Shifting into first after idling in neutral

[WA1DH]

I was thinking about how a standard transmission works, and was wondering about how first gear engages when you just had the transmission in neutral with the clutch engaged. Say I'm sitting at a light, in neutral (to save my throwout bearing), clutch is engaged, and engine is idling at 750 rpm. That means the transmission input shaft, as well as the gearshafts, are running at 750 rpm. Now, the light turns green, I (being at the front of the line) stomp the clutch, click it into first, clutch out and launch. But, if the instant I push the clutch in momentum keeps the input side of the transmission turning at 750 rpm, and I go to click the 0 rpm collar into first gear, aren't I getting a lot of syncro wear to slow the gear down to match the collar? On the other hand, if I held the clutch down a bit longer, how long would it take for the input to lose most of the 750 rpm momentum before clicking it into first?

Another quick tech question: I'm looking at getting a Scangauge for my car with the 'add-a-gauge' option and I noticed Fords seem to have a sensor that measures transmission input shaft speed. Would that be the RPM of the shaft after the clutch, meaning I could read transmission RPM separate from engine RPM? Sounds like a neat idea for perfect rev-matching.

Thanks.

[Leedeth]

The input shaft should be light enough to not put significant wear or strain on the synchros, but I guess there will be SOME wear?

[Rope-Pusher]

If the release system is functioning properly, the clutch disk and clutch cover assy are ok and there isn't rust on the trans input shaft splines, the clutch should coast down to 0 RPM in about 1.5-2 seconds.

You really shouldn't have to concern yourself with wear on the synchro for 1st gear due to not waiting for the clutch disk to spin down. Synchro systems are designed to handle this. That being said, everything wears out eventually, if you use it and sooner if you use it harder or abuse it. If your synchro is so worn out that it clashes when engaging from idle, you need to wait until it spins down (and double-clutch on all your downshifts into 1st also).

The release bearing is a pretty robust beast, too. While the load increases when you have the clutch released, there is ALWAYS a small load on the release bearing and it is always spinning at the same speed as the clutch disk, so the only way to make one last forever is to not drive the car.

Too bad that release bearings and synchronizers were not as easy to replace as brake pads and rotors, or we wouldn't even be having this conversation. Who would put up with having to baby the synchro on 2nd gear if it was 1/2 hour of time and under $100 to fix it in their driveway? I know there are some people who will do anything to make their tires and brakes last longer, but I'm not saving mine for the next guy. I'm here to have fun with the vehicle now and I'll gladly pay for new tires and brakes a little sooner, given the enjoyment I've gotten out of them. To a certain extent, I feel the same way about the synchos and release bearing. While I don't want to abuse them, I will surely use them. If they don't last "long enough" under normal use, that is a fault of the manufacturer. The difference is, I'd get a lot more pissed at a brand known for premature synchro failure than at a brand known for premature brake pad failure, because of the time and money involved.

[WA1DH]

If the release system is functioning properly, the clutch disk and clutch cover assy are ok and there isn't rust on the trans input shaft splines, the clutch should coast down to 0 RPM in about 1.5-2 seconds.

You really shouldn't have to concern yourself with wear on the synchro for 1st gear due to not waiting for the clutch disk to spin down. Synchro systems are designed to handle this. That being said, everything wears out eventually, if you use it and sooner if you use it harder or abuse it. If your synchro is so worn out that it clashes when engaging from idle, you need to wait until it spins down (and double-clutch on all your downshifts into 1st also).

Thanks, that was pretty much what I was looking for. I'm sure the syncros and release bearing would outlast my clutch anyway, but I was just curious as to how that worked in 1st at a dead stop. I've got 103k miles on it now, and as far as I know everything is original (I would assume the clutch as well). Certainly not going to baby it but not going to be rough on it either.

[theholycow]

Another quick tech question: I'm looking at getting a Scangauge for my car with the 'add-a-gauge' option and I noticed Fords seem to have a sensor that measures transmission input shaft speed. Would that be the RPM of the shaft after the clutch, meaning I could read transmission RPM separate from engine RPM? Sounds like a neat idea for perfect rev-matching.

I don't think there's an Input Shaft Speed Sensor on any manual transmission (Rope-Pusher, can you confirm?). I think that's only for automatics, and probably only newish automatics at that.

I made an input shaft XGauge code for my 2002 GMC automatic and I'm pretty sure it's calculated instead of measured, as it doesn't always match what it should physically be (after accounting for torque converter and such). Perhaps the computer could calculate it for a manual also, though it might not have any need for that data.

[Rope-Pusher]

Can I confirm? What do I look like, a Catholic Bishop? Hey wait a minute, do they still legally get to slap confirmation candidates across the face? (as a sign that you may be persecuted for your religion).

Typically, the only electrically wired connections to an Amish transmission are the back-up light switch and maybe the distance sensor (speed/distance can be computed from the ABS tone-wheels, so the trans may not have such a feature any more). Back in the thrilling daze of yester-year and SILs (Shift Indicator Lights), the gear range engaged was inferred from the vehicle speed compared to the engine speed. If it thought you could get higher fuel economy by upshifting, the SIL was turned on. It was smart enough to not tell you to upshift once you got into top gear. In these modem times, there are some cars which are torque-limited in certain gear ranges (transmission or differential strength concerns, typically in lower gears). Again, there is no switch in the trans or in the external trans shift linkage to tell the engine controller what gear the vehicle is being driven in, so the confuser has to earn it's keep and figure that out for itself. It backs off the turbo boost as appropriate for the gear it is in. Makes the torque curve look like it's got a Flat-top haircut.

[WA1DH]

Just confirmed elsewhere that my car wouldn't have that sensor, only automatics. Oh well, seemed like a neat idea if it was there, but probably not worth the cost or hassle if I wanted to create a sensor.

I've got a shift indicator light on my Escort. It seems totally useless. It comes on almost at random and then turns off, and it seems to like to come on to tell me to upshift as I'm slowing to a stop in a high gear (like 4th). If I listened to it I'd stall the car out in a heartbeat

[RITmusic2k]

In these modem times, there are some cars which are torque-limited in certain gear ranges (transmission or differential strength concerns, typically in lower gears). Again, there is no switch in the trans or in the external trans shift linkage to tell the engine controller what gear the vehicle is being driven in, so the confuser has to earn it's keep and figure that out for itself. It backs off the turbo boost as appropriate for the gear it is in. Makes the torque curve look like it's got a Flat-top haircut.

I can't tell you how thankful I am that Carla is equipped with this feature. I know I should man up and learn throttle control, but it's so nice to have that consistency in those lower gears without having to think about it. It also opens up some interesting doors when doing ECU tuning; one could conceivably set custom torque limits for each gear based on the traction limits of his tires.

[IMBoring25]

I think I read somewhere that GM designs their input shafts to spin down in around seven seconds. In all the manuals I drive, I find between 3-5 seconds seems to be a time that will usually let the shifter fall into gear just the way I like it to.

Alternatively, if it fusses, you can stop/readjust the input shaft by putting the transmission into another gear that it WILL go into before going for first.

[Rope-Pusher]

In these modem times, there are some cars which are torque-limited in certain gear ranges (transmission or differential strength concerns, typically in lower gears). Again, there is no switch in the trans or in the external trans shift linkage to tell the engine controller what gear the vehicle is being driven in, so the confuser has to earn it's keep and figure that out for itself. It backs off the turbo boost as appropriate for the gear it is in. Makes the torque curve look like it's got a Flat-top haircut.

I can't tell you how thankful I am that Carla is equipped with this feature. I know I should man up and learn throttle control, but it's so nice to have that consistency in those lower gears without having to think about it. It also opens up some interesting doors when doing ECU tuning; one could conceivably set custom torque limits for each gear based on the traction limits of his tires.

..But then you would have to factor in the temperature, road surface Mu, weight distribution in the vehicle (passengers, fuel load, cargo, level of washer fluid, etc.) and a bunch of other stuff. Probably better off to sense wheel spin and let traction control software apply brakes or cut power.

[Rope-Pusher]

I think I read somewhere that GM designs their input shafts to spin down in around seven seconds. In all the manuals I drive, I find between 3-5 seconds seems to be a time that will usually let the shifter fall into gear just the way I like it to.

Alternatively, if it fusses, you can stop/readjust the input shaft by putting the transmission into another gear that it WILL go into before going for first.

7 seconds is like eternity for clutch coast-down from idle speed. If it takes that long, it must not be fully releasing. It's an easy thing to check.
Apply the park brake.
Place shifter in Neutral
Start engine and let it idle with foot off the clutch.
VERY SLOWLY move shifter toward reverse gear position. Stop when you just start to hear the teeth begin to gnash.
Holding the shift lever in that position, briskly disengage the clutch. Start counting 1-Pizza, 2-Pizza as soon as the clutch pedal hits the floor and continue until the gear gnashing noise stops.

This procedure works for vehicles with unsynchronized reverse. If you have a synchronized reverse gear, there is a lot more finesse involved, but it can still be done. You need to shift into any of the gears first and then VERY SLOWLY shift out of gear until you begin to hear gnashing of teeth (almost Biblical, isn't it?) and then do the clutch pedal and pizza-counting thangs.

[WA1DH]

Apply the park brake.
Place shifter in Neutral
Start engine and let it idle with foot off the clutch.
VERY SLOWLY move shifter toward reverse gear position. Stop when you just start to hear the teeth begin to gnash.
Holding the shift lever in that position, briskly disengage the clutch. Start counting 1-Pizza, 2-Pizza as soon as the clutch pedal hits the floor and continue until the gear gnashing noise stops.

Yeah, but, that slight grinding of the teeth is slowing the shaft down faster than it would spin down on its own. So, that could be off a few fractions of a second

Sounds like a good test though. I'll try it out tonight - I'm curious to see how long it takes.

[94Corolla5Speed]

In these modem times, there are some cars which are torque-limited in certain gear ranges (transmission or differential strength concerns, typically in lower gears). Again, there is no switch in the trans or in the external trans shift linkage to tell the engine controller what gear the vehicle is being driven in, so the confuser has to earn it's keep and figure that out for itself. It backs off the turbo boost as appropriate for the gear it is in. Makes the torque curve look like it's got a Flat-top haircut.

I can't tell you how thankful I am that Carla is equipped with this feature. I know I should man up and learn throttle control, but it's so nice to have that consistency in those lower gears without having to think about it. It also opens up some interesting doors when doing ECU tuning; one could conceivably set custom torque limits for each gear based on the traction limits of his tires.

Isn't her name Carmen? Are you having impure thoughts about another Saab, Kevin?

[RITmusic2k]

Isn't her name Carmen? Are you having impure thoughts about another Saab, Kevin?

Oh my god! I can't believe I did that... Carla was my first 9-3, so that was something akin to being in bed with your girlfriend and calling out your ex's name...

Though it was technically an accurate statement, since Carla had that feature as well. Actually, she had traction control where Carmen, a year older, does not... which applies to:

..But then you would have to factor in the temperature, road surface Mu, weight distribution in the vehicle (passengers, fuel load, cargo, level of washer fluid, etc.) and a bunch of other stuff. Probably better off to sense wheel spin and let traction control software apply brakes or cut power.

Being that Carmen lacks TCS, torque limits are all I've got (again, besides my own throttle-controlling capabilities), and it'd be more than sufficient to set them according to the most-likely scenario in which I'd be utilizing them. That is: empty car, no passengers, half-tank of gas, warmed up tires, decent road surface, nice dry and warm weather. Remove a couple of those conditions and I'm probably not drag racing against anybody.

[WA1DH]

2 second spin-down time using Rope-Pusher's reverse test. Tried it twice just to be sure.