Downshifting: when has slipping the clutch gone too far?

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stimpy77
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Downshifting: when has slipping the clutch gone too far?

Post by stimpy77 » Sun Jan 10, 2016 4:15 am

Just learned tonight that downshifting at stoplights and down hills is generally not bad (trade normal wear on drivetrain for wear on brakes), ONLY so long as you rev match and don't slip the clutch.

As I have yet to learn to rev match, I am wondering how slowly I can let up on the clutch before slipping the clutch has become a genuine problem for the maintenance of the clutch? I would never assume that any slipping of the clutch is bad, there has to be some slip in gear transition even if split second, but I'm not racing, I just want a smooth everyday commute in city streets without a lot of rpm noise or thought. For most of my time doing MT driving I was always using slow clutch releases at stop lights but now I know that that's bad, so I am just wondering about opinions, how slow is "just fast enough to not be too concerned"? One second release? Half a second release?

Driving a 20016 Subaru WRX
Last edited by stimpy77 on Wed Jan 20, 2016 1:36 am, edited 2 times in total.

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potownrob
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Re: Downshifting: when has slipping the clutch gone too far?

Post by potownrob » Sun Jan 10, 2016 7:53 am

stimpy77 wrote:n00b MT driver. (Drove MT for years when I was years younger but didn't have access to mechanical friends or the Internet.) Just learned tonight that downshifting at stoplights and down hills is generally not bad (trade normal wear on drivetrain for wear on brakes), so long as you rev match and don't slip the clutch.

As I am learning and have yet to learn to rev match, I am wondering how slowly I can let up on the clutch before slipping the clutch has become a genuine problem for the maintenance of the clutch? I would never assume that any slipping of the clutch is bad, there has to be some slip in gear transition even if split second, but I'm not racing, I just want a smooth everyday commute in city streets without a lot of rpm noise or thought. For most of my time doing MT driving I was always using slow clutch releases at stop lights but now I know that that's bad, so I am just wondering about opinions, how slow is "just fast enough to not be too concerned"? One second release? Half a second release?

Driving a 20016 Subaru WRX
in general, if it takes more than a couple of seconds to fully engage the clutch, you're probably doing it wrong. It will depend on the gap in rpms you have to gain between gears how much wear will be caused by a slow downshift. For rev-matching your goal should be to be able to engage the clutch right away after adding the gas. You will get the rev-matches wrong even with lots of practice (we all do from time to time), but you should still be able to let the clutch out much more quickly. I'm too tired to write more; will let cow explain in more detail. Goodnight.
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Re: Downshifting: when has slipping the clutch gone too far?

Post by tankinbeans » Sun Jan 10, 2016 11:08 am

Quite honestly, many of the people I know who drive a manual have never heard of, nor have any idea how to downshift. Their cars feel no ill effects. Heck, sometimes when wearing bulky shoes which make bastardized heel-towing difficult I do the slow release.

Play it by feel, but don't linger. If you're already slowing then eventually there comes a point where the speed you're driving and the speed of the engine will intersect.

I'd advise strongly against dumping it if you haven't rev-matched, or at least made the attempt.
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Re: Downshifting: when has slipping the clutch gone too far?

Post by potownrob » Mon Jan 11, 2016 2:52 am

tank makes some good points i want to elaborate on:
tankinbeans wrote:Quite honestly, many of the people I know who drive a manual have never heard of, nor have any idea how to downshift. Their cars feel no ill effects. Heck, sometimes when wearing bulky shoes which make bastardized heel-towing difficult I do the slow release.
it seems very few people know how to rev-match on downshifts. many people either learn on their own (usually means bad habits learned), or whoever taught them doesn't know much beyond the basics and also may be self-taught (as in without the help of the SS!! :cry: ). as for no ill effects, i don't think this is true, at least not always. i've known at least one person who lived to ride the clutch, downshifting multiple gears with just the clutch. hearing those downshifts made me cringe. that's what i call braking with the clutch. that is NOT what the clutch is designed for. he had to replace his clutch within 2 years of getting the car, and it was supposedly replaced not long before he got the car (94 altima). that's extreme abuse and an extreme case, but to say you can't ruin a clutch by abusing it is misleading.

P.S. If i may teach you one habit not to get into or stick with, it would be riding the clutch. this is when you rest your foot on the clutch or otherwise use the clutch when you don't need to be using it. other than when you are launching, shifting or sitting at a light with the clutch in (if that's your thing), keep that foot off the clutch!! 8) :o
Play it by feel, but don't linger. If you're already slowing then eventually there comes a point where the speed you're driving and the speed of the engine will intersect.
this is true. as i alluded to, it's ok to slip the clutch a little, but it should be brief. if you slow down enough in gear (or in neutral - not the best habit to ride around out of gear, but not the end of the world), you will be at close to the right speed for a lower gear without adding gas.
I'd advise strongly against dumping it if you haven't rev-matched, or at least made the attempt.
what i sometimes do is a test to see how well i rev-matched (or didn't) by letting out the clutch to where it starts grabbing. i then let the clutch out a little more to see if it's reacting smoothly. this is all very quick, mind you, or else i'd lose the advantage of having rev-matched (or not). if i added too much gas, the car may lurch forward a little; if i didn't add enough, it may make the clutch burn sound where the revs go up through the clutch and the car pulls back a little. as long as it's not a major gap in revs, it shouldn't be a big deal either way. this is something you can try doing until you get your rev-matches down (how much to add, ability to add gas and then quickly let out clutch). YOU CAN DO IT!! :o
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Re: Downshifting: when has slipping the clutch gone too far?

Post by stimpy77 » Tue Jan 12, 2016 2:57 am

as i alluded to, it's ok to slip the clutch a little, but it should be brief.

OK. This is what I asked and what I hoped someone more in the know might say. Gives me some relief.

.. found a pattern on my 2016 Subaru WRX that seems to work (in 4th slow to 2k, apply clutch, switch to 3rd, rev to 3k, release clutch, brake to 2k, apply clutch, switch to 2nd, rev to 3k, release clutch, brake to 2k, apply clutch, switch to 1st, rev to about 3300, release clutch, brake to 1k, apply clutch, switch to neutral, release clutch, brake to stop. Now just to memorize the sound and vibrations so I'm not staring at the tachometer so as to work towards second nature

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Re: Downshifting: when has slipping the clutch gone too far?

Post by potownrob » Tue Jan 12, 2016 3:25 am

stimpy77 wrote:
as i alluded to, it's ok to slip the clutch a little, but it should be brief.

OK. This is what I asked and what I hoped someone more in the know might say. Gives me some relief.

.. found a pattern on my 2016 Subaru WRX that seems to work (in 4th slow to 2k, apply clutch, switch to 3rd, rev to 3k, release clutch, brake to 2k, apply clutch, switch to 2nd, rev to 3k, release clutch, brake to 2k, apply clutch, switch to 1st, rev to about 3300, release clutch, brake to 1k, apply clutch, switch to neutral, release clutch, brake to stop. Now just to memorize the sound and vibrations so I'm not staring at the tachometer so as to work towards second nature
your downshifting pattern is good practice for rev-matching, but please do not feel the need to downshift through all the gears to come to a stop. i also recommend tapping the brake pedal periodically (one tap, not multiple; can't think of the right word for that) to let people behind you know if you are slowing down without the brakes. i used to do the downshifting through all the gears routine as a (relatively) younger shifter, before i realized the brakes were there to slow down the car :lol: :evil: :P
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Re: Downshifting: when has slipping the clutch gone too far?

Post by stimpy77 » Tue Jan 12, 2016 4:43 am

Sure, my goal though is to train on downshifting w/ revmatching. I'm fine with being excessive with downshifting on every gear if it means months or years from now when and if I feel ready to just brake in neutral always I'll also have much greater natural command of MT clutching and shifting to support the machinery for long life.

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Re: Downshifting: when has slipping the clutch gone too far?

Post by potownrob » Tue Jan 12, 2016 4:46 am

stimpy77 wrote:Sure, my goal though is to train on downshifting w/ revmatching. I'm fine with being excessive with downshifting on every gear if it means months or years from now when I feel ready to just brake in neutral always I'll also have much greater natural command of MT clutching and shifting to support the machinery for long life.
atta boy!! 8)
next challenge: downshifting right before a turn!! :twisted:
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Re: Downshifting: when has slipping the clutch gone too far?

Post by stimpy77 » Sun Jan 17, 2016 10:39 pm

So I'm guessing the technical answer to the question is:

If you "pop" the clutch with an approximate revmatch, you have a teensy little bit of spring action to handle the transition ..

Image

.. but short of "popping" the clutch, as a clutch is halfway engaged you're literally grinding the clutch, to whatever extent you're unsuccessful in rev matching.

https://www.youtube.com/watch?v=pqF-aBtTBnY
https://www.youtube.com/watch?v=FfjGohWy-OU
https://www.youtube.com/watch?v=zgb8-2Y4A8A

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Re: Downshifting: when has slipping the clutch gone too far?

Post by theholycow » Mon Jan 18, 2016 10:39 am

Image

Don't pop the clutch. (By "pop" I assume you mean an uncontrolled engagement, likely accomplished by sliding your foot off the pedal sideways while it's floored.) The springs in the clutch disc don't absorb enough of that shock to avoid abusing the rest of the drivetrain, not to mention the clutch disc itself.

"Grinding" is inaccurate because the surfaces involved are smooth and sufficiently well-matched in hardness that you really can't call it that any more than you can call regular use of your brakes "grinding" the brake pads. By slipping the clutch (within reason) you are using it the way that it was designed to be used. Wear is far less than you think it is.

I used to have the worst clutch wear paranoia. Then in 2010 I converted my Buick and my potential costs for clutch replacement dropped dramatically. Then just a few months ago I replaced the clutch (and transmission) (after 90,000 miles of abuse on a mismatched clutch set with a clutch disc way too small for my car) and found that it really hadn't worn much but my habits of trying too hard to preserve clutch wear (along with the aforementioned too-small clutch) caused a delamination failure. Instead of wearing it down I shocked it to pieces. Now I get it...the thing doesn't look very thick but it really doesn't wear fast at all, you'd have to be a really severely abusive driver to wear a clutch prematurely.

Image

Now, a bit of counterbalance for all of that: If you do abusively slip it for too long, repeatedly, then excess heat could also contribute to such a failure. Actually I don't doubt that it was a combination of both issues in my case.
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Re: Downshifting: when has slipping the clutch gone too far?

Post by stimpy77 » Wed Jan 20, 2016 1:39 am

theholycow, awesome reply, thanks for the followup

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