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How to adjust rear Load Sensing Proportioning and By-Pass Valve (LSP & BV)?

Discussion in '1st Gen. Tacomas (1995-2004)' started by JasonLee, Jun 19, 2019.

  1. Jun 19, 2019 at 8:06 AM
    #1
    JasonLee

    JasonLee [OP] Hello? I'm a truck.

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    I have read the FSM. I don't have the SSTs (LSPV Gauge Set - SST 09709–29018).

    How else can I test and adjust the Load sensing Proportioning and By-Pass Valve (LSP & BV)? (By adjust I mean the process without the SST, not the actual physical adjustments - I know how to do that from reading the FSM).

    The spec states 636 ± 71 psi on the rear brakes with the Rear axle load (1,874 lb).
    Note: these specs are for 4x4.

    Yes, I know a lot of people just buy a manual valve and remove this from their lifted trucks. I'm keeping mine for now, so please keep the recommendations constructive.
     
  2. Jun 19, 2019 at 8:18 AM
    #2
    mechanicjon

    mechanicjon They call me "Jonny Stubs"

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    I'd say adjust it until the rears lock up during hard stop. Then back off some.
    It's kinda a S.W.A.G. without the gauge.
     
  3. Jun 19, 2019 at 8:28 AM
    #3
    jbrandt

    jbrandt ......LOADING

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    What has lead you to this evil place where you think you need to test and adjust the valve?

    Either measure the distance from the valve arm to the body and maintain that measurement (after a lift, for example), or just adjust it until the brakes lock up as Jon mentioned.
     
  4. Jun 19, 2019 at 9:21 AM
    #4
    JasonLee

    JasonLee [OP] Hello? I'm a truck.

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    I bought the truck with the suspension completely worn out and riding right above the bump stops. I installed OME suspension which resulted in ~5" lift from the worn out level. I installed a BAMF relocation bracket and used the 2" setting since that's what the lift should be from stock height.

    I have upgraded to Tundra brakes up front and recently inspected my rear brakes and there is still at least 3mm on the shoes (uneven wear). I am pretty sure these are the original rear brakes with 205k on them now.

    Why? I'd like things to work correctly and have near the best braking power rather than just relying on the Tundra brakes.
     
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  5. Jun 19, 2019 at 10:36 AM
    #5
    jbrandt

    jbrandt ......LOADING

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    Yeah, I've never replaced my brake shoes (~130k) either. Unless you run with a loaded rear end, you won't hardly get any wear even if the valve was adjusted perfectly. There's just no weight back there.

    Adding Tundra brakes shouldn't affect the position of the valve either. Unless you put some weight in the back to give the rear wheels more traction, that's really all your doing is relying on the tundra brakes. That's all I'm doing relying on my stock brakes.
     
  6. Jun 19, 2019 at 11:17 AM
    #6
    RysiuM

    RysiuM Well-Known Member

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    320k and my rear brakes are more then 50% of the original thickness (in the narrowest spot). These brakes are hardly ever used unless the bed is loaded. 99% I travel empty (with only camper shell on it) so my rear brakes are still good (after 24 years).
     
  7. Jun 19, 2019 at 11:58 AM
    #7
    Wyoming09

    Wyoming09 Well-Known Member

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    I seldom drive with less then 1000 pounds then pulling another 2000 pounds or so

    I am on my second set of Shoes at 225,000 .

    I have no clue if the LSPV even works The Evil things

    Without testing the pressure it just a guess at best
     
  8. Jun 19, 2019 at 12:20 PM
    #8
    Reh5108

    Reh5108 Well-Known Member

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    I don't have the answer to your question but.... Most of your braking is done by the front. Theres very little weight over the rear axle and even less when braking. It takes a long time to wear out those pads.

    You don't want your rears to lock up.

    There is a rather simple way to make your own adjustable setup. I've yet to do it but if you cut off the rod from the axle about 1" from the valve. Bolt a piece of angle iron to the valve mount. Then drill a hole directly under the remaining rod into the angle. Find or make a bolt with an eye on the end. Slip the eye over the rod and the threaded portion into the angle and use nuts to adjust it up and down.


    To set it I'd likely adjust it until the rears lock up then back it out a bit.
     
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  9. Jun 19, 2019 at 12:25 PM
    #9
    JasonLee

    JasonLee [OP] Hello? I'm a truck.

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    It's already adjustable ... both at the valve and a two-nut on a bolt setup at the axle end of the rod...

    [​IMG]

    I don't DD my truck and most of my trips are loaded, but I don't want to set it up to bias towards loaded when I don't have a load.
     
  10. Jun 19, 2019 at 12:26 PM
    #10
    jbrandt

    jbrandt ......LOADING

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    I'm not sure why people go out of their way to do this mod. This removes all the automatic adjustments for when you load or unload the bed, unless you do that manually every time you throw stuff in the bed. The whole point is to allow more braking power to be sent to the rear axle when there's more weight (i.e. more traction) back there, and to let off on braking power when the back end comes up so they don't lock up.

    Even if you have a 100% consistent load in your bed, this doesn't seem worth it. Maybe if the road/axle mount broke or something, but if the system is functioning, just leave it...
     
  11. Jun 19, 2019 at 12:31 PM
    #11
    Reh5108

    Reh5108 Well-Known Member

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    How is it adjustable at the valve?
     
  12. Jun 19, 2019 at 12:38 PM
    #12
    Reh5108

    Reh5108 Well-Known Member

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    When it's lifted it all goes to hell. My truck doesn't see much variation in load. I'm confident I can get more braking from the rear without it locking up. I doubt I could lock them up with the valve all the way open. My nuts are seized on the lower adjustment. What I described is practically free.
     
  13. Jun 19, 2019 at 12:55 PM
    #13
    jbrandt

    jbrandt ......LOADING

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    It only goes to hell of you don't move the bracket up the same amount you lifted it.

    Making a bracket that moves the axle mount up the same amount of your lift is also practically free. It's just a piece of 1" flat bar with some holes in it. You can buy one for like $20 from BAMF, or make one for like $6.

    https://www.tacomaworld.com/threads/rear-brake-proportioning-valve-relocate-kit.210865/#post-4772401

    Like I said, it's not just about the variation in load. It also lowers the brake pressure when the rear end starts to lift during a panic stop (brake dive). When the front end goes down, the rear end comes up. Or when the rear is unloaded coming down a steep incline.
     
  14. Jun 19, 2019 at 1:21 PM
    #14
    JasonLee

    JasonLee [OP] Hello? I'm a truck.

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    There is vertical adjustment to where the valve mounts at the frame.
    Position the valve body so that the valve piston lightly contacts the load sensing spring.
     
  15. Jun 19, 2019 at 2:42 PM
    #15
    03_taco_IN

    03_taco_IN Well-Known Member

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    So if I lift the rear 1.25 I need to move this 1.25 away from the axle by adjusting those two nuts

    721110toyota1jp_00000029901.jpg
     
  16. Jun 19, 2019 at 2:47 PM
    #16
    Squeaky Penguin

    Squeaky Penguin Nothing Ventured, Nothing Gained

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    If you have tundra brakes you'll never get the proper proportion with the stock LSPV. There's also a good chance the valve isn't working correctly at this point.

    I would just cut the rod and make a bracket or something to hold it all the way up if you're not going to do a manual valve. Even then, there won't be enough brakes to match the Tundra setup.

    I have a manual valve all the way open and my fronts still lock first.
     
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  17. Jun 19, 2019 at 2:51 PM
    #17
    JasonLee

    JasonLee [OP] Hello? I'm a truck.

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    No, basic geometry proves that completely incorrect. You will need to RAISE the attachment of that 1.25" directly above the axle.
    http://bayareametalfab.3dcartstores.com/BPV-Bracket_p_19.html
     
  18. Jun 19, 2019 at 2:52 PM
    #18
    Reh5108

    Reh5108 Well-Known Member

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    Not easy when I have no idea how much I'm lifted over stock. Larger tires will also put more leverage against the pads requiring more pressure to lock them up.
     
  19. Jun 19, 2019 at 2:55 PM
    #19
    03_taco_IN

    03_taco_IN Well-Known Member

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    Then what are those adjustment nuts for? Sorry first truck with this on it and I have no clue. Thanks for the help
     
  20. Jun 19, 2019 at 3:38 PM
    #20
    jbrandt

    jbrandt ......LOADING

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    Then drill a couple more holes in the bracket. Then set it so the tires don't lock up.
     

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