Auto Box conundrum




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  1. #1
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    Default Auto Box conundrum

    I don't know if I am having a senior moment, I had the cruise control set for 80 Km/h then as I was going down hill the gearbox changed down giving me engine breaking. Has anyone else experienced this?

    I'm not complaining, I'm just curious
    2013 Chev Trailblazer 2.8 4x4 auto.

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  3. #2
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    Default Re: Auto Box conundrum

    Yes, experienced the same.

    It does tend to overdo the down changing coming down a steep hill which sends the rpm's to over 3000. I do not like this and it stops once you cancel the cruise control.

    I have found that the TB brakes quite well without any throttle or brake input downhill, thus maintaining the speed limit.

    When I travel through the knysna hills I cancel my cruise control when I approach a downhill. The TB will then do 80% of the descent at the speed limit and I only have to apply a little bit of brake later on.
    Last edited by NeWKleaR; 2016/08/11 at 09:07 AM.

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  4. #3
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    Default Re: Auto Box conundrum

    Happens all the time on mine but I noticed only at speeds of 80km/h or faster when going downhill and I brake. I find it very handy especially when towing.
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  5. #4
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    Default Re: Auto Box conundrum

    Hi

    I believe this is how the vehicle tries to maintain the set speed when the cruise control is active and the engine does not have enough compression to maintain that speed going downhill.

    My 2007 BMW 530i AT actually uses the brakes to do this. But when the cruise control is switched off and you brake going downhill and the car percieves that you are braking lightly but the speed does not come down, it will also change down on its own. This is just for extra engine braking because of the higher rpms.

    The Ford Kuga my wife used to own did not brake to maintain the set speed, it also changed down. I was never very impressed with this because I felt that it did not maintain the set speed very successfully. It could be because the small 1.6 did not have enough compression to make the feature work well.

    So, last week we traded the Kuga in on a nice 2014 Trailblazer LTZ 2.8 AT. I collected the vehicle from Harrismith and must say I was very impressed with it when I arrived home in Pretoria. I did read somewhere they also change down to maintain the speed on downhills, but I have not spent enough time behind the wheel yet to verify this. Hopefully I can change that soon.

    And by the way, why does Car magazine list the following comment on these vehicles: "Bad: Auto transmission refinement"? Sure it's no ZF like the one in my BMW, but it was never intended to be. I firmly believe that one should judge a vehicle on its intended use, and for the intended use, the automatics in these Trailblazers are just fine.

    Anyway, that is just my 2 cents' worth.

  6. #5
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    Default Re: Auto Box conundrum

    I've experienced this on every single american auto box and cruise control combo I've ever driven.
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  7. #6
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    Default Re: Auto Box conundrum

    I am no big fan of autonomous braking in a car.

    I am sure there a a million interlocks and safety features, but the idea of something going wrong and a locking up its brakes on a busy highway scares me.
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  8. #7
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    Default Re: Auto Box conundrum

    Quote Originally Posted by Fluffy View Post
    I am no big fan of autonomous braking in a car.

    I am sure there a a million interlocks and safety features, but the idea of something going wrong and a locking up its brakes on a busy highway scares me.
    it isn't braking, Fluffs, it just gears down
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  9. #8
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    Default Auto Box conundrum

    My Parejo's way back also used to do this, as does the Jeep. Gearing down to maintain the speed.
    Last edited by Flipside; 2016/09/02 at 05:14 PM.
    Flip

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  10. #9
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    Default Re: Auto Box conundrum

    My pajero does it in normal driving without cruise control going down steep downhill will raise revs gear back

    Riku
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  11. #10
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    Default Re: Auto Box conundrum

    Quote Originally Posted by zeek View Post
    My pajero does it in normal driving without cruise control going down steep downhill will raise revs gear back
    Really? I have to use tiptronic mode to gear down.
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  12. #11
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    Default Re: Auto Box conundrum

    Quote Originally Posted by Andre View Post
    Really? I have to use tiptronic mode to gear down.
    Yes it only happens on one down hill. Wilgerood drive towards Helderkruin travelling about 70km /h as I go over the hill down towards ouklip in those twisties speed goes up to 80 revs about 3000 and goes to 3rd if it was in 4th

    Riku
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  13. #12
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    Default Re: Auto Box conundrum

    Weird. Maybe stability control. Lets hear what the boffins say.
    Andre Botha
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  14. #13
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    Default Re: Auto Box conundrum

    Quote Originally Posted by jelo View Post
    it isn't braking, Fluffs, it just gears down
    Nope, I am talking about real breaking. Read post #4. Some cars actually apply real brakes.

    My RRS will have you're forehead planted on the dashboard if the speedo cruise decides it's necessary.
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  15. #14
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    Default Re: Auto Box conundrum

    All the previous automatics I have owned have never done this, I've owned two Rovers, Jaguar V8 and a V6 Ford Explorer none of them would gear down.
    2013 Chev Trailblazer 2.8 4x4 auto.

  16. #15
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    Default Re: Auto Box conundrum

    Quote Originally Posted by Fluffy View Post
    Nope, I am talking about real breaking. Read post #4. Some cars actually apply real brakes.

    My RRS will have you're forehead planted on the dashboard if the speedo cruise decides it's necessary.
    then I agree

    highly risky
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