakes, on the other hand, are not self-energizing. It takes increased pedal effort to squeeze the pads against the rotor.
Some vehicles have load sensing proportioning valves that change rear brake metering to compensate for changes in vehicle loading and weight shifts that occur during braking. This type of proportioning valve has an adjustable linkage that connects to the rear suspension or axle. As the vehicle is loaded, ride height decreases and pressure to the rear brakes is increased. This type of proportioning valve can be found on many minivans, pickups and even some passenger cars.
Load sensing proportioning valves usually are adjustable, and must be adjusted correctly if they are to properly balance the rear brakes to the vehicle's load. The valve linkage is adjusted with the suspension at its normal height (wheels on the ground) and the vehicle unloaded. The adjustment bracket or linkage is then adjusted according to the vehicle manufacturer's instructions, which typically involves adjusting the linkage to a certain position or height.
Load-sensing proportioning valves are also calibrated to work with stock springs. Any suspension modifications that increase the load-carrying capability (installing helper springs, or overload or air-assist shocks, for example) may adversely affect the operation of this type of proportioning valve. Modifications that make the suspension stiffer reduce the amount of deflection in the suspension when the vehicle is loaded, which prevents the proportioning valve from increasing rear brake effort as much as it normally would. A defective proportioning valve, or one that is not properly adjusted, can also upset brake balance. If the rear brakes on a vehicle seem to be overly aggressive (too much pressure to the rear brakes), or the vehicle seems to take too long to stop (not enough pressure to the rear brakes), the problem may be a bad proportioning valve. Proportioning valves can be tested by installing a pair of hydraulic gauges (one on each side of the valve) to see if the valve reduces pressure as it should.
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.
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yes, you are correct. I was just trying to point him in a general direction to eyeball the thing.
mike
Totally different purpose, I believe.
What you're talking about is a mechanical type ABS system, where in certain situations the pressure to the rear brakes are reduced.
The LSPV's purpose is the opposite, to increase the amount of braking by the rear brakes when there is more weight in the back. This is why when you have loaded your cargo area, or are towing a trailer, your truck still brakes evenly.
I've towed with trucks that don't have anything similar, just straight lines to the rear brakes. The truck brakes totally different when pulling a trailer then when not. Braking with the 80 while towing feels nearly the same, due to the increased braking by the rear brakes.
The attached picture (from the FSM) gives a simple idea of how it works. The more weight, the farther the piston gets pulled down, and the more fluid can squirt to the rear brakes, increasing the amount of braking power.
Squash
SILVER Star
Lexus/Toyota Tech
Both senarios are correct.
The LSVP does comensate for added weight and it will proportion brake force to the rear wheels during a panic stop.
The following link provides additional info and tech some general and some specific to our units.
http://www.autoshop101.com/forms/brake08.pdf
Both senarios are correct.
The LSVP does comensate for added weight and it will proportion brake force to the rear wheels during a panic stop.
The following link provides additional info and tech some general and some specific to our units.
http://www.autoshop101.com/forms/brake08.pdf
I always assumed the proportioning valve was always working. I think it is basically a pressure regulator since the rear brakes require less force than the front, without the valve you would lock-up the rear brakes with a normal load if they received the same pressure as the front brakes. The unique thing about the Land Cruiser valve is that it senses the load and adjusts the valve accordingly.
Rusty
Rusty
If you have ABS, does the LSPV surve the same purpose as no ABS?
I am about to install OME 2.5" and looking at the rusted LSPV I don't think it can be adjusted.
Replacing sounds expensive.
I am about to install OME 2.5" and looking at the rusted LSPV I don't think it can be adjusted.
Replacing sounds expensive.
Squash
SILVER Star
The LSVP is adjustable, they come with and without ABS equiped vehicles. The search feature and link above will offer some help as to lifts.
Some folks use aftermarket units and adjust the to suit their needs, others have bypassed the unit completely, my concern here would be the potential to lock up the rear end on the highway.
The valve is a non-serviable unit. Really soak the connections before trying to bleed.
Some folks use aftermarket units and adjust the to suit their needs, others have bypassed the unit completely, my concern here would be the potential to lock up the rear end on the highway.
The valve is a non-serviable unit. Really soak the connections before trying to bleed.
This is something I've been curious about since I installed my OME Lift. This thread contains a lot of good info as wells as two methods of adjustment. The dirt skid method and the full factory hydraulic pressure gage method. Anyone have any different methods of checking and adjusting the proportional valve?
It's also a bypass valve which redirects fluid pressure if a portion of your brake system loses pressure.
OK so how is the system adjusted for say 2" lift and heavier springs. Do you just bend the arm down 2" at the axle?
You adjust it closer to the top end of the adjustment nut on the rear axle.
Did you adjust yours yet?
