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Thread: Load Sensing Proportioning Valve and Bypass Valve ???

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Back to my brake nightmare, lsp bv was fine. Brand new master cylinder bad from factory! Than bad flare fittings. Blah blah blah. Point being never trust new parts on sale...

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Quote Originally Posted by JFratzke View Post
    So after lifting my van with Mr Gasket Spacers (one on top of the coil and one underneath), I notice that my front brakes seem to be doing all the work all the time. I found this thread and my only question seems obvious but I can't grasp what I need to do. Do I need to add a bracket like Tim and raise my LPS up or do I need to drop it down? My guess is up, as the van is now higher than before. Not sure and having a hard time visualizing what is going on back there.
    I was wondering if you ever resolved this issue after using the Mr. Gasket Spacers? Did you use the spacers on both the front and rear?

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Quote Originally Posted by timsrv View Post
    I raised my van with overload springs. So now when it's loaded heavy the chassis does not drop down as the factory intended. This is why I raised the mount on the rear axle. In my case, since I messed with spring rates my LSPV & BV will never work as intended. It would have made more sense to simply replace the LSPV & BV with an adjustable "non load sensing" type. Instead I raised the arm because it was the easiest/cheapest way to get my rear brakes back.

    On your van, if there's no air in the system then it's not necessary to bleed. You could put your rear axle on jack stands, then get you rear wheels spinning & verify you can stop them by applying the brakes. This isn't a substitute for a correct adjustment, but it will at least tell you if the rear brakes are working.

    Tim, How would you verify a “correct adjustment?” P.O. had a coil spacer lift that I replaced with the Aerostar spring lift and the valve hasn’t ever been moved from its stock location. So I’m unable to verify the amount of adjustment needed by measuring before and after.

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    The only correct way that I know of is to follow the manual and use pressure gauges (see below)




    Other than that, about all you can do is jack and check or drive about 30 mph, then jam on the brakes while you have somebody watching. If you use the last method, I would advise to do so on wet grass or gravel as locking up your brakes on harder surfaces can damage your tires and/or upset your cargo. Tim

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Excellent reference here on the load sencing porportioning valve . I believe its the brake problem im having but just not sure , anyway I bit the bullet and bought one new at $170 , hopefully installed next week . After I ordered it I got in there to spray it down and clean up for removal and I noticed the "spring" seamed to be bent . ,So I guess Ill replace it too at $70 .
    BUT ...my original problem was an occasional soft peddle and sometimes more frequently , I mean it will go ALL THE WAY down out of the blue .
    So , Ive replaced all pads and shoes and everything seams to be right , I thought I was losing fluid , but ive only added once in months . I see no leaks ...and done the booster test above . Could it be the Master Cylinder ?
    Another thought or question , since the spring simply adjusts the valve , could I use a throttle type cable pull to adjust on my own from the cab ?
    Let me know what yall think !

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    That sounds like an internal seal failure in the master cylinder. There are essentially two chambers to the piston separated by seals. One is for the front and one is for the rear. If the seal is failing on the one of the chambers then the pressure and fluid will push past the seal into the other chamber and the pedal will drop usually only giving you brakes on one axle. Typically this is caused by some trash in the system damaging the seal or getting caught under it or some pitting in the cylinder itself keeping it from sealing properly. Since it's an internal seal the fluid doesn't go anywhere and never gets low.

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Thanks! that sounds like what it might be ...but I have NO brakes when it hits the floor . I ordered the master cyl . today , cause its relatively cheap and if I can avoid changing the lspv , Ide rather return it to toyota .I hate buying parts to fix things by elimination , but I might just save that $100 . I played with the spring and tried driving it several different ways and nothing seamed to change , except taking a nosedive at one extreme . Ive done enough master cylinders on these things that it should be fairly easy , and I'm much more concerned about breaking lines at the lspv.

  8. #28
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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Hey Guys,
    I have a 1990 Master Ace Surf, so a Town ace, basically. It is mechanically most similar to a 85' Van. 3YE engine. I installed AirLift brand spring supports this weekend. They're air bags that live inside the spring. Similar to what Tim has in is work vans. I can lift and lower the rear of the van with varied PSI. In reading this write up I got a little worried that my light/heavy/high/low adjustments would totally wreak havoc on my load sensing proportioning valve and it's duties. Then I went looking for it under my van. But, I cannot find anything like this on or near my diff... Is it possible that the JDM vans don't have anything like this? If they do, where is it? Anybody know about this?

    thanks!
    -Ross

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    yo, so its been cold and wet so I have not crawled under my JMD but this guy, https://www.instagram.com/p/BitxOWOnTmB/
    has a JDM and he had to make a bracket after he lifted.

    Maybe I can crawl under mine this weekend.
    I was a member for 2 years before I bought my van.
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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Not sure about your 2WD petrol van, but my 1988 4WD Masterace definitely had the load sensing valve.

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Quote Originally Posted by Duke View Post
    Not sure about your 2WD petrol van, but my 1988 4WD Masterace definitely had the load sensing valve.
    I can’t seem to find it in that location, I attached a photo. Sorry it is uploading upside down. I think I looked all over but I need to look at the axle again.
    Attached Images Attached Images  

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Quote Originally Posted by DangerRoss View Post
    I can’t seem to find it in that location, I attached a photo. Sorry it is uploading upside down. I think I looked all over but I need to look at the axle again.
    Don't worry about the axle, follow the brake lines. On my Previa, the LSPV is on the control arm on one side rather than centered and bracketed to the diff housing.



    As to the earlier (much earlier) questions about ABS and the LSPV, no, ABS is not an alternative to the LSPV. ABS acts to reduce lockup that has already happened. What does replace the LSPV is electronic brake force distribution or whatever each manufacturer decides to call it. Not all manufacturers account for cargo load with it though, it's often more a factor of the vehicle stability control system.
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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Quote Originally Posted by Andywear View Post
    yo, so its been cold and wet so I have not crawled under my JMD ......

    Maybe I can crawl under mine this weekend.
    took me long enough


    Looks attached odd.
    Name:  02.14.20 rear axle  .jpg
Views: 458
Size:  63.3 KB
    I was a member for 2 years before I bought my van.
    Vandi-

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    Quote Originally Posted by Andywear View Post


    Looks attached odd.

    perhaps that is why when I hit my brakes hard 3+ times the brake light on the dash lights up.....
    I was a member for 2 years before I bought my van.
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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    This is getting weird! Mine certainly doesn’t have that. I took a pic of the brake line splitter and it does not seem to have a load sensing function.
    Attached Images Attached Images  

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    Re: Load Sensing Proportioning Valve and Bypass Valve ???

    The splitter has nothing to do with the valve.
    To find the LSP/BV follow the brake lines from the front down the chassis.
    The LSP/BV is not located on the axle itself, only the lever arm that activates is attached there.
    The valve is upstream of the rear axle, well before that splitter in your picture.

    Either trace the lines down from the front, or find the actuator arm and follow it forward.

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    LSP-BV questions

    Alright. This LSP BV thing is giving me a headache. I think i have a general idea on how it works. Im still wondering about a few things though. I noticed some fluid slowly leaking out of the boot on the main part of the valve, where the arm comes out. I will link a video somewhere to show yall whats going on. A few weeks ago i flushed the fluid by gravity bleeding it. Cracked all 4 bleeders (i was unaware of the 5th one at the time) and let the fluid drain out while topping the reservoir off, until clean fluid came out the bleeders. Brakes have been working pretty good since then. I have tested them by jamming on the brakes as if i were about to rear end someone (going 20-30 mph) and the back wheels didnt lock up, nor the fronts. Today i lifted my van by 7/8” (lets just call it 1”) by tightening the two torsion bars in the front. This seemed to lift the whole vehicle, front and rear. Maybe a little bit more in the front, i dont know. I have not driven it yet. I just learned from this useful site that adjusting the suspension can confuse the LSP BV and keep the brakes from working correctly. So ill probably just lower the van back to where it was until i figure the brakes out. Ok im kind of rambling, so here is my main question:

    Is the LSP boot supposed to be filled with fluid? If you watch the video i am going to link, you will see that when i pull the boot back, fluid leaks out, and it looks kind of rusty. I wonder if i could zip tie the boot where it mates with the arm to help stop the slow leak. But im not even sure if that boot is supposed to have fluid in it. Perhaps it is an internal leak and fluid is wrongfully getting into the boot.

    not sure if bleeding that 5th bleeder will help with anything, cause the brakes seem to be working ok, but ill give it shot at some point. Im going to do new pads, shoes and springs soon and keep working to get the brakes dialed in. BTW this is an ‘86 2wd auto van le.
    -Jams

    i uploaded a youtube video that kind of shows what im talking about:
    https://youtu.be/8dzS8jVAVzA
    Last edited by Jams; 07-07-2020 at 11:19 AM.

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    Re: LSP-BV questions

    Hey!

    Have you tried making a lift bracket for the LSP? It’s a small bracket intended to lift the valve up and allow the brakes to work correctly. It made a difference on my van after I lifted everything (torsion and leaf lift)

  19. #39
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    Re: LSP-BV questions

    I have not yet, but i think thats a great idea. I might try to lift my van another inch maybe and make an adjustable bracket with slots so i can try to find the right height for the arm. Thanks for the reply!
    -jams


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