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  1. #1
    Jr. Apprentice Sabre7's Avatar
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    Default Brake proportioning valve adjustment?

    05 silvy 2wd Crew cab... is it possible to adjust the brake proportioning valve? I'm on my 3rd set of rotors in 2 years (70k) I think that I'm getting too much line presure at the fronts and rears aren't taking their share of the braking load..
    Leighton...

  2. #2

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    Yes you can adjust the porportioning valve. The actuating arm has a threaded adjustment on it that will increase or decrease rear braking force when adjusted. Be careful when adjusting it, it's real easy to get to much rear braking force and cause the rears to lock up. Find a road with very little traffic to test the brakes.

  3. #3
    Jr. Apprentice Sabre7's Avatar
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    Thanks.. yeah I was just gonna tweak it a little at a time.. mark starting point and adjust a little at a time untill the rear end starts locking up., mark that.. then adjust it back to somewhere in between.

    I live on a very remote stretch of country road.. so I have plenty of safe space for testing.

  4. #4

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    Yep, thats the best method for adjusting them.

    I've been through Georgetown on my way to Round Rock a few times, I didnt think they had any busy stretches of road down there.

  5. #5
    Jr. Apprentice Sabre7's Avatar
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    Ok I think I found the valve... not what I am used to on other vehicles...

    my brake lines run into this big 'ol pump looking thing on the drivers side frame just behing the tranny crossmember... is that the valve? How the heck do I adjust that thing?

  6. #6
    Jr. Apprentice Sandro's Avatar
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    Quote Originally Posted by Sabre7 View Post
    05 silvy 2wd Crew cab... is it possible to adjust the brake proportioning valve? I'm on my 3rd set of rotors in 2 years (70k) I think that I'm getting too much line presure at the fronts and rears aren't taking their share of the braking load..
    That is perfectly normal. Under braking, a large portion of the vehicle weight is transfered to the front (inertia force). As a result, over time the front pads/rotors do wear much faster than the rear. Front/rear brake bias is induced in order to prevent the rear wheels from locking (easier to lock than the front because unloaded). Putting more pressure on the rear brakes will likely not improve your overall braking power. Most of the labor still has be performed by the front.
    Sandro

    '05 Suburban LS 2500 - 2x4 - 8.1L engine - 3.73 rear - autoride

  7. #7
    Jr. Apprentice Sabre7's Avatar
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    Quote Originally Posted by Sandro View Post
    That is perfectly normal. Under braking, a large portion of the vehicle weight is transfered to the front (inertia force). As a result, over time the front pads/rotors do wear much faster than the rear. Front/rear brake bias is induced in order to prevent the rear wheels from locking (easier to lock than the front because unloaded). Putting more pressure on the rear brakes will likely not improve your overall braking power. Most of the labor still has be performed by the front.
    yes I am aware of the physics involved...Same reason you have dual discs on the front of a mortorcycle.. and why the discs are normally larger up front than on the rear of 4 wheel disc vehicles..
    But it seems that the brake setup on my truck is set too strongly for the front. Brake rotors should last longer than 6 months.. after 3 sets, something is not right.(probably the fact that GM put itty bitty rotors on the front of a net 5000lb vehicle) It's like my rear brakes do not even engage...so I want to test the proportioning setup to see.. I'm not trying to improve my overall braking performance.. I'm just trying to get my rotors to last longer.

  8. #8
    Jr. Apprentice Sandro's Avatar
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    Quote Originally Posted by Sabre7 View Post
    yes I am aware of the physics involved...Same reason you have dual discs on the front of a mortorcycle.. and why the discs are normally larger up front than on the rear of 4 wheel disc vehicles..
    But it seems that the brake setup on my truck is set too strongly for the front. Brake rotors should last longer than 6 months.. after 3 sets, something is not right.(probably the fact that GM put itty bitty rotors on the front of a net 5000lb vehicle) It's like my rear brakes do not even engage...so I want to test the proportioning setup to see.. I'm not trying to improve my overall braking performance.. I'm just trying to get my rotors to last longer.
    Sure, I understand and agree with your concern. I believe I read in some other posts that it may due to the material of the OEM rotors. A relatively soft steel that gets eaten up quickly.

    Another aspect you may want to consider in your test is that if you have 4 wheel ABS, the ABS may overlap with the brake bias induced by the proportional valve (please note I am just thinking aloud - not talking by experience). This should somehow ease the concern of locking up the rear by modifying the bias.

    Please keep us posted.

  9. #9

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    You are on the right track !! And you will improve your braking. As in your example of the motorcycle braking. All motorcyclist know that if you only use front, your stopping is medium good. If you add the right amount of back, you stop better. If you have a load on your back seat, (I won't explain "load"), then adding more back brake squeeze and front will help even more.
    I'm curious,,, does any one have any ideas on the old 68-72 year proportioning valve to "tweak" them?
    the Skidder
    Jay :happy: Waxhaw, N.C.
    70 Chevy C-10 Stepside from 86 lowered 2" front 3" back, 383ci/350hp. elec. seats,functioning cowl, wood bed, hidden hitch, hidden tach, long headers, duel 3" exhaust. perform int., semi-aggressive cam (no specs.)
    69 Chevy C-10 Fleetside 350 ci 3spd. mild cam, 270hp,stock.duel 2.5" exhaust. Lowered 2" made own blocks

    89 Ski Marlin Boat 350 ci:party: pulling machine. 7 skiiers.

  10. #10
    Jr. Apprentice Sabre7's Avatar
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    Quote Originally Posted by Sandro View Post
    Sure, I understand and agree with your concern. I believe I read in some other posts that it may due to the material of the OEM rotors. A relatively soft steel that gets eaten up quickly.

    Another aspect you may want to consider in your test is that if you have 4 wheel ABS, the ABS may overlap with the brake bias induced by the proportional valve (please note I am just thinking aloud - not talking by experience). This should somehow ease the concern of locking up the rear by modifying the bias.

    Please keep us posted.
    I was also thinking that the ABS might help prevent rear lockup... but my problem now is this Proportioning valve..

    Jimminey this thing is huge.. it looks like a giant booster.. has a big electric motor and looks like electronic controls ...

    Anyone Know how to adjust this thing? or do I need to get my tuner buddy to do it through the PCM?

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