Rev Match Downshift and Synchro Wear??!?!

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MidnightInGotham
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Rev Match Downshift and Synchro Wear??!?!

Post by MidnightInGotham » Tue Sep 20, 2016 8:47 pm

Had my first manual car for about 5 months now (2016 GTI performance pack) and upshifts and everything are pretty well set (still hate rev hang and the a/c's affect on rev's but anyway) and now I've been working on my downshifts.

Nothing aggressive just to decelerate towards a turn, round about, stop sign, etc. and I feel pretty good about it, however I do have a question on synchro wear.

I do it in one pretty quick motion, clutch disengaged stick moving and throttle blip, and engage clutch but sometimes I do it so quickly I wonder if the clutch is fully disengaged before I move the stick. Will this cause excess clutch or synchro wear? Do I need to blip the throttle before moving the stick or what should I be doing differently?

Also in a related question, if I'm just coasting to a stop and done want to blip down through gears, I'll get to just above idle, disengage clutch and pull stick out of gear (while breaking). Sometimes it take a bit more effort to slide out of gear than others; it seems more difficult under heavy breaking vs lighter breaking or coasting not on the breaks. Again what excess wear is this causing and how should I be doing this?

Thanks again and I love this community. it's been such a huge help and eased a lot of my worries that my mistakes would destroy my car. Lol.
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IMBoring25
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by IMBoring25 » Tue Sep 20, 2016 11:42 pm

Strictly speaking, the clutch is technically optional once the vehicle is moving above idle speed in first, but that doesn't mean it's a good idea to short it. If you're perfect at finding the throttle position that puts zero load through the transmission while you're moving the shifter, it doesn't hurt anything. If you're less than perfect but don't force it, you'll feel some extra resistance to moving the shifter and cause some extra synchro wear when going into gear. If you're less than perfect and force it you'll feel a thunk as you apply enough force to pull it out of gear against the resistance or hear grinding as you force it into gear, either of which can do significant damage to the gears themselves over time.

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Re: Rev Match Downshift and Synchro Wear??!?!

Post by MidnightInGotham » Wed Sep 21, 2016 10:28 am

IMBoring25 wrote:Strictly speaking, the clutch is technically optional once the vehicle is moving above idle speed in first, but that doesn't mean it's a good idea to short it. If you're perfect at finding the throttle position that puts zero load through the transmission while you're moving the shifter, it doesn't hurt anything. If you're less than perfect but don't force it, you'll feel some extra resistance to moving the shifter and cause some extra synchro wear when going into gear. If you're less than perfect and force it you'll feel a thunk as you apply enough force to pull it out of gear against the resistance or hear grinding as you force it into gear, either of which can do significant damage to the gears themselves over time.
Again because I'm new to this I have a few questions. When is there 0 load on the trans? And I would say that when I downshift I feel slightly more pressure into the next gear than when I upshift.

I assume the stick will never move as easily while moving as it does when sitting in a parking lot with the clutch disengaged. Is that correct or should it literally require 0 effort?

Also you mention a thunk if you're applying too much force. Is this something audible and would one know when they've applied too much force?

Again just wanting to develope good habits and not wreck my car in the process.
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by IMBoring25 » Wed Sep 21, 2016 11:06 am

When you have zero load through the transmission, the car behaves exactly the way it would if you had the clutch in. In the simplest case, you're coasting at some given RPM and you have the throttle at exactly the position where the engine would hold itself at that same RPM if you were running the engine with the clutch in. You can move the clutch in and out and nothing perceptible happens. It's a little more complicated when all the pedals are in motion and under braking, but that should give you the concept.

More resistance on a single-clutched upshift is normal. The synchro has to pull the input shaft RPM up instead of down, which is harder work. Double-clutching is a refinement of technique that improves shift effort on downshifts.

0 is a little ambitious, but most of my shifts actually take less effort than moving the shifter sitting in the car idling. Slight relative motion of the gears helps them mesh.

The thunk is audible and tactile. When the force you're applying exceeds the force holding the shifter in it will pop itself out all at once. If the shifter doesn't move reasonably easily something is wrong. Regroup and try again.

Until you're very familiar with your car, making sure the clutch is floored when you're moving the shifter is the best way to not tear stuff up.

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Re: Rev Match Downshift and Synchro Wear??!?!

Post by MidnightInGotham » Wed Sep 21, 2016 11:35 am

IMBoring25 wrote:
0 is a little ambitious, but most of my shifts actually take less effort than moving the shifter sitting in the car idling. Slight relative motion of the gears helps them mesh.
This surprises me. When I'm idling, my shifter can be moved with just the muscles in my finger but I don't think I would say the same while moving. I'm not ramming through the gears by any means but there's a bit more effort than when stationary.

Could it be that because my car is so new that things are just tighter than a car that has a few more miles on it?
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by MidnightInGotham » Wed Sep 21, 2016 5:58 pm

MidnightInGotham wrote:
IMBoring25 wrote:
0 is a little ambitious, but most of my shifts actually take less effort than moving the shifter sitting in the car idling. Slight relative motion of the gears helps them mesh.
This surprises me. When I'm idling, my shifter can be moved with just the muscles in my finger but I don't think I would say the same while moving. I'm not ramming through the gears by any means but there's a bit more effort than when stationary.

Could it be that because my car is so new that things are just tighter than a car that has a few more miles on it?
Am I nuts here? When I make gear changes I would say it's not by almost? Idk how to describe but there is minimal effort moving the stick it's not like it just slips right into the next gear loosely. Is that what you are describing?
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by theholycow » Wed Sep 21, 2016 6:59 pm

Relax. This isn't an issue. Different cars feel different, and even in the same car different drivers will get different feedback (and I'm not just saying they'll experience it differently; even if it was measured objectively it would be different). A little bit more or less synchro feel is absolutely 100% normal.

With perfectly double-clutched shifts the shifter will fall into gear, rather than snicking into gear the way it does at a stop with the engine idling. Besides the driver actively double-clutching, sometimes the same effect can happen coincidentally; during an upshift in just the right car with just perfect timing the input shaft's natural deceleration while declutched and passing through neutral will result in its speed matching the synchro's speed and the shifter will fall into gear feeling as if it wasn't even attached to the car.

I think maybe my 2008 VW was kinda like that but it's hard to remember. I've driven a lot more miles on more caveman-like transmissions since then.
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by MidnightInGotham » Wed Sep 21, 2016 9:16 pm

theholycow wrote:Relax. This isn't an issue. Different cars feel different, and even in the same car different drivers will get different feedback (and I'm not just saying they'll experience it differently; even if it was measured objectively it would be different). A little bit more or less synchro feel is absolutely 100% normal.

With perfectly double-clutched shifts the shifter will fall into gear, rather than snicking into gear the way it does at a stop with the engine idling. Besides the driver actively double-clutching, sometimes the same effect can happen coincidentally; during an upshift in just the right car with just perfect timing the input shaft's natural deceleration while declutched and passing through neutral will result in its speed matching the synchro's speed and the shifter will fall into gear feeling as if it wasn't even attached to the car.

I think maybe my 2008 VW was kinda like that but it's hard to remember. I've driven a lot more miles on more caveman-like transmissions since then.
Thank you for easing my mind. I've been driving very paranoid and listening and feeling the shifter with every gear change. Back on my original question, should I be applying throttle before moving the stick on a downshift? Or what is the ideal for a single clutch downshift?
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by tankinbeans » Wed Sep 21, 2016 9:20 pm

Clutch in, move stick to neutral, apply throttle to whatever your target is (or close enough for horse shoes and hand grenades), move stick to desired gear, drop clutch, carry on with ya bad self.

*most of this is pretty simultaneous, but the thrust of it is to have the stick out of gear before gassing.
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by MidnightInGotham » Wed Sep 21, 2016 9:47 pm

tankinbeans wrote:Clutch in, move stick to neutral, apply throttle to whatever your target is (or close enough for horse shoes and hand grenades), move stick to desired gear, drop clutch, carry on with ya bad self.

*most of this is pretty simultaneous, but the thrust of it is to have the stick out of gear before gassing.
And before the next gear. This is good, thank you.
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by tankinbeans » Wed Sep 21, 2016 9:51 pm

You're right, my sequence was a bit flubbed. It's gotten to the point where I just do it.
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by theholycow » Wed Sep 21, 2016 10:26 pm

MidnightInGotham wrote:should I be applying throttle before moving the stick on a downshift?
If doing so produces more desirable results, then yes. If not, then no. In that situation, whatever you do with the throttle that makes a smoother result is most likely a better rev match than what you do (or don't) that makes the car jerk.
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Re: Rev Match Downshift and Synchro Wear??!?!

Post by Teamwork » Thu Sep 22, 2016 8:56 am

MidnightInGotham wrote: Thank you for easing my mind. I've been driving very paranoid and listening and feeling the shifter with every gear change. Back on my original question, should I be applying throttle before moving the stick on a downshift? Or what is the ideal for a single clutch downshift?
I do it so quick now it honestly feels simultaneous but if I think really hard about it- I would say that I apply throttle before moving the stick. It's barely noticeable though. If you were to be doing something wrong though the car will definitely let you know as a good rule of thumb. Not all of my rev matches are perfectly spot on and sometimes the clutch has to absorb this but it isn't jerking me around or applying unreasonable amounts of engine braking (as if I didn't rev match at all).

What I always complained about this car is how inconsistent the throttle can be at times. I will feel like I'm applying extremely similar amounts of pressure to the throttle and it will yield extremely different results with the tach and revs. I've said it before many a times but if I know I have to drop multiple gears for a pass or if I'm downshifting from 3rd to 2nd gear I pretty much "hold" the throttle and guide the revs up to the right spot/area as opposed to stabbing the gas pedal. I only really stab the gas pedal for upper gears needing a rev match.

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Re: Rev Match Downshift and Synchro Wear??!?!

Post by Rope-Pusher » Fri Sep 23, 2016 11:47 am

Wear Synchro?



THERE Synchro!
VVVVVVVVVVV

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...and there's another one!
VVVVVVVVVVVVVVVVVVV
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