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I’m a little embarrassed to post this because I fancy myself a half decent mechanic. That being said.. does anyone know what this is? It is located on the rear differential and has a hard line to what looks like a servicing point on the frame. There is another hard line coming off of the servicing point that has been cut. (By previous owners) I have been using the truck for about 4 months with no issues and now that I am in the restoration phase I’m wondering if I should just remove it or try and find a replacement. If anyone has any information on this mythical contraption please let me know.
That's the Load Sensing Proportioning Valve (LSPV). It's an automatically adjusting proportioning valve for the rear brakes. It's purpose is to adjust the brake bias for when you have more or less load in the bed/back. There should be three brake lines plumbed into it. On these older trucks, when the brake fluid is neglected, these valves can get rusted up and possibly blocked causing poor braking performance. I've also seen them leak but still function. It is sometimes bypassed by people who believe they can come up with something smarter. I've opted twice (on two different trucks) to replace it with new OEM and retain the full designed performance of the braking system. Unfortunately for you, whoever removed yours was a serious hack and seems to have butchered and chopped the system all up such that it will be a bit harder to repair correctly.
Here's the manual page for it: http://web.archive.org/web/201204171...12loadsens.pdf
Since you probably haven't been driving both with it fully loaded and fully unloaded, you haven't noticed the change in brake bias.
arlindsay1992 Thank you for the info! It really helps a bunch. I have a few follow up questions.. how do I know if there is a lspv delete? And if I just take what is left of the lspv off will I be effecting the braking system in a negative way?
There is no kit that deletes the LSPV, and in my opinion there is no correct way to delete it because it shouldn't be deleted. A proportioning valve of some sort is usually required to keep the rear wheels from locking up when braking. From factory the front and rear brake circuits are connected through the LSPV. I have no idea how the previous owner of your truck rigged it up.
If you unbolt what you have left it will not make it any worse because in its current state is completely disconnected from the braking system.
arlindsay1992 Thank you for the info! It really helps a bunch. I have a few follow up questions.. how do I know if there is a lspv delete? And if I just take what is left of the lspv off will I be effecting the braking system in a negative way?
I'm sure there are some here who have done the LSPV delete that can offer some insight, but I wouldn't do it.
I do know that the Toyota RVs and trucks with utility or stake beds often had helper/overload springs, airbags, or other rear suspension mods to help them handle the extra weight. Since their rear end didn't drop the LSPV sensed a empty load and didn't increase braking power to the rear, making the front pads do all the work. The good thing was their brake shoes lasted forever since they never did much(not great on a wet road). I'm guessing with a delete they just swag the % to the rear and it never changes. Cars don't need a LSPV, as even with a full load most of the weight is still between the four tires. But with a truck you can put a huge amount of weight directly over the rear, and that changes everything.
I deleted the LSPV when it started leaking on my 4Runner. The rear brakes never worked right. I ended up buying a new OEM valve and plumbing it back in.
Thank you guys a bunch! I think I have to start figuring out how and where to plumb it back into the brake system. Arlindsay1992 If you could share any tips or pictures of how you plumbed the LSPV back into your brakes that would be awesome.
i used a manual prop valve on my old 81 trekker.
on my 94 due to the weight of the 4runner i made a plate to hold the rod up higher to manually bias it slightly to the rear.
When the thing is running it stops like a dream
01-06-2022, 10:46 AM
