"Do not downshift into first when ... moving faster than 15 mph"

[Zooks527]

Like it was already said, due to the very short gear ratio the velocity of the shafts will be much more different than switching between higher gears, so doing a switch into 1st with higher car speed often will burn the friction material down too quickly because of this difference in speed of the two shafts.

I don't see that at all.

At 16 mph in 2nd gear, the engine / flywheel / clutch disk / input shaft are all spinning at ~1550 rpm. If you downshift into 1st, the clutch disk and input shaft will come up to ~2400 rpm before engagement.

At 25 mph in 3rd gear, the engine / flywheel / clutch disk / input shaft are all spinning at ~1600 rpm. If you downshift into 2nd, the clutch disk and input shaft will again come up to ~2400 rpm before engagement.

The differences are effectively the same. Why would one be damaging and not the other?

Sponsored

 

[Zooks527]

....., get stupid answers.

You do appear to be a reliable source.

 

[Zelek]

You do appear to be a reliable source.

Go ahead and keep downshifting into first then. Test the theory.

 

[OnThree]

If you double clutch into first, you aren't going to damage anything. That's what I've always done on all my cars if I need to go down to first when actually driving.

 

[Cruizer]

Glad I don't have a clutch to worry about lol. Someone said who would do this anyways. I have heard plenty of hard downshifts where the driver just likes to make a bunch of noise. That or maybe they just couldn't drive.

 

[Sivi70980]

If you double clutch into first, you aren't going to damage anything. That's what I've always done on all my cars if I need to go down to first when actually driving.

I'm having trouble wrapping my head around how double clutching would make a difference.

 

[dx2]

I don't see that at all.

At 16 mph in 2nd gear, the engine / flywheel / clutch disk / input shaft are all spinning at ~1500 rpm. If you downshift into 1st, the clutch disk and input shaft will come up to ~2400 rpm before engagement.

At 25 mph in 3rd gear, the engine / flywheel / clutch disk / input shaft are all spinning at ~1600 rpm. If you downshift into 2nd, the clutch disk and input shaft will again come up to ~2400 rpm before engagement.

The differences are effectively the same. Why would one be damaging and not the other?

right, I was considering much higher car speeds. Not really sure why the 16 mph is stated.

 

[OnThree]

I'm having trouble wrapping my head around how double clutching would make a difference.

Just helps reduce wear on the syncros. Pretty sure the manual only states that because it assumes not everyone rev matches or does so directly. I see no reason why you can't downshift to any gear if the engine revs match the transmission revs.

Double clutching into first has always felt smoother to me for 1st gear so that's what I do.

 

[Sivi70980]

Glad I don't have a clutch to worry about lol. Someone said who would do this anyways. I have heard plenty of hard downshifts where the driver just likes to make a bunch of noise. That or maybe they just couldn't drive.

The auto rev match is audibly addicting. I usually don't try to announce myself in first gear like that but the new exhaust has me doing it a little bit, just like mpg goes down a bit till the newness wears off. But like I said, I don't reengage the clutch till I'm going much slower. I do usually downshift into second and let compression help the little bit it can with service brakes and then clutch in till stopped. Out of gear and foot off clutch till light is about to change.

 

[Sivi70980]

Just helps reduce wear on the syncros. Pretty sure the manual only states that because it assumes not everyone rev matches or does so directly. I see no reason why you can't downshift to any gear if the engine revs match the transmission revs.

Double clutching into first has always felt smoother to me for 1st gear so that's what I do.

It's Monday, my brain is failing me. Clutch, take out of gear, release clutch. Clutch, put in gear, release clutch. How is this different than clutch, gear change, release clutch? I feel like I'm missing something big here.

 

[ALLSTOCK]

@OnThree your avatar is hilarious lmfao

 

[OnThree]

It's Monday, my brain is failing me. Clutch, take out of gear, release clutch. Clutch, put in gear, release clutch. How is this different than clutch, gear change, release clutch? I feel like I'm missing something big here.

Sorry man, I don't know the engineering behind it I just know from personal experience it helps smooth out the shift when going down to first. Maybe I just rev match better when I double clutch and that's really what's happening.

 

[Sivi70980]

Sorry man, I don't know the engineering behind it I just know from personal experience it helps smooth out the shift when going down to first. Maybe I just rev match better when I double clutch and that's really what's happening.

After I replied I use the ol google machine. It's basically a rev matching thing like you're saying. So you're doing what the auto rev match feature is hopefully doing in mine. Started to read about syncros but got way too deep for current brain activity.

 

[Zooks527]

It's Monday, my brain is failing me. Clutch, take out of gear, release clutch. Clutch, put in gear, release clutch. How is this different than clutch, gear change, release clutch? I feel like I'm missing something big here.

Clutch-Neutral-Release-Clutch-Downshift-Release

1. Before: Flywheel / Input Shaft / Intermediate Shaft all coupled
2. Clutch: Flywheel uncoupled, Input Shaft and Intermediate Shaft coupled at old target rpm
3. Neutral: Flywheel, Input Shaft, and Intermediate Shaft all uncoupled; Input Shaft rpm spinning at old gear ratio rpm via inertia.
4. Release: Flywheel and Input Shaft coupled bringing Input Shaft to Flywheel rpm via clutch face, Intermediate Shaft uncoupled. Assumed throttle blip brings Flywheel and Input Shaft to new gear ratio rpm
5. Clutch: Flywheel, Input Shaft, and Intermediate Shaft all uncoupled; Input Shaft rpm matched to Flywheel rpm.
6. Downshift: Input Shaft couples to Intermediate Shaft already at target rpm.
7. Release: Flywheel connects to Input Shaft already at target rpm.

- as opposed to -

Clutch-Downshift-Release

1. Before: Flywheel / Input Shaft / Intermediate Shaft all coupled
2. Clutch: Flywheel uncoupled, Input Shaft and Intermediate Shaft coupled at old target rpm
3. Downshift: Input Shaft changes to new target rpm via Intermediate Shaft rpm through the synchros. Assumed throttle blip brings Flywheel new gear ratio rpm .
4. Release: Flywheel connects to Input Shaft already at target rpm.

Double clutching brings the Input Shaft speed to the new target rpm via the clutch face instead of the synchros.

 

[ORRadtech]

It doesn't say it will immediately damage the clutch or what damage will be done. But over time I'd think it could cause faster wear and glazing and possibly disintegration if it's dumped hard enough.
Will 16 mph cause more damage, or 17, or 18 probably a little bit but they have to pick a cut-off number. Was it arbitrary or the result of testing and experience? I'd guess, based on the latter, that 15 was a happy medium.

Sponsored