what does lugging do to engine/clutch/gearbox
JimmyCarlBlack
a manual.
I'm finding that 1st gear on my '98 VW Passat
is a bit tall (& 2nd is short, but that's another
matter), so to creep at 5-7mph, I have to run
at only 1000rpm. Idle is 900 & if I engage
the clutch *really* smoothly, I can get the
car moving at 1k-1.1k, but I usually give it
a little more gas & start at 1.2-1.4k, then try to
slow down gently.
This is a real hassle in stop & slow traffic,
particularly on the hilly road I drive. I tend to
do what the trucks do- let the gap in front
stay pretty big so I can move at a constant
slow speed. This reduces the number of
times I have to go from stoppped to creeping,
so less wear on clutch, but how bad is
creeping on the connecting rods, etc. I do
try to keep the engine out of the super-lugging
where it's shaking the car, but @ 1000 rpm,
the engine does run harsher & vibrate more.
Wishing for an automatic just for the commute,
JCB
Chuck Tomlinson
>....and how do you drive in stop & go with
>a manual.[...] I tend to
>do what the trucks do- let the gap in front
>stay pretty big so I can move at a constant
>slow speed. This reduces the number of
>times I have to go from stoppped to creeping,
>so less wear on clutch, but how bad is
>creeping on the connecting rods, etc.
I generally do the same thing, letting the car creep in gear as long
as possible by allowing a moderate gap to open in front of me.
Since the throttle is almost completely closed, I think the bearing
pressures in the engine are very low, almost as low as idling, even
though the loads may not be smooth.
IOW, you feel more vibration because the time between firing is
lower, not because the engine stresses are higher. After all,
redline feels smooth in many engines, even though they're under
tremendous stress.
I have no qualms about using light throttle and low rpm for extended
periods. On some winter trips, I drive for hours at low rpm and
light throttle. The only kind of "lugging" I prefer to avoid is
climbing long grades at low rpm and large throttle openings.
Although my engine might survive that treatment, I don't think it's
wise to combine high cylinder pressures (heavy throttle), extended
load periods per firing cycle (the power stroke lasts longer at low
rpm), and low oil pressure (the oil pump senses rpm only, not load).
That just seems to maximize the risk of squeezing away the oil film
until metal touches metal.
But IMHO, there is almost no chance of problems in the situations
you mentioned, if the engine is in decent mechanical condition.
--
Chuck Tomlinson
NLW TFW NM
pre-emptive differential gear change cost compared to an emegency clutch or
engine repair? I've changed gearing on two vehicles, and was very happy both
times.
But as much as I like sticks, I want slushboxes in heavy stop'n'go traffic.
Mike
Christopher Green
<ya...@excite.org> wrote:
>...and how do you drive in stop & go with
>a manual.
>
>I'm finding that 1st gear on my '98 VW Passat
>is a bit tall (& 2nd is short, but that's another
>matter), so to creep at 5-7mph, I have to run
>at only 1000rpm. Idle is 900 & if I engage
>the clutch *really* smoothly, I can get the
>car moving at 1k-1.1k, but I usually give it
>a little more gas & start at 1.2-1.4k, then try to
>slow down gently.
[snip]
Lugging a stick shift is a good way to wear out
your transmission. The reduced mechanical
advantage translates to increased wear on the
gears. (Lugging in high gear is a common cause
of transmission failure in 5-speeds. Lugging in
second can't be much better.)
--
Chris Green
Advanced Technology Center
Laguna Hills, California
Chuck Tomlinson
>Now that you're stuck with the manual for THIS car and commute, what would a
>pre-emptive differential gear change cost compared to an emegency clutch or
>engine repair? I've changed gearing on two vehicles, and was very happy both
>times.
Maybe if I drove a very heavy manual trans vehicle I'd consider a
gear ratio change, but my clutch is pretty stout for my car's
weight. That, combined with idle-speed control and a decent supply
of low-rpm power, means I don't have to use much throttle (if any)
in stop & go traffic.
IOW, I don't think I'll be wearing out my clutch anytime soon. In
my car, 1st gear idle is about 7-8 mph, which works pretty well for
creeping along in traffic.
Also, my engine controller commands a higher idle speed when the car
is moving (~1000 rpm vs. ~700 rpm). That means my car runs pretty
smoothly even when I'm letting the idle speed controller handle all
the air metering.
I've noticed this faster "moving idle" in my Ford and Chevy V8s, but
I don't recall seeing that behavior in any import cars. I don't
know exactly why Ford and GM do that, but IMHO it helps stop & go
driveability quite a bit.
>But as much as I like sticks, I want slushboxes in heavy stop'n'go traffic.
If I spent the vast majority of my driving time in stop & go
traffic, I'd probably want a slushbox too. In that case, I'd buy
some vanilla sedan for traffic crawling, and keep the real (manual
trans) car at home, ready for evenings and weekends.
--
Chuck Tomlinson
Chuck Tomlinson
>
>Lugging a stick shift is a good way to wear out
>your transmission. The reduced mechanical
>advantage translates to increased wear on the
>gears. (Lugging in high gear is a common cause
>of transmission failure in 5-speeds. Lugging in
>second can't be much better.)
It takes almost no power or torque to sustain a car at near-idle rpm
in 1st or 2nd gear in traffic. The gear loading in that condition
is completely insignificant (for *all* gears in the drivetrain).
And where did you get that tidbit about high gear lugging being a
common cause of manual transmission failure? IMHO, top gear (of all
the gears in the trans) is the one *designed* for use at low rpm,
and failures from low rpm use would constitute truly poor design.
--
Chuck Tomlinson
Mangey
>in 1st or 2nd gear in traffic. The gear loading in that condition
>is completely insignificant (for *all* gears in the drivetrain).
>
3.23 diff ratio, 195/65r16 tyres and gets very interesting to drive if the
traffic is heading uphill without a load of work tools, very few stops and
starts, about 1000rpm minimum necessary to not stall. It's also the only
time the temperature guage climbs despite the half stuffed radiator. But,
hey it starts, stops and I own it, makes a good spare so I can play hard in
the 4x4.
Pat,
Keeper of the Mangeysaurus Rex,
Brisbane, Australia,
http://www.powerup.com.au/~mangey/
Spam will be returned with my collection attached, a small preview of a
special place for SPAMMERS in the next world!
JimmyCarlBlack
a gear for a speed, then mashing the accelerator to get
some oomph out of the engine. Often caused by laziness
when passing- don't want to go through the effort of
downshifting.
My commute road *is* hilly, so I try to let the gap get larger
when going uphill so I can go a little faster.
There are a couple issues here: auto vs. manual &
rpms vs. torque. The latter is complicated for me by
1) turbo and 2) impending chipped ECU, increasing
max turbo PSI.
Auto vs. manual: I commute at off-hours, so the stop & slow
thing isn't everyday. When I get a good commute, the manual
is a blast throught the mountain twisties, but there's been
a lot of roadwork in the morning this week.
I think about a Tiptronic (plus a V6 or a higher-PSI chip to deal with the
increased driveline loss) when this happens. I consider trading
my wife's car for an A4 quattro/V6/Tip & giving her the Passat (she
likes manual too & has a shorter commute). I drove the tip when I
bought the Passat & didn't like it's unwillingness to downshift & give
me some zoom unless & really mashed the throttle, but I could
learn to use the manual mode.
Load vs. RPM: In this case I don't have any choice as there's no
lower gear, but I wonder in other cases 3rd @ 5k vs 4th @ 3k.
I can get reasonable power at the lower revs due to the turbo, but
it means it's developing more boost. This will be even more true
when I chip the ECU-- I'll be able to be even lazier about downshifting,
but does this cause more wear than high RPMs. I know F. Piech
(chairman VWAG) likes redlining his Jetta, but he can get a free
engine when he blows his up.
I don't think I'll be swapping the transaxle gears (this is a FWD car)
for shorter gearing due to cost & availability, but it wouldn't hurt
to get all gears a little shorter. I can go 120mph in 5th, but I don't
have much use for that. It's quieter @ 2.5K @ 65MPH, but that
makes it strictly a cruise (or speeding) gear.
As far as Chuck's (you also drive a Passat or A4, right- seen you around
vwpassat list or somewhere) statement about clutch hardiness goes,
I have heard a story (over the Internet- "it must be true I read it
on the Internet" ha!) about someone in my situation: stop & go
through hills, who melted his clutch in a B5 ('98+) Passat. I
do think it would put an awful lot of stress on it if I stop & slow- crept
like the automatics do- keeping 24" between me & the car in front.
I'd have to use a lot of clutch slip to do that.
Sorry for the length.
-JCB
Chuck Tomlinson wrote in message <74pgmg$j...@sjx-ixn10.ix.netcom.com>...
Chuck Tomlinson
>OK, so "lugging" should really be defined as selecting too high
>a gear for a speed, then mashing the accelerator to get
Yep, that's also how I define lugging, but I'm sure other folks have
their own pet definitions.
>My commute road *is* hilly, so I try to let the gap get larger
>when going uphill so I can go a little faster.
Makes sense.
[...]
>Load vs. RPM: In this case I don't have any choice as there's no
>lower gear, but I wonder in other cases 3rd @ 5k vs 4th @ 3k.
>I can get reasonable power at the lower revs due to the turbo, but
>it means it's developing more boost. This will be even more true
>when I chip the ECU-- I'll be able to be even lazier about downshifting,
>but does this cause more wear than high RPMs.
That's a tough one. Moderate cylinder pressures (medium throttle)
can actually *reduce* the stress levels in bearings and connecting
rods. Sounds silly, but the highest cylinder pressure occurs on the
first half of the power stroke, when the rods are subject to the
highest tension loads (trying to accelerate the pistons downwards).
The combustion pressure load can be lower or higher than the
acceleration load, depending on how much boost/throttle you're
using, and how much rpm you're running. By selecting, say, 4th over
3rd, you increase combustion loads but decrease acceleration loads.
Which is easier on the bearings? IMHO, it's almost impossible to
know without running some kind of full-cycle engine simulation.
>As far as Chuck's (you also drive a Passat or A4, right- seen you around
>vwpassat list or somewhere) statement about clutch hardiness goes,
>I have heard a story (over the Internet- "it must be true I read it
>on the Internet" ha!) about someone in my situation: stop & go
>through hills, who melted his clutch in a B5 ('98+) Passat.
Nope, I'm not a VW Chuck; I'm a pushrod V8 Chuck :-) I try quite
hard to minimize clutch slip, and I've never had a clutch fail on
me, though I suppose some cars might be more susceptible to clutch
heat failures. I don't know how robust Passat clutches are.
>I think it would put an awful lot of stress on it if I stop & slow- crept
>like the automatics do- keeping 24" between me & the car in front.
>I'd have to use a lot of clutch slip to do that.
Clutch slip is bad, for sure. I think some manual trans drivers
don't realize that slipping a clutch puts heat into the clutch, and
the heat takes quite a while to get back out. I've seen some brutal
clutch slipping at the hands (feet) of people who didn't make the
clutch-heat connection (which admittedly is far from obvious).
--
Chuck Tomlinson
Christopher Green
Tomlinson) wrote:
>cjrg...@concentric.net (Christopher Green) wrote:
>>
>>Lugging a stick shift is a good way to wear out
>>your transmission. The reduced mechanical
>>advantage translates to increased wear on the
>>gears. (Lugging in high gear is a common cause
>>of transmission failure in 5-speeds. Lugging in
>>second can't be much better.)
>
>It takes almost no power or torque to sustain a car at near-idle rpm
>in 1st or 2nd gear in traffic. The gear loading in that condition
>is completely insignificant (for *all* gears in the drivetrain).
>
>And where did you get that tidbit about high gear lugging being a
>common cause of manual transmission failure? IMHO, top gear (of all
>the gears in the trans) is the one *designed* for use at low rpm,
>and failures from low rpm use would constitute truly poor design.
>--
>Chuck Tomlinson
>
The less the mechanical advantage, the greater the force placed
on the driving gear. The greater that force, the more rapid the wear
on the gear.
The torque required to get a car moving from a standing start is
not negligible, and in second gear, the wear on the clutch and
transmission should not be ignored. In traffic such as described,
stopping and restarting is a frequent occurrence.
A common failure mode in 5-speeds is that the 5th gear becomes
worn from too long operation at insufficient speed; the transmission
eventually starts coming out of 5th gear spontaneously. This can
be disconcerting at high speed.
Driving a stick shift in stop-and-go traffic is hard enough on the
clutch and transmission. Trying to do it in second gear is like
pulling up a steep hill in addition to that.
--
Chris Green
Chuck Tomlinson
>
>The less the mechanical advantage, the greater the force placed
>on the driving gear. The greater that force, the more rapid the wear
>on the gear.
Thanks to transmission lubricant, gear wear is not significant
unless the torque loads are high enough to squeeze the oil film out
*completely*, or unless the trans has loose metallic fragments in
the oil that are larger than the oil film thickness.
IMHO, average torque loads during highway cruising and normal city
acceleration are *much* larger than the average loads typical of
slow movement in stop & go traffic. Also, even the peak starting
loads in traffic should be far below the level where the minimum oil
film thickness (on meshing gear teeth) approaches zero.
>The torque required to get a car moving from a standing start is
>not negligible, and in second gear, the wear on the clutch and
>transmission should not be ignored. In traffic such as described,
>stopping and restarting is a frequent occurrence.
The torque required just to get a car moving (with low acceleration)
is... very low. Again, the torque load is almost certainly lower
than that required to cruise at *any* typical highway speed.
Even if the loads briefly reach cruising levels, the *duration* of
that load will be very brief, since the car will quickly reach
"creeping" speed and resume near-zero load operation.
>A common failure mode in 5-speeds is that the 5th gear becomes
>worn from too long operation at insufficient speed; the transmission
>eventually starts coming out of 5th gear spontaneously. This can
>be disconcerting at high speed.
Maybe this does happen, but I'm a mechanical engineer, and at this
point, I cannot figure out how extended operation at *low* torque
levels can cause transmission failure, let alone cause the trans to
pop out of gear. If you or anyone else could explain to me
*exactly* how that happens, I'd really appreciate it.
>Driving a stick shift in stop-and-go traffic is hard enough on the
>clutch and transmission. Trying to do it in second gear is like
>pulling up a steep hill in addition to that.
Clearly, a driver can abuse the clutch and trans in traffic. But
IMHO, it is *not* necessary to subject a clutch or trans to high
stress just to creep along in traffic.
I don't know what concerns you have about 2nd gear: I'm not
advocating starting from 2nd gear, but I am convinced that sustained
light-throttle operation in *any* gear will *not* result in undue
transmission wear.
--
Chuck Tomlinson
Chuck Tomlinson
>
> My 83 stock 1600 Sigma has near no power and torque, 4speed manual, a
>3.23 diff ratio, 195/65r16 tyres and gets very interesting to drive if the
>traffic is heading uphill without a load of work tools, very few stops and
>starts, about 1000rpm minimum necessary to not stall. It's also the only
>time the temperature guage climbs despite the half stuffed radiator.
My car runs hotter than t'stat regulation temp if I drive slowly up
long, steep hills. It seems to build heat faster if I "lug" it, or
use low rpm, probably because the water pump speed is lower.
I have electric fans only, and they normally don't operate below
about 220F. Below 35-40 mph, the airflow seems to be insufficient
for engine cooling (without help from the fans), even at those
relatively low power levels.
To keep my coolant temp low (and fans off) on long uphill sections,
I have to drive faster than 40-45 mph. Although I use considerably
more power at the higher speed, the greater airflow is more than
enough to dissipate the additional heat.
--
Chuck Tomlinson
Bob Vail
doesn't match what happens in the real world.
Chuck, ol' buddy; If you want to drive your manual transmission
car around in high gear and/or start out in high gear,
I think you should be allowed to, without ANYONE infringing on your
right to do so.
--
Did our actions today set the proper example for those we lead?
Aim Higher! Bob Vail
sff...@scfn.thpl.lib.fl.us
On Sat, 12 Dec 1998, Chuck Tomlinson wrote:
> cjrg...@concentric.net (Christopher Green) wrote:
snip
> Even if the loads briefly reach cruising levels, the *duration* of
> that load will be very brief, since the car will quickly reach
> "creeping" speed and resume near-zero load operation.
>
> >A common failure mode in 5-speeds is that the 5th gear becomes
> >worn from too long operation at insufficient speed; the transmission
> >eventually starts coming out of 5th gear spontaneously. This can
> >be disconcerting at high speed.
>
> Maybe this does happen, but I'm a mechanical engineer, and at this
> point, I cannot figure out how extended operation at *low* torque
> levels can cause transmission failure, let alone cause the trans to
> pop out of gear. If you or anyone else could explain to me
> *exactly* how that happens, I'd really appreciate it.
snip)
Christopher Green
Tomlinson) wrote:
>"Mangey" <NOSPAM> wrote:
>>
>> My 83 stock 1600 Sigma has near no power and torque, 4speed manual, a
>>3.23 diff ratio, 195/65r16 tyres and gets very interesting to drive if the
>>traffic is heading uphill without a load of work tools, very few stops and
>>starts, about 1000rpm minimum necessary to not stall. It's also the only
>>time the temperature guage climbs despite the half stuffed radiator.
>
>My car runs hotter than t'stat regulation temp if I drive slowly up
>long, steep hills. It seems to build heat faster if I "lug" it, or
>use low rpm, probably because the water pump speed is lower.
It's because the engine is operating at lower efficiency (unless
maybe you are driving a diesel) and with increased load due to
the lower mechanical advantage.
[snip]
-- Chris Green
Christopher Green
Tomlinson) wrote:
>cjrg...@concentric.net (Christopher Green) wrote:
>>
>>The less the mechanical advantage, the greater the force placed
>>on the driving gear. The greater that force, the more rapid the wear
>>on the gear.
>
>Thanks to transmission lubricant, gear wear is not significant
>unless the torque loads are high enough to squeeze the oil film out
>*completely*, or unless the trans has loose metallic fragments in
>the oil that are larger than the oil film thickness.
If that were so, transmissions would never wear out, but we all know
that they do, sometimes even without abuse or neglect.
>IMHO, average torque loads during highway cruising and normal city
>acceleration are *much* larger than the average loads typical of
>slow movement in stop & go traffic. Also, even the peak starting
>loads in traffic should be far below the level where the minimum oil
>film thickness (on meshing gear teeth) approaches zero.
Torque loads are highest during acceleration at any speed.
If you were simply cruising at a low and steady speed, then
your analysis would be correct, but the nature of stop-and-go
traffic is such that this is not possible.
>>The torque required to get a car moving from a standing start is
>>not negligible, and in second gear, the wear on the clutch and
>>transmission should not be ignored. In traffic such as described,
>>stopping and restarting is a frequent occurrence.
>
>The torque required just to get a car moving (with low acceleration)
>is... very low. Again, the torque load is almost certainly lower
>than that required to cruise at *any* typical highway speed.
>
>Even if the loads briefly reach cruising levels, the *duration* of
>that load will be very brief, since the car will quickly reach
>"creeping" speed and resume near-zero load operation.
But "creeping" speed is rarely sustained for long in this kind
of traffic. Your "near-zero-load" occurs only in operation at
that speed and ceases as soon as acceleration becomes
necessary.
>>A common failure mode in 5-speeds is that the 5th gear becomes
>>worn from too long operation at insufficient speed; the transmission
>>eventually starts coming out of 5th gear spontaneously. This can
>>be disconcerting at high speed.
>
>Maybe this does happen, but I'm a mechanical engineer, and at this
>point, I cannot figure out how extended operation at *low* torque
>levels can cause transmission failure, let alone cause the trans to
>pop out of gear. If you or anyone else could explain to me
>*exactly* how that happens, I'd really appreciate it.
I am sure you can find any number of mechanics who will
attest to the existence of this particular kind of failure; I
can. The failure is caused by the mating gear faces
becoming sufficiently worn to allow the gears to dis-
engage.
The forces on the gear faces are increased by
operation in higher gears. Although, because of
the machanical advantage of the drive train, the
torque is less at the gear faces than at the wheel,
it is greater in higher gears and in any case never
negligible when considered over thousands of
hours of operation.
>>Driving a stick shift in stop-and-go traffic is hard enough on the
>>clutch and transmission. Trying to do it in second gear is like
>>pulling up a steep hill in addition to that.
>
>Clearly, a driver can abuse the clutch and trans in traffic. But
>IMHO, it is *not* necessary to subject a clutch or trans to high
>stress just to creep along in traffic.
>
>I don't know what concerns you have about 2nd gear: I'm not
>advocating starting from 2nd gear, but I am convinced that sustained
>light-throttle operation in *any* gear will *not* result in undue
>transmission wear.
>--
>Chuck Tomlinson
Sustained light-throttle operation in any gear is not the problem;
it is the driver's illusion that the car is being operated at light
throttle when in fact it is not. This is the basic problem with
lugging in any gear and at any speed.
--
Chris Green
Chuck Tomlinson
>An educational principle: What they taught me in school frequently
>doesn't match what happens in the real world.
Thanks for the insight, Bob. Another educational principle I picked
along the way is: if the real world doesn't correspond with theory,
try to find out *why*.
Was I presumptuous for mentioning the fact that I'm an engineer?
Please note that I was *NOT* using that fact as some kind of lame
"appeal to authority". I simply mentioned it (perhaps unwisely) to
explain why I'm curious about certain statements that appear to
conflict with what I know and have experienced.
>Chuck, ol' buddy; If you want to drive your manual transmission
>car around in high gear and/or start out in high gear,
>I think you should be allowed to, without ANYONE infringing on your
>right to do so.
Thanks again, Bob. I thought there was a law against driving in
high gear, but you cleared that up...
So what's your point here? Should I blindly accept a statement that
makes no sense to me (based on the information already presented)?
Should I not be curious as to why a transmission could fail from
sustained light loading? What is your point?
--
Chuck Tomlinson
Chuck Tomlinson
>toml...@ix.netcom.com (Chuck Tomlinson) wrote:
>
>>My car runs hotter than t'stat regulation temp if I drive slowly up
>>long, steep hills. It seems to build heat faster if I "lug" it, or
>>use low rpm, probably because the water pump speed is lower.
>
>It's because the engine is operating at lower efficiency (unless
>maybe you are driving a diesel) and with increased load due to
>the lower mechanical advantage.
Actually, the engine is operating *more* efficiently at lower rpm/
higher throttle. For a fixed air-fuel ratio (as with closed loop
fuel control), gasoline engines operate more efficiently (lower
ratio of fuel_in to power_out) as manifold vacuum decreases.
As for the increased load, the engine might be generating more
torque at lower rpm, but the engine's power output is the same (or
lower). Required power is set by speed, grade, and the vehicle's
mass and drag properties.
IOW, I need the same amount of delivered power to climb a grade at a
certain speed, *regardless* of the gear I have selected. In fact,
at higher rpm, the engine will be producing *more* power than at low
rpm: it has to overcome greater internal friction losses before it
can deliver the required amount of output power.
So I'm trying to understand why my cooling system is less effective
when it is dissipating the same amount (or less) waste heat at lower
rpm. Lower water pump speed seems a more likely explanation to me.
--
Chuck Tomlinson
Chuck Tomlinson
>>unless the torque loads are high enough to squeeze the oil film out
>>*completely*, or unless the trans has loose metallic fragments in
>>the oil that are larger than the oil film thickness.
>
>If that were so, transmissions would never wear out, but we all know
>that they do, sometimes even without abuse or neglect.
I guess I'm not familiar with properly-lubricated transmissions that
fail by wearing down the tooth profiles. I know synchros eventually
wear out, which might force a transmission repair or replacement.
I know that some overloaded transmissions can fail through collapse
of the oil film or outright breakage of the gear teeth.
I have a Borg-Warner T5 that failed in my Mustang. It failed
because the torque loads during aggressive driving were too high for
durable operation of the trans. IIRC, the OEM T5 was rated for a
max'm input of 275 lb-ft, but mated to an engine rated at 300 lb-ft.
The failure mode in those trans is *not* a wearing down of the
teeth: the tooth faces pit and spall due to metal-to-metal contact
with mating teeth. People who drive their old 5.0s gently (my wife,
for instance) will *never* experience such a failure.
>Torque loads are highest during acceleration at any speed.
>If you were simply cruising at a low and steady speed, then
>your analysis would be correct, but the nature of stop-and-go
>traffic is such that this is not possible.
But it is possible to accelerate gently in stop & go traffic, to a
speed where the vehicle can cruise slowly.
>But "creeping" speed is rarely sustained for long in this kind
>of traffic. Your "near-zero-load" occurs only in operation at
>that speed and ceases as soon as acceleration becomes
>necessary.
Yes, I agree. But how does that load compare to those sustained in
supposedly less severe conditions (like highway cruising)? I'm
claiming that it is possible and reasonable to drive in stop & go
traffic using less engine torque than is required to overcome aero
drag at highway speeds.
Naturally, if a driver treats stop & go traffic as a series of brief
sprints, he will be doing a disservice to his trans. But that's not
what I'm talking about. When I entered this part of the discussion,
I was talking about relatively long creeping periods, where a manual
trans driver allows a gap to open up ahead of him with the intent of
reducing peak acceleration (and peak torque loads on the trans).
>I am sure you can find any number of mechanics who will
>attest to the existence of this particular kind of failure; I
>can. The failure is caused by the mating gear faces
>becoming sufficiently worn to allow the gears to dis-
>engage.
I know a few mechanics. I will ask around. But... AFAIK, the
effect of excessive tooth face wear is increased backlash. I do not
know why there would be any tendency for worn teeth to put loads
into the shift mechanism, but... I will ask around.
>Sustained light-throttle operation in any gear is not the problem;
>it is the driver's illusion that the car is being operated at light
>throttle when in fact it is not. This is the basic problem with
>lugging in any gear and at any speed.
Are you saying the driver doesn't know how much throttle he's using?
--
Chuck Tomlinson
Matthew T. Russotto
Chuck Tomlinson <toml...@ix.netcom.com> wrote:
}
}Actually, the engine is operating *more* efficiently at lower rpm/
}higher throttle. For a fixed air-fuel ratio (as with closed loop
}fuel control), gasoline engines operate more efficiently (lower
}ratio of fuel_in to power_out) as manifold vacuum decreases.
Huh? That's not so. Engines operate more efficiently with the
throttle open wider.
}As for the increased load, the engine might be generating more
}torque at lower rpm, but the engine's power output is the same (or
}lower). Required power is set by speed, grade, and the vehicle's
}mass and drag properties.
And internal and drivetrain losses, which may be higher at lower RPMs.
--
Matthew T. Russotto russ...@pond.com
"Extremism in defense of liberty is no vice, and moderation in pursuit
of justice is no virtue."
Chuck Tomlinson
>Chuck Tomlinson <toml...@ix.netcom.com> wrote:
>}
>}Actually, the engine is operating *more* efficiently at lower rpm/
>}higher throttle. For a fixed air-fuel ratio (as with closed loop
>}fuel control), gasoline engines operate more efficiently (lower
>}ratio of fuel_in to power_out) as manifold vacuum decreases.
>
>Huh? That's not so. Engines operate more efficiently with the
>throttle open wider.
We both said basically the same thing. Manifold vacuum decreases as
the throttle opens wider.
To be honest, I don't like talking about "manifold vacuum". I'd
rather refer to "manifold pressure", but I'm not sure whether that
would make my point more or less clear.
>}As for the increased load, the engine might be generating more
>}torque at lower rpm, but the engine's power output is the same (or
>}lower). Required power is set by speed, grade, and the vehicle's
>}mass and drag properties.
>
>And internal and drivetrain losses, which may be higher at lower RPMs.
Why would internal and drivetrain losses be higher at lower rpm?
The final drive is delivering the same power at the same speed, so
it doesn't care what combination of load and rpm is being used at
the engine.
At lower rpm: the engine is running higher pressures, but less
often. Sliding speeds are lower, so bearing friction should be
lower. Accessory speeds will be lower, so accessory power will be
lower (including water and oil pumps).
--
Chuck Tomlinson
Matthew T. Russotto
Chuck Tomlinson <toml...@ix.netcom.com> wrote:
}russ...@wanda.vf.pond.com (Matthew T. Russotto) wrote:
}>
}>And internal and drivetrain losses, which may be higher at lower RPMs.
}
}Why would internal and drivetrain losses be higher at lower rpm?
}
}The final drive is delivering the same power at the same speed, so
}it doesn't care what combination of load and rpm is being used at
}the engine.
Agreed there.
}At lower rpm: the engine is running higher pressures, but less
}often. Sliding speeds are lower, so bearing friction should be
}lower. Accessory speeds will be lower, so accessory power will be
}lower (including water and oil pumps).
Since "lugging" the engine is said to cause damage, I thought friction
must be higher in those cases.
Chuck Tomlinson
>
>Since "lugging" the engine is said to cause damage, I thought friction
>must be higher in those cases.
I've also heard that lugging will damage... something. Whether the
engine is at risk, or the transmission, or both, I don't know.
I do know that low road speeds, combined with high torque loads, can
sometimes lead to problems. I mentioned the case of my car, where
low airflow and water pump speed allow the car to get hotter than
normal. I also mentioned cars like the old Mustangs, with trannies
that were spec'd for market availability rather than durability.
But I have people trying to tell me that low rpm, stop & go driving
is somehow hazardous to a manual transmission, and I think that's
incorrect. Apart from lack of any personal supporting evidence, I
don't know how someone could definitively point the finger at stop &
go driving after a failure that supposedly takes *years* to occur.
IOW, I don't understand why a trans would fail prematurely when all
operating parameters (rpm, torque, temps, etc.) remain *normal*.
--
Chuck Tomlinson
Jonathan Hodgson
Christopher Green wrote in message <36737ca9...@nntp.concentric.net>...
[snip]
>On Sat, 12 Dec 1998 08:03:09 GMT, toml...@ix.netcom.com (Chuck
>Tomlinson) wrote:
>>Maybe this does happen, but I'm a mechanical engineer, and at this
>>point, I cannot figure out how extended operation at *low* torque
>>levels can cause transmission failure, let alone cause the trans to
>>pop out of gear. If you or anyone else could explain to me
>>*exactly* how that happens, I'd really appreciate it.
>
>I am sure you can find any number of mechanics who will
>attest to the existence of this particular kind of failure; I
>can. The failure is caused by the mating gear faces
>becoming sufficiently worn to allow the gears to dis-
>engage.
[snip]
That sounds far more like dead synchros to me, with my
(admittedly) limited knowledge - caused by excessively
aggressive gear shifts (guilty as charged there!)
I'd have thought you'd have trouble putting any wear on
road car dogs whilst in any given gear...
Matthew T. Russotto wrote in message
<3EWc2.1025$vg4.1...@newshog.newsread.com>...
>In article <7511qv$d...@dfw-ixnews10.ix.netcom.com>,
>Chuck Tomlinson <toml...@ix.netcom.com> wrote:
>}
>}Actually, the engine is operating *more* efficiently at lower rpm/
>}higher throttle. For a fixed air-fuel ratio (as with closed loop
>}fuel control), gasoline engines operate more efficiently (lower
>}ratio of fuel_in to power_out) as manifold vacuum decreases.
>
>Huh? That's not so. Engines operate more efficiently with the
>throttle open wider.
[snip]
From what I remember of lectures, maximum bsfc (like almost
anything in engineering!) is achieved at a compromise state:
something like 70% torque (read throttle) and ~40% of redline.
Ish.
Although I do remember something about max efficiency being
with an unrestricted intake... From lab work, though, engine
friction does increase significantly with engine speed.
Chuck Tomlinson wrote in message <751m7o$m...@dfw-ixnews10.ix.netcom.com>...
>russ...@wanda.vf.pond.com (Matthew T. Russotto) wrote:
>>
>>Since "lugging" the engine is said to cause damage, I thought friction
>>must be higher in those cases.
>
>I've also heard that lugging will damage... something. Whether the
>engine is at risk, or the transmission, or both, I don't know.
[snip]
I heard engine bearings - are bearing less able to take high loading
(high torque) at low speeds - poorer lubrication/foreign object
removal?
An observation: my C-reg ('85) Cavalier will idle, on the level,
in 1st and 2nd with 'feet off'. Gets a little lumpy in 2nd occasionally,
though, but very handy in traffic.
Answers to any of those...
Jonny
Jason T
Chuck Tomlinson wrote in message <7513fm$d...@dfw-ixnews10.ix.netcom.com>...
>
>effect of excessive tooth face wear is increased backlash. I do not
>
>Chuck Tomlinson
So that is what would cause drivetrain lash? e.g. bucking when releasing
throttle and applying throttle from a closed position mainly. I have a fwd
car that does that and the fact that the throttle sticks slightly off idle
making it hard to apply power smooth doesn't help much. Could this be caused
by the CV joints, or is my tranny going? Thanks
Jason Troxell
email to <jason78 at megsinet.net>
Chuck Tomlinson
>Chuck Tomlinson wrote in message <751m7o$m...@dfw-ixnews10.ix.netcom.com>...
>>
>>I've also heard that lugging will damage... something. Whether the
>>engine is at risk, or the transmission, or both, I don't know.
>
>(high torque) at low speeds - poorer lubrication/foreign object
>removal?
Makes sense to me. At low rpm, oil pressure is low, and each power
stroke lasts longer. That's why I prefer not to sustain WOT at very
low rpm. But that's a far cry from what I (and many other drivers)
do in stop & go traffic.
>An observation: my C-reg ('85) Cavalier will idle, on the level,
>in 1st and 2nd with 'feet off'. Gets a little lumpy in 2nd occasionally,
>though, but very handy in traffic.
Yes. On the way home tonight, I took extra notice of my habits in
stop & go traffic. I realized that most of my standing starts are
done in 1st gear, with my foot *completely* off the throttle. Even
my 1-2 shifts are frequently done at closed throttle.
Given the relatively low torque available at idle *even at WOT*, it
seems absurd to think that closed throttle starts (even with help
from the idle speed controller) and subsequent gentle acceleration
could put significant stress on any part of the drivetrain.
--
Chuck Tomlinson
Chuck Tomlinson
>Chuck Tomlinson wrote in message <7513fm$d...@dfw-ixnews10.ix.netcom.com>...
>>
>>effect of excessive tooth face wear is increased backlash. I do not
>
>throttle and applying throttle from a closed position mainly. I have a fwd
>car that does that and the fact that the throttle sticks slightly off idle
>making it hard to apply power smooth doesn't help much. Could this be caused
>by the CV joints, or is my tranny going? Thanks
All automotive drivetrains have lash built in. Although this lash
will increase as the vehicle is driven, the increase should be quite
small (if not unnoticeable) over the life of the vehicle.
OTOH, a sticky throttle will make even a brand new drivetrain feel
sloppy. I drove through some deep water last year, and my throttle
got a bit sticky afterwards. My car became truly unpleasant to
drive, the worst case being the transition from closed throttle to
cracked throttle at low rpm.
Cleaning my engine's throttle body solved the lash problem
*completely*. I used WD-40, but there might be better solutions.
--
Chuck Tomlinson
Jason T
14k having the crap beat out of it. Actually I believe that I have cleaned
the throttle body and linkage already. Any clue as to what else would cause
it to stick? Thanks
Jason Troxell
Chuck Tomlinson wrote in message <754qd5$5...@dfw-ixnews10.ix.netcom.com>...
Chuck Tomlinson
>Ok, I'll try that. I didn't mention that it has 182k miles. And the last
>14k having the crap beat out of it. Actually I believe that I have cleaned
>the throttle body and linkage already. Any clue as to what else would cause
>it to stick? Thanks
Just try to follow the throttle linkage from your foot to the T/B.
Lube the pivots on your thottle pedal, check your throttle cable for
free movement, and make sure the T/B bushings/pivots are lubricated
(not just clean). Check to see that the TB is not closing too far
(it might be wedging itself closed under vacuum).
--
Chuck Tomlinson
zwge...@gmail.com
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