Load Sensing Proportioning Valve problem - Toyota Nation Forum : Toyota Car and Truck Forums


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Old 02-28-2010, 06:53 PM   #1 (permalink)
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Load Sensing Proportioning Valve problem

I have an 1987 Toyota Pickup, 22R Engine and have recently redone the back/drum brakes.

Now I'm finding that the LSPV seems stuck in the closed position. Providing full braking power to the front and nothing to the rear.

In the process of bleeding all the brake lines I was unable to get any fluid through to the back brakes. I started troubleshooting the problem at the master cylinder. I bled it then move to the disk brakes (front) then back to the rear/ drum brakes. Getting no fluid in either brake at the bleeder valve I traced the line back to the bleeder valve in the LSPV. Plenty of flow to that point and nothing after it.

I've seen a few things on the internet that say that you can fix this problem by adjusting it, but it never says how. Is it that boltish thing towards the back of the truck? If it is should I tighten it or loosen it?

Any help is greatly appreciated.
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Old 02-28-2010, 07:50 PM   #2 (permalink)
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Check the Brakes chapter of the factory service manual - there's a section on the load sensing proportioning valve (LSPV) that gives some troubleshooting help. Google 1993 toyota pickup service manual if you don't have an fsm. (The 93 valve is either the same or nearly the same as on your 87.) If you can't get your LSPV going, I'd get one from the junkyard. http://www.car-part.com is a great portal to hundreds of junkyards.
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Old 03-01-2010, 03:38 PM   #3 (permalink)
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OK, I tried wiggling the lever arm to try to get it to work, and it didn't work, so I tried to loosen that little screw with the nipple on the end to se if that was blocking the flow of the fluid, and I went a litle too far and brake fluid started squirting out. I screwed it back in till it stopped coming out, but now I can only go in just a little bit before it feels like it hits something. I know it can go in further, because the screw in clean for about a half inch, then the rest it covered in brake and exaust gunk. Is this a problem?
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Old 03-01-2010, 06:31 PM   #4 (permalink)
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That little nipple is the bleed screw. Taking it all the way out may have let air into the system.
It should go back in as far as it was before. Maybe there's dirt in the threads or you cross-threaded it.
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Old 03-01-2010, 06:33 PM   #5 (permalink)
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Oh yeah, the adjustment is the long threaded bolt down on the axle.
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Old 03-02-2010, 10:09 AM   #6 (permalink)
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I didn't take it all the way out, I took it out just enough for the brake fluid to come out of it.
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Old 03-02-2010, 11:40 AM   #7 (permalink)
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You were attempting to bleed the brakes with the rear wheels on the ground correct? If not, try bleeding with the wheels on the ground before attempting to adjust the LSPV.

I have only done these trucks that way, so I'm not sure if it works otherwise. I could see brake pressure not being allowed to go to the rear if the frame were several inches above ride height.

The idea of that thing is to increase pressure to the rear brakes as the load in the bed increases, and decrease proportionally as load(weight) is removed to avoid rear lockup. The adjustment is only there for factory setting, and Toyota does not reccomend we adjust. In case of collision you might have to, or to compensate for a lift without an extension bracket possibly.
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Old 03-02-2010, 12:38 PM   #8 (permalink)
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Quote:
I didn't take it all the way out, I took it out just enough for the brake fluid to come out of it.
There's still the possibility air got in, you can bleed the system after you've solved the original problem.

And back to that. Where the LSPV arm connects to the axle bracket there is a single bolt holding it. Remove it and tie the LSPV arm up to the frame. This allows max pressure to the rear axle. Test drive and see if you have better rear brakes.
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Old 03-04-2010, 10:45 AM   #9 (permalink)
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Thanks fourwd, I'll give that a shot when I get home.
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Old 03-04-2010, 01:19 PM   #10 (permalink)
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I tied it up permanently on my 84 years ago. I eliminated the LSPV on my 83.
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Old 03-27-2012, 07:41 PM   #11 (permalink)
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I know this is an old post but I thought I would revive it instead of starting a new one.

My problem is pretty much the same as every one else with a couple new problems.

My mother has a 1987 Toyota 2 wheel drive pickup. At this point the truck has zero brakes. Started out with her having low brake pedal I checked the brake shoes and the rear shoes were thin so I replaced the rear shoes and replace both back wheel cylinders. Tried to bleed back brakes and cannot get any fluid or air through the lines. There is fluid at front brakes and I can bleed fluid from the LSPV at the bleeder but nothing at the rear brakes.

Ok I understand that if the LSPV is bad I wonít have rear brakes but I donít understand why the truck no longer has front brakes either.

I bought a used LSPV from the junk yard and I still canít get any fluid at the back bleeders.

Can some one explain how the LSPV works or tell me where I can get a picture that has details on how the LSPV is suppose to work.

Thank you for any help you can give me.
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