Transmission wear from P&G (pulse and glide)?
 

Hello all, I'm wondering if anyone has experience with prematurely wearing out a manual transmission from constantly shifting in and out of gear.

I used to only shift to neutral on decently long/steep hills (perhaps 10 or less times per day on my daily commute) and got 42-43 MPG average. However, last tank I experimented with shifting to neutral while going down every hill and I averaged 49 MPG over the tank for the first time. Very nice! :thumbup: My previous best was 45.4 MPG over the tank and that was under better traffic conditions, so the new strategy seems like a massive success.

My only concern is that shifting to neutral on every hill is a LOT of shifting, there is no flat ground where I live. There's constant small hills and I drive ~50 miles per day, mostly on country backroads.

I sort of worry that I could eventually wear out 5th gear from shifting in and out of it constantly. For what it's worth, I always blip the throttle before shifting back into gear to speed up the transmission's input shaft to as close to the required RPM as possible as an attempt to minimize synchronizer wear and, to a lesser extent, clutch wear. I'm not too worried about the clutch or its hydraulics since that's not a big deal for me to replace, but I don't want to excessively wear the transmission's internals.

Anyways, I would like to continue to experiment with different coasting and P&G strategies, but only if doing so won't excessively wear my transmission. How concerned do I need to be about this? Have any of you had premature transmission failures as a result of frequent shifting? Thanks very much in advance as always!

I haven't heard of, or experienced transmission problems from P&G. The only excessive wear I noticed on my Civic Wagon was the ignition switch. And it was old enough to have issues from normal use anyway.

Thanks. My ignition switch isn't a concern since I don't shut the engine off to coast, I just shift to neutral and let it idle until I need it again.

I always clutch it, and people tell me I’ll wear it out. By my estimation, clutching had to occur anyhow to get into neutral. Might as well keep it pushed in and avoid the synchro wear.

I assume you mean you hold the clutch down to coast instead of shifting to neutral? Never thought of that. My process has always been shift to neutral as I release the throttle without using the clutch (very easy and smooth if done properly). Then to go back into gear I blip the throttle, push clutch, shift into gear, and release clutch.

I can think of 2 downsides to coasting by holding the clutch instead of shifting to neutral. Obviously there's the leg fatigue and potential clutch/release bearing/thrust bearing wear. I think there would also be somewhat more drag than in neutral since the entire transmission/input shaft assembly is spinning rather than just the output side, but how significant this drag is I'm not sure.

Keeping the clutch pushed in (with the engine running) causes more wear to the clutch release bearing and the crankshaft thrust bearing. I don't want to be the one to find out if it's a significant amount of wear!

Do you mean you blip it, push in the clutch, then shift, then re-engage the clutch?

If you blip it after you push the clutch in it won't spin the input shaft unless you have some clutch drag.

That process should keep the transmission in great shape.

Yes, I blip the throttle before pushing the clutch to shift. That way I manually speed up the input shaft to approximately the RPM it needs to be at instead of forcing the synchros to. It goes back into gear noticeably smoother this way.

My recollection was that in Oregon, one can coast downhill in neutral in cars, or clutch in only in trucks,but...

Stack Exchange says
skeptics.stackexchange.com/questions/14159/is-it-illegal-in-any-u-s-jurisdiction-to-be-in-neutral-at-a-red-light

Not a primary source, that would be the DMV, but the article lists a number of other States as well.

When I worked at a feed & seed company in high school. I knew a driver that could shift the International truck up and down through the gears without the clutch.

I think coasting downhill is illegal in NY too. I doubt I'll ever get arrested for unlawful coasting on a downgrade!

Coasting is illegal here in Tennessee too but I don't see how that law is enforceable:confused: I don't understand the logic behind the law anyways.

You could overheat your brakes going down a big hill.

That's true but you could easily overheat your brakes going down a big hill in high gear too if you ride the brakes. Only an idiot would coast in neutral just to overuse the brakes though.

I'd like to meet the 1 person in the world cited for coasting with the clutch in.

Likewise, I'd like to meet the 1 person that became ill from a malfunctioning backflow preventer on a sprinkler system.

Why don't we require a permit and annual training to climb a ladder?

They're everywhere! :D

I took a second look at my link at #10, and counted about 18 States that don't have a summary. the first one with no proscription:
With my Notchback, downhill in the mountains, the brakes would overheat the tires.

You guys have some realy weird laws...

That's the Grand Experiment. Rights proscribed to the Federal level are reserved for the States and people. Then you can see what works and what doesn't. Compare, for instance Texas and Florida vs California. Indiana is offering hiring bonuses to the police officers being defunded in Chicago.

Or, for coasting, Alaska vs maybe 40 other states.

Compare Canada, which restricts travel between Provinces.

I think part of the illegal aspect of shifting into neutral has more to do with vehicles from the era before transmissions had synchros than anything else. There was a school bus that infamously lost its brakes and went off the side of a steep mountain pass killing many of the children because the driver had shifted into neutral and couldn't get it back into gear. The same can be said of if you need to accelerate. So even if you don't need any sort of braking for a certain grade, if it's a bear to get back into gear to accelerate you could have a safety problem.

However, I'm not going to recommend braking the law, but I don't see how shifting into neutral with a manual transmission in a modern car that you can shift back into gear in a fraction of a second is going to cause a safety concern, as long as you aren't riding your brakes as a result. If you have a hard time getting it into gear, with or wihtout synchromesh, then it's probably better to just leave it in gear for safety.

As far as transmission wear, there are some modern manual transmissions that do have a lubrication pump that only works if the tranmission is engauged. They are rare, I think mainly on bigger vehicles, but it's something to be sure of before coasting in neutral (or towing your vehicle in neutral).

Double clutching (blipping the throttle before stepping on the clutch and shifting into gear) is definitely a good idea in my opinion. It may wear out your clutch linkage a bit quicker, but helps save the transmission and even the cluch itself. Replacing a cable or clutch cylinder is a lot easier than replacing a clutch and/or flywheel or rebuilding a transmission. I double clutch anytime I'm downshifting, regardless of the vehicle (well, with a few exceptions honestly.)

Although if you're idling down a hill you're still burining fuel. Shutting off the engine would burn zero fuel, but then you can't blip the throttle to get the gears to mesh.

Of course if you need to brake at all you're better off leaving it in gear. If you think you're still burning fuel, you could install some sort of fuel shut off and get even more engine braking. Of course if you need to down shift again you would be able to blip the throttle without turnin the fuel back on again.

In my Super Beetle I had fun shutting off the ignition, which also closes the idle shut off valve. Then I'd turn the ignition back on. The high vacuum of engine braking would keep the idle shut off valve closed. But once I got to the bottom, all I had to do was touch the throttle or shift into a lower gear and the vacuum would drop enough to open the idle shut off valve again and away I'd go.

Prior to single-speed electric drive as well. :)

When you were rolling in reverse did you shift R-2-1 to put it in first and start forward without touching the brake?

Now that I have two hybrids, I question if there really exists a neutral in them because the motors and engine are always connected to the wheels. TBH I shift into "N" all the time. I let the engine shut its self off by holding the pedal at a neutral position and then shift into "N" and let it coast, engine off.

I've come to love hybrids. I can't believe I used to not like them.

No, I never tried that. Why would you go into 2 then 1 and not just 1 to begin with?

Reverse to first while you're rolling grinds the gears, does it not? R-2-1 tickles the syncros or something technical like that. Buy any Beetle and try it. ;)

Even the Chevy Bolt EV has a motor and gears cooled and lubricated in an oil bath that shuts off when "shifting to neutral". I've not heard of anyone wearing anything out from coasting like this, but I suppose it's possible.

I installed a kill switch in my Metro in early 2015, when the car had ~130,000 miles. Ever since then, I've used P&G with EOC 100% of the time. That's right: no "normal" driving for 6+ years. Even the shortest trips I make involve dozens of bump starts and dozens of shifts between fifth gear and neutral.

The car now has 276,000 miles, and the transmission still shifts perfectly into and out of every gear.

I wouldn't worry about it.

-Funkhoss

Wow that's great to know, exactly the kind of information I was looking for. I guess it can't be that bad then. Thanks for sharing!

:thumbup:

-Funkhoss

Recalling back, in the 1985 VW Diesel I would some times also coast with engine off. But man! Pop-starting that thing must have hit some number on the Richter scale. It depended on the circumstances.

I also once lost the clutch cable at the beginning of about a 700 mile trip over several mountain passes and drove the whole way matching revs and starting in gear at stop lights and didn't have any transmission or starter problems afterwards.

The current owner didn't ever get it registered and I'm temped to just go pick it up since he no longer wants it...

Another curious thing I meant to ask about is the effects of travelling with the engine off and the trans in neutral. I always thought manual transmissions were fine coasting or being towed engine on or off and autos should only coast or be towed with the engine running, but my car's owners manual recommends against flat towing and says if it must be done to keep speed low and distance as short as possible, not to exceed 35 MPH or 50 miles I believe. No distinction is made for auto or manual transmission, although that may be an oversight.

I understand why towing an automatic transmission with the engine off would be bad since without the engine running there's no oil being pumped around to lubricate and cool components, but I am almost certain my transmission is simply splash lubricated so I don't see why it would matter? Unless the input shaft needs to be spinning to splash the oil around.

This doesn't matter much to me since I leave the engine idling while coasting, I'm just curious.

maybe you could google and see if your car is flat towable behind a RV. If it is than shouldn't be a problem coasting engine on or off.

The flat towing restriction might be for the whatever passes for the differential. I have had many that had a diff restriction, but not on the trans

I found that the auto isn't flat towable as I expected, but I wasn't able to find anything but speculation for the 5 speed. I'm sure coasting with the engine running was a scenario the trans was designed to cope with, but I'm not sure about EOC. I wouldn't expect it to be a problem, but I'm no engineer.

The diff is part of the trans on my Civic. That's interesting that the diff could be adversely affected by flat towing though, never heard of that. I don't see how that would matter to the diff? It's spinning when the vehicle is rolling either way and should lube itself :confused:

The guy my ex-wife left me for put his sweet Zenith Blue 1967 Beetle behind a motorhome and towed it hundreds of miles in gear, and then abandoned it in AZ.

Spinning that motor against compression probably killed the mileage in the motrhome.

Did he intentionally leave it in gear for some reason or was that an accident?

I'd say negligent rather than accidental. The 'some reason' part was cutting it loose instead of towing it home again and repairing it.

I also saw someone towing a vehicle for sale into the NW Bugrun in gear.

What car are we talking about again? I've heard of manual transmissions that have a lubrication pump (or maybe splasher) that needs the input shaft spinning. But I understand those are rare and mostly used on larger vehicles (Pickups and SUV's).

Generally speaking the gears should all still be spinning and getting lubbed up as the bottom ones dip down into the oil. The input shaft would be still with the gears spinning around it. But some of those gears would be spinning at several thousands of RPM's. What's a thousand or two more from the engine being off?

Good to know, thank you for the information! My car is an 05 Civic, thought I said that but looks like I forgot to. I don't think my transmission has any type of splasher or pump, I didn't see anything like that when I had it apart.

There seems to be a lot of people who have towed these with all four wheels on the ground with no issues (quick google search). It seems logical to me that there'd be no harm in coasting with the engine off.

Just don't get pulled over for speeding and tell the officer that it was because you were coasting in neutral with or without the engine off and you'll probably be fine.

Thanks. I don't think the hills I encounter on my daily commute are really long enough to be worth shutting the engine off for (1/2 to 3/4 mile of coasting at a time at the most), so the only EOC I normally do is shutting the engine off once I pull into my driveway and coasting into my garage.