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Rear Brake Adjustment, theory and practice.

Discussion in '1st Gen Tundras (2000-2006)' started by Aerindel, Dec 15, 2021.

  1. Dec 15, 2021 at 12:56 PM
    #1
    Aerindel

    Aerindel [OP] New Member

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    Mushy brake pedal, non-function parking brake, even when brakes have been properly and repeatedly bled.

    As I keep seeing frequents posts on this topic I think we need a sticky post on the subject.

    Brake theory.

    To understand brake problems, you have to understand how brakes work.

    Fundamentally, your brake system functions on the principle of leverage. It takes a large, low effort movement, that of your brake pedal, and turns that into a very tiny, but very powerful movement of your brake pads and shoes against your brake rotors and drums.

    It's important to understand that this movement is very very small. If your brake pads are not in contact with the drums or rotors at the start of this movement, you will use up all your brake travel, before you can apply maximum braking force to the rotors.

    Your front brakes are are automatically adjusting, after the first time you pump your brakes following a brake job, your pads will always be lightly touching the rotors, with no freeplay in the system so that when you step on the brakes pedal, all the force goes into squeezing the rotor, rather than into having to first move the pads into contact.

    If all four of your brake pads/shoes are not in close contact with your rotors and drums your brake pedal will feel soft, and your brakes will not work poorly.

    Your REAR BRAKES are also automatically adjusting, but in an entirely different way which will be the focus of this post.

    Your rear brake shoes are expanded against the inside of your drums by hydraulic pistons, similar to your front brakes, but unlike the front brakes, they are pulled back from the drums by springs.

    There is a threaded sleeve with a threaded rods on each end, which control how far back from the drums the shoes can be pulled by the springs.

    What you want, is as close to zero freeplay as possible between the brake shoes and the brake drums.

    The PARKING BRAKE also works by pressing these same shoes against the drum, but instead of doing this hydraulically, it uses a series of several cables and levers, to pull a lever which presses the brake shoes against the drums.

    The parking brake system has a secondary function, which is to automatically adjust the brake shoes so that there is no freeplay. It does this everytime you apply the parking brake by moving a lever against the ratchet teeth off the adjuster. If there is enough freeplay, that parking brake lever will move the adjuster gear by one tooth. If the shoes are already properly adjusted, the lever will not be able to move far enough to reach the next tooth, and no further tightening will happen.

    Because this is a very small (but very forceful) movement, a loose or non-functional parking brake, will not move the adjustment lever far enough to ever reach the next tooth on the adjustment gear. Your rear brakes will have too much freeplay in them, which will result in poor braking, and poor pedal feeling.

    There is an access port on your brake backing plates, through which you can use a screwdriver to manually adjust brake free play. THIS IS THERE ONLY FOR BACKING OFF HE SHOES TO REMOVE THE BRAKES. It is not there to adjust new brakes, that is the job of the parking brake auto-adjuster.

    It IS possible to manually adjust the brakes through that access port, but it is very difficult to do so properly and requires frequent readjustment to maintain. If you have to do it this way for some reason, keep in mind the rear shoes must be adjusted much tighter than you probably think. Adjusting them until they lightly drag is not enough, the proper point is usually past that and its hard to find without going too far.

    There is no procedure in the factory service manual to do this. Instead you are supposed to adjust new brake shoes via the parking brake, this will precisely adjust your rear brakes, and keep them adjusted.

    The problem is, the parking brake/auto adjuster system is often non-functional at this point on our 20 year old trucks.

    If you are have either a non working parking brake, and or a mushy brake pedal and have already bled your brakes properly, this is most likely your problem.


    To check this, manually turn your adjuster back back three or four teeth, and then had a assistant fully apply your parking brake multiple times, you should be be able to see and hear the brake adjuster click an equal number of times as it re-adjusts itself.

    You can also check by doing the same thing with the drums removed, although keep in mind, with no drums to push against the system will simply keep tightening to the limits of the mechanism.


    There are two main ways this happens:

    The parking brake cables stretch over time (or even rust and break completely)

    and, the various intermediate brakes levers become rusted and seized in place.

    What is wrong with YOUR truck, I cannot say. But those are the things to check.

    If the cables have simply stretched, you can tighten the cables at the intermediate lever located on the frame, just behind the cab.

    The places to check for seized levers are at this lever, the 'splitter' lever on your rear axle where the cable divides in two, and at the bellcrank levers on your brake backing plates.

    Relevant pages from the FSM:


    Screen Shot 2021-12-15 at 1.53.22 PM.jpg

    Screen Shot 2021-12-15 at 1.54.01 PM.jpg

    Screen Shot 2021-12-15 at 1.50.34 PM.jpg

    Places to check for stuck levers:

    IMG_2865.jpg

    IMG_2866.jpg
     
    Last edited: Dec 15, 2021
  2. Dec 15, 2021 at 1:05 PM
    #2
    alb1k

    alb1k I've got two chickens to paralyze.

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    It's good
    Great!
     
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  3. Dec 15, 2021 at 1:15 PM
    #3
    ColoradoTJ

    ColoradoTJ I drink…and I know things. Staff Member

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    A metric buttload
    Stickied.
     
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  4. Dec 15, 2021 at 2:02 PM
    #4
    Sirfive

    Sirfive Master Procrastinator

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  5. Dec 15, 2021 at 6:09 PM
    #5
    shifty`

    shifty` trying to remember when but it makes me dizzy

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    Thanks for throwing us 1GT folks some love on this. Much appreciated.
     
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  6. Dec 15, 2021 at 6:12 PM
    #6
    ColoradoTJ

    ColoradoTJ I drink…and I know things. Staff Member

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    A metric buttload
    Of course. You all have a lot of good tech that should be available to all and easy to access.
     
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  7. Dec 16, 2021 at 5:31 AM
    #7
    NetGnome

    NetGnome New Member

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    Also disc brakes want high brake line pressure, thousands of psi, while drums want lower pressure, hundreds of psi. So you need a pressure reducing/proportioning valve going to the drums.
     
  8. Dec 18, 2021 at 4:44 PM
    #8
    dbittle

    dbittle New Member

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    After the rear drums are properly adjusted, one can further improve the pedal feel and overall braking performance by adjusting the LSPV to increase the participation level of the rear brakes. The LSPV adjusts the amount of braking that the rear brakes provide, so that they participate more when the truck is loaded and less when it is not loaded. If the rear brakes lock up before the front brakes do, the truck will attempt to swap ends during hard braking. That is a really bad outcome, so the rear brakes were dialed way back, at least on my truck. About two complete revolutions of the adjustment nut outboard on the threaded rod (on my truck) improved the pedal feel, reduced stopping distance and still retained a comfortable margin of safety when braking on wet or slick surfaces.
     
    Aerindel [OP] likes this.
  9. Dec 18, 2021 at 7:21 PM
    #9
    Aerindel

    Aerindel [OP] New Member

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    I do think a contributor to the common problem of warped front brakes, is rear brakes out of adjustment and LSPV adjusted too far to the front, leaving the front brakes to do all the work.
     
    dbittle, des2mtn and Lil Steve like this.
  10. Jan 2, 2022 at 7:08 AM
    #10
    DarkMint

    DarkMint just gettin by

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    Last edited: Jan 2, 2022
    dbittle likes this.
  11. Jun 20, 2022 at 2:32 PM
    #11
    bamdone

    bamdone New Member

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    New Parking Brake Cable, Relocated Differential Breather
    2006 Tundra SR5 4x4 Double Cab

    It tried to adjust my parking brake and from the years of rust, the turnbuckle under the driver’s door just snapped in half. :(

    I purchased the replacement cables. There are two. One for the front and one for the rear. The one for the front is pretty standard, but the one for the rear comes in different lengths. Since I have a double cab, I think I have to find the long one.

    Today, I replaced the front cable that goes from the parking brake foot pedal to the middle of the cab. It routes though the firewall around where the firewall and floor pan meets. The trick to removing it is to loosen the heat shield on the drivers side (10mm sockets), extensions, and ratchet wrench are necessary. Rotate the heat shield around and remove all the 10mm nuts that keep the parking brake cable ties in place. I think there were 4 or 5 of them. The hardest one is located behind the heat shield. In the cab, you have to remove the panel under the steering wheel, the bottom door jamb cover ( Phillips head screws) and the panel right by the fuse box that makes up the door jamb.

    After removing the mounting points and cable in the front completely from the floor boards, you can fish it out from within the cab and release it from the pedal.

    Installation is opposite of the reverse. Took me three hours to do the front cable alone. I still have to do the rear. Then, do the adjustments.

    In summary, adjusting the brake can become catastrophic if the turnbuckle is rusted. Replacing the cable is a lot of work. Be prepared to have your hair and face showered in rust. Replacing the rear brake cable isn’t as bad as the front. But, I somehow sheared off two bolts and will have to drill and tap some mounts to re-attach the rear cable after I locate one.
     
    Last edited: Jun 20, 2022
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  12. Jun 24, 2022 at 6:55 PM
    #12
    HAL69000

    HAL69000 New Member

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    Just want to report that after rehabilitating my rusty parking brake situation last fall, it is only in recent weeks that my parking brake has actually started biting pretty well (I got it to hold the truck months ago but as soon as I gave it any throttle, it would roll). I think the new shoes had to wear down the drums a bit or something.
     
  13. Jun 25, 2022 at 5:48 AM
    #13
    Dave8699

    Dave8699 Trackrat

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    I will be changing out all the rear drum components and also the parking brake cables. Snice we are on the topic. What's the best grease to use on the drum components?
     
  14. Jun 25, 2022 at 5:53 AM
    #14
    FirstGenVol

    FirstGenVol New Member

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  15. Jun 25, 2022 at 5:59 AM
    #15
    Dave8699

    Dave8699 Trackrat

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    That is what I have just a different brand buts it's a Silicone brake lubricant. Only reason I ask what to use is that I believed I read that you need to use 2 different types. One for the contact points and a different type for the adjuster.
     
  16. Jun 25, 2022 at 6:05 AM
    #16
    FirstGenVol

    FirstGenVol New Member

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    According to the cool kids I'm not a real wrencher so maybe go with what you find in your research. I replaced my self adjusters and they came lubricated already. I may have added a little more Sil-Glyde to those but I can't remember now.

    We're also supposed to use two different types of grease for the driveshaft but I only use one. I like to live dangerously.
     
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  17. Aug 2, 2022 at 4:00 PM
    #17
    typhoon

    typhoon New Member

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    I just replaced the rear drums and shoes(not oem). I adjusted the brakes with the star adjuster until they had a slight drag, then used the park brake.
    The issue now is they are over adjusted and I can't spin the wheel. I can drive through it, but the drums get too hot to touch.
     
  18. Aug 2, 2022 at 7:38 PM
    #18
    Dave8699

    Dave8699 Trackrat

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    You have to loosen them back up and start again.
     
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  19. Aug 3, 2022 at 4:36 AM
    #19
    Aerindel

    Aerindel [OP] New Member

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    Something is wonky then, mechanically, it should not be possible for the parking brake to over adjust the drums. The adjuster arm can only move, if there is space between the drums and the shoes, once that gap is closed up to less than about 1mm, the arm can't move far enough to catch the next tooth on the star.

    Back the drums off several clicks and then use ONLY the parking brake to re-adjust them. I suspect you just got them too tight to begin with by doing it manually.
     
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