Disengage cruise control with a breath on the brakes. A final solution?

Discussion in 'Gen 3 Prius Technical Discussion' started by thbjr, Apr 8, 2010.

  1. thbjr

    thbjr Member

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    I am one that fell into the group that found the cruise control far to difficult to deactivate with the brake for my taste. After reading a post from bryceb04 here on how to adjust the brake light switch, (that also controls the cut off switch for the CC) I decided to give it a try. It's an easy fix, even for the less mechanically inclined of us. To recap his post, remove the 2 Philip's screws, push in the clip, lower the plastic cover and remove the punch pin clip to release the wires from the TPMS reset switch so you can get the plastic out of the way. Look under the dash for the green brake light switch. Twist it counter clockwise 1/4 turn to loosen it. Move it out a couple threads and turn clockwise 1/4 turn to lock it back into position and test it.
    While I was under the dash, I noticed what appeared to be an adjustment screw attached to a U clamp that was pinned to the brake pedal itself. Further investigation revealed that indeed it was an adjustment screw and could be used to micro adjust the brake pedal to the point that the slightest touch on it would activate the brake lights and deactivate the cruise control.
    To make this fine tuning adjustment you will need to first adjust the brake light switch out as far as possible, with the brake lights remaining off, with the adjustment threads on the switch as described in briceb04's post. (See pic of adjustment threads on switch) Once that is done, loosen the 14mm locking nut on the adjusting screw behind the U clamp on the brake pedal (see picture of Fine Tuning adjusting). Using your finger, screw the adjuster screw into the U clamp, pulling the brake pedal away from the brake switch, until the brake lights just come on. Then back off the adjuster screw about 1/3 to 1/2 turn and tighten the 14mm lock nut. The brake lights should then be off. Test by ever so lightly touching the brake pedal. Adjust/re-adjust to taste. The brake lights should light up with the lightest touch (breath :D) on the pedal.

    I've driven mine now for several miles over lots of bumps and the CC has not deactivated on it's own, so I'm not worried about my brake lights flashing when I go over a bump, but I sure like being able to just touch, and I do mean just touch the brake pedal to disengage CC.

    I hope the pictures help those of you considering this yourself. It really is EASY. A Philip's screwdriver and if you want to fine tune it, a 14mm wrench is all you need. (well, OK, a flash light come in REALLY handy).
     

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    R-P, jsmithy, J5A and 9 others like this.
  2. LulzChicken

    LulzChicken Prius Enthusiast

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    Excellent information! I might try this over the weekend. I appreciate the effort to post pictures!
     
  3. mad-dog-one

    mad-dog-one Prius Enthusiast

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    Great info; thank you. I was afraid this was going to be an example of locomotive breath.
     
  4. qbee42

    qbee42 My other car is a boat

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    The term "Final Solution" in the title gave me a little pause.

    Tom
     
  5. tumbleweed

    tumbleweed Senior Member

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    Good to know. Your pictures are great.
     
  6. thbjr

    thbjr Member

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    Yeah, I thought about that after posting it. What I meant by it was the simplicity with which it can be done at home. Save yourself the time and aggravation of going to the dealer and hearing all the excuses about how it's a safety issue, or it's not a warranty covered adjustment, it can't be adjusted to any less brake pressure, you folk know how many excuses they can come up with when they want to. So I figured with a good detailed how too and clear pictures, I could call it a 'final solution'.
    For those of us that go buggy, not being able to just touch the brake pedal to disengage the CC, the fine tuning adjustment of the brake pedal really helped my car.
    Tom
     
  7. hobbit

    hobbit Senior Member

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    Your "fine adjust" appears to be for the master cylinder pushrod,
    having nothing to do with the brake light switch itself. This
    begs the question, does the CC release based on input from the
    light switch, input from the master cylinder pressure sensor, or
    perhaps both? You probably *don't* want to be messing with master
    cylinder position adjustments just to achieve this small fix.
    .
    _H*
     
  8. Fuel Miser

    Fuel Miser Junior Member

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    I was just about to say the same thing. That is not for the light activation.
     
  9. tumbleweed

    tumbleweed Senior Member

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    I think it may work fine. The adjustment looks like it moves the brake pedal arm in or out which will effect the position of the flat piece that contacts the switch. Even though the adjustment is located on the rod that goes to the master cylinder it appears that the adjustment shouldn't effect the position of that rod, it changes only the position of the pedal arm. The actual position of the brake pedal at rest will change but it would only move by such a small amount as not to be noticeable.
     
  10. thbjr

    thbjr Member

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    Yes, it is the push-rod, but Tom (tumbleweed) has correctly identified how it works. The position of the brake pedal at rest is all that is changed, and only slightly, but enough to change the position of the brake light switch de-activation plate to that perfect just touch it spot with the brake pedal.
    Tom

    Picture attached for those wondering what on earth is he discribing.
     

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  11. eric1234

    eric1234 Active Member

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    Are you saying (in other words) that you used the brake light switch (Green Plastic guy) as a 'coarse' adjustment and tweaked the pushrod as a 'fine' adjustment?

    I only adjusted the brake light switch, and found that satisfactory for what I wanted to accomplish - the graduations on the outside seemed sufficient to get it to where I needed.

    But - it's always nice to know that if I want to get really detailed, I can spend more time contorted under the dash to get it 'just so'.

    The pics are great. I wish they were here when I did mine!!!! :)
     
  12. LetsGoCamping

    LetsGoCamping New Member

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    Thank you for this post. Among the many things my husband does not like about the Gen. III (as opposed to our Gen. II) is the CC giving us a jolt when it finally disconnects because he has to press on the brake so hard to disengage. Can't wait to show him this fix. It's totally safe, right?
     
  13. eric1234

    eric1234 Active Member

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    Lawyer Speak: "Although there is much evidence to support the safety of this modification, I don't think any of us here can (or should) advise that it's "totally safe".

    Based on most of our experiences, it appears very safe. Keep in mind that the brakes are a safety system component of the vehicle. In this case, you'll be adjusting a switch that -to the best of my capability to determine - turns on the brake lights, and disengages the cruise control. At this point, I have no reason to believe that the modification effects any other vehicle behavior.

    That said, the Prius is quite a complex vehicle, and there may be other interactions of which I (we) are not aware, and which may have an influence on vehicle safety."

    English: It looks OK, but don't blame us if something goes wrong...

    Friendly advice (absent any responsibility for unexpected events): - go ahead, you'll be fine... I've done it and it has responded just as expected...

    Sorry for the disclaimer - but whenever asked the question "It's totally safe, right?" - any answer should have a healthy dose of disclaimer...

    There are at least 2 other posts on this topic that include further background information that you may find helpful.
     
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  14. tumbleweed

    tumbleweed Senior Member

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    I consider it safe, as Eric points out nothing is totally safe from a legal standpoint.

    Recommend adjusting the big green thing first, it turns 90 degrees to unlock (turn the green thing with your hand not the brown thing) then move it up or down (up in your case) to adjust and then relock. You can check the adjustment by watching the brake lights. The threaded adjustment on the rod would be for a fine adjustment only and may not be needed. Mine came out just right by moving the green switch up a notch or two.
     
  15. thbjr

    thbjr Member

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    I guess you could say it that way. I like to say I used the pedal possition adjustment threads on the push rod to do the fine adjustment, but I'm probably splitting hairs. Point being your not moving or adjusting the push rod, it's the pedal that's moving and adjusting.


    I'll 2nd the "I consider it safe". If I had any personal reservations about the safety of it, I wouldn't have posted the instructions with pictures. I also agree with Tom (tumbleweed) to just adjusting the green switch first. The vast majority will be very happy with just that adjustment. In my case, it just happened that the 1st adjustment left a smidgen more pedal travel than I wanted, so the answer to get it just perfect for me was the second adjustment.
    Happy CC adjustments.
    Tom
     
  16. XMAN LIVE

    XMAN LIVE "Just have Fun!"

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    please provide link to instructions with pictures
     
  17. LakePrius

    LakePrius Special member

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    Great post! The disengagement of the CC is my #1 gripe about the Prius. I'm going to try this and see if I can make this better.
     
  18. vinnie97

    vinnie97 Whatever Works

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    Modifying one's behavior to disengage CC by way of the steering column switch is an obvious alternative to this more technical method, of course. :D
     
  19. Syclone

    Syclone Member

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    Is everybody aware that pulling back on the speed control lever disengages cruise control? No need to touch the break pedal if you just want to coast or manually control the car's speed.
     
  20. ibnird

    ibnird New Member

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    That is true, but the adjustment also causes the brake light to come on much earlier and thus gives earlier warning to following drivers that you are hitting the brake. That is why I did the adjustment since I almost always disengage the cc with the stalk lever. I'd only disengage with the brake in an emergency.
     
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