Just wondering if anyone is concerned with premature transmission wear, when coasting in neutral, with a mt?
In general in a mt trans, the main shaft rides inside of a bearing, inside the input shaft. Under most conditions, the difference in speed, is maybe 1000-rpm +/-
When coasting in N, at 65 + mph, The input shaft is at engine speed. (approx 700 rpm) but the mainshaft, which is spinning inside the input shaft, on a small bearing, is turning maybe, 3000 rpm (whatever the engine speed would be, in gear at 65 mph)
Just curious if this will result in premature wear.

Years ago, in another life, working on cars, I have had to replace the input shaft, and mainshaft, on customers cars, because the little needle bearings in the input shaft wore out, and ruined both shafts.

I coast in neutral in my new Fit, mt. but just around town, so the difference in shaft speeds is not that much.

Something to think about. I'm sure a lot of people have 100,000 miles, with coasting, and have not had trans problems, but I kind of want mine to last forever!

 

Just curious but why would you want to be coasting in N at 65+ mph anyway? Usually at that speed I am in 5th and on the highway. I dont really want to be coasting along in N at all in that situation, i'd prefer to be in gear if i suddenly need to accelerate. But to answer your question, i guess no i am not worried about it.

 

This would not save fuel, might use more fuel. Not sure what the point is.

(ECU shuts off fuel when throttle is closed above 900 or so RPM).

 

Point being, transmission wear, and getting better mpg.

Lets say I have 1/8 mile between stop signs, and want to get from one to the other, in X amount of time.

Which do you think uses more gas.

1. Coasting in neutral after 1/2 the distance?

2. Coasting in 3rd or 4th gear after 3/4 the distance? If coasting in gear after 1/2 the distance. the speed would drop so much, that it would take more time.

Coasting gear, if fine, but you just can't coast as far.

 

Coasting in neutral will use more fuel as injectors are turned back on; otherwise fuel is shut off costing above 900 RPM. So leaving in gear will save fuel over the same distance (ok there are lots of variables, it's not so simple, but you're not saving as much as in gear no fuel being burned).

Saving transmission? mmmmm ok. Seems like it's still turning lots of gears/shafts when the clutch engaged, and rolling; just not IN gear.

 

I'm not sure the main shaft and input shaft are concentric on the fit (and on many front wheel drive cars). There's no particular reason why they would need to be, and it adds unnecessary complexity. It doesn't look to me like they are concentric from the parts diagrams available online, but they aren't the clearest in that regard, so I may be misinterpreting them.

At any rate, I would not worry about transmission bearing wear from coasting in neutral. I would not generally recommend coasting in neutral (it's illegal in some places, and any fuel economy differences one way or the other would be negligible at most).

Regarding your question on coasting: option 2 may well be the more fuel efficient if it enables you to drive at a steadier (and somewhat slower overall) speed, as you're cutting down on the frictional losses due to air resistance.

 

It sounds like you know more about the actual construction of MT than I do. But I do have some useful advice.

1) I agree that coasting at highway speeds is not very useful. I am not of the camp that considers it "dangerous" to not be able to immediately accelerate; a Corvette driver probably considers it dangerous to have an engine making only 120hp in case he wants to accelerate suddently, but that doesn't stop people from buying Fits. BUT, I do think that at high speeds, air friction slows the car so much that coasting provides no benefit of any sort. Might as well leave it in gear even when slowing, especially if you think that you're going to fetch up on your stopping point before your RPMs drop to idle.
2) At lower speeds, to get best efficiency while slowing, you have to trade off between a) coasting out of gear, where there is lower drivetrain drag but the injectors are "on" to keep the engine at idle and b) coasting in gear, where you use no fuel but the car slows more quickly because of the additional powertrain drag.

It IS illegal to not be in gear at all times in some places, that is true. This means that as an MT driver you can count on breaking the law at least 4 times before you get up to cruising speed. The people who draft these laws are idiots. If you re-submitted the law as "it is illegal to forget to put your car back into gear when you want to accelerate," then it would expose how absurd such a law is.

In general I advocate for in-gear, however I do sometimes feel the Fit's powertrain is so low-friction that I can go a lot further leaving it out of gear.

I guess I haven't really answered your question of, "will coasting ruin my transmission," so I'm probably going to go with "no, as long as you don't do 100% of your driving coasting downhill." And if that is how your driving goes, I think you'd do fine with a wagon, and you can forget about the engine entirely :P

 

Well don't if this helps you but I've owned '89 & '94 Civic Si's both with MT, both drove them well over 100,000 miles and never replaced anything in the tranny itself and they were still running on factory clutches when I junked them. I didn't abuse the car/trannies, but neither did I baby them either. Yes I coasted in a lot of cases, but I find it's always better to be in gear so you're ready to react if need be.

IMO your worry may be much ado about nothing.

 

To answer your question NO. While in neutral with a MT there is no load on the moving parts of the transmission and they are still bathed in lubricating fluid so no wear problems.

 

Why do people think rolling in neutral down hills saves gas? Its actually quite the opposite. With the car in gear the force of the hill/gearbox keeps the engine at revs not gas. When the car is in neutral the injectors have to keep firing to keep the engine idling.

 

because racecar

 

actually, rolling down in neutral does save some gas... but only on certain grades and speeds.

there are some grades that are steep enough, such that leaving in gear, will still have enough energy to go down the hill without losing speed.

but sometimes the hill is not steep enough for your do leave it in gear without losing speed. if you leave it in gear and don't apply any gas, it will lose speed too quickly. In these situations, you have a few options, you could apply a bit of gas, or you could let it coast in neutral - if the slope is steep for it to coast in neutral and not lose speed. I've found that in a lot of cases, letting it coast in neutral uses less gas.

 

I have always noticed my mpg gauge is higher when coasting. I have NEVER seen it increase by leaving it in gear

Your car does NOT use hardly any gas to idle the motor, especially once the motor is hot and oil is flowing easier.

The only hondas I have seen that truly cut gas while coasting in gear is OBD0
Since they screwed up the wiring on OBD1, it always sees at least 1% throttle and wont cut injectors, and they did away with it on OBD2 96 and above civics

They decided with the increased compression as the years went by caused a chance of a detonation whenever they did have it on their HF/CX/VX trims

The california 92-95 VX, for example, did this, but only because the california edition was different. It used a normal 4 wire O2 and dod NOT have the 5 wire o2 and lean burn that the 49 state edition had. Too much nX emissions for california's taste apparently. Yeah, who else would give up 5-10mpg on average for the extra emissions in a year that a friggin truck does in a week of driving?

 

Never noticed myself but I would guess that the stock mpg gauge is pegged at max for either coasting in gear or out.

Get an ODBII gauge and you will definitely find out what you stated above is incorrect. The GE8 when coasting in gear completely cuts off the injectors. Zero gas is used until revs dip below ~1,000 rpm. When you coast in neutral your are using gas to idle. Nominal yes but still more than zero. And coasting in gear saves your brakes also. Why coast faster to a stop and then have to brake more? Coast slower and then brake less or in many cases I completely avoid having to apply my brakes.

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So you are saying that coasting in gear requires NO gas above 1000rpm? But idling does? I simply cannot accept that you say ZERO gas is used. It is impossible. While coasting your spark is still running and the fuel pump is running. Combustion IS happening! I guarantee that you are not just pumping air, as you seem to indicate. The fuel usage might be low, but it's not actually 0.

And I would not rely on an OBD guage for determining that. Use a scan gauge or actual fuel pump meter.

Just to consider, if you idle a carbuerated car, the intake is "closed" but you're using gas. It gets through. The engine doesn't die. If fuel flow was cut to actually 0, any engine will die and stop running.

 

I think you're confusing carbureted cars with modern electronic fuel injected cars.

Here's another thread on the topic quoting the shop manual (don't have mine handy).

 

You are mistaken. We are not discussing idle operation.

Both Generations of the Fit, and indeed nearly every single modern EFI car employs Deceleration/Coasting Fuel Cut schemes.

The Fit's is a function of TPS/VSS/RPM and the OE settings dictate that 40ms after all those criteria are met the injectors are shut off until one of the three of those cross the threshold again and the injectors are brought back online.

With the Flashpro You can actually change this as well as the Over-run and Coasting Fuel Cut offset time values.

 

 

That's exactly what I'm saying and confirmed thousands of times myself while driving. gph displays 0.00 and mpg is off the meter at 9999
When coasting in neutral gph displays from 0.18 to 0.26 depending on what accessories you are running and mpg dependant on the speed you are coasting. Usually 100 to 300 mpg.

I do use a ScanGaugeII. I mentioned OBDII gauge to include any guage reading directly from OBDII port. X-Gauge, SG, AGPtech mini bluetooth, etc.

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