LSPV

Let's discuss the load sensing proportioning valve. I understand this valve works by sensing weight in the bed, and adjusting the amount of brake fluid pressure sent to the rear wheels. I'm assuming it sends more fluid to the rear when weight is back there, not less.

I mentioned before that when I have my dirt bike on my hitch hauler, my brakes are noticably better. The pedal has less pre-travel, is firmer, and the truck stops better. It seems clear that the rear brakes are doing more work.

I want to replicate this the other 95% of the time for when I'm not hauling a dirt bike. I have tried doing minor adjustments to the LSPV and I cannot get the same results.

Stealing this picture from @shifty` I have the same setup with the extension bracket. I notice that his is nearly maxed out.



Knowing that my brakes get better with weight in the bed, what should I do with this info? Would it make sense to max out the adjustment to send more bias to the rear all the time?

Also, what do people gain by deleting the prop vale entirely? How does that even work?

 

So you've already installed a bracket?

 

I think there's a tuturiol out there on the web on just how that works. Normally, brakes are 80% up front and 20% in the rear without loading.

I seem to be having no issues with my rears grabbing unloaded and unmodified and I know what they felt like when nothing was really grabbing back there (fronts always vibrating decelerating from highway speeds downto a stop. It only required a two man brake bleed to get the air out. Speedi-Bleed didn't seem to the do the job for me.

 

Yes. Shifty convinced me to. I never did it because the lousy ICON AAL yielded basically zero lift back in 2019. I got maybe .5" so I didn't think it was necessary.

 

Here is mine for reference as well. Granted my truck is suspended in the air, but I adjusted mine close to the run out just as shifty did and it has made a more noticeable difference. Move it up about an inch at a time and test. Move and retest until you have what you want.

 

Did you notice any change in braking with the LSPV relocate bracket? I thought I heard you mention with the bracket you were grabbing a little too much, or locking up, but my memory is fuzzy.

With the setting, I think TBM is right; but I’d move at smaller increments (1/2” at a time) knowing the LSPV relocation bracket is already there, and is probably longer than what you lifted; I’m having some difficulty mechanically visualizing what impact the LSPV reloc bracket would have on this without being under the truck. Maybe have the missus stand on the bumper while you’re under the truck to see what is articulating and how, then split the difference with the setting.

Be sure to mark your starting point with a paint marker, on the lower side, so you can return back to that spot after w/o thinking twice, if needed. You may also try adjusting down half inch to see if the brakes get softer or not, knowing the LSPV bracket was installed, but given your experience of better brakes with load in the bed, I doubt it’ll be the case.

 

Yes that's right. When I initially installed the bracket I was locking up the rear tires on dry pavement. It was fun. I realized that the rear shoes were too tight though. With the truck in neutral, off the ground, I couldn't spin the tires by hand. After replacing the rear shoes they are now dialed in correctly and lightly drag.

I'm having the same difficulty understanding what the extra weight on the rear is doing. It's crazy that my 200lb bike is making a noticeable difference.

I'll mess with it more and see what I can find out.

 

Extra weight is flexing the leafs, which is allowing the body to drop in relationship to the axle. That, in theory, pushes up on the lever going over to the LSPV, which opens a port inside the LSPV allowing more fluid (thus more pressure) to the rear brakes.

Unless I'm understanding wrong, that's the whole point behind that bar/lever system: The longer bar opens/closes the fluid port to the rear brakes at the LSPV. The more weight you have in the rear, the lower the body sits in relation to the axle, and with the LSPV arm being attached to the axle, the lever pivots up, increasing fluid flow/pressure to the rear brakes. Just using the relocation bracket should've had a similar effect.

 

Can someone confirm their lever is curved too?

I'm assuming it's designed that way to give the spare tire clearance but wanted to confirm mine wasn't bent somehow.

 

Confirmed

 

Also, your pics remind me that I want to do a read diff breather

 

There is a willwood proportioning valve that is a direct fit, incase you want to set the brake bias that way.
Wilwood Engineering 260-12627 Adjacent Proportioning Valve Knob Style (M10 x 1.0 BF inlet)

$52 Wilwood Engineering 260-12627 Adjacent Proportioning Valve Knob Style (M10 x 1.0 BF inlet)

https://www.amazon.com/dp/B011B4UX5U

 

So I would remove the prop valve and then make adjustments with the knob? I assume the bleeder valve stays in place so you can bleed the air out?

 

You would bleed the brakes with the valves on the drums The knob will allow more brake fluid to flow, firmer rear brakes or less flow for less rear braking.
Look up “LSPV delete” and you should find posts talking about this product.

 

In short, you’re basically going from an automatically adjusting PV to a manually-adjusted PV. Which just means your PV will act the same all the time after, loaded or not, and if hauling loads, if the braking isn’t good enough, you need to manually get under the truck and adjust up or down.

 

I pretty much maxed mine out last night and drove the truck this morning. It helped a little. It doesn't seem like the prop valve works perfectly. Deleting it sounds appealing.

 

Wilwood makes quality parts. Like @Paxmanhp mentioned, there are ample write-ups online for LSPV delete on Toyotas.

 

Now that I have the camper shell on the back, I have noticed the exact same thing you speak of. I thought it was a phenomenon on my return trip home with the top, but I really noticed it yesterday on the way home from work. Much happier.

 

I have an extra 320lb in my bed right now by the way of (4) unopened boxes of APC rack-mount batteries (adding to the ~150lb the shell probably weighs). I'm absolutely loving the feel of my brakes right now. I also noticed, as soon as those batteries landed in my bed, my brakes are no longer squealing up front anymore. But I am sitting about 1/8" lower in the rear now, which I'm not loving.

 

Mine keep fluctuating, day to day. It doesn't make much sense. I'm seriously considering removing the prop valve for the Wildwood option.

 

Time for the big brake upgrade?

 

I'm too lazy to read through your history , when was the last time you performed a PROPER brake fluid flush?

 

All things considered: I'm seriously considering watching how it goes for you and then considering my options based on your considerations.

 

I guarantee I've bled my brakes more than anyone on this forum. Probably 20 times since 2020 when I tried the big brake calipers. I don't think there is any air left trapped.

 

Just dropping this here because it seems related. Haven't researched any of this yet but hope it helps...

https://www.firstgentundra.com/firs...te-kit-for-wilwood-manual-proportioning-valve

 

Came across this yesterday. I’ll probably go pickup the parts and knock it out today or tomorrow. Mine is already maxed out.