How a manual transmission works... a question

Don Bruder wrote:
> In article . com>,
> wrote:
>
> > Trying to understand more about manual's, and came across this
> > excellent article:
> >
> > http://auto.howstuffworks.com/transmission5.htm
> >
> > However, here's the part I don't get: What is preventing the driver
> > from shifting into reverse while going 60 miles an hour?
>
> Nothing whatsoever, beyond the difficulty likely to be encountred in
> trying to get the involved gears to mesh at those speeds. (never mind
> the fact that the tranny is likely to actively fight you due to the fact
> that the reverse gear is being driven "the wrong way" by the
> forward-turning wheels/driveline)

I understand that if the clutch is engaged, but why would it be turning
if the clutch is pressed in?

If you look at the 2nd diagram on that page above, but input shaft
(green), layshaft (red) and blue gears should NOT be turning when the
clutch is pressed in and the tranny in neutral, right? If I'm
incorrect in this, please explain why.

wrote:
> Don Bruder wrote:
> > In article . com>,
> > wrote:
> >
> > > Trying to understand more about manual's, and came across this
> > > excellent article:
> > >
> > > http://auto.howstuffworks.com/transmission5.htm
> > >
> > > However, here's the part I don't get: What is preventing the driver
> > > from shifting into reverse while going 60 miles an hour?
> >
> > Nothing whatsoever, beyond the difficulty likely to be encountred in
> > trying to get the involved gears to mesh at those speeds. (never mind
> > the fact that the tranny is likely to actively fight you due to the fact
> > that the reverse gear is being driven "the wrong way" by the
> > forward-turning wheels/driveline)
>
> I understand that if the clutch is engaged, but why would it be turning
> if the clutch is pressed in?
>
> If you look at the 2nd diagram on that page above, but input shaft
> (green), layshaft (red) and blue gears should NOT be turning when the
> clutch is pressed in and the tranny in neutral, right? If I'm
> incorrect in this, please explain why.

The reverse gear is still being driven "backwards" by the rear wheels
so even if the input shaft and layshaft have completely spun down,
you'll have quite a bit of speed mismatch. Now some modern vehicles
have synchros on reverse so you theoretically *could* engage reverse at
speed if you wanted to; not that that wouldn't be a spectacularly bad
idea...

nate

wrote:
> Some cars used to have a reverse lockout which helped to prevent disaster
> when overvigorously
> shifting.
>
> It isnt likely you would get it completely into reverse while moving
> forward, but even to snag a little
> bit of the gear could, would, cause splinters to fly.
>
>
>
The percentage that had that lockout was small, in my experience. None
of my cars had it. I have driven ones that did, however. Usually it
required an upward 'lifting' of the lever when going into reverse.

N8N wrote:
> wrote:
> > Don Bruder wrote:
> > > In article . com>,
> > > wrote:
> > >
> > > > Trying to understand more about manual's, and came across this
> > > > excellent article:
> > > >
> > > > http://auto.howstuffworks.com/transmission5.htm
> > > >
> > > > However, here's the part I don't get: What is preventing the driver
> > > > from shifting into reverse while going 60 miles an hour?
> > >
> > > Nothing whatsoever, beyond the difficulty likely to be encountred in
> > > trying to get the involved gears to mesh at those speeds. (never mind
> > > the fact that the tranny is likely to actively fight you due to the fact
> > > that the reverse gear is being driven "the wrong way" by the
> > > forward-turning wheels/driveline)
> >
> > I understand that if the clutch is engaged, but why would it be turning
> > if the clutch is pressed in?
> >
> > If you look at the 2nd diagram on that page above, but input shaft
> > (green), layshaft (red) and blue gears should NOT be turning when the
> > clutch is pressed in and the tranny in neutral, right? If I'm
> > incorrect in this, please explain why.
>
> The reverse gear is still being driven "backwards" by the rear wheels
> so even if the input shaft and layshaft have completely spun down,
> you'll have quite a bit of speed mismatch.

How is it driven backwards if the tranny is in neutral? The reverse
gear isn't engaged, is it? IOW, on that diagram, the blue gears are
riding on bearings, are they not? They'not not connected to the
differential, only the purple dogs are, right?

wrote:
> N8N wrote:
> > wrote:
> > > Don Bruder wrote:
> > > > In article . com>,
> > > > wrote:
> > > >
> > > > > Trying to understand more about manual's, and came across this
> > > > > excellent article:
> > > > >
> > > > > http://auto.howstuffworks.com/transmission5.htm
> > > > >
> > > > > However, here's the part I don't get: What is preventing the driver
> > > > > from shifting into reverse while going 60 miles an hour?
> > > >
> > > > Nothing whatsoever, beyond the difficulty likely to be encountred in
> > > > trying to get the involved gears to mesh at those speeds. (never mind
> > > > the fact that the tranny is likely to actively fight you due to the fact
> > > > that the reverse gear is being driven "the wrong way" by the
> > > > forward-turning wheels/driveline)
> > >
> > > I understand that if the clutch is engaged, but why would it be turning
> > > if the clutch is pressed in?
> > >
> > > If you look at the 2nd diagram on that page above, but input shaft
> > > (green), layshaft (red) and blue gears should NOT be turning when the
> > > clutch is pressed in and the tranny in neutral, right? If I'm
> > > incorrect in this, please explain why.
> >
> > The reverse gear is still being driven "backwards" by the rear wheels
> > so even if the input shaft and layshaft have completely spun down,
> > you'll have quite a bit of speed mismatch.
>
> How is it driven backwards if the tranny is in neutral? The reverse
> gear isn't engaged, is it? IOW, on that diagram, the blue gears are
> riding on bearings, are they not? They'not not connected to the
> differential, only the purple dogs are, right?

Sorry, I mis-spoke. The reverse *dog* is being driven by the wheels,
and the reverse *gear* will be driven by the input shaft/layshaft.
There's going to be a speed differential between the two at any speed.
Even if the clutch is held disengaged long enough for the clutch/input
shaft/layshaft/reverse gear assembly to spin down to 0 RPM the reverse
dog will still be spinning with the output shaft at whatever RPM the
driveshaft is turning. Thus if there is no synchronizer at any speed
above a couple MPH you will get a lot of metal on metal noises and
nothing much will happen when attempting to shift into reverse. If
there *is* a synchronizer, when you try to engage the dog the synchro
will spin up the gear/layshaft/input shaft/clutch etc. *in the opposite
of normal direction* which will allow engagement of reverse but
probably wouldn't yield very desirable results should you release the
clutch after doing so.

nate

N8N wrote:
> wrote:
> > N8N wrote:
> > > wrote:
> > > > Don Bruder wrote:
> > > > > In article . com>,
> > > > > wrote:
> > > > >
> > > > > > Trying to understand more about manual's, and came across this
> > > > > > excellent article:
> > > > > >
> > > > > > http://auto.howstuffworks.com/transmission5.htm
> > > > > >
> > > > > > However, here's the part I don't get: What is preventing the driver
> > > > > > from shifting into reverse while going 60 miles an hour?
> > > > >
> > > > > Nothing whatsoever, beyond the difficulty likely to be encountred in
> > > > > trying to get the involved gears to mesh at those speeds. (never mind
> > > > > the fact that the tranny is likely to actively fight you due to the fact
> > > > > that the reverse gear is being driven "the wrong way" by the
> > > > > forward-turning wheels/driveline)
> > > >
> > > > I understand that if the clutch is engaged, but why would it be turning
> > > > if the clutch is pressed in?
> > > >
> > > > If you look at the 2nd diagram on that page above, but input shaft
> > > > (green), layshaft (red) and blue gears should NOT be turning when the
> > > > clutch is pressed in and the tranny in neutral, right? If I'm
> > > > incorrect in this, please explain why.
> > >
> > > The reverse gear is still being driven "backwards" by the rear wheels
> > > so even if the input shaft and layshaft have completely spun down,
> > > you'll have quite a bit of speed mismatch.
> >
> > How is it driven backwards if the tranny is in neutral? The reverse
> > gear isn't engaged, is it? IOW, on that diagram, the blue gears are
> > riding on bearings, are they not? They'not not connected to the
> > differential, only the purple dogs are, right?
>
> Sorry, I mis-spoke. The reverse *dog* is being driven by the wheels,
> and the reverse *gear* will be driven by the input shaft/layshaft.
> There's going to be a speed differential between the two at any speed.
> Even if the clutch is held disengaged long enough for the clutch/input
> shaft/layshaft/reverse gear assembly to spin down to 0 RPM the reverse
> dog will still be spinning with the output shaft at whatever RPM the
> driveshaft is turning. Thus if there is no synchronizer at any speed
> above a couple MPH you will get a lot of metal on metal noises and
> nothing much will happen when attempting to shift into reverse.

Ok, now we're getting somewhere... Is there no reverse synchronizer in
transmissions?

wrote:
> N8N wrote:
> > wrote:
> > > N8N wrote:
> > > > wrote:
> > > > > Don Bruder wrote:
> > > > > > In article . com>,
> > > > > > wrote:
> > > > > >
> > > > > > > Trying to understand more about manual's, and came across this
> > > > > > > excellent article:
> > > > > > >
> > > > > > > http://auto.howstuffworks.com/transmission5.htm
> > > > > > >
> > > > > > > However, here's the part I don't get: What is preventing the driver
> > > > > > > from shifting into reverse while going 60 miles an hour?
> > > > > >
> > > > > > Nothing whatsoever, beyond the difficulty likely to be encountred in
> > > > > > trying to get the involved gears to mesh at those speeds. (never mind
> > > > > > the fact that the tranny is likely to actively fight you due to the fact
> > > > > > that the reverse gear is being driven "the wrong way" by the
> > > > > > forward-turning wheels/driveline)
> > > > >
> > > > > I understand that if the clutch is engaged, but why would it be turning
> > > > > if the clutch is pressed in?
> > > > >
> > > > > If you look at the 2nd diagram on that page above, but input shaft
> > > > > (green), layshaft (red) and blue gears should NOT be turning when the
> > > > > clutch is pressed in and the tranny in neutral, right? If I'm
> > > > > incorrect in this, please explain why.
> > > >
> > > > The reverse gear is still being driven "backwards" by the rear wheels
> > > > so even if the input shaft and layshaft have completely spun down,
> > > > you'll have quite a bit of speed mismatch.
> > >
> > > How is it driven backwards if the tranny is in neutral? The reverse
> > > gear isn't engaged, is it? IOW, on that diagram, the blue gears are
> > > riding on bearings, are they not? They'not not connected to the
> > > differential, only the purple dogs are, right?
> >
> > Sorry, I mis-spoke. The reverse *dog* is being driven by the wheels,
> > and the reverse *gear* will be driven by the input shaft/layshaft.
> > There's going to be a speed differential between the two at any speed.
> > Even if the clutch is held disengaged long enough for the clutch/input
> > shaft/layshaft/reverse gear assembly to spin down to 0 RPM the reverse
> > dog will still be spinning with the output shaft at whatever RPM the
> > driveshaft is turning. Thus if there is no synchronizer at any speed
> > above a couple MPH you will get a lot of metal on metal noises and
> > nothing much will happen when attempting to shift into reverse.
>
> Ok, now we're getting somewhere... Is there no reverse synchronizer in
> transmissions?

Traditionally no, but some newer transmissions do have one.

nate

Shifted into reverse once while driving a automatic Ford Crown
Victoria. It was a rental car I had just picked up at the airport and I
hadn't taken the time to "adjust" everything before I left the lot.

Decided to adjust the height of the steering wheel while hitting about
60 mph. Only the "steering wheel adjustment lever" I grabbed was
actually the gear shifter.

Car came to a complete dead stop with as mentioned a horrrific
screeching of tires. Started right up however and I drove it some 25
hours with no problem before returning it to Hertz. Don't know what
happened to it a month down the line, however.....

wrote:

> Ok, now we're getting somewhere... Is there no reverse synchronizer in
> transmissions?
>

Most didn't in years past. In theory there shouldn't be a need for it...
since its not intended to be shifted into while moving. I think some
newer trannies have reverse synchros just to stop the clutch plate from
spinning when people jump in, punch the pedal, and slam the lever into
reverse without waiting for the clutch plate to stop spinning.

Lots of older vehicles had unsynchronized first gear, for the same
reason- no need to shift into first when moving (except when
dowhshifting, and a quick double-clutch fixes that problem).

Steve wrote:
> wrote:
>
> > Ok, now we're getting somewhere... Is there no reverse synchronizer in
> > transmissions?
> >
>
> Most didn't in years past. In theory there shouldn't be a need for it...
> since its not intended to be shifted into while moving. I think some
> newer trannies have reverse synchros just to stop the clutch plate from
> spinning when people jump in, punch the pedal, and slam the lever into
> reverse without waiting for the clutch plate to stop spinning.
>
> Lots of older vehicles had unsynchronized first gear, for the same
> reason- no need to shift into first when moving (except when
> dowhshifting, and a quick double-clutch fixes that problem).

A simplistic explanation of what happens when trying to exit a slow
corner in an old American car with the 3-on-the-tree "suggestion lever"
Unless you have that mechanical sympathy and a certain level of
understanding between you and your car, you usually end up at a dead
stop before you find first gear, which I guess, does solve the
problem...

nate