manual transmission damage with EOC?
Received this comment through MetroMPG.com, and not being an expert in transmission design, I thought I'd bring it here for discussion, and then point the writer here.
My initial response is - if the description of lubrication is right, then yes, the potential exists to do damage to a manual tranny from very extended ICE-off coasting. However, in practice, the length of ICE-off glides is generally short enough that it's pretty unlikely that all lubricant will be flung from the output shaft causing it to effectively run "dry" and be subject to significant increased friction. The comment seems to have been triggered by a statement I made in my ICE-on vs. ICE-off coasting experiment that 40% of my driving on that route was done ICE-off. This may have created the impression that I was coasting uninterrupted for long stretches, rather than several times per km (which "reloads" the lubrication each time). Anyway, his message to me: Quote:
Any comments on the lubrication issue from the assembled GS gearheads? |
Interesting points. I think they are valid, though I don't know at what point it would become a problem.
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More times than not the final drive shaft and gear are in the lowist spot in a MT FWD tranny. Its been my experiance that this kicks more than enough lube up on the other parts to keep them lubed up. Ive never had issue with coasting a MT or AT tranny. Have been doing it for years.
Almost all tranny distruction is cause by redline gear jammers. Clutchs also take a beating in there hands. And then theres the folks that hold a car on a hill with the clutch. That will smoke a clutch and throw out bearing in nothing flat. I flat out dont worry about tranny damage. psy |
Thanks for the info, psy. It's worth noting that you haven't exactly been doing this in junkyard Metros either.
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Huh... That's odd. My Bentley shows that the output shaft and input shaft are always bathed in oil, so even if the input shaft isn't spinning it's always lubed, and the spinning output shaft should be enough to lube the ring and pinion above it. I suppose if the oil level doesn't reach the output shaft by design or lack of changes, it may be trouble, but I know the transmission in the truck and rabbit are always being lubed when the wheels are spinning.
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There are very few manual transmissions that will be hurt by engine off coasting. Just look at the cars being towed behind RVs they never have trouble out of the transmissions. The ring gear is big enough that it throws more than enough oil at anything important when the engine is off while the car is moving.
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Agreed on starter and clutch wear. For Hondas anyhow, I disagree on his analysis.
He forgot to mention that regardless of during EOC when gears 1-5 are not turning, the countershaft and the differential are still turning. The majority of the lubrication in the transmission takes place due to the oil being slung around by the diff. This is for a few reasons - the ring gear (bolted to the diff) is the largest "gear" in the transmission. It's teeth get to the lowest point of any gear in the box, thus it is the one that slings the oil. Not only does the diff sling the oil, it is essentially the "pump" inside the box. Strategically placed narrowing channels are around the ring gear in the cast housing. While the transmission is turning, the ring gear pushes oil into these channels, which force oil to the support bearings on both shafts. It also forces oil into the hollow shafts through the oil guides and lubricates the needle bearings under the gears. While it may not sling around as much oil while EOCing, it still lubricates the components enough for no worries (in my mind). Hope that helps. :) |
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Sorry,,, i didnt know metro's where so diff. than 98% of the other MT FWD trannys ever built. |
No, I wasn't saying the Metros are different - I was saying that since you're not driving a cheap car (Metro), you're obviously comfortable in your assessment of the risk of (not) damaging your vehicles.
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Hope you find the answers.... psy |
In a FWD transmission setup where the diff and the tranny are in one unit, the ring gear could provide enough lubrication, however what about those of us utilizing a RWD or 4WD setup? Doesn't the output shaft have an oil slinger on it? Else how would you flat tow something?
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Here's a good read on the subject.
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https://www.reanimotion.com/ToyMods/i...ideon_-new.jpg |
Considering how long I've been EOC'ing with an auto that has more miles on it than most autos last, I think that all of these claims of destroyed trannies are unfounded. Has anyone had a problem apart from people doing things like towing cars for thousands of miles at high speeds, or are these people focusing on hypothetical situations? I think that it's the latter.
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There is no load on the parts and the bearing are getting enough oil to not be harmed. I do get a whine when coasting in neutral with the engine on may be caused by no loads on the shafts.
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I would agree with the starter and clutch possibilities, but I don't think I can buy into his assesement on the manual transmission. As long as you have the right amount of oil, in a reasonable weight, I don't think that coasting, engine on or off is going to cause any appreciable damage to a manual transmission.
The only problems I have encountered in manual transmissions is failures due to not having enough oil. I am not particularly comfortable with running to light of an oil, but my expectation is that in most cases that is even Ok, because to a large extent people are not loading the daylights onto the transmission, because of their efforts to get better mileage. Additionally, on a manual transmission, you can minimize syncro wear, significantly, just by shifting at a speed that the engine input and the gear you are shifting into are spinning at the same, or close to the same speeds. If you are careful and reasonable, you can shift through all of your gears, by a little wise use of the gas pedal and speedometer, without using the clutch at all. You can also shift into neutral, without using the clutch, if you just let up on the gas a little and slip the shifter into neutral, without forcing it. Anyways, a little wordy, but I don't think their is a problem. |
I did massive amounts of engine off and engine on coasting for all 225,000 miles of my Civic VX ownership. And before the VX, even more EOC coasting w/ my '86 CRX hf which I bought used w/ 40k miles and put 100,000 miles on. Both cars saw both short and very long coasts (i.e. 1,2,3,4+ miles at a time when the hilly/mountainous or exit ramp conditions were present). I never replaced a clutch or starter in either car. And I never had any transmission problems in either car.
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Wait, so, if the gears aren't turning why are you so concerned about lubrication? If your in engine off or engine on, if the clutch is pushed in why exactly would this matter?
This doesn't make sense to me at all. Unless you were starting the car by dropping the clutch in 4th at 60mph, or if you constantly were on the starter, I really don't understand the harm. |
The gears in the differential & the output shaft turn whenever the car is moving, regardless of whether you're in gear or what you're doing with the clutch.
So those parts need constant lubrication - this was the area of concern in the original message. |
Oh, got it. Sorry, I'm a little slow.
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Just kidding, but don't worry, we're all a little slow here, ;) |
Yeah, don't worry about it. That's the reason I started the thread - I didn't know how it worked either.
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On a rwd car disconnecting the driveshaft would prob be easy but not on a fwd car that most people tow behind stuff now. I have towed lots of cars with manual transmissions and usually the way I do it is on a rwd if the oil fill plug on the case is high enough the output shaft is getting some oil on it's gears then I don't worry about it. On a fwd car I have never bothered to check since the ring gear always slings oil when the car is moving.
It works for a briggs and stratton engine so it should work for a transmission :) I have never towed an automatic with the engine off though. I have towed one for hours at 65mph with the engine idling and the trans in N though. I would check the manual that came with the car to find out how fast and how far you can coast with the engine off without damage. The speed is prob faster than most people here drive and the distance is much farther than you can coast before you start the engine and drive it back up to speed. Only transmissions I have had die are a ford aod and my metro trans lost a bolt on the shifter mechanism once. So I have had pretty good luck on not blowing them up that often except on my jeep and it blows a transmission along with pretty much all of the drivetrain pretty regular. |
Hi guys, I'm the one who originally sent the e-mail to MetroMPG. Lots of good info here, I hadn't thought about the fact that the diff and trans are in the same case on a FWD car. I there is a reason that you see old RWD often towed backwards so the front wheels are on the grount and you see FWD cars towed forwards so the back wheels are on the ground.
My point in the e-mail, though I didn't make it all that well, is that you don't know what kind of car the person reading has, and EOC may or may not damage that car depending on design, maybe a disclaimer would be in order. I've been experimenting with EOC in my Fit since reading MetroMPGs experiment and the results seem to be dramatic (I had one short trip show 280 MPG because it was mostly down hill). I live in a very hilly area so things are probably magnified. I haven't gone a full tank since I started EOC so I can't really judge yet but the scanguage results look good. One interesting thing with my car though is when the engine is off the odometer doesn't read, unless I turn the key back to the on position as soon as the engine dies. Have any of you that have done a lot of EOC noticed much of a change if you EOC with the key in the on-position vs in the off position? I have noticed though that after a long period of EOC (sometimes upwards of 2 miles) the transmission makes a whining noise after I get back into gear. Maybe the diff and output are getting lube but all of the sudden starting the gears going again after they have been still long enough for the oil to drip off is causing the noise? It goes away after a short period of normal driving. Having fun saving fuel - Bennet |
Hey Bennet - nice to see you here.
I agree with your point that there should be a disclaimer. Regular participants here know about "caveat experimentor", but you're right: I should post something to that effect with the coasting article on metrompg.com FYI, I'd expect you will see a significant increase in mpg through EOC use. 10% is a good guess, based on my own results & those of others here. |
Well I've only done one before and after on the same route, both from a cold start, and similar times of day.
The first trip with no EOC I got 34.6 on the way there and 36.7 on the way back. The second trip with a fair amount of EOC was 41.8 there and 46.4 back! That?s a 23% change! I did a little bit of pulse and glide style in there as well, and the first trips numbers are likely low because the scanguage doesn't read injector shut-off, but still that is huge. |
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