Write-up: Toss the LSPV and install a manual proportioning valve (3 Viewers)

[jkeithw]

The LSPV has no affect on the brake force applied from the MC to the front calipers, it only regulates the pressure to the rear brakes.

Is that correct? Does not the "sensing" line divert pressure back to the front brake circuit - thereby increasing the front circuit pressure?

(bear with me, I'm just not researching the 80 brake system to decide about deleting the LSPV and possibly the ABS altogether, and will have more questions)

 

[jkeithw]

per the Wilwood spec sheet, fully turned inward it puts the bias at 0%.
Fully tuned outward it puts the bias at 57%.

I’m trying to wrap my head around how that equates to front/rear bias. Can someone explain that?

At 57% bias mean the rear brakes are performing 57% of the 100%. Or is it performing 43% of the bias?

People need to hire better technical writers because I interpreted that differently than you did, but that doesn't make me right and you wrong.

What I read was that the lowest you could go is 43% less line pressure with the knob all the way out counterclockwise and by turning the knob incrementally clockwise the line pressure will increase all the way up to 100%.

So, I would assume (probably horribly) that no valve present is a balanced 50/50 braking pressure. If the knob is all the way out, does that take 57% of the pressure off the rear calipers and then all the way in restores the set back to 50/50?

This is why I don't mess with my brakes...I'm not even smart enough for a portioning valve conversation....

According to Wilwood, the knob controls the pressure at which the proportioning of the rear circuit begins (knob screwed out lowers the pressure threshold for the proportioning, tightening the knob raises that breakover point). Regardless, the proportioning valve does affect rear pressure - it's a matter of how much pressure triggers the action (according to this description)

That is, unless I am misreading it, but it seems to be stated pretty clearly.

 

[jkeithw]

I marked the "W" on the top of the Wilwood proportioning valve. At full open, the rear would lock sooner than the front. I set it to 3 turns from full open. I recently replaced the brakes and found the rear brake pads almost gone with a decent amount of meat still left on the front brakes. I installed new OEM pads (100 series in the front) and set the proportioning valve to 6 turns from full open. I think I measured 15 turns from open to closed.

This seems opposite to the Wilwood literature:

"Adjusting the valve does not directly change how much pressure goes to the brakes it is plumbed into; it is not like a hose spigot. Adjusting the knob or lever changes the pressure level at which the valve is triggered; sometimes called the "knee point" because it is the point where, on a graph of brake pressure, the line bends. It may seem counterintuitive, but when the knob or lever is adjusted all the way out, the valve delivers the most substantial reduction to maximum pressure. Screw it in, or click the lever over the other way, and the proportioning valve will allow a greater amount of pressure to reach the rear brakes before proportioning is triggered."

Wilwood Blog: How Does A proportioning Valve Work?

 

[alia176]

I'd start with deleting the ASPV and the ABS then drive it around to see if you actually need the proportioning valve. In my case, i didn't need it. In some cases, folks leave the Wilwood all the way open, which means it really wasn't needed !!

 

[jkeithw]

In some cases, folks leave the Wilwood all the way open, which means it really wasn't needed !!

From what I’m reading, it reduces the pressure in the rear circuit regardless of setting - so, significantly different than not having a valve (which should be the only way to not affect the rear bias during hard braking)

Anyone have data regarding the dimensions of the two sections of the factory master cylinder? I’m curious if they are sized the same (which I doubt) and would like to know what the factory bias is.

 

[lumbee1]

This seems opposite to the Wilwood literature:

"Adjusting the valve does not directly change how much pressure goes to the brakes it is plumbed into; it is not like a hose spigot. Adjusting the knob or lever changes the pressure level at which the valve is triggered; sometimes called the "knee point" because it is the point where, on a graph of brake pressure, the line bends. It may seem counterintuitive, but when the knob or lever is adjusted all the way out, the valve delivers the most substantial reduction to maximum pressure. Screw it in, or click the lever over the other way, and the proportioning valve will allow a greater amount of pressure to reach the rear brakes before proportioning is triggered."

Wilwood Blog: How Does A proportioning Valve Work?

Thanks for that. I read the tech page and will be revisiting my setup. I am currently 6 turns from full pressure. However the other day I was messing around and locked up the rear brakes before the front. I need to turn the screw out for more reduction to the rear.

Proper Initial Adjustment​

For safety, start with the proportioning valve set with maximum reduction setting, knob fully screwed out, and work from there. Next, find an assistant to observe and an empty parking lot with no chance of hitting anything. You'll need to repeatedly stop from 30 mph with the wheels locked up without attracting too much attention.

• Make sure your tires are correctly inflated to the recommended pressures.
• For best results, you'll want half a tank of gas or less, no passengers, and minimal junk in your trunk.
• Accelerate to 30 mph, then stop hard enough to lock up the wheels.
• Have your assistant watch (from a safe distance) and confirm that the front and rear wheels lock.
• If only the front locked, adjust the knob in two full turns to allow more pressure to the rear brakes and test again.
• Continue adjusting in, two turns at a time, until the front and rear wheels lock in a hard stop.
• Adjust knob out one complete turn and test again.
• Continue these adjustments 1/2 turn in or out at a time until maximum braking can be achieved and no wheel rear lock is observed.
• Test the vehicle again at 50 mph to judge the effects of a more dramatic weight transfer and make any additional adjustments as needed. Typically by turning the knob out to decrease pressure to the rear.

 

[White Stripe]

From what I’m reading, it reduces the pressure in the rear circuit regardless of setting - so, significantly different than not having a valve (which should be the only way to not affect the rear bias during hard braking)

Anyone have data regarding the dimensions of the two sections of the factory master cylinder? I’m curious if they are sized the same (which I doubt) and would like to know what the factory bias is.

The fsm has adjustment bias settings for the lspv with instructionson how to do so. The lspv is a propotioning valve. The manual aftermarket propotioning valves has a knob for adjustment, and the oem lspv has a threaded rod for adjustment on the axle. Either way you can adjust brake bias however you want for the braking characteristics you want. If your lspv has never been replaced it certainly is faulty by now, they dont last forever. Replacements are still available.