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Thread: Rev-matching vs not matching downshifts?

  1. #1
    Nickname: "Rally" MirageRally's Avatar
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    Question Rev-matching vs not matching downshifts?

    l accidentally downshifted today from 4th to 2nd going 40mph to make a turn that required me to be in 2nd gear and blipped the throttle up to 4k, interestingly-the throttle blipped higher to 5k and no damage to the trans or engine...bc the Mirage has a synromesh gearbox, does it blip the rpms? Does it have a safety measure in place if l don't rev-match my downshifts? Or something else? Thanks.


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    Still Plays With Cars Loren's Avatar
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    Were you expecting damage?

    Okay, you hit on the answer to your own question with one word.

    Synchromesh.

    Look it up. It doesn't "blip", but sort of works like a clutch and spins the gear up to speed so that it will slide into place. There are some great videos that will show this much better than I can explain it.

    If you didn't have synchros on your gears, then every time you didn't rev-match, the gears would grind horribly. Synchromesh is how the transmission handles matching the speed of the gear so that it slips into place. Proper rev-matching with a throttle blip, or a well-timed up-shift just makes it a lot "easier", the synchro rings don't have as much work to do, so it's a little smoother and quicker and is causing less wear to those synchro rings.

    You're not going to instantly break your transmission by not rev-matching. You're just causing more wear to your synchros. So, maybe instead of lasting 300,000 miles, they'll only last 150,000 miles.
    Simplify and add lightness.

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    Quote Originally Posted by Loren View Post
    Were you expecting damage?

    Okay, you hit on the answer to your own question with one word.

    Synchromesh.

    Look it up. It doesn't "blip", but sort of works like a clutch and spins the gear up to speed so that it will slide into place. There are some great videos that will show this much better than I can explain it.

    If you didn't have synchros on your gears, then every time you didn't rev-match, the gears would grind horribly. Synchromesh is how the transmission handles matching the speed of the gear so that it slips into place. Proper rev-matching with a throttle blip, or a well-timed up-shift just makes it a lot "easier", the synchro rings don't have as much work to do, so it's a little smoother and quicker and is causing less wear to those synchro rings.

    You're not going to instantly break your transmission by not rev-matching. You're just causing more wear to your synchros. So, maybe instead of lasting 300,000 miles, they'll only last 150,000 miles.
    Good to know Thanks Loren
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    Quote Originally Posted by MirageRally View Post
    Good to know Thanks Loren
    I had a bad shift from second to third gear a few weeks ago. Didn't engage into 3rd, and my car made a bunch of grinding noise, bunch of loud racket. I don't think I broke my car. Seems fine, I seem to go through periods when I stall my car 3 times in 1 week, then don't stall for 6 months.

    I have had my Mirage over 5 grand rpm numerous times, even cruising at high speed once or twice on an empty freeway.. but not often. I try to shift for fuel economy, like the plan is meant to be for Mirages. The Mirage can be in 3rd over 100 km's an hour. I don't drive like that, but my Dad use to.

    Edit: sorry it's worthwhile to see this info in your owner's manual. One of those things I remember.
    Last edited by dspace9; 09-04-2020 at 10:20 PM.

        __________________________________________

        click to view fuel log View my fuel log 214 Mirage ES 1.2 manual: 41.8 mpg (US) ... 17.8 km/L ... 5.6 L/100 km ... 50.2 mpg (Imp)


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    Quote Originally Posted by dspace9 View Post
    I had a bad shift from second to third gear a few weeks ago. Didn't engage into 3rd, and my car made a bunch of grinding noise, bunch of loud racket. I don't think I broke my car.
    Sounds like you were accidentally shaving the gear...or it was the syncros grinding to match the higher speed. Not sure.
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    Also double clutching will help syncros...l know in winter l'll need to downshift correctly and not use my brakes as much bc the road that l take to work is an S curve down and S curve up...l've seen SUV's in the ditch and trucks flipped over (last year) in the ditch....Hey Loren, you said if l abuse my syncros they will last 150,000? Or would it be sooner? Again l'm practicing more with rev-matching and want to be comfortable when winter starts so l don't wear them...advice?
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    Senior Member dspace9's Avatar
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    Quote Originally Posted by MirageRally View Post
    Sounds like you were accidentally shaving the gear...or it was the syncros grinding to match the higher speed. Not sure.
    The gears didn't align lol. But I have done the same mistake with my old Rabbit. My thinking to myself is, don't make a habit of it.

        __________________________________________

        click to view fuel log View my fuel log 214 Mirage ES 1.2 manual: 41.8 mpg (US) ... 17.8 km/L ... 5.6 L/100 km ... 50.2 mpg (Imp)


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    Quote Originally Posted by MirageRally View Post
    Does it have a safety measure in place if l don't rev-match my downshifts?[/B] Or something else? Thanks.
    Since Loren's Mirage needed a replacement engine due to a wrong/bad shift, I would assume there are no safety measures in place for over-revving in the wrong gear.

    https://mirageforum.com/forum/showth...into-2015-car)

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    Still Plays With Cars Loren's Avatar
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    Quote Originally Posted by MirageRally View Post
    Also double clutching will help syncros...l know in winter l'll need to downshift correctly and not use my brakes as much bc the road that l take to work is an S curve down and S curve up...l've seen SUV's in the ditch and trucks flipped over (last year) in the ditch....Hey Loren, you said if l abuse my syncros they will last 150,000? Or would it be sooner? Again l'm practicing more with rev-matching and want to be comfortable when winter starts so l don't wear them...advice?
    I just threw out a "for instance". If you never rev-match and make your synchros work a lot on EVERY shift, vs being a very smooth driver who perfectly rev-matches every shift... perhaps that's the kind of difference it could make. Don't take that as a hard and fast rule. I was just trying to point out that missing one rev-match isn't going to make a damned bit of difference in the grander scheme of things.

    If you flat out abuse your transmission, it's not going to last 150k miles. There are no simple answers here. Search the forum, you'll find people who have trashed clutches and/or transmissions in under 100k miles. And you'll find people with well over 200k on their original clutch without a hint of a problem. How you drive the car makes a difference. But, nobody can tell you with any degree of accuracy that "your transmission will last 150k if you do this".

    Advice: Don't over-think it. Watch some videos. Learn how things work. Do your best to practice "mechanical empathy", and the transmission will last as long as it's going to last. Anything less than that and it will last somewhat less than that.
    Simplify and add lightness.

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    Question

    Quote Originally Posted by Loren View Post
    I just threw out a "for instance". If you never rev-match and make your synchros work a lot on EVERY shift, vs being a very smooth driver who perfectly rev-matches every shift... perhaps that's the kind of difference it could make. Don't take that as a hard and fast rule. I was just trying to point out that missing one rev-match isn't going to make a damned bit of difference in the grander scheme of things.

    If you flat out abuse your transmission, it's not going to last 150k miles. There are no simple answers here. Search the forum, you'll find people who have trashed clutches and/or transmissions in under 100k miles. And you'll find people with well over 200k on their original clutch without a hint of a problem. How you drive the car makes a difference. But, nobody can tell you with any degree of accuracy that "your transmission will last 150k if you do this".

    Advice: Don't over-think it. Watch some videos. Learn how things work. Do your best to practice "mechanical empathy", and the transmission will last as long as it's going to last. Anything less than that and it will last somewhat less than that.
    lf l don't rev-match l wait until the appropriate speed then shift down while holding in the clutch a tad longer. lt's complicated for me right now while rev-matching as l sadly do overthink things and take too long to rev-match downshift which results in jerking...also when upshifting: do you slowly push in the clutch, or "punch it" to push the revs up before shifting? l know newbie questions...but l'd like to make the car last at least 3 years.


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