What is this thing? [SOLVED - Load Sensing Proportioning Valve]
- Thread starter quatin
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JRZEE2000TR4LTD
Senior Member
mtbtim
Elite Member
<a href="https://ibb.co/jWSC52C"><img src="https://i.ibb.co/gPx07p0/20190330-121921.jpg" alt="20190330-121921" border="0"></a>
LSPV. Load sensing proportioning valve. It adjusts how much fluid pressure goes to the rear brakes based off the load on the rear of the vehicle. When the load is higher, I believe it will allow more fluid pressure to the rear brakes to increase the braking power. When the load is lighter, it doesn't allow as much fluid pressure to decrease the amount of of braking force to the rear tires to prevent locking of the rear wheels.
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Thanks. Can't believe I've never noticed it before. $400 for a little valve assembly ouch. Do you know if this valve can cause a hard brake pedal if the piston locks up somehow?
gamefreakgc
Elite Member
Whoa, I've never seen one of those before. And I've owned a 98, 99 and 02. Weird.
gamefreakgc
Elite Member
That would be why!
96RedRunner
Senior Member
I have only owned limited models 96 & 01 both ABS, have looked at all in the yards never seen this on a Runner.
Must be on the cheapest optioned Runners you could buy.
[MENTION=73949]quatin[/MENTION], just curious what frame code do you have?
Must be on the cheapest optioned Runners you could buy.
[MENTION=73949]quatin[/MENTION], just curious what frame code do you have?
SaulG
Member
Adjust the fluid pressure by changing the A or B length.
1. Low pressure - Lengthen A, B
2. High pressure- Shorten A, B
HINT: Fluid pressure change for one turn of the lock nut is 100 kPa (1.0 kgf/cm2, 14 psi) and fluid pressure change for 1 mm (0.04 inch) sliding of the adjust bolt within the long hole position is 40 kPa (0.4 kgf/cm2, 6 psi).
Initial set length (Unladen): 222.5 mm (8.760 inch)
Nate_GB
Member
What exactly do you mean by "hard brake pedal?" Is it hard to depress the brake pedal all the way from the top of it's travel? Are you feeling a hard pedal but not getting much braking force?
If I was trouble shooting my braking system, the proportioning valve definitely wouldn't be in the top 3 things I would check first while diagnosing.
If you provide some more details of your issue, we might be able to provide some more guidance.
JZiggy
Senior Member
You can bleed that little guy along with your brakes. My rig is non-ABS and has one too. I always bleed it as the last step of the process.
[MENTION=151010]SaulG[/MENTION] good info on the specs of the LSPV. I've seen adjustment brackets on leaf sprung axles that raise the connection point so the LSPV can't tell the suspension has been lifted. Without the adjustment it doesn't send much pressure to the back wheels. I wonder if something similar is necessary for coil sprung vehicles like ours?
[MENTION=151010]SaulG[/MENTION] good info on the specs of the LSPV. I've seen adjustment brackets on leaf sprung axles that raise the connection point so the LSPV can't tell the suspension has been lifted. Without the adjustment it doesn't send much pressure to the back wheels. I wonder if something similar is necessary for coil sprung vehicles like ours?
phattyduck
Elite Member
Yes! Same deal - you want the brake bias to match stock when unloaded (or, if you really know your brakes, maybe adjusted from there).
It just isn't talked about much on here because so few were non-ABS. Kinda like all those discussions of crank windows.
-Charlie
JZiggy
Senior Member
Yes! Same deal - you want the brake bias to match stock when unloaded (or, if you really know your brakes, maybe adjusted from there).
It just isn't talked about much on here because so few were non-ABS. Kinda like all those discussions of crank windows.
-Charlie
Charlie,
Are there lift brackets for our rigs? I don't think I've seen one.
phattyduck
Elite Member
Probably not. A little bit of aluminum bar and a couple holes should be all you need.
It looks like the valve is attached to the panhard rod - if so, the Eimkeith PCK would work too (using just the axle side section).
-Charlie
HiluxSurf SSR-G
Senior Member
this is one option to adjust and maintain effectiveness of the LSPV:
Brake Proportioning Valve/Brake Cable Extension Kit for 1995-2004 Tacoma, 1996-2002 4Runner, 1999-2006 Tundra (BPV-K)
alternatively, if your lift is more or less permanent, you can replace the bracket with a longer one
Brake Proportioning Valve/Brake Cable Extension Kit for 1995-2004 Tacoma, 1996-2002 4Runner, 1999-2006 Tundra (BPV-K)
alternatively, if your lift is more or less permanent, you can replace the bracket with a longer one
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JZiggy
Senior Member
That is designed to lift the LSPV rod on leaf-sprung axles. Our coil-sprung axles don't use a rod but rather a big coil spring. Wheelers notes that we can still use this bracket to reposition the e-brake cable but not to address the LSPV.
This is a long saga spanning several years. It started with a "catch" in the brake pedal, as in you depress the pedal, it would get hard halfway down as if catching something. Then if I press the pedal harder, it would give and I get full brakes again. During the catch period, I would get partial brakes. Once it gives, i can hear a "clank" noise coming from the rear of the car. Everytime I use the parking brake lever, it would catch in the first 2-3 brake pedal uses. I have also had it happen randomly when driving.
My mechanic couldn't figure it out so I went brute force approach with replacing things. Here's where I'm at so far:
Things I've replaced in order:
- brake booster hose and valve. No effect
- Mechanic replaced the brake booster. No effect.
- front calipers & rotors, flushed brake fluid (brake fluid was dark). Problem improved, with less force required to get pass the catch.
- wheel cylinders in the drum, no effect
- master cylinder, no effect
- drum shoes, shoe adjuster, parking brake cable (the 8'' one inside the drum) Problem improved, now only catching lightly with parking brake lever up and me pumping the brake pedal in park.
From what I've read, this sounds like a "tripped valve" in the proportioning valve. It can be the valve being faulty itself or something tripping the valve. However, I'm not sure what else is left for me to replace.
Things I haven't replaced (let me know if there's anything I've missed)
- Brake hoses. (inspected and doesn't look cracked or leaky)
- LSPV (Just discovered it recently, bled it, problem persists)
- Drum springs & clips (autozone parts didn't fit so I reused the originals, looked fine)
- Drums (looked fine)
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